Structure and Elasticity of Loose Step Polyaddition Networks - ACS

21 Structure and Elasticity of Loose Step Polyaddition Networks

Downloaded by FUDAN UNIV on February 14, 2017 | http://pubs.acs.org Publication Date: July 19, 1982 | doi: 10.1021/bk-1982-0193.ch021

KAREL DUŠEK and MICHAL ILAVSKÝ Czechoslovak Academy of Sciences, Institute of Macromolecular Chemistry, 162 06 Prague 6, Czechoslovakia

For imperfect epoxy-amine or polyoxypropyleneurethane networks (M =10 -10 ), the front factor, A, in the rubber e l a s t i c i t y theories was always higher than the phantom value which may be due to a contri bution by trapped entanglements. The crosslinking density of the networks was controlled by excess am ine or hydroxyl groups, respectively, or by addition of monoepoxide. The reduced equilibrium moduli (equ al to the concentration of e l a s t i c a l l y active network chains) of epoxy networks were the same i n dry and swollen states and f i t t e d equally well the theory with chemical contribution and A~1 or the phantom network value of A and a trapped entanglement con tribution due to the similar shape of both contri butions. For polyurethane networks from polyoxypropylene t r i o l (M=2700), A~2 if only the chemical contribution was considered which could be explained by a trapped entanglement contribution. 3

5

c

Experimental examination of predictions of the new rubber e l a s t i c i t y theory (1,2) continues to be of great interest. However, numerous conflicting data as to the f e a s i b i l i t y of reaching the phantom state behaviour and possible contribution coming from permanent (equilibrium) interactions between e l a s t i c a l l y active network chains (EANC)-usually called trapped entanglements-have accumulated i n the literature (2-15). Experimental d i f f i c u l t i e s i n reaching true equilibrium stress-strain isotherms may be a source of discrepancies, but the disagreement does not disappear even if there i s no doubt about reaching the equilibrium state. A poor description of the network structure in terms of the concentration of EANC's, v>, may be, however, very serious. Perfect (and there fore, well-defined) networks, i n which v i s given by the concen tration of precursor elastomer chains, are sometimes preferred, but i t i s practically impossible to obtain a perfect structure due to (a) d i f f i c u l t y in reaching f u l l conversion of functional e

e

0097-6156/82/0193-0403$06.00/0 © 1982 American Chemical Society

Mark and Lal; Elastomers and Rubber Elasticity ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

404

ELASTOMERS

AND

RUBBER

ELASTICITY

groups and (b) wastage of some bonds i n closing e l a s t i c a l l y i n active cycles (EIC) which always competes with the formation of EANC's. Possible small errors i n the determination of the concentration of functional groups or molar ratios i n alternating type polyreactions may further contribute to a poor description of the network structure. Although the resulting degree of imperfection may be small (e.g., a few percent i n conversion or bonds wasted i n EIC) (16-19), a loss i n v i n endlinked networks amounting to 20-40% would not be surprising. A statement l i k e that the sol fraction was below 1%, which should have indicated the perfectness of the structure, does not mean much, because an increase in the gel fraction from 99 to 100% usually means an increase i n V by a factor of 1.3-1.4. I t follows that "perfect" networks do not have any perfect structure and, if the existing degree of imperfectness i s neglected, these networks are not well defined any more. Well defined but imperfect networks widely d i f f e r i n g i n , that are chemically inert and are prepared using non-stoichiometric alternating step polyaddition systems, offer another object of study of relations between equilibrium e l a s t i c i t y and concentration of EANC s. Instead of using precursor chains of varying length, the length and concentration of EANC's i s varied by an excess of functional groups of one kind. In this way, dangling chains are produced and the network chains are branched with many side chains attached to them i n contrast to the majority of smooth unbranched chains i n "perfect" networks. In this contribution, we report equilibrium modulus and s o l fraction measurements on diepoxide+monoepoxide-diamine networks and polyoxypropylene triol-diisocyanate networks and a comparison with calculated values. A p r a c t i c a l l y zero (epoxides) or low (polyurethanes) Mooney-Rivlin constant C« and a low and accounted for wastage of bonds i n e l a s t i c a l l y inactive cycles are the advantages of the systems. Plots of reduced modulus against the gel fraction have been used, because they have been found to minimize the effect of EIC, incompleteness of the reaction, or possible errors i n analytical characteristics (16-20). A f u l l account of the work on epoxy and polyurethane networks including the s t a t i s t i c a l derivation of various structural parameters w i l l be published separately elsewhere.


