Silyl-protected hydroxystyrenes: living anionic polymerization at room temperature and selective desilylation

Abstract

Both 4- and 3-(tert-butyldimethylsilyl)oxystyrene (MSOST) undergo living anionic polymerization at room temperature with sec-butyllithium (sBuLi) in cyclohexane or methylcyclohexane upon injection of a small amount of tetrahydrofuran. Desilylation can be conveniently afforded with hydrogen chloride or tetra(alkyl)ammonium fluoride to provide poly(hydroxystyrene) (PHOST) with a narrow molecular weight distribution, which could be further transformed to other polystyrene derivatives. 13C NMR spectra of poly(tert-butyldimethylsilyloxystyrene) (PMSOST) and PHOST prepared under different conditions (tetrahydrofuran vs. cyclohexane, -78°C vs. 20°C) have indicated that the room temperature living polymerization in the hydrocarbon-rich solvent produces polymers with high syndiotacticity. Similarly, 4-(tert-butyldiphenylsilyl)oxystyrene (PhSOST), a new monomer, provides living anionic polymerization at room temperature. Desilylation of this polymer can be achieved using tetra(n-butyl)ammonium or tetraethylammonium fluoride. Inertness of the phenylsilyl ether to HCl allows selective desilylation of the dimethylsilyl ether with HCl in the presence of the phenylsilyl ether group, providing a new route to interesting macromolecules. Application of the selective desilylation technique to the synthesis of a block copolymer of HOST and 4-tert-butoxycarbonyloxystyrene (BOCST) is described.