Experimental Studies of the Formation and Properties of Polymer

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20 Experimental Studies of the Formation and Properties of Polymer Networks J. L. STANFORD and R. F. T. STEPTO The University of Manchester Institute of Science and Technology, Department of Polymer and Fiber Science, Manchester, M60 1QD, England

The paper f i r s t considers the factors affecting intramolecular reaction, the importance of intra molecular reaction i n non-linear random polymer isations, and the effects of intramolecular re action on the gel point. The correlation of gel points through approximate theories of gelation i s discussed, and reference i s made to the deter mination of effective functionalities from gel -point data. Results are then presented showing that a close correlation exists between the amount of pre-gel intramolecular reaction that has occurred and the shear modulus of the network formed at complete reaction. Similarly, the Tg of a network i s shown to be related to amount of pre-gel intramolecular reaction. In addition, materials formed from bulk reaction systems are compared to i l l u s t r a t e the inherent influences of molar masses, functionalities and chain structures of reactants on network properties. Finally, the non-Gaussian behaviour of networks in compression i s discussed. The properties of a polymer network depend not only on the molar masses, functionalities, chain structures, and proportions of reactants used to prepare the network but also on the condi tions (concentration and temperature) of preparation. In the Gaussian sense, the perfect network can never be obtained in practice, but, through random or condensation polymerisations(Γ) of polyfunctional monomers and prepolymers, networks with imper fections which are to some extent quantifiable can be prepared, and the importance of such imperfections on network properties can be ascertained. In this context, the use of well-characterised random polymerisations for network preparation may be contrasted with the more traditional method of cross-linking polymer chains. With the latter, uncertainties can exist with regard to the

0097-6156/82/0193-0377$06.25/0 © 1982 American Chemical Society

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d i s t r i b u t i o n of primary chain lengths, chains between junction points, loose ends and entanglements. The present paper presents a survey of published and more recent work on correlations between network properties and reactant structures and reaction conditions. The reaction systems used have been generally polyoxypropylene(POP) t r i o l s or t e t r o l s of various molar masses reacting i r r e v e r s i b l y with diisocyanates (to give polyurethanes) or diacid chlorides (to give polyesters), the l i k e functional groups having equal r e a c t i v i t i e s . Reactions have been carried out i n bulk and at various dilutions i n inert solvents. Reaction systems with equimolar amounts of reactive groups have been used, and emphasis has been placed on the extent to which pre-gel intramolecular reaction defines the physical properties of the networks formed at complete reaction. Pre-gel intramolecular reaction can introduce e l a s t i c a l l y ineffective loops into a rubbery network. In general, loops produce the opposite effects on physical properties to those expected from entanglements. Pre-gel Intramolecular Reaction Previous studies (2) have shown how ring structures formed during i r r e v e r s i b l e linear random polymerisations leading to polyurethanes may be measured. The work has been extended(3,4) to non-linear polyurethane formation using hexamethylene d i i s o cyanate(HDI) and POP t r i o l s . For non-linear polymerisations, i t i s found that the number of ring structures per molecule at extent of reaction ρ i s always s i g n i f i c a n t , even i n bulk reactions. For example, Figure 1 shows the number of ring structures per molecule (N ) versus extent of reaction for bulk, linear and non l i n e a r polyurethane-forming reactions with approximately equi molar concentrations of reactive groups(2,3). The much larger number of ring structures per molecule i n the non-linear compared with the linear polymerisation i s due to the larger number of opportunities per molecule f o r intramolecular reaction i n the former type of polymerisation. The other factors influencing intramolecular reaction i n the two reaction systems i n fact predict more intramolecular reaction i n the linear system, as i s now discussed. An i l l u s t r a t i o n Ç5) of the competition between intermolecular and intramolecular reaction, f o r the RA2 + RB2 and RA2 + RB3 type random polymerisations of Figure 1, i s shown i n Figure 2. The probability that a given A group reacts intramolecularly rather than intermolecularly depends on the concentration of nearby Β groups from the same molecule compared with the concentration of Β groups from other molecules. In random polymerisations only ring structures of certain sizes can form as defined by the number of bonds i n repeating units of the chain structures. The situation i s i l l u s t r a t e d i n Figure 3 with respect to the smallest rings i n RA2 + RB2 and RA2 + RB3 polymerisations, where the reacting groups fÂ] and [F] are separated by ν bonds(5). r

