Small angle x-ray scattering study on role of trapped entanglements in structure of swollen end-linked poly(dimethylsiloxane) networks

Abstract

Amorphous structure of swollen end-linked poly͑dimethylsiloxane͒ ͑PDMS͒ network has been investigated by means of small angle x-ray scattering ͑SAXS͒ technique as a function of molecular mass of precursor PDMS (M p) and junction ͑cross-link͒ functionality. The M p dependence of the SAXS profiles for tetra-functional PDMS networks shows a striking crossover at around M p ϷM c where M c represents the critical molecular mass to form entanglement couplings in the PDMS melt. These results strongly suggest that structure of swollen end-linked networks significantly depends on whether precursor chains are well entangled or not before end-linking, and that when precursor chain is long enough to form entanglement couplings, trapped entanglements formed in cross-linking ͑instead of cross-links͒ play a major role in elementary mesh of the resulting networks. For the networks of M p ӷM c , the correlation length for the network structure is fairly small and comparable to that of dynamic density fluctuation for the solutions of the precursor polymer, and in addition, no appreciable effect of junction functionality on long-range network structure is observed. These observations imply that the contribution of cross-link to static heterogeneity in network structure is screened by trapped entanglement dominant in number.

Viscoelastic Relaxation of Guest Linear Poly(dimethylsiloxane) in End-Linked Poly(dimethylsiloxane) Networks

“…These ratios were obtained in such an optimization that the amount of unreacted materials extracted from the final networks would be minimum. The deviation of the optimized ratio from stoichiometric ratio (unity) was also reported in other studies. − …”

“…The deviation of the optimized ratio from stoichiometric ratio (unity) was also reported in other studies. [26][27][28][29] The mixtures were poured into a leveled Teflon mold after vigorous mixing and removal of bubbles. The cross-linking reaction hydrosilylation was carried out at 80 °C for 72 h under dry nitrogen atmosphere.…”

Optimized Decomposition of Simulated Polymer Networks Into Meshes

“…Especially the role of entanglements as topological links in addition to the chemical cross-links is unknown. Recent X-ray scattering experiments of end-linked PDMS networks by Kawamura et al [1] indicate that for molecular masses M p F 23 800 the structural properties are dominated by topological links. We performed simulations of end-linked unimodal networks using the BondFluctuation-Model.…”

Some experimental results for the end-linked polydimethylsiloxane network system

“…In addition to mechanical methods, experimental techniques for characterizing polymer networks include IR spectroscopy, small-angle neutron (SANS) [72][73][74][75][76][77][78][79][80], X-ray (SAXS) [3,[77][78][79][80][81][82][83][84] and light scattering studies [85,86]. Brillouin scattering [76,[87][88][89][90] studies together with investigations of the hyper-sonic viscoelastic behaviour by multi-pass Fabry-Perot spectroscopy (MPFPS) [91] and dielectric relaxation [92] have been performed as well in order to investigate the cross-link density.…”