Wu S, Yang H, Chen Q. Nonlinear Extensional Rheology of Poly(
n-alkyl methacrylate) Melts with a Fixed Number of Kuhn Segments and Entanglements per Chain.
ACS Macro Lett 2022;
11:484-490. [PMID:
35575329 DOI:
10.1021/acsmacrolett.2c00072]
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Abstract
Molecular theories for dynamics of entangled polymers are based on both the number of Kuhn segments per entanglement Ne and the number of entanglements per chain N/Ne. Extensive studies have shown that, for polymer chains in the solutions or melts, linear viscoelasticity can be properly normalized, whereas the nonlinear extensional rheological properties cannot be normalized when N/Ne is kept the same. The failure of the latter normalization has been attributed to a difference in Ne. Nevertheless, nonlinear rheological studies are lacking for a suitable model system with fixed Ne and N/Ne. In this study, we identify poly(n-alkyl methacrylate)s with the number of carbons per alkyl group below seven as a model system. We find that the degree of the transient strain hardening during extensional flow strengthens with increasing the size of the alkyl group even when Ne and N/Ne are kept the same, which is attributable to the weaker friction reduction when the main backbones are more separated.
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