Random‐coil dimensions of poly(methylphenylsiloxane) and their dependence on stereochemical structure

Mark, J. E.; Ko, Jaehyoung

doi:10.1002/pol.1975.180131112

Cited by 30 publications

(19 citation statements)

References 27 publications

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“…One may then conclude that the excellent agreement found between experiment and the RIS calculations indicates that intermolecular interactions do not significantly influence the PMPS mean-squared dipole moment; the temperature dependence of 〈μ 2 〉 must have an intramolecular origin. An important intramolecular interaction was elucidated by Mark et al . They applied the RIS model, calculated 〈 r 0 2 〉/ nl 2 for PMPS chains, and found an attractive interaction between phenyl rings on adjacent skeletal silicon atoms.…”

Section: Resultsmentioning

confidence: 99%

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

Fitz¹,

Mijović²

1999

Macromolecules

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The segmental dynamics of PMPS chains are determined in the bulk liquid and cross-linked networks of varying cross-link density by broad-band dielectric relaxation spectroscopy. A large fragility index [τ(T g*/T) dependence], F 1/2 = 0.77, is found, independent of cross-link density, molecular weight, and T g. Also independent of the above variables is the relaxation shape (characterized by a KWW β parameter of 0.45). Since these parameters quantifying the α process in PMPS networks are insensitive to cross-linking, it is concluded that the length scale of cooperatively rearranging domains in PMPS networks is smaller than the distance between cross-links, i.e., less than 5 nm, in agreement with the current consensus. An argument based on the temperature dependence of the dielectric relaxation strength, dipole moment, and ensemble average chain configuration was advanced, suggesting that the high fragility of PMPS has an intramolecular origin.

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Section: Resultsmentioning

confidence: 99%

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

Fitz¹,

Mijović²

1999

Macromolecules

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“…6 Theoretical calculations of these properties have been performed by matrix multiplication methods and by Monte Carlo techniques. [20][21][22][23][24][25][26][27][28] In all cases, a fixed geometry for the molecule was used: fixed bond lengths and bond angles, plus rotational isomers also at fixed positions, either as discrete states 20,23,24,27 or allowing a small oscillation around these states. 21,22,25,26,28 However, recent calculations by Mattice et al on PDMS 29,30 and other poly(dialkylsiloxanes) 31,32 have shown the need for a more realistic description of siloxane chains.…”

Section: Introductionmentioning

confidence: 99%

Conformational Analysis of Methyl−Phenyl−Siloxane Chains

Freire¹,

Piérola²,

Horta³

1996

Macromolecules

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The conformational energy of chain fragments of poly(methylphenylsiloxane) is studied, considering contributions from bond stretching, bond angle bending, bond torsion, and van der Waals interactions. Energy is minimized without constraints, so that minima correspond to fully relaxed conformations. The energy minima of this phenyl-substituted polymer differ notably from those of the parent poly(dimethylsiloxane), due to the importance of the attractive interactions between pairs of phenyl groups. For two repeat units (diad), the stable conformations occur when the pair of phenyl rings is coupled parallel, face-to-face. For three repeat units (triad), the stable conformations occur also when a pair of phenyl rings is coupled parallel, face-to-face, but not necessarily those in consecutive units. Instead, the chain can coil to couple together the phenyl rings of alternate units, leaving uncoupled the phenyl ring in between. This coiling of the chain to yield a stable conformation is a genuine triad effect that cannot be predicted from the diad energies. In longer chain sequences, the contribution of this coiled triad conformation is significant.

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“…It can be observed that PMPS has a dipole moment ratio similar to that of PDMS and PDES. Therefore, the substitution in a siloxane chain of an alkyl side group for a phenyl group yields very similar values of (µ 2 )/nm 2 , though the intramolecular interactions change significantly (as a consequence of a particularly strong energy preference for C 6 H 5 • · · C6H 5 interactions 31 ). In all the cases the difference between them is less than 20%.…”

Section: Discussionmentioning

confidence: 62%

Dipole Moment of Poly(methylphenylsiloxane) and Copolymers

Salom

Freire

Hernández-Fuentes

1988

Polym J

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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

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Random‐coil dimensions of poly(methylphenylsiloxane) and their dependence on stereochemical structure

Cited by 30 publications

References 27 publications

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

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

Conformational Analysis of Methyl−Phenyl−Siloxane Chains

Dipole Moment of Poly(methylphenylsiloxane) and Copolymers

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