Addition and Condensation Polymerization ... - ACS Publications

26 Ring-Opening Polymerization of Cycloolefins

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0091.ch026

Some Mechanistic Aspects KENNETH W. SCOTT, NISSIM CALDERON, E. A. OFSTEAD, W. A. JUDY, and J. P. WARD The Goodyear Tire & Rubber Co., Research Division, Akron, Ohio 44316

The ring-opening polymerization of cycloolefins by WCl /ROH/RAlCl catalysts is a special case of olefin metathesis, a new reaction operating via a transalkylidenation mechanism. Hence, the ring-opening polymerization site involves the double bond itself rather than a single bond adjacent to the double bond. Ring-opening via a transalkylidenation reaction produces macrocyclics. All observable polymeric species up to the undecamer are monocyclic compounds whose structures depend on the number of carbons per double bond in the monomer. The same macrocyclic species are obtained from either polymerization of monomer or depolymerization of high polymer. This ring-opening polymerization is an equilibrium reaction, and it is predicted that ring-chain equilibrium may be attained if acyclic olefins are available to form chain ends. 6

2

'Tphe ring-opening polymerization of unsubstituted cyclo-monoolefins ^- leading to polymers with unsaturated polymeric repeat units having the general formula [ — ( C H ) — C H = C H — ] , has been reported recently (4, 7, 9, 10). Natta et al. (9) demonstrated that the monomers cyclopentene, cycloheptene, cyclooctene, and cyclododecene, when exposed to catalyst combinations derived from WC1 and either (C2H ) A1 or (CoH ) AlCl, will undergo ring-opening polymerization leading to their respective polyalkenamers. In addition, unsaturated alicyclic monomers possessing more than one double bond in the ring—namely 1,5-cyclooctadiene and 1,5,9-cyclododecatriene—and the substituted, un2

n

6

5

2

399 In Addition and Condensation Polymerization Processes; Platzer, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1969.

5

3


400

ADDITION AND CONDENSATION

POLYMERIZATION

PROCESSES

saturated alicyclic monomers—3-methylcyclooctene and 3-phenylcycIooctene—have been shown to undergo ring-opening polymerization i n the presence of W C 1 6 and C 2 H 5 A 1 C 1 2 (4). The latter work demonstrated two basic features of the ring-opening polymerization of cycloolefins by tungsten-based catalysts. First, there is no double bond migration by rearrangement during polymerization, thus maintaining a regular spacing between double bonds in the polymer chain. Secondly, the polymerizability of substituted cycloolefins provides a convenient route to several perfectly alternating interpolymers. Natta et al., while discussing the thermodynamic factors which influence the polymerizability of cycloolefins, suggested that the ring-opening proceeds by cleavage of carbon-to-carbon single bonds which are a to the double bond ( 1 0 ) and that the main energy contribution to the driving force of the reaction is ring strain energy (9). In view of our recent results in connection with the recently discovered olefin metathesis reaction ( 1 , 2 , 5 , 6 ) , Natta's suggestions require drastic revision. Experimental

Materials. Ethylaluminum dichloride, Texas Alkyls Inc., obtained as a 25% solution in hexane, was diluted with the appropriate amount of benzene (dried over silica gel) to form a 0.2M solution. Tungsten hexachloride, Climax Molybdenum Co., was purified prior to use by sublimation of the volatile impurities (mostly W O C l 4 ) at 2 0 0 ° C . under a nitrogen atmosphere ( G . E . Lamp Grade). Cyclooctene ( C O ) , 1,5-cyclooctadiene ( C O D ) , and 1,5,9-cyclododecatriene ( C D T ) , Columbian Carbon Co., were purified prior to use by distillation from molten sodium under a nitrogen atmosphere. Catalyst Preparation. C O M P O N E N T A . A weighed amount of purified W C 1 6 was dissolved in dried benzene, under a nitrogen atmosphere, to form a 0.05M solution. A n appropriate amount of ethanol was added to the solution, maintaining a W C l 6 / C 2 H 5 O H molar ratio of 1.00, and the mixture was allowed to react at room temperature for about 30 minutes. A color change from dark purple to deep red was noticed. C O M P O N E N T B. C 2 H 5 A 1 C 1 2 was used as the 0.2M solution i n the mixed hexane/benzene solvent (see above). C O and C O D Polymerizations: Effect of Monomer Concentration on Low Molecular Weight Macrocyclics. The polymerizations were carried out i n narrow-mouthed bottles equipped with screw caps which were fitted with self-sealing gaskets and Teflon liners. E a c h reaction bottle was filled with 100 ml. of the appropriate monomer/benzene solution which had been pretreated by passing through a silica gel column. A l l operations were conducted under a nitrogen atmosphere. A l l bottles were injected with 1.0 m l . of Component A followed by 1.0 m l . of Component B, thus obtaining a molar ratio of A l / W / O of 4 / 1 / 1 . The polymerizations were carried out at room temperature, ca. 25 ° C , for 30 minutes, then terminated by injecting 4.0 ml. of a terminating solution

In Addition and Condensation Polymerization Processes; Platzer, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1969.


