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A homologous series of poly(n-alkylmethylsiloxanes), [SiMe(R)O]n, were prepared by cationic ring-opening polymerization (ROP) of cyclotrisiloxanes containing n-alkyl substituents, such as C2H5, n-C3H7, n-C4H9, n-C5H11, and n-C6H13, on the Si. The resultant polymers were characterized by NMR, GPC, and DSC measurements. All of these asymmetrically substituted polymers were obtained in high molecular weight form and were found to have an atactic configuration. Their glass transitions were found to increase smoothly from Et to n-Hex (i.e., −139, −120, −115, −111.9, and −108 °C, for Et to n-Hex, respectively). These Tgs are much lower than those of the corresponding polyolefins, [C(H)(R)CH2]n. Moreover, in the case of these polyolefins, the Tgs decrease continuously from R = Me to n-Hex. The calculated Tgs for the polysiloxanes that were obtained by using published empirical equations show the same general trend as the experimental values.

The molecular structure of the monosilicon analog of poly(ethylene), poly(silylenemethylene), CH3[SiH2CH2]nSiH3, or poly(silaethylene) (PSE), was characterized by means of high-resolution 1H, 13C, ...

This chapter focuses on the application of such nucleophilic substitution reactions toward the synthesis of hyperbranched polycarbosilanes, with particular emphasis on those preparations that have resulted in relatively well characterized products. These syntheses are organized by the type of AB n monomer unit used (see Section 1.2), where A and B refer to the (C)X and (Si)X n , respectively, functional ends of the monomer unit and where the nature of the coupling reaction leads to entirely or primarily Si–C bond formation. In most cases, these are “one-pot” reactions that employ monomers that bear halogen or alkoxy groups on the C and Si ends of the unit. Indeed, hyperbranched polycarbosilanes have been described, in general, as “obtained in one synthetic step via a random, one-pot polymerization of multifunctional monomers of AB n type” [2]. Treatment of the AB n monomer with either elemental Mg or an organolithium reagent, ideally (but not always) forms a complexed carbanion (the nucleophile) by reaction with the C–X end of the monomer unit, resulting in an intermediate of the type, (X x M)CSiX n , where M = Mg or Li, X = halogen or alkoxy