512
Im? Eng. Cham. Prod. Res. Dev. 1980, 19. 512-528
REVIEW SECTION Triazolinedione Modified Polydlenes George B. Butler Center for Macromolecular Scbnce, Univers#y of FlorMa. GainesviRe. FlwMa 32611
Triazolinediones are exceptionally strong electron acceptors and thus are among the most powerful enophiles known. They react with vinyl ethers and esters, styrenes, Pdiketones, and allyl cimpounds to yield novel copolymers. However, the major t,ojective of this report is to review the use of triazolinediones as low-temperature modifiers for diene polymers and to report their effects on polymer propetiies. The reaction is exceptionally versatile, the number of diene units undergoing reaction being proportional to the triazolinedione ratio. Properties vary widely from thermoplastic elasticity at low conversion to rigid, amorphous polymers with high softening points at high conversion. The mcdiied polymers (1)have higher T i s , (2)become increasingly soluble in polar solvents with increasing conversion, (3)possess a remarkably acidic proton, and (4) show dramatic deNeaSeS in molecular size. Poly(l,2-butadiene),5 % modified, gave values for elongation-to-break, Youw's modulus, and tensile strength twice those for the parent polymer, and tensile recoveries were >90 % . Bistriazolinediones result in efficient cross-linking at room temperature. Introduction 4-Phenyl-1,2,4-triazoline-3,5-dione (PhTD) (1) is an
George B. Butler was born in Liberty, Miss., and received his B.A. in 1938 at Mississippi College and the Ph.D. in 1942 at the Uniuersity of North Carolina. After four years as Research Chemist at Rohm and Haas Company, Inc., he joined the faculty of the Uniuersity of Florida. He wos promoted to Professor in 1957 and appointed Director, Center for Macromolecular Science, in 1970. Dr. Butler's research interests and actiuities have been predominantly in the areas of organic chemistry, polykerization reictions, polymerization mechanism, and polymer chemistry in general. He has been active in ACS affairs, having been Chairman of the Florida Section in 1954 and General Chairman of the 1958 southeastern Regional Meeting of the ACS. He is the recipient of a number of awards, the most recent being the 1980 ACS Award in Polymer Chemistry sponsored by Witco Chemical Corp. Foundation. (DVE) and maleic anhydride (MA), DVEMA (3) (IO).
1
extremely reactive dienophile (1-9) and enophile ( 6 9 ) having been shown to be 1000 times more reactive in the Diels-Alder reaction with 2-chlorobutadienethan (TCNE) tetracyanoethylene and 2000 times more reactive than maleic anhydride. 4-Methyl-1,2,4-triazoline-3,5-dione (MeTD) (2) was found to he at least 30000 times more 3
2
reactive toward cyclohexene than its open chain analogue, ethylazodicarboxylate (6). The many reactions of these powerful electron-acceptor molecules are generally very rapid, often being complete within a matter of seconds within the temperature range of 0 "C to room temperature. Our interest in 1 and its derivatives developed as the result of an attempt to locate a substitute monomer for maleic anhydride that would yield a structurally analogous copolymer t~the alternating cyclocopolymer of divinyl ether
Reactions of Triazolinediones with Vinyl Ethers Substitution of PhTD for MA in structure 3 would greaty simplify the 'H NMR spectrum and permit more effective structural interpretation. However, the assumption that PhTD would undergo a free-radically initiated cyclocopolymerization analogous to maleic anhydride was quickly shown to he erroneous. Much to our surprise, an attempt t o duplicate the above copolymerization led to spontaneous copolymerization of DVE with PhTD at room temperatwe without the addition of the free radical initiator, the reaction being complete within a few seconds (11). An extensive investigation of this unexpected occurrence led to the conclusion that PhTD and vinyl ethers in general spontaneously generate
0196-4321/EO/ 1219-051290 1.0010 0 1980 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 513
an intermediate “zwitterionic” or dipolar species which can
A===o -
I
RO
~ ;OR ~ H - C H Z T E ~ ]
CH=CH2
-
t 0
I
l , R = C,H, 2, R = CH,
C6H5 C6H5
1
4 copolymer
disappear either via ring closure to yield the diazetidine (5) or produce alternating copolymer of structure (6) or (7). When R = -CH=CH2, structure 5 was isolated as H
I
H2C-C-0-R
OQO
I I1
p---i-cj
Ph
n
5a, R = -CH,CH, b, R = -CH=CH,
6
I
d-YR
0
R
9a, R = C,H,
l o a , R = C,H, b, R = CH,
b, R = CH,
came apparent that this Diels-Alder-ene reaction sequence could be adapted to polymer formation via reaction of the bifunctional styrene molecule with a bifunctional triazolinedione as represented by (11). Such copolymers were
R
7
well as copolymer of both structures 6 and 7; however, when R = -CzH5, only copolymer of structures 6 and 7 was obtained. The most convincing evidence for the intermediacy of the zwitterion (4) is based on the fact that it can be trapped by a novel cycloaddition reaction with alkyl ketones (12) to yield a novel 1,3,4-tetrahydrooxadiazine ring structure (8) I
n--R Y
b, R = -(CH2),-
I
C6H5
4
Ph
8a, R = CH,CH, b, R = CH,CH(CH,), c , R = CH=CH,
Although reports of spontaneous copolymerization of pairs of alkenes in the absence of added initiator have been previously reported (13, 14), this appears to be the first example of spontaneous copolymerization of a pair of unsaturated compounds via a zwitterionic or dipolar mechanism. Reactions of Triazolinediones with Styrenes Extension of these investigations to other vinyl monomers led to a study of styrene as a comonomer. The literature revealed that the reaction of PhTD with styrene had been investigated (2) and was reported to give 33% yield of a double Diels-Alder product (9). However, reinvestigation of this reaction in our laboratories (15) revealed that the Diels-Alder-ene adduct (10) was also formed in 67% yield as the major product. Thus, it be-
prepared and their properties studied. Reaction of concentrated solutions of 11 in dimethylformamide (DMF) with equimolar quantities of styrene rapidly yielded high molecular weight polymer (12), [ q ] = 0.33 dL/g. Gel permeation chromatography (GPC) studies on a sample having [q] = 0.12 dL/g indicated Mn = 36000, AZw = 120000, and Mw/Mn= 3.34. Spectral analysis indicated the structure of the copolymer to consist of 33% 12 A and 67% 12 B units. A reasonable explanation of the predominance of B units is that although generation of the initial Diels-Alder adduct with styrene must overcome the resonance energy of stabilization of the aromatic ring, formation of B units permits regeneration of the aromatic ring with its associated resonance energy of stabilization, whereas formation of A units does not. Further investigations in our laboratories (16) have shown that the regioselection of the second step of the double reaction sequence can be controlled by substituent effects. Thus, p-tert-butylstyrene only undergoes the Diels-Alder-ene sequence. a-tert-Butylstyrene only undergoes the double Diels-Alder sequence while a,p-di-tert-butylstyrene13 does not participate in the second step of the two-step sequence
514
I d . Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980
6
+oJiko@H -5
C6H5
13
13a
2,6-Dichlorostyrene also participates only in the first Diels-Alder reaction, the product being 14. n
sb
14
Reactions of Triazolinediones with Vinyl Esters The nature of the reactions of triazolinediones with vinyl acetate and other enol esters came as another surprise. It was predicted that this reaction should lead to the intermediate zwitterion in a manner analogous to the enol ether case; however, because of the destabilizing effect of the carbonyl group on the developing cation, the reaction was predicted to be slower. The latter prediction was correct in that temperatures above room temperature (60"C) were necessary for complete reaction. However, the product of the reaction of VA could only be explained satisfactorily via an intramolecular rearrangement of the zwitterion (route c, 19) (17-19). 0
II
H
I
N= N +
15a, R = CH,; b. R = CH(CH,L; c ; R = C(dH,);jd, R = C,H,; e, R = CH,CI. '
I R4
R'= CH, 1,R = C,H, 2,
16
1
coupling
(b) d i a r e t i d i n c l
( c ) dipolar rearrongeIrnent
R
0
and
18
IkJ
w
263
Figure 1. Temperature vs. the addition of PHTD and MeTD to random polybutadiene: 0,N-methyltriazolinedione;A,N-phenyltriazolinedione. (Reprinted with permission from ref 31. Copyright 1979 John Wiley and Sons,Inc.)
Although cycloaddition reactions of 1,Cdipoles are well documented (20, 21), intramolecular rearrangements of such dipoles have rarely been observed (20). In fact, our literature survey revealed no such intramolecular rearrangement having been reported. Stabilization of the above dipolar species via intramolecular rearrangement appears to be the pathway of lowest activation energy by which the reactive intermediate can produce stable, covalently bonded products. There are at least two additional pathways, however, by which this can be accomplished by intermolecular coupling (a) to produce alternating linear copolymers 17 or by intramolecular coupling (cyclization) (b) to yield the relatively stable diazetidine 18.