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379

Formation of Polymer Networks

OA N

O.3

r

non-linear

-

HDI • L G 5 6

O.2

O.1 linear

0

Ο

O.2

OA

r>

HDI + P E G 2 0 0

O.6

O.8

1.0

Mgure 1. Number fraction of ring structures per molecule (N ) as a function of extent of reaction (p) for bulk, linear, and nonlinear polyurethane-forming reactions with approximately equimolar concentrations of reactive groups (r = [NCO] / [OH] » 1)(2, 3). Conditions: O-linear polymerization, HDI + poly(ethylenegly~ col) at 70°, [NCO] = 5.111 mol/kg, [OH] = 5.188 mol/kg; number-average number of bonds in chain forming smallest ring structure (v) = 25.2, and nonlinear polymerization, HDI and POP triol at 70°C, [NCO] =O.9073mol/kg, [OH]ο = O.9173 mol/kg; ν = 115. Reproduced with permission from Ref. 5. r

0

0

0

0

0

int

(a)

ext

c

ext

2

S

int

c

int

( b )

c

ext

2

2

Figure 2. Concentrations of Β groups around a reference Q U group. From left to right: RA and RB polymerization; RA and RB polymerization. c is the concentration of Β groups from the same molecule. c is that from groups on other molecules (5). Reproduced, with permission, from Ref. 5.

C

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381


Overall, ring structures can be formed from chains of v, 2v, 3v,. ... bonds. Considering for a moment linear polymerisations, the proba b i l i t y of intramolecular reaction for equimolar reaction mixtures w i l l be characterised by the ring-forming parameter(5, where p and pb are the extents of reaction at gelation of A and Β groups, respectively, and X b i s the ringforming parameter defined by the equation c

a

a

a

λ

ab

= c. /(c. +c J , i n t mt ext

(4)

v

with °int

=

f

( -2)Pab.(l,3/2).

(5) f

Equation(3) was derived from a generalisation of K i l b s linear sequence(20) for the gelation condition i n an RA2 + RB3 polymerisations, as depicted i n Figure 4. In equation(5), (f-2) represents the number of opportunities for intramolecular reaction at each branch unit along the linear sequence i = 1, 2, 3, The sequence grows from B through A* to B and 1

φ(1,3/2) = I l V = 2.612 (6) i=l sums over the r e l a t i v e p r o b a b i l i t i e s for intramolecular reaction at various branch points. With X taken as constant for a given polymerisation reaction, Cext has to be chosen a r b i t r a r i l y ) , and c x t = ao cbo and c x t = c + cbc> respectively the i n i t i a l and gel-point concentrations of reactive groups, are used as extreme values. To analyse gel-point data equations(4) and (5) are combined 3

aD

c

e

+

e

a c

/

2

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( a

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383


)

(

b)

Figure 3. Repeating units of the chain structures. From left to right: RA and RB polymerization; RA and RB polymerization. The repeating units have ν bonds separating the reacting groups 2 ) andJÏÏ] (5). Reproduced, with permission, from Ref. 5. 2

2

2

Β

S

Β Α

Β

Β

Α

f-2

Β Α

Β Α

Α

f-2

Α

f-2

Figure 4. Development of Kilb's linear sequence to define the conditions for gela tion in RA and RB polymerization (21). Reproduced with permission, from Ref. 5. 2

f

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to give(21) V

( 1

- ab>

" ab " i n t e x t = ( « Î P a l M C l . S / / c . X

X

C

/ C

(7)

with X fc evaluated from equation(3) using experimental values of a . Thus, X fc can be plotted versus c£xt and the slopes of the straight lines obtained interpreted i n terms of Pab (see equation (2)). Figure 5 shows gelation data for t r i f u n c t i o n a l polyesterforming systems(22) analysed(21)according to equations(7), with Cext ao bo« e x t varied by carrying out reactions i n various amounts of inert solvent. As indicated i n the caption, the s i x systems were chosen to have different values of v, and, at a given i n i t i a l d i l u t i o n , the value of i s seen to increase as ν decreases, as predicted by equation(2). Plots of X versus (cac Cbc)" show slight curvature with slopes decreasing as d i l u t i o n at gel increases. However, the i n i t i a l slopes of such plots and the slopes of the plots i n Figure 5 can be analysed in terms of equation(2) to give values of b characteristic of the chains forming the smallest ring structures. * The values so obt ained are reproduced i n Table 1, where the systems are l i s t e d i n decreasing order of ν /v. a