26.

SCOTT E T A L .

Ring-Opening

Polymerization

401

prepared by dissolving 6.0 grams 2,6-di-ferf-butyl-p-cresol i n 100 m l . of an 80/20 benzene/methanol mixture. The terminated solutions were transferred quantitatively into preweighed receivers where all volatile solvents and residual monomer were removed by evaporation under reduced pressure for 48 hours at 5 0 ° C . The dried products were analyzed for the low molecular weight extractable macrocyclic fraction (described under Analyses). C O Polymerization: Effect of Conversion on Low Molecular Weight Macrocyclics. A series of polymerizations of cyclooctene was carried out in a manner similar to that described above, using a constant monomer concentration of 1.57M. The polymerizations were terminated at various reaction times, thus obtaining different conversions. The products were isolated, processed, and analyzed for percent extractable macrocyclics as described previously. C D T Polymerization. Following the general polymerization procedure described above, 1,5,9-cyclododecatriene was polymerized using 100 ml. of 1.57M solution of monomer i n benzene and initiated b y 2.0 m l . each of the catalyst Components A and B. The reaction was terminated after 30 minutes, and the product was isolated, processed, and analyzed for the low molecular weight extractable macrocyclic fraction as before. Macrocyclics from C O and C O D Polymers. H i g h molecular weight polymer samples, prepared i n the C O and C O D polymerizations and extracted to remove their respective low molecular weight macrocyclic fractions were dissolved i n dried benzene forming a 4% solution of polyoctenamer and also one of poly-l,5-octadienamer. Into 50 ml. of each of these solutions we added 2.0 m l . of catalyst Component A , followed by 2.0 m l . of Component B. After 30 minutes at room temperature, the reactions were terminated, and the products were isolated as described. The material was analyzed for newly formed low molecular weight extractable macrocyclics (see Analyses). Polymers from C O and C O D Macrocyclics. L o w molecular weight extractable macrocyclic fractions, obtained from the polyoctenamers and poly-l,5-octadienamers prepared i n C O and C O D polymerizations by the extraction procedure described i n Analyses, were dissolved i n benzene, forming 20% solutions. Each 10 ml. solution was treated with 2.0 ml. of catalyst Component A , followed by 2.0 m l . of Component B. The mixtures turned highly viscous within a few minutes, indicating the formation of a high molecular weight material. After 30 minutes, the polymerizations were terminated, and the solid high molecular weight polymers were isolated as described. Analyses

Determination of Low Molecular Weight Extractable Macrocyclics. A weighed sample of dried polymer ( about 10 grams ) was extracted at room temperature for 72 hours with 100 ml. of a 50/50 hexane/2-propanol extracting mixture, changing the extracting mixture every 24 hours. After drying the extracted polymer i n vacuum for 48 hours at 5 0 ° C , it was



402

ADDITION

A N D CONDENSATION POLYMERIZATION

PROCESSES

reweighed, and the weight fraction of extracted material was thus determined. The extracting liquor containing the oily low molecular weight extractable fraction and some antioxidant (2,6-di-£er£-butyl-p-cresol) was concentrated b y evaporation of the volatile solvents and dried i n vacuum at 5 0 ° C . for further analysis b y G L C , N M R , and low voltage mass spectrometry, or used i n other experiments as previously described. NMR Spectrometry. T h e N M R analyses of the high molecular weight extracted polymers and their respective low molecular weight extracted fractions, obtained i n the various polymerization reactions of cyclooctene and 1,5-cyclooctadiene, were carried out i n 4 r - 6 % C C U solutions using the Varian A60 spectrometer at room temperature as previously described (4). Gas Chromatography of Macrocyclic Extractables. Analyses of the various macrocyclic extractable fractions b y G L C were performed using an F & M M o d e l 810 Research Chromatograph, equipped with a flame ionization detector, a 20-ft. silicone Hi-Pak column and using helium gas as carrier. The analyses were conducted at a carrier gas rate of 50 cc./min., injection port temperature of 2 8 0 ° C , and programmed at 2 0 ° C . / m i n . i n the 60-^300°C. range and holding isothermally at 3 0 0 ° C . for an additional 8 minutes. Low Voltage Mass Spectrometry of Macrocyclic Extractables. Nominal parent mass analyses of the macrocyclic extractables, obtained from typical polymerization products of cyclooctene and 1,5-cyclooctadiene, were performed on a M o d e l MS-9 double focusing mass spectrometer (Associated Electrical Industries, England) at a resolution of 1/1000 and an emission of 7.0 e.v. Samples were introduced directly into the source chamber b y the direct-probe technique. The temperature range during the experiment was 1 2 5 o - 2 0 0 ° C . , and the source pressure was maintained i n the 0.1-3 X 10"6 torr range. In addition, a high resolution measurement was carried out on the mass number 220 to identify the two components present at that mass number. Results