AN&
0
1
( 0 ) 1.4-dipolar
Id0
x,
Vinyl ethers and 1,2,4-triazoline-3,5-diones (1, 2) have been shown to copolymerize predominantly via route a. A kinetic study (18) of a variety of enol esters with 1 have shown that the distribution of products is strongly dependent upon electronic and steric factors in the ester. Energy of activation for dipole formation between 1 and vinyl acetate was found to be 12 kcal/mol. In this case the distribution of products via routes a, b, and c was 7, 9, and 84%. When steric factors were introduced via R, as in vinyl isobutyrate or vinyl pivalate, E, remained unchanged, but the product distribution via routes a, b, and c was now 15,8,77 and 16,42,42%, respectively. The E, for the reaction between 1 and vinyl benzoate was only slightly lower (11kcal/mol), but again distributions among products were entirely different (87,7,6%, respectively). When strong electronic factors were introduced via R, e.g., chloroacetate, E, was increased to 14 kcal/mol; however, the product of route c was then formed in 95% yield. Route c can be envisioned schematically as R"
I fi6 19
or
17
Thus it can readily be seen that when R is an electronwithdrawing group (cation destabilizing) (R = CH2C1),E, for dipole formation was increased. However, when h t e a d of H, R" was introduced, which can be electron-releasing group (cation stabilizing) (R"= C H , C6H5),E, for dipole formation would be reduced. 1,4-Dipolar rearrangement reactions for substituted vinyl esters and attempts to em-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 515
ploy these reactions in polymer forming processes have been studied further. As can easily be seen from route c, where R is very bulky, this route is hindered and routes a and b now become sterically favored routes for dipole disappearance. As shown below, the dipolar rearrangement route (c) can become polymer forming when reaction occurs between a bisvinyl ester of a dibasic acid (20)and a bistriazolinedione (21)
?\
20 N
I1
N-7-N
Y
o
-
k N
//
-
0
23
that the competing ene and the rearrangement reactions proceed by different mechanisms. If both proceeded via the dipolar intermediate, the ester group (dipole stabilizing) should lower the energy of activation for the ene reaction between 1 and the enol ester. Thus the rate constants for the reaction between 1 and olefin should have been much smaller, but they were not. This observation also indicated that the ene reaction proceeded via a concerted or biradical mechanism (24). The ene product 23 is not thermodynamically stable and can slowly rearrange to 22
L
21a,b
Route b between 20 and 11 is also polymer forming, but it leads to a polymer of different structure and stability. On the other hand, route a between 20 and 11 is crosslinking. Therefore the proper polymerization conditions (solvent, temperature, concentrations, and ratios between comonomers) should be chosen so that route c is a favorable pathway for dipole disappearance. The yield of soluble, linear polymer of structure 21 varied from 5 to 70% depending on the connecting unit in 11, solvent and monomer concentrations; influence of temperature was of minor effect. When aromatic substituents were used in 11 and solvents noninteracting with 2 the yield of soluble polymer of M = 2000 and [ ~ 7 = 0.10 dL/g was about 70%. For example, when 20 and lla were copolymerized in methylene chloride at room temperature, the yield of soluble polymer was 69%, [9]250cDMF= 0.109 dL/g. GPC studies indicated the presence of two fractions, M = 2860 and 1680. The NMR spectra showed that the polymers consisted of more than 80% of structures described by 21a,and that less than 20% was formed by route b. The polymer still contained a small amount of the intra- and intermolecular dipolar coupling products (routes b and c) which could decompose and form insoluble polymer in very low yield. Differential scanning calorimetry (DSC) analysis indicated the onset of decomposition at 170 f 2 "C for both soluble and insoluble fractions. Competing with dipolar formation, however, is the electrocyclic ene reaction when structural features of the enol ester permit (22). For example, isopropenyl acetate yielded both the rearranged product the rate con(route KR) and the ene product (route KE), stant for the former being an order of magnitude greater than that for the latter. Comparison of the rate constants of this ene reaction with that for a simple olefin (e.g., for 1 and 1-hexene K E = 2.9 X 10P M-' s-l in benzene at 22 "C) (23),indicates
23 n
22 ]
The ~ reverse ~ ~ reaction ~ ~ is~ rather unlikely because the 1acetylmethyl-2-acetyl-4-substitutd-1,1,4-triazolidine-3,5dione (22)is much more stable, while 23 contains the easily hydrolyzable enol ester bond. The rearrangement occurred relatively fast in highly polar solvents such as Me2S0 (k = 2 X 10" s-l at 22 "C) and much slower in less polar CHC13(k = lo4 s-l at 22 "C). Addition of silica gel increased the rate of the reaction. When the reaction was run with nondried solvents also l-acetylmethyl-2-yl-4-substituted-1,2,4-triazoline-3,5dione (24)was formed by hydrolysis of 22
ii
0
It
C-NCHZCCH~
R--N(
I
'TiH Q
24
Because the conversion of the ene product to the rearranged product was much slower than the reactions between l and isopropenyl acetate, the ratio between 22 and 23 was almost constant during reaction.
516
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980
Table I. Chemical Conversions on Polydienes with Triazolinedionesb polymer modified 45 46 47 43 43 43 43 43 43 43 43 43
solvent
modifier 1 1 1
THF THF THF
THF
1 1 1 1 1 1
benzene benzene benzene benzene benzene benzene benzene benzene
2 2 2
modified polymer 48c 4 9c 50' 5lC 5 2c 53c 54c 55 56 57c 5 8c 59
% of incorp of modifier 85 78 93 92 87 75 45 20
feed, % 100 100 100 100 100 75 47 20 10 75 50 25
11 63 47 23
Tsa 185 175 195 210 210 190 145 49 d 175 150 d
Rough estimate from standard Fisher-Johns mp. Reaction time is 48 h, at which time reaction is complete or Soluble in 0.08 N KOH. stopped. T, is lower than room temperature.
Rearrangement and ene reactions became polymer forming when diisopropenyl esters and bistriazolinediones 11 were used. U
isolation of a substitution product (27), formed via a reasonably slow reaction.
Ayko
U
0
II
I1
-
I
A literature survey revealed that product 27 had previously been isolated (2). Use of tetrahydrofuran (THF) in our laboratories also led to a slow reaction so that only the very fast reactions of the triazolinediones could reliably be conducted in THF. The product of PhTD with T H F has recently been identified (28) (26).
1l a , Z = f-CH,-),
b, Z =
0
0 t CH3CCH3
+w-@ I
OCHl
n
OCH,
C6H5
1
FH3
L
,l
b2H5
28
It was proposed that the reaction with acetone may occur via an ene reaction on the enol (25). Investigations were initiated in our laboratories to utilize this reaction in polymer formation, and led to studies of triazolinediones with 8-diketones and related compounds ( 2 7 , B ) .
An
26 27
When diisopropenyl adipate 25 was copolymerized with the bistriazolinedione 11 (22)polymers (26) of molecular weights in the range of 5000 (GPC, DMF), [ S ] ~ " ~ D M=F 0.3 f 0.1 dL/g, were obtained. These higher molecular weights can be atributed to the decreased energy of activation for dipolar rearrangement effected by the cation stebilizing methyl group. DSC analysis of all soluble polymers indicated decomposition to begin at 190 f 50 OC with the maximum rate at 237 f 5 "C. Reaction of Triazolinediones with B-Diketones Suitable solvents for the highly polar and electron-deficient triazolinediones are difficult to find. Attempts in our laboratories (25) to use acetone as a solvent led to
It was shown (28) that 4-substituted-1,2,4-triazoline3,5-diones rapidly add to p-dicarbonyl compounds at room temperature to yield both 1:l (29) and 2:l adducts (30). The 1:l adducts showed a dramatic stabilization of the enolic tautomer in comparison to the original 8-dicarbonyl compound. Kinetic studies supported reaction through a 1,4-dipolar pathway involving triazolinedione and the enolic form for the 6-dicarbonyl. The extent of enolization of the /3-dicarbonylcompound is solvent dependent. Since the enolic contribution to the structure of the 1:l adduct is much greater than that of the original 8-dicarbonyl compounds, the second addition is generally faster than the first. (Compound 29 was 100% enolized in all solvents studied.)
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 517
compounds capable of undergoing a double-ene reaction. For the latter, we selected diallyldimethylsilane 33 for the reason that the product of the first ene reaction would be predicted to be much less reactive in a second ene process because of steric effects
80%
enol C6H5
50%
CH3
I
29
enol
lhT0
Of
30
33
L
34
29
30
Thus it became apparent that /3-dicarbonylcompounds are bifunctional toward the addition reaction with triazolinediones and should form linear polymers via reaction with bistriazolinediones. This prediction was borne out experimentally (28).
The second ene reaction or a Diels-Alder reaction could lead to undesirable cross-linking reactions from simple dienes such as 1,bhexadiene (35).