e

e

-

Experimental Epoxide networks were prepared from d i g l y c i d y l ether of 4,4 -dihydroxydiphenyl-2,2-propane (98.2% by gas chromatography), phenyl glycidyl ether (99.3%) and r e c r y s t a l l i z e d 4,4~-diaminodiphenylmethane. The crosslinking density was controlled by the i n i t i a l molar ratio 2[NH 1/ [epox] = r = 2.3-1.0 and by the fraction of epoxy groups i n the monoepoxide, s. The reaction time was 16 h at 65 *C and 5 h at 130*C. The residual concentration of -

2

A

—1

epoxy groups was determined by IR spectrometry at 915 cm


.

21.

DUSEK

Elasticity of Loose Step Polyaddition Networks 405

A N D ILAVSKY

Equilibrium stress-strain dependences were determined in extension using a stress relaxation arrangement described e a r l i e r (21). Dry non-extracted Samples were measured at 150"C i n nitrogen atmosphe re and extracted samples swollen in dimethyIformamide were meas ured at 25 *C. The equilibrium value of stress (> was reached within 2-4 min except of a few dry samples with the lowest V , for which the equilibrium stress was determined using an extrapolation procedure described e a r l i e r (21). Polyurethane networks were prepared from polyoxypropylene (POP) triols(Union Carbide Niax Polyols) after removal of water by azeotropic d i s t i l l a t i o n with benzene. For Niax LHT 240, the number-average molecular weight determined by VPO was 710 and the number-average functionality f , calculated from and the con tent of OH groups, determined by using excess phenyl isocyanate and t i t r a t i o n of unreacted phenyl isocyanate with dibutylamine, was 2.78; the content of residual water wasO.02wt.-%. For the Niax LG-56, =2630, f =2.78, and the content of H 0 was O.02wt.-%. The t r i o l s were reacted with r e c r y s t a l l i z e d 4,4 -diphenylmethane diisocyanate i n the presence ofO.002wt.-% d i b u t y l t i n dilaurate under exclusion of moisture at 80*C for 7 days. The molar r a t i o 0H [OH]/ [NC0] varied between 1.0 and 1.8. For dry samples, the stress-strain dependences were measured at 60*C i n nitrogen atmo sphere. The relaxation was s u f f i c i e n t l y fast and no extrapolation to i n f i n i t e time was necessary. e


e

n

n

2

-

r

=

Calculation of structural parameters The required structural parameters of the networks - the sol f r a c t i o n , w , the concentration of EANC's i n the gel, V , the number-average functionality of e l a s t i c a l l y active crosslinks (21), f , and the trapping factor (22,23) , T , were calculated using the theory of branching processes based on a t r e e - l i k e model. For epoxide networks, the substitution effect i n the amine groups of the diamine was taken into account. The calculation procedure was described i n ref. 20. For polyurethanes, the procedure derived for a random ring-free diol-triol-diisocyanate reaction (17) can be used i n the calculation of w„ and S> ; the calculation of f. and ο. eg " T follows from an analogy with epoxy networks. We do not give e x p l i c i t relations for the network parameters here, but only summarize the principles on which the calculation i s based. The key parameter for the postgel stage is the extinction probability. I t i s the probability that a bond issuing from a given building unit has only a f i n i t e continuation, i . e . that the respective subtree i s f i n i t e . The other p o s s i b i l i t y for the i s s u ing bond i s that i t has a continuation to i n f i n i t y (to the surface of the sample). The sol fraction i s composed of building units issuing bonds with f i n i t e continuation only. The number of EANC s i s derived from the number of e l a s t i c a l l y active crosslinks; an e l a s t i c a l l y active crosslink i s a junction issuing at least three bonds with i n f i n i t e continuation. Each junction issuing j bonds g

