Field-cycling NMR realaxation spectroscopy of poly(di-n-alkylsiloxanes in solid, mesomorphic, and isotropic liquid phases

The frequency dependence of the proton spin-lattice relaxation times T1 and T1., in the laboratory and rotating frames, respectively, is reported for solid and liquid phases of poly(diethylsiloxane) (PDES) and in melts of poly(dimethylsiloxane) (PDMS). The total frequency range is 5 X 102 -3 X 108 Hz and is mainly covered by field-cycling NMR relaxation spectroscopy. The relaxation behavior of PDES in the liquid but ordered mesophase is compared to that of isotropic melts of PDES and PDMS and also to that of nematic main-chain liquid-crystal polymers. The frequency dependences of PDES and PDMS liquids can be represented at low and high frequencies by power laws, section by section. The relaxation behavior in the isotropic melts is entirely equivalent to that previously reported for other polymer species. In the PDES mesophase, the exponents of the power laws are significantly larger and the crossover frequency between the two regimes is reduced. The dynamics in this phase are discussed with respect to the influence of chain modes and order director fluctuations. The main conclusion is, on the whole, that data of the liquid phases are determined by chain modes rather than by local segment fluctuations. The chain dynamics in the PDES mesophase resemble the chain modes in isotropic melts modified for a microstructure with reduced randomness, whereas the influence of order director fluctuations can neither be confirmed nor ruled out

Mesomorphic flexible chain polymers based on silicon

Poly(dialkylsiloxane)s and poly(dialkylsilane)s form a similar type of columnar mesophase. Although, the polysilanes are stiffer than polysiloxanes, both classes of polymers may be considered to be flexible due to the ability to form chain-folded crystals. Chain flexibility rather than the presence of chain stiffness determines whether the columnar mesophase is formed. A certain amphiphilic character does not appear to be required, as polysiloxanes with short side groups, e.g. polydiethylsiloxane display the same mesophase behaviour as polydialkylsilanes with long side chains and other nonpolar flexible chain molecules. The importance of the entropy gain upon conformational disordering is reflected in the increase in temperature stability with increasing alkyl side group length and the absence of mesophase behaviour in the case of the dimethyl substituted polymers

Multihydroxy-functional oligophenylene oxide

Multihydroxy-functional oligophenylene oxide obtainable by reacting a compound containing hydroxyaryl comprising at least three hydroxyaryl groups according to formula (I), wherein R = an aromatic, aliphatic or cycloaliphatic group containing 1-50 carbon atoms, R, R = H or an aromatic, aliphatic or cycloaliphatic group containing 1-50 carbon atoms, or two of the R, R or R groups together constitute a ring structure containing 4-50 carbon atoms with a polyphenylene oxide in the presence of a catalyst complex comprising a transition metal and and amine

Model polydiethylsiloxane networks I. Synthesis and phase behaviour

The preparation and hydrosilylation crosslinking of well-defined vinyl and ally polydiethylsiloxane (PDES) telechelics are described. End functionalization has been achieved by using divinyltetramethylsiloxane as a chain stopper during the cationic polymerization of hexaethylcyclotrisiloxane or by anionic polymerization of hexaethylcyclotrisiloxane with allyllithium followed by end capping with allyldimethylchlorosilane. Hydrosilylation crosslinking yielded model PDES networks which have been characterized by equilibrium swelling, determination of the sol fraction, differential scanning calorimetry and wide angle X-ray diffraction