R'
\
K,\=@
t
11
R?=O '
31a, R = R' = CH, b, R = CH,; R' = OC,H, c , R = R' = C,H, d , R-R' = -(CH2),-
36
These reactions have been studied (29) and although conditions for polymer formation via the reaction of 11 with 33 have been identified, a variety of competing reactions complicate the simplified stepwise mechanism for polymer propagation envisaged above. A model compound study between allyltrimethyl silane (37)and 1 and 2 revealed formation of three products, 38 a bicyclic structure formed by an unknown mechanism, 39, the ene product, and 40 formed by hydrolysis of product 41.
11
L
O L
N
'
4
HYN%@ N
W
0
\H
R'
CH~=CH-CH~-SI(CH~)~
p
t O=C,
37
r
-
R
32a-d
All @-carbonylcompounds studied in this work were shown to be bifunctional. Equimolar quantities of the dicarbonyl compounds and 11 at room temperature resulted in spontaneous reaction. Intrinsic viscosities of the polymers in the range of 0.12 dL/g suggest that molecular weights are not high; however, efforts to date have not been directed toward attaining high molecular weights. The molecular weight of one sample based on the intensity of an upfield NMR signal due to end groups was calculated to be 21000. All polymers were soluble in aqueous 0.8 N KOH solutions due to the acidic amide proton on the urazole unit. The glass transition temperatures (T,)were in the range of 152-227 OC. Reactions of Triazolinediones with Allyl Silanes The high reactivity of triazolinediones in the ene reaction prompted us to investigate the use of bistriazolinediones as propagating species in reactions with
Y=N\ ,C=O
1, R = C,H, 2, R = CH, SI(C H3 )3
I 6 H, HZ7 /CH2 N-N
\
,c=o
0 4 ,
N
I
R
38a, R = C,H, b, R = CH,
C, H=C
H-SI(C
H3)3
CH=CHz
HzC!
HzC/
\ Y-N,I
t
o=c,
t
o=c\
N,c=o
I
R
R
39a, R = C,H, b, R = CH,
\ y-yI
R = C,H, b, R = CH,
40a,
It was postulated that all of the products were formed via a common intermediate dipolar species, 42; however, the results do not rule out the possibility that the normal ene product could also be formed via the usual electrocyclic (nonpolar) mechanism. Polarity of solvent and temperature of reaction varied the ratio of the three products
518
Ind. Eng. Chem. Prod. Res. Dev., Vol.
‘I’
19, No. 4, 1980
R
R 38
t H
\
k
R
\
\
\
.. 42
R
41
R
40
considerably. The most favorable conditions for polymer 34 formation appeared to be nonpolar solvents, e.g., benzene, and high temperatures, e.g., 65 “C.
Modification of Dienic Polymers and Copolymers via the “Ene” Reaction with Triazolinediones Polydienes may be modified by changing the electrostatic and steric characteristics and adding new functionality along the chain. Changes in the physical properties resulting from chemical conversions can come from one or all of four fundamental changes (30):(1) changing the energy associated with rotation about carbon-carbon single bonds; (2)introduction of electrostatic bonding by adding polar functionalities; (3)covalently joining two chains; (4) disturbing the ability of a relatively stereoregular polymer to crystallize by changing its temperature transition points. The predictability of a successful chemical conversion with respect to the properties of the final product rests in part with four criteria: (1)temperature requirements, (2) chain flexibility, (3)attainable degree of modification, and (4)singularity of reaction. (1) Temperature Requirements. Excessive temperatures can be detrimental to a chemical process in that it may produce side reactions of an intra- and intermolecular nature, e.g., chain scission and/or cross-linking. (2) Chain Flexibility. The ability of a suitable chemical reaction to give specific properties is improved if it has the ability to accomplish the modification process without affecting the functionality that would account for the changes in physical properties desired; for example, a substituent may be present on the reactant which may readily undergo other chemical reactions that compete with addition reactant. This concept can be extended to latent
functionality on the reactant which may be chemically altered after reaction with the polymer and could be a desirable feature rather than an undesirable one. (3) Attainable Degree of Modification. Changes in the physical properties of polydienes in the past by most chemical processs demanded somewhat adverse conditions of temperature and/or pressure and/or reactants. Many chemical reactions have been tried on polydienes in an attempt to modify the properties of these structures, but they have usually gone only to low conversions. (4) Singularity of Reaction. In much the same manner that depolymerization and cross-linking processes are seriously affected by simultaneous but competitive reaction pathways, chemical reactions that are prone to more than singular reaction pathways will affect the final physical properties in more than a singular manner.
Thermal and Radical-Initiated Chemical Modifications of Polydienes A variety of “enophiles” such as maleic anhydride, Nmethylmaleimide, chloromaleic anhydride, y-crotonolactone, fumaric acid, maleic acid, p-benzoquinone, acrylonitrile, and tetrahydrophthalic anhydride have been studied as modifiers for diene polymers both by thermal and radical-initiated reactions. Although the radical-initiated reactions are more effective at lower temperatures, up to 22% conversion, they are accompanied by unfavorable radical-initiated side reactions such as cross-linking and chain scission. The thermal reaction, assumed to proceed by the electrocyclic ene mechanism, resulted in an extent of reaction of about 12% and has the desirable feature of inclusion of only the reactant in the product of the reaction. Temperature up to a maximum of 240 “C, however, must be used with this reaction to obtain this extent of addition. Higher temperatures that increase the extent of addition are accompanied by depolymerization. Butler and Williams (31) initiated a study of the ene with reaction of 4-substituded-1,2,4-triazoline-3,5-diones preformed diene polymers and copolymers to synthesize a series of new polydienes. The reactions were conducted at ambient temperatures. The extent of chemical conversion could be varied widely and essentially all of the 0
H-N/Nyo
diene-repeating units of the parent polymer chain underwent reaction. Yields of the new polymers based on the reactant ranged from 90 to 95% at room temperature; their physical properties ranged from secondary crosslinking effects or elasticity at low degrees of conversion to rigid, amorphous polymers with high softening points at high degrees of conversion. The polymers showed a predictable correlation between the extent of conversion and the softening point. A similar correlation existed between the polarity of the polymers and the extent of conversion. Polydienes with conversions to the extent of 45% or greater were soluble in aqueous sodium hydroxide, and those with conversions of 60% or greater were soluble in aqueous sodium bicarbonate. Thus, in general, the polymers (1) had higher Tg,(2) became increasingly polar, hence were soluble in polar solvents, and (3)possessed a reasonably acidic proton, hence formed salts. Bis-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4,
triazolinediones resulted in room temperature cross-linking. A kinetic study with model compounds suggested that the rate of the reaction could be varied, depending on the electronic nature of the 4-substituent. Phenyl triazolinedione reacted about 50% faster than the corresponding methyl derivative. p-Nitrophenyltriazolinedione reacted more than twice as fast as the corresponding p-methoxyphenyl derivative, and the reaction proceeded about thirteen times as fast in THF as in CHC13. Chemical Conversions of Polydienes The following polydienes were included in the initial study: random cis-trans-polybutadiene (43), cis-polybutadiene (45), cis-polyisoprene (46), and random styrene (&%)-butadiene copolymer (47). Solvents were generally T H F or benzene. Polymers in which addition was greater than 6% were insoluble in benzene. These polymers, however, remained swollen in the solvent and allowed reaction to continue long after dissolution. Some properties of the modified polymers are shown in Table I. Triazolinediones may be substituted in a multitude of ways at the 4-position. This, in theory, allows all alkyl and aromatic substitutions as well as those that may be synthesized containing reactive functionality. It is reasonable to assume that the 4-substituent would affect the rate of addition of a given number of this family to polymers. A kinetic study was undertaken on a model system that used a range of substituted reactants designed to simulate a range of electronic effects that might be encountered. Electron-withdrawing substituents had the effect of increasing reactivity while electron-donating and aliphatic groups were reactivity decreasing. A small solvent effect was observed as was noted above. Additions ranging from lo%, an arbitrary lower limit investigated, to 93% on a mole reactant:mole repeating unit basis as determined by nitrogen analysis of the polymers were obtained. Here 93% is the maximum obtained under the reaction conditions used. It is theoretically possible to add as many as four moles of reactant per repeating unit; however, more recent studies have shown that reactivity of a given allyl system decreases rapidly with substitution. Additions conducted in THF, in which the polymer remained in solution during reaction, yielded the highest extents of addition. Reaction Singularity. Triazolinediones appear to react with allylic systems only by the ene reaction. The model reactions produced material balances indicative of complete reaction. Nuclear magnetic resonance (NMR) analysis of the product indicated only the presence of the expected ene adduct. The infrared spectrum (IR) of the adducts showed strong amide absorption, also characteristic of the ene product. No cross-linking occurred as all the modified polymers dissolved completely in compatible solvents. All reactions were carried out at room temperature for a maximum of 48 h. Although this reaction time is not really necessary, the extension was used to ensure complete reaction in those cases in which high conversions were attempted and the product was precipitated from solution before reaction was complete. UV inspection showed that the initial reaction was rapid, that is, when solution was maintained, and fell off after precipitation began, Softening points of the new polymers 51-59 (Table I) showed a predictable correlation between the percentage conversion and change in softening points (Figure 1). Those not represented are rubbery in texture and somewhat tougher than the original polymer. The polymers of lowest percent conversion demonstrated elasticity indica-
1980 519
Table 11. GPC Analysis of Selected New Polymersa modified polymer 52 50
51 54
53 57 a
elution counts 12.5 15.5 16.0 12.5 16.0 12.5 14.5 12.5 15.0 12.0 14.0
M w lMn
1.5 1.3 1.9 1.4 1.6 1.2 1.6 1.2 2.5
... 6.6
In DMF
Figure 2. Gel permeation chromatography elution peaks of random polybutadiene in benzene and PHTD-modified random polybutadiene in DMF. (Reprinted with permission from ref 31. Copyright 1979 John Wiley and Sons, Inc.)