and

Discussion

Metathesis of Cycloolefins. The same general catalysts which promote the ring-opening polymerization of cycloolefins are also effective i n the olefin metathesis reaction i n which acyclic internal olefins undergo a unique redistribution process ( J , 2, 5, 6). 2 Ri—CH=CH—R 2 ±? R x —CH=CH—R x + R 2 —CH=CH—R 2

(1)

Analyses of the products obtained from the metathesis of 2-butene and 2-butene-d 8 (2, 5) and also from the metathesis of 3-hexene and 2butene-d 8 ( 5 ) , proved that the interchange process i n Reaction 1 definitely does not proceed via SL simple transalkylation process—i.e., a cleavage and reformation of the carbon-to-carbon single bond situated a to the double bond. The data are, however, consistent with a transalkylidenation process—i.e., a scheme which contemplates an interchange


26.

SCOTT

ET

AL.

Ring-Opening

403

Polymerization

via cleavage and reformation of the carbon-to-carbon double bond as represented in Reaction 2. R!—CH=CH—R2

i

Rt—CH ç±

CH—R2 (2)

+

I


Rx—CH^CH—R.,

Rx—CH

CH—R.>

This model compound work provides the basis for our contention that the ring-opening polymerization of cycloolefins, promoted by tungstenbased catalysts is, in fact, a special case of the more general reaction of olefin metathesis. Information obtained from studies of the olefin metathesis reaction on acyclic vinylenic hydrocarbons indicates that the site of cleavage in the polymerization of cycloolefins to form polyalkenamers is not a carbon-to-carbon single bond but the double bond itself and that ring strain energy is not an essential source for the driving force of the polymerization since one is able to conduct the basic reaction on presumably strain-free macrocyclics and even on open chain olefins which, of course, do not possess any ring strain. The following important implications, which bear directly on the nature of the cycloolefin polymerization, have precipitated out of our understanding of the basic properties of the olefin metathesis reaction. (a) A given alkylidene portion of a double bond of a cycloolefin monomer, which has undergone metathesis and has thus become an integral part of a higher molecular weight species, remains eligible for further reaction and may participate i n additional metathesis steps with other double bonds, which may be constituents of another cycloolefin monomer unit, another macromolecule, or the same macromolecule. (b) The polymerization possesses the basic features of equilibrium polymerization. ( c ) Macrocyclic species, resulting from intermolecular ring enlargement of two smaller rings or from the intramolecular metathesis of two double bonds on the same macromolecule according to Reaction 3 are present i n the polymerization mixture at equilibrium.

(CH2)n

M.

( C H 2 ) — M„

Mx represents χ polymeric repeat units


404

ADDITION

AND CONDENSATION

POLYMERIZATION

PROCESSES

(d) The composition of macrocyclic species depends on the spacing between double bonds i n the macromolecule (number of méthylène groups between neighboring double bonds). (e) In the absence of all side reactions the application of the olefin metathesis reaction to cycloolefins yields only macrocyclic species. (f) A n olefin metathesis reaction between a macrocyclic species and an acyclic vinylenic compounds leads to scission of the macrocyclic resulting i n an open chain polymer whose end groups are the alkylidene moitiés of the acyclic vinylenic compound.