e

eg

e

t

e g

-


ELASTOMERS

406

AND

RUBBER

ELASTICITY

with i n f i n i t e continuation (j>3) contributes j/2 to the number of EANC's. The value of f i s the mean number of bonds with i n f i n i t e contribution averaged over e l a s t i c a l l y active crosslinks. The Langley's type trapping factor (23,24) i s derived from the pro b a b i l i t y of a contact between two monomer units located i n EANC's. The EANC's are composed of units issuing just two bonds with i n f i n i t e continuation. Units issuing more or less such bonds cannot be part of an EANC, because they would themselves be e l a s t i c a l l y active crosslinks or part of a dangling chain. The trapping factor thus increases as the square of the fraction of units i n EANC's. Of interest are the c r i t i c a l exponents m i n the proportion a l i t y between network parameters X = w , V , v , T , T , f (the subscript g indicates that the respective quantity i s related only to the gel) and the distance from the gel point measured as a difference between the gel point ( c r i t i c a l ) £ and the actual £ conversion Χ«(ξ - £ ) for lim (ξ - £ ) = O. For the tree-like model, the following values of the c r i t i c a l exponents have been found: e


g

e

e g

e

eg

e

c

m

c

c

eg

eg

In the foregoing considerations, formation of e l a s t i c a l l y inactive cycles and their effect have not been considered. For epoxy networks, the formation of EIC was very low due to the stiffness of units and could not been detected experimentally: the gel point conversion did not depend on d i l u t i o n i n the range 0-60% solvent; therefore, the wastage of bonds i n EIC was neglect ed. For polyurethanes, the extent of c y c l i z a t i o n was determined from the dependence on d i l u t i o n of the c r i t i c a l molar ratio [OH] /[NCO] necessary for gelation (25) and this value was used for the s t a t i s t i c a l calculation of the fraction of EIC and i t s effect on V as described i n (16). The calculation has shown that the fraction of bonds wasted i n EIC was 2-2.5% and 1.5-2% for network from LHT-240 and LG-56 t r i o l s , respectively. e g

Results and Discussion According to the rubber e l a s t i c i t y theory ( J , 2 ) , the equi librium shear modulus, G , i s proportional to the concentration of EANC's and an additional contribution due to trapped entangle ments may also be considered: e

G

e

= G

where for dry non-extracted G and

ec

= ART y

e

= ART V w

ec

+ G

(1)

ee

networks

eg g

, G

ee

= RTeT = RTeT w e

eg

g

f o r e x t r a c t e d swollen networks


(2)

21.

DUSEK

G

AND

Elasticity of Loose Step Polyaddition Networks 407

ILAVSKY

ec = ARTVeg v 2!

/

3

w

2

g

/

3

*. Gee =

RTe.-vl

2

(3)

2 / 3

/ 3

W

g T eg

Here, R i s the gas constant, Τ i s temperature i n Κ, ν and υ are concentrations of EANC's i n the unit volume of the non-extracfed sample and g e l , respectively, and T are the corresponding values of the trapping factor, and v i s the volume fraction of the polymer; £ and £* are proportionality constants. According to the theory (1,2), for phantom imperfect (cf. a l so (17)) network the front factor A assumes the value A - (f - 2) /f (4) pn e e for chemically tetrafunctional crosslink f increases from 3 to 4 and for t r i f u n c t i o n a l crosslinks i t i s 3 and independent of conversion. The phantom network behaviour corresponding to volumeless chains which can freely interpenetrate one through the other and thus to unrestricted fluctuations of crosslinks should be approached i n swollen systems or at high strains (proportionality to the Mooney-Rivlin constant C ) . For suppressed fluctuations of crossl i n k s , which then are displaced affinely with the s t r a i n , A for the small-strain modulus (equal to Cj+C ) approaches unity. This situation should be characteristic of bulk systems. The constraints arising from interchain interactions important at low strains should be reflected i n an increase of Aabove the phantom value and no extra G contribution to the modulus i s necessary. The upper l i m i t of the predicted equilibrium modulus corresponds therefore, A = 1. The G contribution of the form given Eq.(2) represents the simplest form of permanent interchain interactions. The value of G at T =1 and w =1, i . e . the G contribution of a perfect network, has been assumed equal to the plateau modulus of the corresponding linear polymer (10,15,23). This assumption has not always been confirmed and, therefore, for the purpose of this work we prefer to consider ζ of £ as proportionality constants. The analyses of experimental data with respect to the value of A and G contribution are usually carried out by rearranging Eqs. (1) and (2) into the form çg