c

a

=

c

+

c

c

w a s

a D

+

1

Table I. Values of b for polyester-forming systems derived(21) from Figure 5 and p l o t s of X versus ( c + % ) ~ 1 according to equations(7). v / v - f r a c t i o n a l length of acid chloride residue i n the chain of ν bonds, ( i ) c t = c + CQQ. ( i i ) c t = ac bcexplanation of reactants see Figure 5. a o

a c

0

AC

e x

c

+

c

a o

e x

F o r

System sebacoyl chloride + LHT240 adipoyl chloride + LHT240 sebacoyl chloride + LHT112 adipoyl chloride + LHT112 6. sebacoyl chloride + LG56 5. adipoyl chloride + LG56 2. 1. 4. 3.

V

41 37 70 66 136 132

V

V

AC/ O.268 O.189 O.157 O.106 O.081 O.053

b/nm(i) O.318 O.313 O.293 O.270 O.267 O.280

b/nm(ii) O.508 O.480 O.433 O.399 O.390 O.371

The values of b i n Table I and the results i n Figure 5 indicate that for chemically similar systems of a given function a l i t y the amount of pre-gel intramolecular reaction depends primarily on the size (v) of the smallest ring structure with a secondary dependence on chain stiffness (b). The dependence on ν i s clear from Figure 5, whilst the dependence on b i s indicated by the different values of b for the various systems. With regard to thelatter, the acid chloride residues of the chains of ν bonds are reckoned to be s t i f f e r than the oxypropylene r e s i dues (8,9). Accordingly, b i s found to decrease as v / v decreases, with v £ being the number of bonds i n the acid chloride residue. It should be noted that, because b varies from system to system, the slopes of the lines i n Figure 5 are not d i r e c t l y proportional to v / , although they do decrease as ν increases. F i n a l l y , the A

- 3

O.2

OA O.6

c

O.8

a o

+

c

b /

1

/

k

g

o

1.0

m

f

1

1.2

ext

Key: 1, adipoyl chloride and LHT240, ν is 37; 2, sebacoyl chloride and LHT240, ν is 41; 3, adipoyl chloride and LHT112, ν is 66; 4, sebacoyl chloride and LET 112, ν is 70; 5, adipoyl chloride and LG56, ν is 132; 6, sebacoyl chloride and LG56, ν is 136.

b0

ao

Figure 5. Analysis (21) according to Eq. 7 of gel-point data (22) from reactions of diacid chlorides (adipoyl and sebacoyl chlorides) and POP triols (LHT240, LHT112 (oxypropylated 1,2,6-hexane triols), and LG56 (oxypropylated glycerol)) in bulk and in diglyme solution at 60°C, with c = c + c .

Ο

i

386

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pair of values of b given f o r each system i n Table I encompasses the value expected from solution properties(8,9). Hence, the true average value of c x t l i e s somewhere between c o cbo and cac + cbc, as i t should. Behaviour similar to that shown by the polyester-forming systems i s shown by the several polyurethane-forming systems which have been studied(?,4,6,15,23-28), and Figure 6 and Table II give the results(29) f o r polyurethane-forming systems from which network materials have been formed at complete reaction. In general, compared with the polyester-forming systems, curved +

e

a

Table I I . Values of b for polyurethane-forming systems derived(29) from Figure 6 and plots of Xab versus (cac b c ) ~ * according to equations(7). vpj/v - fractional length of d i i s o cyanate residue i n the chain of ν bonds ( i ) cext = c o cbo( i i ) cext = cac + cbc- For explanation of reactants see text and Figures 5 and 6. +

c

+

a

1. 2. 3. 4. 5.