(CH2)n—CH

CH—Rx ---

M*

CH

R ! H C = C H — ( C H 2 ) W — M , . — C H = C H R 2 (4)

CH—R2

Acyclic vinylenic compounds, on reaction i n this system, end up only as chain ends of open chain species. (g) Ring-chain equilibrium occurs when Factors b, c, and f are operative. (h) Some control on the configuration of the polymeric double bonds is possible (3). It has been speculated (5) that the olefin metathesis reaction mechnism involves a four-centered "quasi-cyclobutane" transition state. The three basic steps postulated for the reaction, namely, formation of a bis-olefin-tungsten complex, transalkylidenation and olefin exchange, may account, i n general, for the initiation and propagation steps i n the ringopening polymerization of cycloolefins. Several modes of termination have been considered, but suitable data to test these are not yet available. It is possible to suggest a polymerization scheme which is compatible with the mechanism suggested for the olefin metathesis reaction. For conciseness the polymerization scheme shown at the top of the next page assumes the strict absence of any acyclic olefins which might participate i n the process. Reaction 5 (the initiation step) suggests the eventual formation of a complex of two cycloolefin molecules coordinated to tungsten. Reaction 6 indicates that the transalkylidenation step results in a macrocyclization of two monomeric rings into a cyclic dimer. This is followed by the olefin exchange step (Reaction 7) whereby a monomer replaces one of the double bonds coordinated to the transition metal. Repetition of Reactions 6 and 7 constitutes the propagation step. W * is used i n Reactions 5-7 because the exact composition of the remaining ligands about the coordination sphere is not known. For example, the ultimate fate of the ethanol is uncertain. In addition, the participation of A l i n the complex


26.

Ring-Opening

SCOTT E T A L .

W*

Initiation:

C H / \ CH

RA1CL, + [WCI + ROH] + 2 C H = C H — (CH,)„

W*

CH/ \CH

CH-

\

(CH.),

CH

w*

W* • CH

(CH )„

(CH )

2

2

/1

H

CH

S

(CH )„

CH---CH

Τ

CHr^rCH ,

2

CH

(5)

(CH.

\ CH

Propagation:


\

* (CH.)

e

\

405

Polymerization

\ (CH )„

1

2

CH — C H

CH.

CH \

(CH )„ 2

/

(CH.,),

(6)

CH=CH

CH \

(CH,), \

CH =

/

ι

CH

1

( C H ) + C H = C H — (CH )„ 2

H

2

CH

CH/\CH

\

(CH )„ 2

=

CH

CH

(7)

CH

NcH,)/ is strongly suspected, and this could occur through a μ-chloride bridge to the tungsten. One of the possible termination steps considered involves a version of the olefin exchange step—Reaction 7—as W* CH—ML

-CH,

+ C H = C H — (CH2)„ (CH2)

W

-CH

CH—(CH2)

W

W* M

R

C H / \ C H

(CH2)W—CH

\

C H

C H — My (CH2)N

(8)

+ CH-(CH2)

N

Termination in this polymerization is not completely final since the My+1 species formed i n Reaction 8 may participate again via Reaction 7; hence, Reaction 8 represents a type of chain transfer mode of termination.


406

ADDITION AND CONDENSATION POLYMERIZATION PROCESSES

In the complete absence of acyclic olefins in the system, this poly merization scheme predicts a macrocyclization mode of propagation, whereby the resulting polymer is a mixture of cyclic macromolecules. A general equilibrium for this process can be represented by Reaction 9:

R/n + η ^


R# + y

R# +

m R»i + y

(^)

where Ri represents a ring of i polymeric repeat units. However, if minute amounts of acyclic olefins are present to participate i n the process (they might originate as products of reaction of the tungsten and alumi num catalyst components, be present as an impurity, or added intention ally) a mixture of rings and open chains w i l l result from the process depicted i n Reaction 10.

Under such conditions it is possible to obtain an equilibrium ring-chain system as described by Reaction 11. C

W + N

^ C W + RN

(11)

where C m is a chain of m polymeric repeat units and R„ is a ring of η polymeric repeat units. Presently available information is insufficient to permit deciding whether the high molecular weight polymers obtained i n ordinary poly merizations of cycloolefins consist of macrocyclics alone or mixtures of rings and chains. Nevertheless, the intentional introduction of known amounts of chain ends via addition of vinylenic olefins should result i n ring-chain equilibrium of the type presented i n Reaction 11. For this type of equilibrium, the weight fractions and size distributions of rings and chains present in the system may be compared with the Jacobson and Stockmayer theory (8). Experiments to test theory in this area are currently underway. Formation

of

Macrocyclics

Concentration and Conversion Effects on Macrocyclics Formation. The dependence of the extractable fraction on initial monomer concen tration has been determined for cyclooctene and 1,5-cyclooctadiene poly merizations and are plotted i n Figure 1. In this set of experiments all polymerizations were carried out to high conversions (88% or higher). The catalyst concentration was maintained constant throughout at an


26.