2

e

2

ee

ee

ee

eg

g

ee

-

ee

G /T = ART(V /T ) + RT£ (5) e e e e The plot G /T vs. /T yields then A from the slope and from the intercept (Langley-Greassley p l o t ) . The a p p l i c a b i l i t y of this plot w i l l be commented on below and i t w i l l be shown that this plot i s not very suitable for endlinked networks with *J varying as a function of the conversion or molar r a t i o of com ponents. The s i m i l a r i t y between the shapes of V and T and the resulting relative constancy of /T i s the reason. The other disadvantage of analysis of experimental data using Eq.(1) or (5) based on the difference between the values G and V i s the sene

e

e

e

e

e

e

e

e


408

ELASTOMERS AND RUBBER ELASTICITY

s i t i v i t y of v and T to composition, conversion, formation of e l a s t i c a l l y inactive cycles, etc. This s e n s i t i v i t y i s greatly reduced if one replots the data as G or against w (16-20). For different i n i t i a l compositions (cf. e.g. (20)), the log * log w plots are close and run i n p a r a l l e l , so that a small vert i c a l superposition can y i e l d a single generalized curve. Although this treatment does not allow the determination of A and S i n one step, i n contrast to the Langley-Greassley plot, i t i s much safer due to a considerable reduction of the effect of structural uncertainty. e

e

e

e

g

vs


g

Epoxide Networks. The sol fraction (Figure 1) f i t s well the calculated dependence for the f i n a l conversion of epoxide groups determined by IR spectrometry, which may serve as evidence of the a p p l i c a b i l i t y of the tree-like model. Only for the highest sol fraction, the experimental points l i e somewhat below the theore t i c a l curve; d i f f i c u l t y involved i n a f u l l extraction of a r e l a t i v e l y high-molecular-weight and branched material may be the reason. The calculated dependences of log v vs. low w obtained by varying the molar ratio r or conversion run very close to each other and are p a r a l l e l . They have been superimposed by a small v e r t i c a l s h i f t . This s h i f t has been applied to the reduced moduli G =G /w and G

V

/A-(f -2)/f e

•

e

-50

ι

-04

I

ι

-0-3

-0-2

I

-01 log

w

g

Figure 2. Theoretical curves for superimposed reduced moduli G//RT(mol/ cm ) of epoxy-amine networks versus the gel fraction w . Fraction of epoxy groups in monoepoxide is O, 0; Q O.2; Δ , O.33; V , O.5. Key: O, • , Δ , V, dry net works; Φ, | , A , Y , swollen networks; value of front factor A indicated. 3

g


21.

DUSEK

AND

Elasticity of Loose Step Polyaddition Networks

ILAVSKY

411

e l a s t i c a l l y inactive cycles are taken into account (the data are shown i n Fig.3). The results on e l a s t i c i t y measurements can be summarized as follows: (1) There exists a weak Mooney-Rivlin dependence characterized by the ratios C2/C.=O.1-O.1 for networks from the smaller t r i o l LHT 240 andO.1-O.3±O.1for LG 56; (2), If the trapped entanglement contribution i s not considered, the value A for the networks from the smaller t r i o l decreases with decreasing V from 1 to about O.5 (phantom network value of A i s 1/3) (Figure 4a); such a decrease i n A with decreasing crosslinking density has already been observed for polyurethane networks (17);(3) Networks from the larger t r i o l , however, exhibit a much larger modulus than would correspond to A=1, approximately by a factor of 2 (Figure 4b); (4) The trapping factor T and V have again a similar shape. Therefore, for a network from LG-56 the difference between the phantom network value and experimental moduli can be well described by the trapped entanglement c o n t r i bution, but for the network from LHT-240 the f i t i s not so good and a change i n the A value i s probable. The result (3) means that the value of the equilibrium modulus considerably exceeds the upper l i m i t of the theory (i.e. A=1 corresponding to constraints forcing the crosslink to move a f f i n e l y with the macroscopic s t r a i n ) , if a contribution from permanent interchain i n t e r actions (trapped entanglements) i s not allowed.


e

eg

eg

A p p l i c a b i l i t y of the Langley-Gfaessley Plot. According to Eq. (5), the plot of G /T vs. V / T extrapolated to V / T =0 gives £ as the intercept. I t i s sometimes assumed that v /T —* 0, if \) -*0, i . e . if the system approaches the gel point. However, a closer examination of " /T shows that this r a t i o diverges if V -?0 and this divergence occurs because, as has been shown above, v 0 invalid the use of the Langley-Graessley plot? We w i l l examine two ways for controlling V characteristic of step polyaddition networks: (1) by changing the reaction conversion or, i n alternating types of reaction, by taking excess of functional groups of one type, and (2) i n stoichiometric systems, by varying the molecular weight of the components (e.g. of the precursor chains). Figure 5 shows the calculated dependence of V / T on the sol fraction for the diepoxide+monoepoxide-diamine networks. The curves representing either a conversion dependence for the i n i t i a l composition given by r and s, or a dependence on the excess of amino groups r a t fixed s and conversion close to 100%, show that " /T cannot f a l l below a l i m i t i n g value - some e

e

e

e

e

e

e

e

e

e

e

3

ç

4

c

e

c

e

e

e

e

e

e

e

e

e

e

e

H

e

e


412

ELASTOMERS

!