tive of secondary cross-linking in the highly polar modifier. Those having T, values above room temperature were soft, white, fluffy powders. The intrinsic viscosity of polymer 43 (benzene) was 1.46 dL/g. The polymers with greater than 80% conversion had greatly reduced viscosities in the range of 0.35 dL/g. Although vastly different solvents necessary for the viscosity study were used, this alone was not enough to explain the observed decrease. The effect was therefore assumed to be due to a marked change in the hydrodynamic volume of the new polymer caused by preferential solvation of the polar urazole moiety in the viscosity solvent. It is also possible that the viscosity constants were drastically changed by a dramatic increase in repeating unit weight-380% in a polymer of 90% conversion. Chain scission during the chemical reaction was ruled out. Analysis of the DMF-soluble polymer by GPC (Table 11) resulted in elution counts of 12-16 that corresponded to a molecular size of 4 X lo4 A and molecular weights of approximately 500 000-2 000 000. (GPC calibration was based on DMF analysis of monodispersed known molecular weight polystyrene.) Analysis of polymer IV resulted in a higher elution count of 18 in benzene. Because the new polymer was expected to be larger, the observed decrease in elution count was significant. Each of the samples gave what appears to be bimodal elution peaks (Figure 2). Because the parent polymers were completely insoluble in DMF, it is unlikely that one of the peaks was due to unreacted polymer. This was also rejected on the basis of elution counts. Polymer 43 was k n o y to be relatively polydispersed, having M,,= 60000 and M , = 360000. Ita GPC elution peak in benzene was broad, with shoulders in the high-molecular-weight range (Figure 2) and appeared to be close to bimodal. It was postulated that chemical conversion aided in separation of these components by GPC. Polymers with conversions greater than 45% were soluble in N-methylpyrrolidone, hexamethyl triphosphor-
520
Ind. Eng. Chern. Prod. Res. Dev., Vol. 19, No. 4, 1980
amide, DMF, Me2S0, and dimethylaniline. Those polymers with lower conversions required mixtures of solvents, one of which dissovled the original polymer. Only those polymers with the lowest degree of conversion were soluble in the original reaction medium (benzene). All polymers with greater than 45% conversion were rapidly solubilized in 0.8 M KOH, and those greater than 60% converted in 1.0 M NaHC03 with slow evolution of COZ. This base solubility was attributed to the formation of the resonance-stabilized salt of the relatively acidic amide function.
000
0 80
wq-+ -
H-NAYo
7 NoOH
N.NyO
N a t - h N 0 R'
0
44
0.20
% PhTD 0.60
040
0.00 I
0
0.80
I
I
60
80
1
1.00 I
I
I
20
40
100
46 PhTD
Figure 3. Intrinsic viscosity plot of SBS modified with 1 (31.2 OC). (Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
60
Leong and Butler (32) have extended these studies to a wide variety of polymers and coopolymers of 1,3-dienes. The polymeric olefins chosen for study were block copolymers of styrenebutadiene (SBS) and styrene-isoprene (SI),random copolymers of styrenebutadiene (S/B) and acrylonitrile-butadiene (A/B), and homopolymers of butadiene, cis-trans (B), butadiene, 1,2-(1,2-B),and isoprene, cis (I). These polymers were modified at room temperature via the ene reaction with triazolinediones 1 and 2. The resulting modified polymers were characterized via infrared spectroscopy (IR), nuclear magnetic resonance (NMR), intrinsic viscosity ( q , dL/g), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), solubility tests, and tensile measurements. Physical properties measurements supported the postulate that the highly polar pendant urazole groups contributed intermolecular and intramolecular hydrogen bonding interactions and thus imparted to the modified polymers thermoplastic elastomer properties. Changes in the solubility character, thermal behavior, and tensile properties of the modified polymers were in accord with this postulate. Since the association between molecules is physical in nature, the modified polymers remained soluble in appropriate solvents. They also showed dramatic decreases in molecular size; for example, the average mblecular size of polymers at 1% modification was about one-tenth that of unmodified polymer due to intramolecular interactions, a size reduction of the same order of magnitude as that of chemically cross-linked polymers. Poly(1,2-butadiene) (1,2-B), when modified to the extent of 5 % , gave values for elongation-to-break, Young's modulus, and tensile strength twice those for the parent polymer, while tensile recoveries were >go%. In general, the ene reaction is so fast that the rate cannot be measured by usual methods such as UV absorption techniques. However, in the case of A/B copolymer, of acrylonitrile (AN) content of 4570, the rate is very slow. The steric effect caused by the AN units should be no greater than that caused by the phenyl group of S/B. However, the reaction rates at 25 "C in CHzClwere found to be very low compared to S/B, which indicates that the electronic effect of the -CN groups is the controlling feature of this copolymer. The rate constant K2 was found L mol-' s-' i.o be 1.2 x L mol-' s-' for 1 and 5.8 X for 2. The reactivity of the various polymers toward triazolinedione modification were qualitatively compared in terms of the length of time elapsed for the red triazolinedione color to fade completely at room temperature. Whereas the color disappeared instantaneously in the SBS, SI, and I polymers, B required about 1min, S/B about 5
min, 1,2-B 1-2 h, and A/B 6 h.
Evidence of Intra- and Intermolecular Association in Polymers Modified with PhTD and MeTD Infrared Spectroscopy. The IR spectra for the modified polymers exhibited characteristic absorption bands associated with the N-H stretching and bending frequencies of the urazole substituent as well as carbonyl stretching frequencies, and hydrogen bonding was confirmed by the appearance of the bonded N-H stretching absorption bands. The SBS polymer samples were considered to have the styrene segments associated into a plastic phase which tended to draw the butadiene segments closer to one another, resulting in enhancement of hydrogen bonding through the urazole groups. Thus, no free N-H stretching bond was observed in SBS polymers of low modification. On the other hand, when the concentration of urazole groups was high, steric effects and conformational changes due to the presence of urazole pendant groups were considered to markedly change the effective intermolecular association. For instance, when poly(cisisoprene) I had undergone 50% modification with 1 and 2, the product became very brittle, and the IR spectra indicated the amount of free N-H to bonded N-H to approximate 1:l. NMR Analysis. The NMR technique was not considered to be very accurate in determining the extent of modification. NMR integration techniques generally indicated only 80445% of urazole content indicated by nitrogen analysis. Although several ene reactions could conceivably occur at each allylic site, a recent model compound study (23, 33) indicated that the ene reaction is generally very slow and probably does not occur. Viscosity Measurement. The intrinsic viscosity, [77] of modified polymers was plotted against the ?% of triazolinedione incorporation. Typical results are shown in Figures 3-5. In general, a significant decrease in [ q ] was recognizable even at 1% modification, perhaps due to intramolecular interaction between the urazole pendant groups. The modified polymer chains became tightly coiled and decreased in molecular size when dissolved in nonassociating solvent such as benzene and chloroform. A comparison of [ q ] between the unmodified polymers and the modified polymers at 1%and 5% modification is shown in Table 111. Diethylamine, being a fairly strong base as well as a very polar solvent, could theoretically destroy the hydrogen bonding between urazole groups. In the absence of intramolecular interaction, the modified polymer should have a higher intrinsic value due to increase in molecular weight. Even in diethylamine, the [ q ]
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 521
0.50
0.40
Cnl 030
0.20
t
010
000
210 200 40
20
0
60 % PhTD
100
BO
Figure 4. Intrinsic viscosity plot of SI modified with 1; solvent, pyridine. (Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
["I 4.0
c
0
I
I
20
40
60
80
100