SCOTT E T A L .

Ring-Opening

Polymerization

407


A l / W / O ratio of 4 / 1 / 1 . The monomer/catalyst ratio necessarily i n creased with initial monomer concentration. Figure 1 indicates that large amounts of the extractable fraction are formed i n polymerizations carried out i n dilute systems.

[M]"'

f

Liter χ Mole"'

Figure 1. Dependence of extractable macrocyclics on reciprocal of initial monomer concentration, [ M ] 0 . Polymerizations conducted at [ W ] = 5 X I0~* and [AZ] = 2 X 10'3 for 30 minutes at room temperature. Conversion: >8S% O: 1,5'Cyclooctadiene Δ : Cyclooctene

The effect of conversion on extractable fraction formation is pre sented i n Figure 2 for cyclooctene polymerization. A l l variables were held constant except polymerization time. The results are plotted i n two forms. The left plot illustrates the extractable fraction as a percentage of the converted monomer. Note that at low conversions the percent of low molecular weight extractable material on the basis of the reacted monomer is much higher than the final cumulative level attained at the end of the polymerization where conversions reach 90% or higher. The cumulative percentage of the extractables formed on the basis of the initial amount of monomer is plotted on the right side of Figure 2 and increases monotonically to reach a value of 12-13% at high conversions which is typical of a cyclooctene polymerization at [ M ] 0 = 1.57. Composition of Macrocyclic Extractables. The quantitative proce dure used i n this work to separate and determine the level of the low molecular weight oily fraction is based on using a solvent mixture (hex-


408

ADDITION

AND CONDENSATION

POLYMERIZATION

PROCESSES


ane and 2-propanol) which is capable of dissolving the low molecular weight material which accompanies the very high molecular weight polymer. The present technique commonly isolates fractions having a number-average molecular weight i n the 400-500 range. The selection of this specific solvent pair is arbitrary, and other extracting solvent com binations would lead to somewhat different results. Nevertheless, on a comparative basis, the results are valuable for demonstrating basic trends of the ring-opening polymerization of cycloolefins i n forming low molecu lar weight material. Various techniques were used to establish the macrocyclic character of the low molecular weight extractable fraction. w

«2

Monomer Conversion, Percent Figure 2. Dependence of extractable macrocyclics on conversion in cyclo octene polymerization. [ M ] = 1.57; [ W ] = 5 Χ 10~*; [Αΐ] = 2 X 10s. Room temperature. Polymerization time varied 0

L o w Voltage Mass Spectrometry. The nominal parent mass numbers of the various components i n the low molecular weight extractable frac tions obtained from polyoctenamer and poly-l,5-octadienamer are listed i n Table I. Quantitative estimation of the relative amounts of individual components were not carried out owing to experimental difficulties. The large variation i n the volatilities of the various oligomers limits this pro cedure to the determination of molecular weights of the oligomers. The basic difference between the homologous series of the polymers of C O and C O D is that mass numbers found i n the C O low molecular



26.

SCOTT

ET AL.

Ring-Opening

409

Polymerization

weight extractable fraction consist of "whole" multiples of the monomer, cyclooctene, ( C 8 H i 4 ) n = H O n , while the C O D fraction consists of two series, one of which contains "whole" multiples of the monomer, 1,5-cyclooctadiene, ( C 8 H i 2 ) n = 108n, and a second series consisting of the "sesqui-" oligomers, ( C 8 H i 2 ) n - C 4 H 6 = 108n-54. Alternatively, the C O D series can be described as a single series consisting of multiples of half a monomer unit, ( C 4 H 6 ) m = 54m for m ^ 3. This indicates that the significant polymeric repeat unit contains only one double bond and is not necessarily an original monomer unit. In addition to the mass numbers reported i n Table I, a peak at 188, corresponding to phenylcyclooctane, and a peak at 186, corresponding to Table I.