1

I

A N DRUBBER

I

997.

0-6


1

α

y w

ELASTICITY

1

s

/

OA

/o / /°

rv

-

ι

I

I-

k

/

y

s

f " "~ "

100%

/

/

A)

0-2

/

1 fc

1

1—

/97%

b

h

/°

06 /

04

/

/° U

/

y 02

Ο

10

1-2

100% /

/

/

—

/

/

/ 1

1

1

1-4

1-6

18 Γ

0Η

Figure 3. Sol fraction w vs. the molar ratio r = [OH]/[NCO] for polyme thane networks from polyoxypropylene triols. Key: , theoretical curve for indicated conversion of NCO groups in mole percent, taking into account formation of elastically inactive cycles (cf. (16)); , theoretical curve for full conversion of NCO groups without formation of EIC; a, LHT-240; b, LG-56. s

0H


DUSEK

AND

ILAVSKY

Elasticity of Loose Step Τolyaddition Networks 413


21.

3

Figure 4. Theoretical curves for reduced moduli G /RT (mol/cm ) of polyurethane networks from polyoxypropylene triols versus the gel fraction w . Value of A indicated. Networks from LHT-240. Continued. d

g


AND

RUBBER

ELASTICITY


ELASTOMERS

3

Figure 4. Continued. Theoretical curves for reduced moduli G /RT (mol/cm ) of polyurethane networks from polyoxypropylene triols versus the gel fraction w . Value of A indicated. Networks from LG-56. d

g


21.

DUSEK

A N D ILAVSKY

Elasticity of Loose Step Ψolyaddition Networks 415

dependences even pass through a minimum. In general, the variation of V /T i n the significant range of w~O-O.6 i s small; both the slope and intercept of the Langley-Greasley plot would be greatly affected if less accurate data at high sol fractions were taken into account. Therefore, the Langley-Greassley plot i s not suitab le for networks with crosslinking density controlled by the degree of network imperfectness. A somewhat different situation arises for "perfect networks, in which the crosslinking density i s controlled mainly by the molecular weight of the elastomeric component and not by the network imperfectness. The situation i s schematically shown i n Figure 6: While the i n i t i a l concentration of functional groups in the system,CQ, f a l l s approximately l i n e a r l y with the inverse of molecular weight of the elastomer component, a constant small residual concentration of functional groups, c , i s expected to remain i n the system after long but f i n i t e reaction times. Laws of chemical kinetics predict c to be independent of M at least for high M. For the network build-up, the reaction conversion ξ = 1 - c /cQ i s decisive and this quantity f a l l s sharply if C Q approaches c . Therefore, a "perfect" network becomes very imper fect at high Mdue to incompleteness of the reaction. This fact i s the reason for the sharp upturn of V /T as a function of 1/M shown i n the right part of Figure 6. The value of V /T does not approach zero either, but there exists a r e l a t i v e l y broad range of •V /T values which can make the extrapolation of the LangleyGreassley plot r e l i a b l e . e

e

g


11

r

r

r

e

e

e

e

g

e

Conclusions The sol fraction follows well the predictions of the tree l i k e model and so does the shape of the dependence of the equlibrium modulus on the gel fraction irrespective of the value of the front factor A and magnitude of the trapped entanglement con tribution. The equilibrium e l a s t i c i t y measurements show s i g n i f i cant departures from the predictions of the rubber e l a s t i c i t y theory which assumes that the only effect of interchain i n t e r actions constraints i s reflected i n the fluctuation freedom of crosslinks. For epoxy networks, the departures can be seen i n the fact that A does not change with swelling and strain although i t is much higher than the phantom value. An additional contribution due to permanent interchain interactions caused by i n c r o s s a b i l i t y of chains (trapped entanglement contribution) seems l i k e l y and the observed differences can be described adequately by the approximation offered by Langley (23). The most convincing argument i n favor of such a contribution was obtained by analyzing the data on polyurethane networks from the larger t r i o l : the front factor A would exceed the theoretical upper l i m i t (A=1) by a fac tor of two, if an extra (trapped entanglement) contribution were not taken into account. Such "excess" equilibrium moduli have already been observed and have (7,8,10,11,12,14,15,24) or have not