MOLE Yo Figure 6. Glass transition temperature plot of SBS modified with 1 (-) and 2 (---). (Reprintedwith permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
I
3 .o
2.0
0
I.o
20
40
60
80
100
MOLE Yo ~
Figure 7. Glass transition temperature plot of SI modified with 1 (-) and 2 (---). (Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
~~
1
2
3
4
5
6
7
MOLE %
Figure 5. Intrinsic viscosity plot of I modified with 1 (-) and 2 (-); solvent, CHCIB. (Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.) Table 111. Change of Intrinsic Viscosity of Various Polymers with Degree of Modification Poly mer
solvent
SBS benzene diethylamine SI pyridine B benzene I chloroform SIB benzene
with 1 unmodified 1% 5% 1.05 1.07 -0.78 -0.64 0.53 0.28 0.19 2.18 1.33 -4.10 1.31 0.60 2.60 2.25 1.47
with 2 1% 5% 1.05
---
2.09 1.36 2.50
__--
-_
--
0.30 1.75
of SBS modified with 5% 1 was lower than that of unmodified SBS polymer. In most cases, the intrinsic viscosity decreased to a much lower value with an increase in triazolinedione addition. In the cases of SBS and S/B, where the polymer systems were already associated through physical interaction between polymer blocks, little change in [ q ] was observed at low modifications. The styrene segments were considered to interact with each other via hydrophobic interaction, even in dilute solution. As a result, the effect due to a small amount of hydrogen bonding became insignificant. The hydrogen bonding character of phenyl and methyl urazole groups could be observed through the [9]data. In general, the phenyl urazole groups cause slightly larger decreases in [ q ] than the methyl groups, implying that the hydrogen bonding tendency is stronger in phenyl urazole than in methyl urazole. The phenyl groups are capable
of undergoing hydrophobic interaction with one another, and this would enhance the intramolecular H-bonding effect. Gel Permeation Chromatography. Since hydrodynamic volume, V,, is proportional to retention or elution volume, V,, any change in the hydrodynamic volume due to intramolecular interaction would result in increase or decrease of retention volume in GPC. As the urazole pendant groups form H-bonding within the polymer molecule, V, in nonprotic solvents should decrease, resulting in a decrease in v,. This behavior was observed among all polymer samples modified with 1 and 2. Some typical data are summarized in Table IV in which the apparent GPC molecular weights were used for comparison. Expression of V, in terms of molecular size in A gave a better indication of the size reduction due to the intramolecular hydrogen bonding effect of the urazole pendant groups. A very dramatic change in molecular size was observed in the case of SI, B, I and A/B polymers. The average size of polymers at 1% modification due to intramolecular interaction was only about one-tenth that of the parent unmodified polymers. This magnitude of size reduction was observed to be comparable to that of chemically cross-linked polymer systems. Differential Scanning Calorimetry. Any changes in the molecular association forces should be reflected in the glass transition temperature, T , and melting temperature, T,, of the polymer although t i e former is more sensitive to such changes. The increase in intra- or intermolecular interaction, in fact, imposes a higher energy barrier to the free rotation of the polymer chain and decreases its free volume, resulting in increase in Tgvalue. In general, this
522
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980
Table IV.= GPC Data of Modified Polymers unmodified polymer SBS SI B I 1,2-B SIB AIB
1% 1 added
Vn
Mw 224 000 29 500 126 000 74 100 196 000 6 6 100 1 122 000
M W 178 000 2 510 14 800 7 940 200 000 56 200 794 300
4 677 7 08 3 162 1778 5 129 1995 26 920
1%2 added
Vn
MW 148 000 2 510 22 400 9 330 132 000 41 700 63 100
4 467 63 355 178 5 623b 1413 19 050
Vn
3 631 63 537 224 3 388b 1000 1349
All measurements were done in CH,Cl, at room temperature, 25 O C , and the Mw values were calibrated using polystyrene standards of narrow MWD. At 5%modification, molecular size of 1,2-B was reduced to 2399 A with 1 and 2690 A with 2.
TP (OK
1
240
290
t
0
2
4
6
8
I I
1.24
/
I
/p%2-B
Y
P
IO
MOLE % Figure 8. Glass transition temperature plot of S/B modified with 1 (-) and 2 (---). (Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
was observed to be the case among the polymer samples modified with 1 and 2. Specifically, the Tgof the olefinic polymer segments increased with the amount of urazole pendant groups present in the segments. Some typical data are shown in Figures 6-9. The authors observed several interesting features among the Tgdata. First of all, the Tgof S/B copolymer modified with 1 and 2 was split into two values when the extent of modification exceeded 5%. Secondly, the Tgof A/B copolymer decreased instead of increased with % modification when the PhTD content was below 5%. These observations in the case of the S/B copolymer system were accounted for on the basis that even though the styrene and butadiene units are arranged in a random fashion, they can be treated as a random distribution of small blocks of styrene and butadiene units. The reaction rate of S/B copolymer with triazolinediones indicated some steric hindrance to the approach of the triazolinedione molecule onto the butadiene double bond due to adjacent phenyl groups resulting in a nonhomogeneous reaction. The unmodified S/B segments might be so isolated from the rest of the modified SIB segments that they form a separate phase which was reasoned as possibly accounting for the occurrence of two separate T values on the DSC thermogram. The upper value wodd account for the modified segments, whereas the lower one, the unmodified segments as shown in Figure 8. The observations in the case of the A/B copolymer system, the initial decrease in Tg, was explained in terms of changes in free volume of the polymer molecules. It is well known that the introduction of nonreactive branches or side chains would result in an increase of free volume and subsequent decrease in Tg.Since at low % modifi-
230'
5
IO
IS
MOLE % Figure 9. Glass transition temperature plot of 1,2-B and A/B modified with 1 (0) and 2 ( 0 ) . (&printed with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
cation the probability of one urazole pendant group interacting with another one is very low, the intramolecular interaction due to H-bonding becomes negligible. Therefore, the increase in free volume due to the urazole side groups becomes significant, resulting in the observed decrease in Tgvalue. As more and more urazole groups are added to the polymer chain, the probability of one urazole group interacting with another one increases. When the attractive forces due to intramolecular Hbonding exceeds the repulsive forces due to presence of pendant groups, the T value would increase again. The authors also reasoned &at this expansion and contraction of free volume might account for the fluctuation in Tg values among the modified SBS and SI polymers shown in Figures 6 and 7, respectively. As was mentioned before, T, is not sensitive to molecular changes in amorphous polymer systems. However, in these studies the authors noticed some unusual effects on the decomposition temperature Td (an exotherm) of the polymer samples as modification was increased. Some representative data are shown in Figures 10-12. The decomposition pattern did not seem to follow any trend. At high % modification, the urazole groups seemed to provide additional thermal stability to the polymer, but at low % modification, i.e., below 10% level, they had a destabilizing effect. The methyl urazole groups appeared to stabilize the I polymer but destabilized the B and 1,2-B polymers toward thermal decomposition. At low % modification, the phenyl urazole groups had destabilizing
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 523
I
I
0
.
,
:
:
.
,
0.4
0.2
:
;
0.6
0.8
1.0
Figure 10. Plot of decomposition temperature (Td)for B modified with 1 (0) and 2 (0).(Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
B
4
5
6
8
IO
Table V. Maximum % of Modification Possible before Loss of Thermoplasticitv
I 1,2-B SIB AB
3
6
Figure 12. Plot of decomposition temperature (Td)for 1,2-B modified with 1 (0) and 2 (0). (Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
polymer SBS SI
2
4
MOLE %
MOLE %
I
2
,
7
MOLE %
Figure 11. Plot of decomposition temperature (Td)for I modified with 1 (0) and 2 (0).(Reprinted with permission from ref 32. Copyright 1980 Marcel Dekker, Inc.)