Parent Masses (tn/e) of Low Molecular Weight Extractable Fractions Obtained from the Polymerization Products of Cyclooctene and 1,5-Cyclooctadiene CO

Homologous Series: (n^2)

COD

(Oligomers)

(Oligomers)

220° 330 440 550 660 770 880 990 1100 1210

216 324 432 540 648 756 864 972 1080

(C8H14)n

(C8H12)n

( Sesquioligomers)

220ft

162 270 378 486 594 702 810 918 1026 (C8H12)w-C4He

β A high resolution mass analysis of the 220 peak reveals the presence of two com pounds (220.1824 and 220.2190). The 220.1824 corresponds to the antioxidant, di-terf-butyl-p-cresol, which has a theoretical mass number of 220.1827. The 220.2190 peak corresponds to CieKks which has a theoretical mass number of 220.2191. * Corresponds to 220.1824 and is thus attributed to antioxidant.

phenylcyclooctene, were observed in the C O and C O D series, respec tively. These apparently are products of the cationic alkylation of the benzene solvent by the monomers. Mass numbers which could account for the presence of open chain oligomers plus two hydrogens were not detected within the examined region. Gas Chromatography Data. Under the testing conditions used i n the G L C analyses it is apparent that the resolution decreases with an increase i n temperature. Thus, in Figures 3-7 a tendency of peak broad ening is noticed for the higher molecular weight components. Neverthe less, the data are adequate to support an important feature of this work— namely, that this cycloolefin polymerization is reversible.


410

ADDITION

AND CONDENSATION

POLYMERIZATION

PROCESSES

Ο to


b.

CO

Extractables

and References

a. CO

M.

I

I

'

II ·

·

ι

Extractables

ι

ι

ι

I

0

2

4

6

Figure 3.

•

8 10 Minutes

I

12

I

14

ι

16

Comparison of chromatograms of cyclooctene extractable rocyclics with standard reference materials

I

18

mac-

Figures 3a and 4a show the G L C charts obtained from the C O and C O D low molecular weight extractable fractions, respectively. Figures 3b and 4b are chromatograms of the same tested samples with added known standard materials which were all normal paraffins except for 1,5,9-cyclododecatriene (40/60 c,t,t/t,t,t) which was used as a reference material i n the C O D analysis of Figure 4b. The main peaks i n the C O series differ by eight carbons while i n the C O D series the peaks are spaced at every four carbons. In comparing the first doublet peak i n Figure 4a at an elution time of 6-7 minutes with its counterpart i n Figure 4b, to which 1,5-9-cyclododecatrine was added to a reference materials, one finds a perfect overlap



26.

SCOTT

Figure 4.

ET

AL.

Ring-Opening

411

Polymerization

Comparison of chromatograms of 1,5-cyclooctadiene macrocyclics with standard reference materials

extractable

of the two peaks. Combined with the data from the low voltage mass spectrometer, where a peak corresponding to a mass of 162 was observed, it is evident that the lowest member of the C O D extractable fraction is 1,5,9-cyclododecatriene. The shaded peaks i n the various chromatograms presented i n Figures 3-7 are caused by antioxidant and alkylated benzenes whose presence had been confirmed by mass spectrometry. Figure 5 compares the G L C charts of the low molecular weight extractable fractions obtained from C O D and C D T polymerization products. Both samples exhibit the same major peaks up through the component possessing 32 carbons, which is the highest resolvable com-



412


ponent under the conditions used. A l l the major components consist of multiples of four carbons. It is also observed, on a semiquantitative basis, that the ratios of peak heights for the C, 2 0 , C 2 4 , C 2 8 , and C 3 2 com ponents are of the same order of magnitude. This leads to the reasonable conclusion that the spectrum of components i n a given sample of an extractable fraction depends primarily on the structure of the polymeric repeat unit. C O D and C D T have the same repeat unit, — ( C H 2 ) 2 — C H = C H — and thus w i l l yield similar mixtures of macrocyclic extractable fractions. Similarly, 1,4-polybutadiene, with the same polymeric repeat units as the C O D and C D T polymers, gives the same spectrum of macrocyclic species when exposed to these catalysts.

Ε ο c ο 2 Ι Ο Ο

b. CDT

Extractables

ι

ι

a. COD Extra eta bits

ι

ι

0

2

Figure 5.

ι

4

ι

6

I

I

8 10 Minutes

I

12

I

14

Comparison of chromatograms of 1,5-cyclooctadiene cyclododecatriene extractable macrocyclics

I

I

16

18

and 1,5,9-



26.

SCOTT E T A L .