System HDI/LHT240 HDI/LHT112 MDI/LHT240 HDI/OPPE-NHI HDI/0PPE-NH2

f 3 3 3 4 4

V

33 61 30 29 33

b/nm(i) O.247 O.222 O.307 O.240 O.237

VDI/V

O.303 O.164 O.233 O.345 O.303

b/nm(ii) O.400 O.363 O.488 O.356 O.347

plots of A versus c-jL are always obtained, and the values of b, from the i n i t i a l slopes of such plots are smaller, at least for systems based on a l i p h a t i c diisocyanates and POP t r i o l s (3,4,6,23,28). In Figure 6, the larger values of X f o r systems 4 and 5 compared with the other systems i l l u s t r a t e the increased oppor t u n i t i e s for intramolecular reaction i n tetrafunctional compared with t r i f u n c t i o n a l systems. Further, the smaller values of b for system 5 compared with those for system 1, with the same value of v, probably indicated that equation(3) r e l a t i v e l y undercounts the opportunities f o r intramolecular reaction for tetrafunctional as compared with t r i f u n c t i o n a l reactants, so that smaller values of b are required i n compensation. System 3, based on aromatic diisocyanate, gives the largest values of b, characteristic of i t s s t i f f e r chain structure. a D

a

Determination of Effective Functionalities from Gelation Data. Gelation data from reactions at various dilutions are sometimes used to determine chemical f u n c t i o n a l i t i e s of reactants(30,31). Such a procedure should be viewed with caution as i t assumes that the functional form of the dependence of ring-forming parameter upon d i l u t i o n which i s predicted by theory i s that obtained i n practice, and, as Figure 6 indicates, t h i s assumption i s not always j u s t i f i e d .

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O.4 h

Figure 6. Analysis (29) according to Eq. 7 of gel-point data (25, 26,2%) from reactions of HDI and diphenylmethane diisocyanate (MDI) with POP tnlos (LH1240, υ π 112) and tetrols (OPPE-NH1, OPPE-NH2-oxypropylated pentaerythntols) in bulk and in nitrobenzene solution at80°C, with c = c + c . ext

ao

h0

Systems 1 and 2, HDI and POP triols; 3, MDI and POP triol; 4 and 5 HDI and POP tetrols. Key: 1, HDI and LHT240, ν is 33; 2, HDI and LHT112, ν is 61; 3 MDI and

LHT240, ν is 30; 4, HDI and OPPE-NH1, ν is 29; 5, HDI and OPPE-NH2, ν is 33.

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One system studied by the authors(3) used LG56 t r i o l which had been characterised by molar-mass as well as end-group deter minations. The data for the samples used are given i n Table I I I , indicating a true number-average functionality ( f ) of between 2.95 and 2.99. The t r i o l was reacted with HDI i n bulk (see Figure 1) and at various dilutions i n benzene, and values of Nr and a determined. To estimate functionality from a , equations n

c

c

Table I I I .

Characterisation of LG56 t r i o l samples(3)

EW* M /g mol-1 bampie (/g(molOH)-l) (M /g mol-1) 1 1007 3016 2 1011 2985 *Equivalent Weight.

fn (= Mn/EW) 2.99 2.95

n

n

(3 - 5) may be recast to give Λ 1 (f-2) Pab.2629) for dry networks formed from system 3 of Figure 9 at different i n i t i a l d i l u t i o n s of reaction mixtures. Measure ments were carried out at 1Hz using a torsion pendulum(26). The results were shown i n Figure 10. The two l i m i t i n g values of Tg for t h i s system correspond to networks with Mc = and M = Μ£. Thus, the horizontal broken l i n e gives the minimum Tg, that of a linear MDI/POP polymer having a repeat unit of molar mass equal to Mc, and the maximum value of Tg at a = O.5 was obtained by extrapolation of (1/M , Tg) data to 1/Μ£. The variation of Tg with a (or M ) i s a r e f l e c t i o n of the influence of junction-point density on the freedom of segmental motion. The maximum range of Tg values shown, 301 to 312K, possibly r e f l e c t s the maximum influence for these MDI/POP t r i o l systems. c

00

c

c

C

c

c

Gel Point and Properties of Networks from Bulk React ionSvstemsThe results i n Figure 9 show c l e a r l y that the modulus of (dry) networks formed at complete reaction depend strongly on the amount of pre-gel intramolecular reaction that has occurred. Even reactions i n bulk, as indicated by the points at the lowest values of pr,c for the various systems, y i e l d networks with moduli less than those predicted for the perfect networks f o r given reactants. As i s clear from the e a r l i e r discussions of pre-gel i n t r a molecular reaction, such reaction i n principle always occurs i n random polymerisations, although i t s amount may be reduced by using reactants of higher molar mass, lower f u n c t i o n a l i t i e s , and s t i f f e r chain structures. Thus, the use of end-linking reactions to produce model networks (for example(35) and references quoted

c

c

repeat

0

o

Figure 10. Τg versus a for dry, trifunctional polyurethane networks, Φ (26). Reaction systems: MDI/LHT240 (system 3 of Figure 9), M ° is 710 g/mol, ν is 30, at various initial dilutions of reactants. is MDI/POP diot. M = M.

