1992
DOI: 10.1021/ma00041a028
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Effect of crosslinks on the glass transition temperature of end-linked elastomers

Abstract: Changes in the glass transition temperature of end-linked networks as a result of the cure process have been studied by examination of a series of stoichiometrically imbalanced PDMS networks covering a wide range of stoichiometric ratio values. The data were compared to existing theories in an effort to resolve the question of cross-link contribution to Tt. The results support the notion based on the Gibbs-DiMarzio theory that elastically effective junctions rather than any branch point dominate the contributi… Show more

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Cited by 61 publications
(45 citation statements)
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“…Here, we assume that crosslink points and entanglement points have the same effect on T g ; this may overestimate the influence of entanglements but it provides an estimate of the magnitude of any T g depression that might be observed from changes in entanglement concentration. By choosing K 2 Z0.82 [41], we estimated that the T g change for a change in the molecular weight between entanglements (M c ) from the bulk value of 17,300 [42] to 34,600 g/mol, is only a 0.9 K decrease. We note that a change in M c of this magnitude would occur with an increase in J N of 100% on freeze-drying, which is greater than that observed in creep measurements [4].…”
Section: Discussionmentioning
confidence: 99%
“…Here, we assume that crosslink points and entanglement points have the same effect on T g ; this may overestimate the influence of entanglements but it provides an estimate of the magnitude of any T g depression that might be observed from changes in entanglement concentration. By choosing K 2 Z0.82 [41], we estimated that the T g change for a change in the molecular weight between entanglements (M c ) from the bulk value of 17,300 [42] to 34,600 g/mol, is only a 0.9 K decrease. We note that a change in M c of this magnitude would occur with an increase in J N of 100% on freeze-drying, which is greater than that observed in creep measurements [4].…”
Section: Discussionmentioning
confidence: 99%
“…However, previously reported values of gel conversion for several aromatic dicyanates lie in the vicinity of 0.6 17,24 due probably to the formation of intramolecular cycles. If only elastically effective crosslinks indeed contribute to T g (as suggested previously 4,21 ) in a manner different from simple branching points, effects of the intramolecular cycles should be taken into account to modify the crosslink density of the system.…”
Section: Comparison Between Experimental Data and Theoretical Expressmentioning
confidence: 90%
“…However, for the present TDPC system, the observed gel point was delayed (␣ gel ϭ 0.58) 17,26,27 due presumably to the formation of intramolecular cycles. As suggested by Shefer and Gottlieb, 21 only elastically effective crosslinks should be considered instead of all junction points formed during network development. This implies that one would observe a more pronounced increase in T g after gel point, because the elastically effective crosslink density remains zero before the gel point and starts rising immediately thereafter.…”
Section: Effect Of Crosslink Density On T Gmentioning
confidence: 99%
“…The T g always shifted to higher temperatures upon the cure reaction [41]. This well-known trend can possibly be explained in terms of additional stiffness arising from the crosslinks.…”
Section: Dscmentioning
confidence: 72%