Ring-Opening

413

Polymerization

L o w molecular weight extractable fractions produced by adding catalyst to dilute solutions of previously extracted high molecular weight C O and C O D polymers (Figures 6b and 7b) are compared with "conventional" extractable fractions (Figures 6a and 7a). Obviously, these low molecular weight extractable fractions can be prepared from the polymers i n the absence of any monomer, and they bear a marked resemblance to the extractable fractions prepared during polymerization. N M R Spectrometry. Figures 8 and 9 reproduce the N M R spectra of (a) the high molecular weight polymer fraction, ( b ) the low molecular weight extractable fraction, and ( c ) the high molecular weight polymer obtained by polymerization of the low molecular weight extractable frac-

b. CO Extractables by Polymer-Catalyst

Interaction

a. CO Extractables by Conventional Polymerization

0

2

4

6

10 8 Minutes

12

14

16

18

Figure 6. Comparison of cyclooctene extractable macrocyclics obtained by catalyst treatment of high molecular weight polyoctenamer with extractable macrocyclics obtained during cyclooctene polymerization




414

b. COD Extractables by Polymer-Catalyst Interaction

a. COD Extractables by Conventional Polymerization ι

Ο

ι

2

ι

4

ι

6

ι

ι

8 10 Minutes

·

12

ι

14

ι

16

ι

18

Figure 7. Comparison of 1,5-cyclooctadiene extractable macrocyclics ob tained by catalyst treatment of high molecular weight poly-l,5-octadienamer with extractable macrocyclics obtained during 1,5-cyclooctadiene polymerization

tion, for both the cyclooctene and the 1,5-cyclooctadiene cases. The data clearly demonstrate that for a given monomer these are structurally indistinguishable. W i t h i n the limits of N M R resolution, there is no evidence for the presence of any methyl or vinyl group protons i n the low molecular weight extractable fractions, and thus open chain species, which might be expected to possess such protons, are not present i n sig nificant amounts i n the extractable fraction. Combining the results of N M R , low voltage mass spectrometry, (Table I ) , and gas chromatography (Figures 3 - 7 ) with the undisputed fact that the low molecular weight extractable fractions can be polymer-


26.

2.0

3.0

1000 500 250 100 50


Ring-Opening

SCOTT E T A L .

ppM(r) 5'Ό 6.0

4.0

70

80

9.0

,

t 10,

200

300

400

415

Polymerization

- A

8.0

6.0

7.0

5.0

ΡΡΜ(ό)

4.0

3.0

2.0

1.0

Figure 8. NMR spectra of polyoctenamer, éxtractahle macrocyclic from polyoctenamer and polyoctenamer obtained by polymerization extractable macrocyclic fraction

fraction of the

(a) : Polyoctenamer (b) : Extractables from polyoctenamer (c) : Polymerized extractables from polyoctenamer

2.0

4.0

3.0

1000 500 250 100 50

'

70

'

6Ό

ΊΓθ

70

8.0

4Ό

9Ό 100

200

300

400

SO

PPM(r) 5'.0 6.0

3Ό~

2Ό

.•o TMS

1.0

0

ΡΡΜ(ό)

Figure 9. NMR spectra of poly-1,5-octadienamer, extractable macrocyclic fraction from poly-1,5-octadienamer, and poly-1,5-octadienamer obtained by polymerization of the extractable macrocyclic fraction (a) : Poly-1,5-octadienamer (b) : Extractables from poly-1,5-octadienamer (c) : Polymerized extractables from poly-1,5-octadienamer



416

ADDITION

A N D CONDENSATION

POLYMERIZATION

PROCESSES

ized to high molecular weight polymers leads to the conclusion that the low molecular weight fractions are mixtures of macrocyclic species and essentially free of open chain compounds. As described earlier, open-chain olefins in this system are a source of chain ends, and if any appreciable amount of the low molecular weight fraction consisted of open-chain olefins, one would not be able to polymerize these to a solid, high molecular weight polymer. Since the polymer prepared by polymerizing the extractable macrocyclic fraction is gel-free the macrocyclic fraction must be essentially all monocyclic species because polycyclic species would serve as crosslinkers and could lead to gel formation. The results above support four basic features, characteristic of cycloolefin polymerization: ( 1 ) The macrocyclic nature of the low molecular weight extractable fraction. (2) The composition of a given macrocyclic mixture is controlled primarily by its polymeric repeat unit. (3) Macrocyclics can be prepared, i n the absence of monomer, starting from the high molecular weight polymer. (4) The low molecular weight extracted macrocyclics can be converted to high molecular weight polymer, whose structure is indistinguishable from polymer prepared by the normal polymerization of the respective cycloolefin monomer. These features are all well understood when it is above reactions of monomer and polymers are simply general olefin metathesis reaction which operates via change of alkylidene groups as described in our previous

