Dipole Moment of Poly(methylphenylsiloxane) and Copolymers

Abstract

ABSTRACT:The dielectric constant and the refractive index of several poly(methylphenylsiloxane) fractions (1.17 x 10 5 ,;;; M w,;;; 4.56 x 10 5 ) with well known tacticity and two copolymers of (dimethylsiloxane--methylphenylsiloxane) (4,200,,;;M.,;;;6,400) were measured in cyclohexane solution, and in the case of the copolymers also in the bulk state. The copolymer compositions calculated by V-UV spectrometry were 54.3% and 9.5%, in (methylphenyl)siloxane content. A rotational isomeric state model was used to calculate the dipole moment ratio of the homopolymer. The theoretical value is in good agreement with the experimental one. A comparison of our results with those corresponding to other substituted polysiloxanes shows a very small variation of the dipole moment ratio with the nature of the substituent. The smaller values obtained for the dipole moment ratio of the copolymers in comparison with that of the homopolymer, could be attributed to the short chain length of the copolymers.KEY WORDS Poly(methylphenylsiloxane) / Conformation / Dielectric Constant / Dipole Moment / Dipolar Ratio / ambiguity in the conclusions. Solution properties of cyclic and linear poly(dimethylsiloxane)s have been widely studied. 1 -14 Theoretical and experimental works about other polysiloxanes (represented at +RR'SiO---h) with substituent groups R and R' aliphatic 15 -17 or aromatic 18 -21 have been also reported. Bibliografic results show that in polysiloxane chains, the nature of the side groups, R and R' (at least in symmetrically substituted chains) generally has not a very pronounced effect on the statistical properties of the chain such as dipole moment, as indicated by the values of the dipole moment ratio, <µ 2 )/nm2, of poly(dimethylsiloxane) (PDMS) and poly(diethylsiloxane) (PDES) in cyclohexane at 25°C. 13 · 1 7 In this work the experimental and theoretical dipole moment of poly(methylphenylsiloxane) (PMPS) samples of well defined tacticity has been determined in order to study the influence the change of a methyl substituent by a phenyl substituent has on the dipole moment of polysiloxane chains.In the case of chains with asymmetric centers, however, experimental studies have been so far restricted to samples with unknown tacticity 18 that introduces a certain degree of * To whom all correspondence should be addressed.Moreover the influence of the composition on the dipole moment ratio of copolymers has been also studied using samples of ( dimethylsiloxane-methylphenylsiloxane) copolymers in cyclohexane solution. The properties of these copolymers of fluid nature in their bulk state have been also investigated. EXPERIMENT AL PolymersThe polymers studied in this work have been 1109

Segmental Dynamics in Poly(methylphenylsiloxane) Networks by Dielectric Relaxation Spectroscopy

“…For example, the highest cross-link density PMPS374 shows the greatest deviation from the Curie law, while the deviations in the other samples do not follow a simple monotonic law with decreasing cross-link density. As mentioned above, Salom et al 55 have theoretically and experimentally obtained 〈µ 2 〉/nm 2 on neat PMPS chains at 25 °C. Their calculations were based on a rotational isomeric state (RIS) model, 57 which did not take into account intermolecular interactions.…”

“…From these data we calculate the mean-squared dipole moment relative to the dipole moment of a freely rotating chain (dipole moment ratio), 〈μ 2 〉/ nm 2 , where n is the number of skeletal bonds and m is the dipole moment of a skeletal bond. For our neat PMPS sample, we obtain 0.26 at 25 °C, in good agreement with the value found by Salom et al of 0.28. A value less than one indicates hindered rotation around the Si−O skeletal bonds.…”