Stress‐optical behavior of polydimethylsilmethylene [Si(CH₃)₂CH₂], a hydrocarbon analog of polydimethylsiloxane, and a silicon analog of polyisobutylene

Abstract

Elastomeric networks were prepared from polydimethylsilmethylene (PDMSM) [Si(CH3)2CH2], a polymer closely related to polydimethylsiloxane (PDMSO) [Si(CH3)2O] and polyisobutylene (PIB) [C(CH3)2CH2]. The birefringence of PDMSM in elongation was found to be qualitatively similar to that of PDMSO, in that there was no evidence for strain‐induced crystallization. However, the values of the optical‐configuration parameter Δa were considerably larger, and both Δa and its temperature coefficient are essentially the same as those of PIB. Swelling the PDMSM networks generally decreased Δa; the largest decreases, obtained as expected with the most nearly symmetrical diluent, were also approximately the same as those observed for PIB. Use of cyclic PDMSO pentamer as diluent in a PDMSM network was found to increase the birefringence, presumably because of orientational effects. Various network‐diluent combinations involving the significantly anisotropic PDMSM and the more nearly isotropic PDMSO should be extremely useful for elucidating the nature of these intermolecular correlations. Results obtained from rotational isomeric state theory considerably underestimate both Δa and its temperature coefficient for PDMSM, as they do for PIB. Although the origin of the discrepancy is not necessarily the same for both polymers, the results on PDMSM suggest that the discrepancy for PIB is not due to the severe steric congestion known to be present in this polymer.

Strain birefringence studies on poly(vinyl acetate) networks

“…For example, over the total range of stereochemical structure, the molar Kerr constant , K can change by more than three orders of magnitude and even change ~i g n .~,~ Other optical properties used to characterize chain molecules are the stressoptical coefficient C and the related optical configuration parameter Aa. [5][6][7][8][9][10][11] Some studies of these quantities have been carried out, on a variety of long-chain molecules. In the case of symmetric chains, the agreement between experiment and the results of rotational-isomeric-state theory have not been very good; in asymmetric chains, including the vinyl type, very little has been done.…”

Thermoelastic and strain-birefringence studies on poly(methylphenylsiloxane) networks

“…A similar situation was found with poly(dimethylsilamethylene) swollen with cyclic PDMS pentamer. 29 In the case of PMPS, the swelling of the network with decalin increases the value of (decreases its absolute value) by roughly 30% and it departs from the theoretical value. However, the theoretical value can be brought into agreement with the experimental result obtained in the swollen sample by an adequate adjustment of the parameters used in the calculations.…”

Stress‐optical behavior of poly(cis/trans‐1, 4‐cyclohexane dimethanol‐alt‐formaldehyde) (PCDO) networks

“…6%. Nevertheless, the very unlikely value of [5][6] A3 for TCc would be required in order to accommodate theoretical and experimental values of Au.…”