Synthesis, Characterization, and Glass Transitions of Some Asymmetrically Substituted Poly(siloxanes)

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 T gs are much lower than those of the corresponding polyolefins, [C(H)(R)CH2] n . Moreover, in the case of these polyolefins, the T gs decrease continuously from R = Me to n-Hex. The calculated T gs for the polysiloxanes that were obtained by using published empirical equations show the same general trend as the experimental values.