Silphenylene polymers

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

The Tg was then evaluated as - 52 °C which is close to the value of - 48 °C given by Stern et al. and no melting temperature was detected, contrary to the equivalent p-silphenylene polymer. TGA measurements revealed very good high temperature properties with the onset temperatmes for degradation being 415 °C imder nitrogen and 495 °C in air. 

Insertion of a silphenylene group [-Si(CH3)2C6H4-] into the backbone of the PDMS repeat unit yields either the siloxane meta and para silphenylene polymers (32-38). The Tg of the former polymer is increased to -48 C, but no crystallinity has been... 

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). 

Besides poly(siloxanes), a few other silicone containing polymers have been synthesized. One such polymer is poly(dimethy-1,4-silphenylene). Thermal decomposition of this polymer at 400° C in argon [3] generates methane, dimethylsilane, benzene, dimethylphenylsilane, HSi(CH3)2-C6H4-SiH(CH3)2, H(Si(CH3)2-C6H4)2-H, dimethyl-diphenylsilane, and C8H4-(Si(CH3)2-C6H4)2H. 

Silarylene Polymers Containing m-Xvlvlene Units. A majority of the silarylene type siloxane polymers which have been worked on to date contain silicon-phenyl bonds. After an extensive literature search, only one type of polymer was found which contained an arylene group that does not have silphenylene bonds in the polymer backbone. The work, done mainly by Rosenberg and Choe 15-17 of the Air Force Materials Laboratory, is based on polymers which have a general structure as shown below, referred to as poly(m-xylylene-siloxanylenes), (9). 

ALTERNATIVE NAMES, TRADE NAMES Silphenylenes, silaiylene-siloxane polymers CLASS In-chain modified polysiloxanes... 

Professor of Polymer Chemistry, and Research Scientist, Michigan Molecular Institute, Midland Poly(amidoamine) dendrimers Poly(silphenylene-siloxanes)... 

Pd2(dba)3 is an excellent catalyst to give a high molecular weight polymer (M = 16,300) at room temperature in a short time (2h). We extended the reaction to the polymerization of p-BSB with other labile-hydrogen-containing compounds, such as ammonia, disilanol, aliphatic and aromatic diols, and dicarboxylic acids to prepare a series of silphenylene-containing polymers, including polycarbosilazane, polycarbosiloxanes, poly(silyl ether)s, and poly(silyl ester)s. 

The synthesis and the properties of silphenylene-siloxanes have been summarized in a chapter of a monograph on silicon polymers [18] ... 

Cyanopropylphenyldimethylsiloxane(50% cyanopropylphenyl and 50% dimethyl) 3-cyanopropyl-silphenylene co-polymer (equivalent to 70% dicyanopropyl) 40 230 290... 

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