Silphenylene

The synthesis213,214, thermal215 and mechanical properties216, crystallization behavior 217,218,339) and morphology 217,218,339 of tetramethyl-p-silphenylene-... 

There is considerable interest in inserting a silphenylene group [-Si(CH3)2C6H4-] into polysiloxane backbones.92 127-133 In the case of the PDMS repeat unit, this yields the... 

Figure 4.7 Meta and para silphenylene polymers and their transition temperatures.92 Reproduced by permission of John Wiley and Sons.

Figure 11.27 29Si-NMR spectrum of a silphenylene-siloxane block copolymer (67 mol % DMS), observed at 59.6 MHz [29]...

The polycondensation reaction between telechelic hydride and telechelic methoxy siloxane in the presence of very low levels of B(CgFj)3 has been described. The compromise between large polymer content and reasonable molar masses is found by tailoring the addition rate and excess content of L H reagent. Rubinsztajn et al. showed that with silphenylene-co-PDMS copolymers, the reaction was completed... 

I ILPHENYLENE-SILOXANE POLYMERS (I) are, in a sense, modified polysi-loxanes in which every third siloxyl group in the main chain backbone is replaced by a suitable silphenylene group see structure on page 742). 

Partial replacement of siloxane units with silphenylene groups also increases polymer crystallinity (5, 6), results in a higher viscosity (7), increases the mechanical properties, and improves thermal stability. On the other hand, incorporation of the rigid silphenylene units into the poly siloxane backbones could decrease the low-temperature elasticity of these polymers (8). 

Previous reports from this laboratory described the preparation of silphenylene-siloxane polymers (I), in which both R and R are CH3, R = CH3 and R = CH = CH2, or R = CH3 and R = CeHs, by the low-temperature condensation polymerization of l,4-bis(hydroxydimethyl-... 

Hani Lenz Studies of Silphenylene-Siloxane Polymers... 

Preparation of Silphenylene-Siloxane Polymers. The basic reaction for the preparation of exactly alternating silphenylene-siloxane polymers from bis(ureido)silanes, Va-Vh, and the disilanol monomer is step-growth polymerization. This reaction was carried out at -20 °C, at which temperature the possible side reactions described previously can be prevented or at least decreased in rate. To obtain a high-molecular-weight polymer, a solution of the bis(ureido)silane monomer was added slowly to a slurry of the disilanol monomer in chlorobenzene (ii). After addition of 95%... 

The second calculation is more involved. The only values of Co listed in Table 2 that are relatively free of error in setting W = 0 are those for poly(dimethyl siloxane) and poly(tetramethyl-p-silphenylene silo-xane) since for these polymers Tq 0 and the modified Vogel expression reduces to the simpler Vogel equation. Unfortunately, these materials are also studied far from their T, a and T,... 

Merker, R. L., and M. J. Scoxx Random and block copolymers of poly-(tetramethyl-p-silphenylene-siloxane) and polydimethylsiloxane. J. Polymer ScL 2A, 31 (1964). 

Silphenylenes, aromatic-containing silicon monomers, can be produced in 50 88% yields by the reaction of halo- and dihalobenzenes with chloro- and alkoxysilanes under Barbier conditions. Iodine, bromine, and cuprous chloride are used as initiators with THE, TMEDA, toluene, or xylene as solvents. Shavings or powdered magnesium can be used [Eqs. (66) and (67) 134,135]. 

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