effects, whereas at high % modification, they appeared to stabilize the polymer. The authors speculated that this peculiar behavior of the phenyl urazole might be due to an increase in thermal oscillation during heating as a result of the presence of large phenyl rings. At low concentration, the H-bondings of the phenyl urazole groups could be overcome easily, since the strength of H-bonding is only about 5 kcal/mol. At high concentration, the H-bonding as well as the hydrophobic interaction via the phenyl groups might develop enough strength to withstand the thermal stress. As the amount of polar groups increased, the polymer samples lost their thermoplastic properties, i.e., they failed to melt without undergoing decomposition. A summary of the degree of modification before thermoplasticity was adversely altered is shown in Table V. It appeared that
%1 1 15
1 I 0.3 1 1
%2
1 5 1 I 0.2 1 1
2 can adversely affect the thermoplasticity to a greater degree than 1. Solubility Tests. The effect of intermolecular forces is quantified by cohesive energy density or solubility parameter, 6. Branching increases the solubility of high polymers, whereas polarity decreases it. In general, the introduction of polar groups into a polymer chain tends to decrease its solubility in the original solvent as strong polymer-polymer interaction develops. In the present studies, the modified polymer samples precipitated out of the reaction solvent when modification exceeded 10-20%. The strong H-bondings formed by the urazole groups prevented the hydrating solvent molecules from penetrating the polymer coils. The addition of more urazole pendant groups on the olefinic polymer led first to solubility in organic and inorganic bases, which only swelled the parent polymer, and then to water solubility. At higher degrees of modification or triazolinedione addition, water solubility was accompanied by alcohol solubility, and then solubility in polar organic solvents such as DMF and Me2S0. In other words, the solubility parameter of the polymer sample increases with increase in urazole content. Some typical solubility characteristics of the polymers modified with 1 and 2 are shown in Table VI. A sample of poly(butadiene), B, was modified to 75% 1 incorporation and converted to the potassium salt which was soluble in MeOH, DMF, Me2S0, and H20, had a decomposition maximum at 255 "C and was very brittle. Tensile Measurements. The tensile data are shown in Table VII. The 1,2-B series (samples 20-24) best illustrated the effect of urazole pendant groups in the polymer. A 5.0% modification doubled the elongationto-break, the Young's modulus, and tensile strength values. The tensile recoveries became greater than 90%, and the stress decay values became measurable. In the B series (samples 7-11), the urazole groups appear to increase tensile strength, improve tensile recoveries, and
524
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19,No. 4, 1980
Table VI. Data Showing Maximum % Modification for Polymer To Remain or Become Soluble in Various Solvents
plying evidence for intermolecular H-bonding was concerned. However, a phenomenon involving phase mixing could be recognized. The samples modified with 2 were not much different from unmodified films, since unmodified samples were already physically associated by the styrene phase. Thus, a small increase in physical association by methyl urazole groups might not have been noticed in the tensile data. The samples modified with 1 exhibited poorer tensile recoveries and increased stress decays, which could be manifestations of phase mixing or a perturbation of the phase interface. The increased phase mixing might be accounted for as a result of the increased solubility of the phenyl substituent on the urazole ring in the styrene phase. Chen and Butler (34) further investigated the ene reaction of triazolinediones 1 and 2 on diene polymers. The polydienes used were polypentenamer (pptm), cis-1,4polypiperylene (cis-ppp), high vinyl polybutadiene (HVPB), and medium vinyl polybutadiene (MVPB). The modified polymers were characterized by infrared spectroscopy (IR),nuclear magnetic resonanc spectroscopy (NMR), differential scanning calorimetry (DSC), and solubility tests. IR was used as a qualitative tool to prove the molecular association through hydrogen bonding. The presence of the carbonyl stretching frequency and both N-H stretching and bonding frequencies were generally observed. The latter was considered to be indicative of
6,
solvent benzene CHCl, CH,CI, pyridine DMF EtOH Me,SO acetone
(call CC)''~
SBS
SI
I
B
1,2-B SIB
9.2 9.3 40 >40 >454
0.8 M KOH used, and when the modification was >60%, the samples were soluble in 1.0 M NaHCO,.
reduce stress decays even at the 1%modification level. The I series (samples 12-14,18,19) was difficult to work with and in every case either solubilization was never achieved or the films were weak and tacky. No changes a t all were noted for the A/B series (samples 15-17) as physical association already exists between the acrylonitrile units. The SBS series (samples 1-3) and SI series (samples 4-6 and 25-27) were not particularly revealing as far as supTable VII. Tensile Dataa samPle no. description
casting solvent b
sample thickness, mils
elongation to breakC %
Young's modulus, kg/cm2
tensile strength,c kg/cm2
1 2 3 4 5 6 7 8 9 10
SBS SBS? 1%1 SBS, 1%2 SI SI, 1%1 SI. 1%2 B' B. 1%1 B; 1%2 B, 75% 1
toluene toluene toluene toluene toluene toluene toluene toluene toluene pyridine
11
B,75%1Ksalt
water
12 13 14 15 16 17 18 19 20
I I, 1% 1 I, 1%2 AI B A/B, 1%1 A/B, 1%2 I, 5% 1 I, 5% 2 1,2-B
toluene toluene toluene chloroform chloroform chloroform chloroform chloroform chloroform
4.2 (0.3) 648 (30) 218 (95) 138 (37) 3.8 (1.0) 879 (167) 758 (82) 77 (13) 4.1 (0.7) 794 (38) 1038 (142) 226 (52) 3.0 (0.4) 1245 (20) 25 (1.3) 234 (21) 220 (1.3) 2.1 (0.4) 788 (46) 22 (1.8) 3.2 (0.7) 1361 (48) 1 6 (2.4) 80 (7.1) 1.3 (0.3) 1453 (167) 32 (2.0) 14 (0.7) 3.3 (0.5) 1782 (58) 22 (5.0) 28 (2.7) 3.0 (0.9) 1680 (216) 20 (43) 23 (3.9) Sample too brittle to test. Wide angle X-ray photo shows polymer t o be amorphous. Sample too brittle t o test. Wide angle X-ray photo shows polymer to be amorphous. ----Unable to cast a useful film-------Unable to cast a useful film-------Unable to cast a useful film---3.2 (0.3) 1124 (35) 62 (3.4) 39 (1.7) 3.4 (0.2) 1286 (47) 61 (5.5) 27 (2.8) 3.3 (0.3) 1028 (58) 69 (9.2) 36 (6.7) ----Unable to cast a useful film-------Unable to cast a useful film---3.3 (0.5) 136 (13) 46 (8.9) 97 (21.3)
21
1'2-B, 0.5% 2
chloroform
3.4 (0.3)
126 (8)
45 (3.4)
107 (9.7)
22
1,2-B, 0.5% 2
chloroform
3.2 (0.6)
150 (11)
40 (5.3)
111 (11)
23 24 25 26 27
1,2-B, 5.0% 1 1,2-B, 5% 2 SI, 5.0% 1 SI, 5.0% 2 SI, 15% 1
chloroform chloroform chloroform chloroform chloroform
3.4 (0.1) 3.2 (0.2) 3.8 (0.5) 3.1 (0.2) 3.8 (0.5)
367 (17) 394 (24) 650 (65) 773 (52) 650 (65)
112 (3.0) 96 (12) 59 (11) 25 (2.7) 59 (4.4)
267 (32) 229 (49) 82 (11) 133 (14) 8 2 (11)
tensile recovery,
stress decay?
%
%
95 (0.2) 87 (0.9) 94 (0.2) 97 (0.4) 90 (1.4) 94 (0.4) 82 (2.2) 88 (0.9) 89 (0.5)
20 (2.7) 45 (4.5) 23 (0.2) 1 5 (0.4) 32 (0.9) 1 3 (0.5) 44 (1.1) 28 (0.8) 28 (1.4)
64 (2.0) 66 (1.4) 63 (1.4)
40 (1.8) 39 (2.3) 38 (2.0)
Stress decay too high to measure tensile recovery sample fractured in less than 1 min Same results as for sample 20. Same results as for sample 20. 92 (0.5) 52 (1.0) 93 (0.2) 43 (1.7) 76 (0.2) 61 (0.2) 86 (0.4) 42 (0.3) 65 69
Data in parentheses are standard deviations. Unless otherwise indicated, five measurements were made for sample thickness, elongations to break, Young's moduli, and tensile strengths. Three measurements were made for tensile recoveries and Samples were Four-gram samples were dissolved in 400 mL of solvent (800 mL for samples 7, 8, and 9). stress decays. extended at a rate of 20 in./min. d Samples were extended at 20 in./min t o '1, their elongation to break and held there for 1.5 min to measure stress decay. The sample was then returned t o a zero stress level t o measure tensile recovery. e Fourteen measurements were made for sample thickness, elongation to break, modulus, and tensile strength. Five measurements were made for tensile recovery and stress decay.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 525 Table VIII. Relative Reactivity of Different Polymers Modified by PhTD completion time, min, for % modification polymer 1% 5% 10% solvent (5% soln) 6 7 8 pptm benzene benzene 12 13 14 cis-ppp 8 10 12 HVPB benzene 5 6 7 MVPB benzene Table IX. Maximum Percent of Modification Permissable before Loss of Thermoplasticity
.Dolsmer -
%PhTD
%MeTD
PPTM cis-ppp HVPB MVPB
1 12 1 5
1 5 1 5
*O1
-70'
2
'
4 ' 6
'
i 'I b '
(2'1'4
Mole %
Figure 13. Glass transition temperature of cis-ppp modified with PhTD ( 0 )and MeTD (A), (Reprinted with permission from ref 34. Copyright 1981 Marcel Dekker, Inc.)
