Structurally controlled polymerizations of methacrylates and acrylates

Abstract

Progress in the structure control of polymethacrylates and polyacrylates through stereospecific living polymerization are described. Three types of stereospecific living polymerizations have been developed for methacrylate polymerization: isotactic with t-C4H9MgBr, syndiotactic with ­t-C4H9Li/R3Al, and heterotactic with t-C4H9Li/bis(2,6-di-t-butylphenoxy)methylaluminium [MeAl(ODBP)2]. The last initiator system has been proved effective for monomer-selective living copolymerization of methacrylates. The living nature of these polymerizations allows extensive use for the syntheses of stereoregular block polymers and copolymers, and end-functionalized polymers such as macromonomers. Through stereospecific polymerizations and copolymerizations of macromonomers, comb polymers and graft copolymers with defined stereoregularities in the main chain and side chains could be obtained. Some properties of these stereoregular polymers are also described, including stereocomplex formation and solution viscosity. Stereospecific polymerizations of crotonates leading to diisotactic, diheterotactic and disyndiotactic polymers are also discussed. Supercritical fluid chromatography (SFC) has been proven to be useful for isolating uniform polymers from stereoregular poly(methyl methacrylate)s (PMMAs) with narrow molecular weight distribution. Uniform end-functionalized polymers have been used to construct more elaborate uniform polymer architectures such as stereoblock, star, and comb polymers, and copolymers. The uniform polymers have been proven quite useful for the studies of the relationship between structures and properties such as glass transition temperature, melting temperature and solution viscosity. Particularly interesting is the use of isotactic and syndiotactic uniform PMMAs for the understanding of stereocomplex formation in certain solvents such as acetone. Furthermore, a uniform stereoblock PMMA was found to undergo intramolecular complexation in addition to intermolecular complexation in acetone. Uniform star and comb PMMAs were also prepared and found useful for discussing the effect of branching on the solution viscosity. © 2000 Society of Chemical Industry