H

•H

Π

•Ή

H

03

>

s« c w « m m r

α

>

03

m

S

Η Ο

>

w

vo 4^

CO

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A N D STEPTO

therein) does not i n general lead to perfect networks. However, the results i n Figure 9, i n p a r t i c u l a r , show that the use of given reactants at various i n i t i a l d i l u t i o n s , linked with the determination of gel points and moduli, can give a measure of the network imperfections introduced by pre-gel intramolecular reaction. The moduli and Tg s of the networks formed from the bulk reactions of the five systems of Figure 9 are shown i n Table IV(29). The f i r s t five columns define the systems, the next two give the experimental values of G(at 298K) and Tg, and the last three give the values of pr,c, M , and G/G°. The last quantity i s the reduction i n rubbery shear modulus on the basis of that expected for the perfect network(G°). G/G° i s i n fact equal to Mc/M . The network from system 3 i s d i s t i n c t from the rest, being a glass at room temperature and also having a rubbery shear modulus near the value expected on the basis of G°. Possible reasons for t h i s high value of G/G° follow those discussed previously with reference to Mc/Mc and Figure 9. The more f l e x i b l e chains of the aliphatic systems give lower values of Tg, resulting i n elastomers at room temperature. In general, the factor by which G i s reduced depends on Mc, f, chain s t i f f n e s s , and the i n i t i a l concentrations of reactive groups obtainable i n bulk, i n a manner which s t i l l needs to be resolved i n d e t a i l . However, for bulk reaction mixtures, the moduli of networks with r e l a t i v e l y f l e x i b l e chain structures can be reduced by a factor of f i v e below those expected for network formation i n the absence of pre-gel intramolecular reaction. f

c

c

Deviations from Gaussian Behaviour. It was generally found that the networks studied i n compression(25,28,32) had small but significant deviations from Gaussian stress-strain behaviour. These have been discussed i n d e t a i l for the polyester systems(32), where i t was found that the deviations decreased as Mc increased, and for values of Mc greater than about 10 g mol" the deviations became negligible. They depend p r i n c i p a l l y on M and not on whether a network was measured i n the dry or swollen state. Thus, for the short chains between junction points i n the present networks, the deviations were taken as reflecting the departures of the density d i s t r i b u t i o n of end-to-end vectors from Gaussian form. 1

c

system 1 HDI/LHT240 2 HDI/LHT112 3 MDI/LHT240 4 HDI/0PPE-NH1 5 HDI/0PPE-NH2

f 3 3 3 4 4

O.71 O.71 O.71 O.58 O.58

c

(a )i

33 61 30 29 33

V

635 1168 705 500 586

MçVg mol" 1

6

6

6

6

2

G(298K)/NnT Tg/K 1.0 χ 10 (a) 255 O.8 χ ΙΟ (a) 228 3.0 χ 10f(b) 311 275 1.1 χ 10 (b) 271 1.2 χ 10 (a)

c

Pr,c M /g mol" O.053 3024 3650 O.055 O.034 881 2273 O.108 O.100 1953

1

Table IV. Shear modulus and Tg of polyurethane networks prepared from bulk reactios (29). G(298K) - shear modulus at 298K, (a) from uniaxial compression, (b) from torsion pendulum measurements. G/G° i s the rubbery shear modulus relative to that expected for the perfect network well above Tg. G/G° O.21 O.32 O.80 O.22 O.30

H

H

s κ;

>

m r

5β

m

5β

Ο

>

5*3

m

H Ο

C/î

w r >

Os

20.