intermolecular hydrogen bonding. NMR spectra were used to establish the amount of triazolinedione combined with the polymer. The triazolinedione phenyl and methyl signals were easily distinguished from those of the parent polymer. The degree of modification could be obtained by comparing the ratios from the urazole pendant groups to those of the main chain protons. DSC measurements taken as the intersection of were performed to obtain Tg, the extrapolated low temperature baseline with the tangent to the endotherm signal resulting from the heat capacity increase. The decomposition temperatures were defined as the point of maximum expansion of the exotherm from the baseline. The relative reactivity of the various polymers toward triazolinedione modification was qualitatively established by comparing the period of time required for the red triazolinedione color to fade fully in each reaction mixture. The data are illustrated in Table VIII. As was pointed out earlier, the glass transition temperature, T should be increased with an increase in intraor intermofkular interaction. The experimental results of this study confirmed this among the polymer samples modified with 1 and 2. The Tgof the polymers increased proportionally with the amount of urazole pendant groups incorporated. An example is shown in Figure 13. The decomposition temperatures data for cis-ppp are shown in Figure 14. The polymer samples lose their thermoplastic properties as the quantity of polar groups incorporated increases. The degree of modification possible before thermoplasticity was lost is summarized in Table IX. Polymer solubilities varied in a parallel manner to previous studies (31). Some typical solubility characteristics of the modified polymers are shown in Table X. Thus, it can be concluded that this method of modifying polydienes is quite simple and effective. Triazolinediones
250 240-1
w
//-
2301
220 'lo
i . , , . , , . , . , 2
4
6
8
IO
12
14
Mole % Figure 14. Decomposition temperature (Td)for cis-ppp modified with PhTD ( 0 )and MeTD (A). (Reprinted with permission fro= ref 34. Copyright 1981 Marcel Dekker, Inc.) Table X. Maximum % Modification for Polymer To Retain Solubility in Various Solvents solubility paramcissolvent eter,& pptm ppp HVPB MVPB 5 10 5 8.8 5 xylene 9.2 < 1 2 < 1 5 < 1 5 < 1 2 benzene 12 10 chloroform 12 5 9.3 15 5 chlorobenzene 9.5 12 10 5 5 10 5 dichloromethane 9.7 10 5 10 12 pyridine 10.7
as enophiles have a great advantage because of their high reactivity. The substituents on the triazolinedione molecule can be readily changed in order to provide commercially useful polymers with properties tailor-made to fit specific applications. The extent of modification is subject to no specific restrictions, and the modification reaction can be carried out readily at room temperature or lower. The highly polar modifying groups provide hydrogen bonding sites which have a remarkable effect on Tg, solubility character, viscosity, and tensile properties of the polymer. Rout and Butler (35)have recently studied the ene reaction of bistriazolinediones (BTD's) to synthesize a large number of highly cross-linked or vulcanized polydienes. BTD's were found to be effective cross-linking agents at room temperature. The cross-linked polymers were swollen in benzene, and the cross-link density and the molecular weight between cross-links were determined by the Flory-Rehner equation. BTD's were found by Williams and Butler (3) to be much more reactive than triazolinediones, and the modification reaction was easily followed at room temperature by the disappearance of the characteristic pink color of the bistriazolinedione. The first report of the reaction of BTD's with polydienes was by Saville (36),who made an unsuccessful attempt to cross-link natural rubber with a BTD. However, in the study by Rout and Butler (35) polydienes were suitably cross-linked with BTD's. Modified polymers swelled in the original reaction medium (benzene), and the reaction proceeded instantaneously. The possibilities of unreacted N=N ends were ruled out by the absence of the characteristic absorption.
11
vulcanized elastomer
526
Ind. Eng.
Cham.
Prod.
Res. Dev., Vol. 19, No. 4, 1980
Table XI. Reactions of Polydiene with a Bifunctional Triazolinedione (BTD)= % of incorp
%
of reactant (% N )
6 15 25 6, 50
21 (12.04) 53 (15.06)
feed, polymer 43 43 43 43 a
solvent benzene benzene benzene benzene
reactant BTD BTD BTD 1, BTD
__ __
Room temperature; reaction time of 8 h.
Butler and Williams (31) reported on cross-linking of random cis-trans-polybutadiene with bistriazolinedione as well as a combination of this reactant and 1 (Table XI); 25% (molar basis) BTD and 6% BTD-50% 1 converted polymers to gels that swelled in most solvents as well as in 0.8 M KOH. The 6% and 15% BTD converted polymers were soluble in the original reaction medium (benzene), which implied a cyclic addition because these rather high percentages of the cross-linking agent were expected to yield gels. The presence of unreacted -N=N- ends was ruled out on the basis of the absence of the characteristic absorption for this group. Reaction rates were rapid in relation to those observed with the additions of 1. In this preliminary study, the authors described the low-temperature cross-linking of various polydienes'with BTD and characterized the polymers by infrared spectroscopy using the Multiple Internal Reflection Accessory (MIRA). A swelling equilibrium method was employed to evaluate the cross-link density and the molecular weight between cross-links of the modified polymers by using the Flory-Rehner equation (37). Determination of Cross-Link Density by Equilibrium Swelling Measurements Cross-linked polymers have a great variety of structures, and it is important to have techniques to characterize these structural parameters, such as cross-link density or the molecular weight of the chains between the cross-links. The first step in the solution of a polymer is swelling and, in the m e of a cross-linked polymer, it is the last step since chains cannot be further separated because of the presence of cross-links. Swelling is accompanied by an increase in the volume of the polymer as it imbibes the solvent, and it is usual to assume, consistent with the Flory-Huggins theory of the thermodynamics of polymer solutions, that mixing occurs without change in the total volume of the system. A sample of cross-linked polymer placed in a solvent swells until the chemical potential of the solvent inside the gel is equal to that of the outside phase. During the process, solvents reduce or damage secondary bonds between chains, especially when the solvents are of remarkable polarity. Thus the number of cross-links determined by this method depends on the nature of the solvent. This value was found by employing the Flory-Rehner equation (37) in the form -In (1- VR) + Vr + xVr2
where u/V stands for effective crosslink density in moles/cm3, Vr is the volume fraction of the polymer in the swollen sample, x is the polymer-solvent interaction parameter of the Flory-Huggins theory, and Vo is the molar volume of the solvent. Knowing the value of v/ V, one can then calculate the average molecular weight of the network chains
where P is the density of the polymer. To calculate cross-link density and the molecular weight of chains between cross-links, the values of the FloryHuggins polymer-olvent interaction parameter must be known. In this report, the method of Rutkowska and Kwiatkowski (38) was used to obtain these parameters. The variation in swelling degrees from swelling measurements with temperatures using the Flory-Rehner equation for all samples was measured -d Vr
The presence of urazole groups in the modified polymers was confirmed by the carbonyl stretching frequencies (IR), and hydrogen bonding was confirmed by the bonded N-H stretching band. Density of Cross-Linking. There are several methods of studying network structures (39) but the available techniques are not as good as those used conventionally to determine the molecular weights of linear soluble polymers. Among them, the chemical method is the most suitable and fairly accurate method of characterizing network structures. In a chemical method, it is observed that if the concentration of the cross-linking reagent is known, and if it reacts completely, then it is possib_le to estimate reasonably the average molecular weight, M,, of the polymer between the cross-links. In our system in the modification of diene polymers with bistriazolinediones, it was assumed that the reaction went to completion because the pink color of the BTD was discharged completely at the end of the reaction. If an uncross-linked polymer is soluble in a solvent, then the same polymer when cross-linked should swell in the same solvent. This fact has been taken advantage of to measure cross-link density and the average molecular weight between the cross-links for the modified diene polymers. It was earlier shown by Hergenrother (4% in the peroxide initiated cross-linkingof poly(butadiene),that the Flory-Rehner equation is valid down to a value of 63Mc,that is to a highly cross-linked network. Recently, Gancarz and Kaskowski (41) have shown that the FloryRehner equation may also be used for cross-linked networks of low molecular weight polydienes. In the present investigation, cross-link density was calculated by the Flory-Rehner equation (37). Benzene was used as the swelling solvent for the cross-linked polymers, and the Flory-Huggins polymer-solvent interaction parameter, x , was determined by employing the method of Rutkowska and Kwiatkowski (38). Table XI1 summarizes the cross-link density, the Flory-Huggins polymer solvent interaction parameter, and the average molecular weight between the cross-links of the BTD modified diene polymers. Figure 15 represents the plots of cross-link density of modified polymers against the mole percentage of bistriazolinedione incorporated in the diene polymers. The plots show that as the percentage of bistriazolinedione content in the diene polymer increases, the cross-link density also increases in a linear fashion. Thus by increasing the extent of modification of polydienes with BTD, highly cross-linked networks are produced at room temperature. It was observed that beyond 5% modification of the diene polymers with BTD resulted in immediate gelation.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 527 Table XII. Cross-Link Density and Average Molecular Weight between Cross-Links of Modified Polymers Determined from Swelling-Equilibrium Method Flory-Huggins cross-link av mol wt % mole of polymer-solvent density v / V between BPMTD interaction mol/cm3 cross-links, polymers added parameter, x at 25 "C M,, g/mol 0.507 8.75 1038 poly(isoprene), cis 0.507 10.58 860 0.507 12.34 7 37 0.509 12.69 708 poly(butadiene), cis and trans 0.509 14.63 615 0.509 17.26 521 copolymer of styrene-butadiene 0.512 13.63 694 0.512 17.50 533 0.512 21.58 43 2
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Figure 15. Plot of cross-link density of modified PI (O), PB (A), and S/B (0) with mole percentage of BPMTD incorporated. (Reprinted with permission from ref 35. Copyright 1980 SpringerVerlag.)
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Figure 16. Plot of average molecular weight between cross-links of modified PI (A),PB (o),and S/B (0)with mole percentage of BPMTD added. (Reprinted with permission from ref 35. Copyright 1980 Springer-Verlag.)