Additional

Mechanistic

realized that the examples of the a random interwork (1,2,5,6),

Aspects

Selective Formation of Macrocyclics. The scheme suggested and supported by the experimental results provides, at least theoretically, a route for attaining equilibrated mixtures of macrocyclic rings of selected sizes, the smallest being one polymeric repeat unit (cyclobutene for poIy-l,5-octadienamer and cyclooctene for polyoctenamer ) and the largest being a huge macrocyclic with essentially an infinite number of polymeric repeat units. In practice we have not been able to detect any cyclobutene formation in polymerizations involving the — ( C H 2 ) 2 — C H = C H — r e p e a t unit. Even for the eight membered repeat u n i t — ( C H 2 ) 6 — C H = C H — , the equilibrium concentration of cyclooctene monomer is lower than 2 X 10" 3 M. Evidently, in the formation of small- and mediumsized rings from higher molecular weight polyalkenamers configurational


26.

SCOTT

ET

AL.

Ring-Opening

Polymerization

417


and conformational factors play an important role. A l l rings permitted by the repeat unit structure and having at least 12 carbons have been detected up to molecular weights of 1000 and higher (Table I ) . Every Double Bond Eligible for Reaction. In this polymerization system, the double bonds in a given macromolecule may participate i n either intermolecular or intramolecular transalkylidenation. The intermolecular process cannot lead to a lowering of the number average molecular weight. This is true regardless of the ring or chain content of the high molecular weight polymer. The intramolecular process, which "pinches off" a macrocyclic ring from a species of higher molecular weight (Reaction 3), does lead to a net lowering of the molecular weight. The ratio between intra- and intermolecular processes, which affects the fraction of macrocyclics formed in the system, w i l l depend inversely on concentration. Figure 1 clearly confirms this expectation. Actually, by exposing a dilute (4%) solution of high molecular weight polymer to the catalyst (see Experimental discussion on macrocyclics from C O and C O D polymers ), where enhancement of the intramolecular transalkylidenation process relative to the intermolecular one takes place, large amounts of extractable macrocyclics are obtained. The reverse is also true since exposing a concentrated (20% ) solution of the low molecular weight macrocyclics to the catalyst (see Experimental discussion on polymers from C O and C O D macrocyclics) yields a high molecular weight polymer. Since these experiments clearly indicate that macrocyclic formation is a reversible, concentration-dependent process, one is led to the conclusion that ring-opening polymerization of cycloolefins by the olefin metathesis reaction is an equilibrium polymerization. E q u i l i b r i u m Polymerization. The transalkylidenation mechanism provides a convenient reaction path to ring-chain equilibrium for this polymer system. The final, necessary and sufficient condition for ringchain equilibrium is the presence of chain end groups. This requirement is not too difficult to fulfill since theory (8) suggests that less than 0.1 mole % of acyclic olefin out of the total olefin content w i l l yield ringchain equilibrium approximating some of our qualitative observations. O n this basis, an ultrapure polymerization system w i l l be required to produce very high molecular weight macrocyclic species. The distribution of ring sizes in an equilibrated system w i l l be treated in a future publication. Acknowledgment

The authors acknowledge the assistance of J. K. Phillips for the low voltage mass spectra analyses.


418


Literature

Cited

(1) Calderon, N., Chen, H. Y., Scott, K. W., Tetrahedron Letters 1967, 3327. (2) Calderon, N., Chen, H. Y., Scott, K. W., ''Abstracts of Papers," 154th Meeting, ACS, Sept. 1967, S172. (3) Calderon, N., Morris, M. C., J. Polymer Sci. Pt. A-2, 5, 1283 (1967). (4) Calderon, N., Ofstead, Ε. Α., Judy, W. Α., J. Polymer Sci. Pt. A-1, 5, 2209 (1967). (5) Calderon, N., Ofstead, Ε. Α., Ward, J. P., Judy, W. Α., Scott, K. W., J. Am. Chem. Soc. 90, 4132 (1968). Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0091.ch026

(6) Chem. Eng. News 45 (41), 51 (1967).

(7) Eleuterio, H. C., U. S. Patent 3,074,918 (1963). (8) Jacobson,H.,Stockmayer, W. H., J. Chem. Phys. 18, 1600 (1950). (9) Natta, G., Dall'Asta, G., Bassi, I. W., Carella, G., Makromol. Chem. 91, 87 (1966). (10) Natta, G., Dall'Asta, G., Mazzanti, G., Angew. Chem. 76, 765 (1964); see also Makromol. Chem. 56, 224 (1962).

RECEIVED

March 22, 1968.


Addition and Condensation Polymerization ... - ACS Publications

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