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397

The deviations from Gaussian stress-strain behaviour intro duce uncertainties into the values of M /M£ discussed previously i n t h i s paper. However, such uncertainties have been shown to be of secondary importance compared with the ranges of Mc/Mc values found for networks from different reaction systems(25,32). The observed deviations from Gaussian stress-strain behaviour i n compression were i n the same sense as those predicted by the Mooney-Rivlin equation, with modulus increasing as deformation ratio(Λ) decreases. The Mooney-Rivlin equation i s usually applied to t e n s i l e data but can also be applied compression data(33). According to the Mooney-Rivlin equation c

σ/(Λ-Λ" ) = 2 C 2

X

+ 2C /A,

(10)

2

where σ i s the stress on the basis of undeformed cross-sectional area and Οχ and C2 are constants, with Οχ associated with the shear modulus. Figure 11 shows plots according to equation(10) of stressstrain data for triol-based polyester networks formed from the same reactants at three i n i t i a l d i l u t i o n s (0% solvent(bulk), 30% solvent and 65% solvent). Only the network from the most d i l u t e reactions system has a s t r i c t l y Gaussian stress-strain plot (C2 = 0), and the deviations from Gaussian behaviour shown by the other networks are not of the Mooney-Rivlin type. As indicated previously, they are more sensibly interpreted i n terms of depar tures of the d i s t r i b u t i o n of end-to-end vectors from Gaussian form. The deviations from Gaussian s t r e s s - s t r a i n behaviour for the tetrafunctional polyurethane networks of Figure 9 are qualitat i v e l y similar to these found for the t r i f u n c t i o n a l polyester net works (25), and the error bars on the data points for systems 4 and 5 i n Figure 9 indicate the resulting uncertainties i n M /Mc. I t i s clear that such uncetainties do not mask the increases i n Mc/Mc with amount of pre-gel intramolecular reaction. c

Conclusions The factors which influence pre-gel intramolecular reaction i n random polymerisations are shown to influence strongly the moduli of the networks formed at complete reaction. For the polyurethane and polyester networks studied, the moduli are always lower than those expected for no pre-gel intramolecular reaction, indicating the importance of such reaction i n determin ing the number of e l a s t i c a l l y i n e f f e c t i v e loops i n the networks. In the l i m i t of the ideal gel point, perfect networks are pre dicted to be formed. Perfect networks are not realised with bulk reaction systems. At a given extent of pre-gel intramolecular

398

ELASTOMERS

%

Ο

I

Ο

2

A

8

I

10

I A-A

ELASTICITY

strain

6

-O.158

A N DRUBBER

-2

-O.298

12

I

-0Λ51

Figure 11. Mooney-Rivlin plot of stress-strain data (32) for three triol-based polyester networks prepared from sebacoyl chloride and LHT240 at various initial dilutions in diglyme as solvent. Conditions: Ρ100 is 0% solvent; PI30 is 30% solvent; Ρ165 is 65 % solvent.

20.

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399

reaction (pr,c)> the reductions i n moduli below those expected for the perfect networks are larger for t r i f u n c t i o n a l as compared with tetrafunctional networks of similar chain structures, f o r more f l e x i b l e chains, and for reactants of lower molar mass. Interesting deviations from Gaussian stress-strain behaviour in compression have been observed which related to the Mc of the networks formed, rather than t h e i r degrees of swelling during compression measurements. The reactants used to form the networks studied are generally of lower molar mass than those used by other workers to form perfect networks (e.g. (35)). However, the present results do indicate that very l i t t l e pre-gel intramolecular reaction can have a marked effect on modulus. For example, for Pr,c =O.05,or =O.58,with a t r i f u n c t i o n a l polyurethane-forming system of Mc = 635g mol-1, the modulus i s reduced by a factor of f i v e below that calculated on the basis of the small-strain(affine) behaviour of the perfect network. As a result, i t i s recommended that the effective absence of pre-gel intramolecular reaction i n endlinking reactions to form 'perfect networks be confirmed by experiment rather than be assumed. The use of the same reactants at different i n i t i a l dilutions to give dry networks of different moduli not only helps to define a scale of network imperfections but also enables the range of materials which can be prepared from given reactants to be usef u l l y extended. 1