Very low incorporation of BTD into the polydienes resulted in cross-linked networks, substantiated from the average molecular weight, Mcvalues, as illustrated in Table XII. However, when the average molecular weight between cross-links was plotted against the percentage incorpora-
Figure 17. Plot of mole percentage of BPMTD content vs. reciprocal of average molecular weight of modified PI (O), PB (A),and S/B (0).(Reprinted with permission from ref 35. Copyright 1980 Springer-Verlag.)
tion of BTD in the diene polymers, in all cases, linear plots were obtained as shown in Figure 16. The linear plots demonstrate that as the extent of modification via BTD increases in the modified polymers, the average molecular weight decreases steadily, showing that the extent of incorporation of BTD into the diene polymers is inversely related to the average molecular weight between the cross-links. This was further confirmed from the plots of extent of modification via BTD vs. the reciprocal of the average molecular weights, which were straight lines, as shown in Figure 17. Thus, it can be concluded that diene polymers can be effectively vulcanized at room temperature with BTD. Cross-link parameters determined for the modified polymers were in good agreement with experimental observations, and an inverse relationship was found between the extent of modification and the average molecular weight between cross-links in the modified polymers. Acknowledgment The author and publishers acknowledge with thanks the kind permission of John Wiley & Sons, Inc., to use Figures 1and 2, of Marcel Dekker, Inc., to use Figures 3-14, and of Springer-Verlag to use Figures 15-17. Literature Cited (1) cookson, R. C.; Gilanl, S. S. H.; Stevens, I. D.R. Tefrahedw,Lett. 1982, 815. (2) cookson, R. C.;Wnl. S. S. H.; Stevens, I. D.R. J. chem. SOC. ClS87, 1905. (3) Gilani, S. S. H.; Trlggle, D. J. J. Org. Chem. 1986, 37, 2397. (4) Solo, A. J.; S a w , H.; Gilanl, S. S. H. J . Org. Chem. 1985, 30. 789. (5) Sauer, J. Angew. Chem. Int. Ed. €ng/. 1987, 6,18. (6) Plrkle, W. H.; Stickler, J. C. Chem. Commun. 1987, 760. (7) Stlckler, J. C.; Pirkle, W. H. J. Org. Chem. 1988, 37, 3444. (8) Sauer, J.; Schroder, B. Angew. Chem. Int. Ed. Engl. 1985, 4 , 71. (9) Hoffmann, H. M. R. Angew. Chem. Int. Ed. €ng/. 1989, 8 , 556.
528
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1980, 79, 528-532
fom.
(10) Butler, G. B. J. folym. Sci. 1980, 48, 279. (11) Butler, 0. B.; Guilbault, L. J.; Turner, S. R. folym. Lett. 1971, 9 , 115. (12) Turner, S. R.; Guilbault, L. J.; Butler, G. B. J. Org. Chem. 1971, 36, 2838. (13) Miller, F. F.; Gilbert, H. Canadian Patent 569262, Jan 20, 1959. (14) Yang, N. C.; Gaonie, Y. J . Am. Chem. SOC.,1984, 86, 5023. (15) Wagener, K. B.; Turner, S. R.; Butler, G. B. folym. Lett. 1972, 70, 805. (16) Lai, Y. C. Ph.D. Dissertation, Unlversity of Florida, 1980. (17) Wagener, K. B.; Turner, S. R.; Butler, G. B. J . Org. Chem. 1972, 37, 1454. (18) Wagener, K. B.; Butler, G. B. J . Org. Chem. 1973, 38, 3070. (19) Matyjaszewski, K. A.; Wagener, K. B.; Butler, G. B. folym. Lett. 1979, 77. 129. (20) Huisgen, R. 2.Chem. 1988, 8 , 290. (21) Von Gustorf, E. K.; White, D. V.; Kim, 8.; Hess, K.; Leitlch, J. J . Org. Chem., 1970, 35, 1155. (22) Matyjaszewski, K. A.; Wagener, K. B.; Butler, G. B. fotym. Lett. 1979, 17. 65. (23) Ohashi, S.; Butler, G. B. J . Org. Chem. 1980, In press. (24) Hoffmann, H. M. R. Angew. Chem. Int. Ed. Engl. 1989, 8 , 556. (25) Ruch, W. E. M.S. Thesls, University of Florida, 1973. (26) Wamhoff, H.; Wald, K. Chem. Ber. 1977, 770, 1699. (27) Williams, A. G.; Butler, G. B. J . Org. Chem. 1980, 45, 1232.
(28) Williams, A. G.; Butler, G. 8. Lett. 1980, 76. 313. (29) Ohashi, S.; Ruch, W. E.; Butler, G. 8. J. Org. Chem. 1980, In press. (30) Fettes, E. “Chemical Reactions of Polymers”, Why-Interscience: New York, 1964. (31) Butler, G. B.; Wllliams, A. G. J. folym. Sci., folym. Chem. Ed. 1979, 77s 1117. (32) LeOng, K. W.; Butler, G. B. J . Maaomol. SCi.-chem. 1980, A74(3), 287. (33) Ohashi, S.; Leong, K. W.; Matyjaszewski, K.; Butler, G. 8. J . Org. chem. inso. .- - -, 45. . - , 3467. - .- . . (34) Chen, T. C. S.; Butler, G. 8. J. Macromol. Sci.-Chem. 1980. In press. (35) Rout, S. P.; Butler, G. B. folym. Bull. 1980, 2, 513. (36) Saville. B. J . Chem. Soc.. D 1971. 72. 635. i37j Flory, P. J.; Rehner, J. J . Chem. fhys. W43, 7 7 , 521. (38) Rutkowska, M.; Kwiatkowskl, A. J . folym. Sci. Symp. 1975, 53, 141. (39) Nlelsen, L. E. J. Macroml. Sc/.-Rev. Macromol. Chem. 1989. C3(1), 69. (40) Hergenrother, W. L. J . Appl. folym. Sci. 1972, 76, 2611. (41) Gancarz, I.; Kaskawskl, W. J . folym. Sci., folym. Chem. Ed. 1979, 77, 1523.
Received for review July 2, 1980 Accepted August 4, 1980
Cyclopolymerization of N,N-Dialkyldiallylammonium Halides. A Review and Use Analysis Raphael M. Ottenbrlte’ and Wllllam S. Ryan, Jr.’ Department of Chemistty, Virginia Commonwealth Un/vers&, Richmond, Virginia 23284
The formation of cyclic structures during the polymerization process has led to many interesting and useful potymers. The most extensively studied have been the diallyl systems which were initially reported to form six-membered rings. However, studies of monocyclic reactions and model compounds and polymers indicate that the reaction is kinetically controlled and preferentially produces five-membered rings.
The formation of cyclic structures in the polymer chain from acryclic monomers and comonomers during the polymerization process was first discovered in the early 1950’s. During the next 20 years several interesting cyclopolymerization systems have been developed and their mechanism of cyclization investigated as reported by Cotter and Matzner (I). However, the one system that has the greatest industrial potential and utilization is that of diallylammonium halide. This polymer alone accounts for over 200 patents and publications. Because of ita general importance and uniqueness, a survey of its discovery, characterization, and utilization is presented here.
Initial Discovery of Cyclopolymerization For a number of years polymer chemists have been interested in developing ion-exchange resins for purification and isolation of materials. In 1949,Butler and Bunch (2) prepared tri- and tetraallyl quaternary ammonium salts which were polymerized to form highly cross-linked, water-insoluble polymers. These materials proved to be very brittle as well as having low tensil and mechanical strengths. In an attempt to improve the properties of this polymer system, Butler and Ingley (3) reacted diallyl quaternary ammonium bromide salts (1) to produce a polymer that was water-soluble and non-gel forming. Later, Butler and Goette ( 4 ) observed that diallyl-Pvinyloxyethyl quaternary ammonium bromides (2) also produced a water-soluble polymer and that the P-vinylDepartment of Applied Research, Philip Morris Research Center, Richmond, Va. 0198-4321/80/1219-0528$01.00/0
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oxyethyl group was unreacted. Additionally, Butler and Johnson (5)found that diallylammonium bromides containing propargyl groups (3) produced water-soluble polymers with the propargyl groups remaining unreacted. Thus, it was found that (a) allylammonium bromide itself does not polymerize (3),(b) bis (N,N-disubstituted)-1,4diamino-2-butene dibromide does not polymerize (6),(c) those monomers containing NJV-diallyl groups produced water-soluble polymers (3),and (d) water-insoluble polymers were obtained from monomers that had three or more allyl groups attached to a quaternary ammonium site (4). To explain the formation of water-soluble, noncrosslinked polymers when diallyl quaternary ammonium salts were polymerized, Butler and Angelo (7) proposed a chain growth mechanism which produced cyclic structures. The mechanism involved an attack by the radical initiator on the y-carbon of one of the allyl double bonds, followed by intramolecular cyclization at the y-position of the second allylic double bond (Figure 1). The resultant cyclic radical then attacks a second monomer molecule, and the chain grows by an alternating repetition of the process. This type of polymerization has become known as cyclo0 1980 American Chemlcal Society
