Synthesis of Branched Polysiloxanes with Controlled Branching and Functionalization by Anionic Ring-Opening Polymerization

Abstract

Functionalized branched polysiloxanes with star-branched, comb-branched and dendritic-branched topologies were synthesized. The branched macromolecules were generated by coupling of reactive blocks using a grafting technique ( ACS Polym. Prepr. 2001, 42, 227; ACS Symp. Ser. 2003, 838, Chapter 2). The living anionic ring-opening polymerization (ROP) of vinyl-substituted cyclotrisiloxanes (ViMeSiO) 3, V 3, and, VD 2, and the copolymerization of these monomers with hexamethylcyclotrisiloxane, D 3, was explored to obtain reactive blocks. Termination of the living polymer, having a lithium silanolate end group, on a reactive core containing SiCl groups led to the grafting of living polysiloxane on the core. Transformation of vinyl groups in the polymer into the reactive SiCl groups by hydrosilylation with Me 2 HSiCl made possible the grafting of a successive generation of branches. The reactive blocks of high and low density of the precursor vinyl group were obtained by the polymerization of monomers V 3 and VD 2, respectively. While the homopolymerization led to a uniform density of vinyl groups along the chain, the copolymerization of V 3 or VD 2 with D 3 produced a gradient distribution with the density decreasing in the direction of the chain growth. This arrangement led to a higher density of the vinyl group in the external part of the branched macromolecule. Study of kinetics of the copolymerization of V 3 with D 3 in THF initiated by BuLi gave the reactivity coefficients k V 3 = 17.8, k D 3 = 0.036 (25 °C), from which the density distribution of vinyl groups in reactive blocks may be determined. Four-arm star copolymers were obtained using (MeCl 2 SiCH 2 ) 2 as the core, whereas the comblike polysiloxane was obtained from a linear copolymer of ViMeSiO and Me 2 SiO treated with Me 2 HSiCl. Dendritic polysiloxanes of the first and second generation were obtained using the functionalized starlike polysiloxane as the core.