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Literature Cited 1. Stanford, J.L.; Stepto, R.F.T. J.Chem.Soc.Faraday Trans.I 1975, 71, 1292. 2. Stepto, R.F.T; Waywell, D.R. Makromol.Chem. 1972, 152, 247; 263. 3. Stanford, J.L.; Stepto, R.F.T. Br.Polymer J. 1977,9,124. 4. Ahmad, Z. Ph.D. Thesis, University of Manchester, England, 1978. 5. Stepto, R.F.T. "Developments i n Polymerisation-III'; Haward, R.N., Ed.; Applied Science Publishers Ltd.: London, i n press; Chap. 3. 6. Stepto, R.F.T. Faraday Disc.Chem.Soc. 1974, 57, 69. 7. Stanford, J.L.; Stepto, R.F.T. J.Chem.Soc.Faraday Trans. I 1975, 71, 1292; Stanford, J.L., Stepto, R.F.T.; Waywell, D.R. J.Chem.Soc. Faraday Trans.I 1975, 71, 1308. 8. Kurata, M.; Iwama, M.; Kamada, K. "Polymer Handbook"; Brandrup, J . ; Immergut, E.H., Eds., Interscience Publishers: London, 1966; sect. IV-1. 9. Flory, P.J. " S t a t i s t i c a l Mechanics of Chain Molecules"; Intersciences Publishers: London, 1969; p.40. 10. Flory, P.J., "Principles of Polymer Chemistry"; Cornell University Press: Ithaca, New York, 1953; Chap. IX. 11. Gordon, M.; Temple, W.B. Makromol.Chem. 1972, 152, 277. 12. Gordon, M.; Temple, W.B. Makromol.Chem. 1972, 160, 263. 13. Temple, W.B. Makromol.Chem. 1972, 160, 277. 14. Stanford, J.L., Ph.D. Thesis, University of Manchester, England, 1972. 15. Cawse, J.L.; Stanford, J.L.; Stepto, R.F.T. Proc. 26th IUPAC Int.Symp. on Macromolecules, Mainz 1979, p.693. 16. Askitopoulos, V.; M.Sc. Thesis, University of Manchester, England, 1981. 17. Lloyd, A.C., M.Sc. Diss., University of Manchester, England, 1981. 18. Stepto, R.F.T. Polymer 1979, 20, 1324. 19. Frisch, H.L. 128th Meeting Amer.Chem.Soc., Polymer Div., Minneapolis, 1955. 20. Kilb, R.W. J.Physic.Chem. 1958, 62, 969. 21. Ahmad, Z.; Stepto, R.F.T. Colloid and Polymer Sci. 1980, 258 663. 22. Smith, R.S.; Stepto, R.F.T. Makromol.Chem. 1974, 175, 2365. 23. Hopkins, W.; Peters, R.H.; Stepto, R.F.T. Polymer 1974, 15, 315. 24. Hunt, N.G.K.; Stepto, R.F.T.; Still, R.H. Proc. 24th IUPAC Int.Symp. on Macromolecules, Dublin 1977, p.723. 25. Hunt, N.G.K.; Stepto, R.F.T.; Still, R.H. Proc. 26th IUPAC Int.Symp. on Macromolecules, Mainz, 1979, p.697. 26. Cawse, J.L. Ph.D. Thesis, University of Manchester, England, 1979. 27. Yoji Hirasawa; Stepto, R.F.T.; Still, R.H. Proc. 28th IUPAC Int.Symp. on Macromolecules, Strasbourg, 1981, p.117.

20.

STANFORD A N D S T E P T O


401

28. Rose, S.V.; Stanford, J.L. unpublished work. 29. Stanford, J.L.; Stepto, R.F.T.; Still, R.H. i n press; Presented i n part at Div.Organic Coatings and Plastics Chem., 181st ACS National Meeting, Atlanta, 1981, p.164. 30. Fogiel, A.W. Macromolecules 1969, 2, 581. 31. Guise, G.B.; Zoch, C.G. J.Macromo1.Sci.-Chem. 1976, A10, 1161; J.Polymer Sci. 1976, Symp. No. 55, 61. 32. Fasina, A.B.; Stepto, R.F.T. Makromol.Chem. 1981, 182, 2479. 33. Dusek, K.; Prins, W. Adv.Polymer Sci. 1969, 6, 1. 34. Flory, P.J. Polymer 1979, 20, 1317. 35. Mark, J.E. Pure and Appl.Chem. 1981, 53, 1495. RECEIVED February 2,

1982.

Experimental Studies of the Formation and Properties of Polymer

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