416

ELASTOMERS

AND

RUBBER

ELASTICITY

3

Figure 5. Calculated dependence of the ratio v /T (mol/cm ) on sol fraction w for the epoxy-amine networks. Varying conversions for s = 0 and r for 1, 2, and 3 are 2.3, 1.9, and 1.5, respectively. 4 and 5 are 100% conversion and varying r, for s = 0 andO.5,respectively. e

e

8

A

Figure 6. Sketch of expected variation of the initial (c ) and residual (c ) concentration of functional groups, reaction conversion $, and the ratio v /T in end-linked networks as a function of molecular weight of elastomer component M. For discussion see text. 0

r

e

e


21.

DUSEK A N D ILAVSKY

Elasticity of Loose Step Polyaddition Networks 4 1 7

(26,27) been explained by the trapped entanglement contribution. However, i d e n t i f i c a t i o n of the proportionality constant ε with the plateau modulus of the corresponding linear chains may be too far reaching at least for step polyaddition and imperfect networks. The a b i l i t y of network chains to become involved i n trapped en tanglements depends not only on the structure of the backbone but also on the number bulkiness of the side branches. The results given here indeed show that, at the same length of EANC s, the non-chemical contribution i s the lower the more dangling chains the network chain bears. -


Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

Flory, P. J. Proc. R. Soc. London 1976, A351, 351. Flory, P. J . Polymer 1979, 20, 1317. Erman, B.; Flory, P. J . J . Chem. Phys. 1978, 63, 4990. Erman, B.; Wagner, W.; Flory, P. J . Macromolecules 1980, 13, 1554. Mark, J. E. Makromol. Chem., Suppl. 2, 1979, 180, 87. Llorente, Μ. Α.; Mark, J . E. Macromolecules 1980, 13, 671. Valles, E. M.; Macosko, C. W. Macromolecules 1979, 12, 673. Gottlieb, M.; Macosko, C. W.; Benjamin, G. S.; Meyers, K. O.; M e r r i l l , E. W. Macromolecules 1981, 14, 1039. Oppermann, W.; Rehage, G. Proc. IUPAC Macro Mainz 1979, Vol.3 1360. Dossin, L. M.; Pearson, D. S.; Graessley, W. W. Macromolecules 1979, 12, 123. Allen, G.; Holmes, P. Α.; Walsh, D. J . Faraday Disc. Chem. Soc. 1974, 57, 19. Allen, G.; Egerton, P. L.; Walsh, D. J . Polymer 1976,17,65. Stepto, R. F. T. Polymer 1979, 20, 1324. Meyers, K. O.; Bye, M. L.; M e r r i l l , E. W. Macromolecules 1980, 13, 1045. Pearson, D. S.; Graessley, W. W. Macromolecules 1980,13,1001. Dušek, K.; Vojta, V. Brit. Polym. J . 1977, 9, 164. Dušek, K.; Hadhoud, M.; Ilavský, M. Brit. Polym. J. 1977, 9, 172. Dušek, K. Makromol.Chem., Suppl. 2, 1979, 180, 35. Dušek, K. Rubber Chem. Technol. in press. Dušek, K.; Ilavský, M. Colloid Polym. Sci. 1980, 258, 605. Ilavský, M.; Prins, W. Macromolecules 1970, 3, 415. Dušek, K. Faraday Disc. Chem. Soc. 1974, 57, 191. Langley, N. R. Macromolecules 1968,1,348. Langley, N. R.; Polmanteer, K. E. J . Polym. Sci., Polym. Phys. Ed. 1974,12,1023. Matějka, K.; Dušek, K. Polym. Bull. 1980, 3, 489. Sung, P. H.; Mark, J . E. Polym. J. 1980,12,835. Llorente, Μ. Α.; Andrady, A. L.; Mark, J. E. J . Polym. S c i . , Polym. Phys. Ed. 1980, 18, 2663.

RECEIVED December 24, 1981.


Structure and Elasticity of Loose Step Polyaddition Networks - ACS

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