SYNTHESIS, CHARACTERIZATION, AND GLASS TRANSITIONS OF SOME ASYMMETRICALLY SUBSTITUTED POLY(SILOXANES)

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