Synthesis of hyperbranched and highly branched methacrylates by self-condensing group transfer copolymerization

We report a study of the self-condensing g-roup transfer copolymerization o f the initiator-monomer ("inimer") 2-(2-methyl-1-triethylsiloxy-1-propenylo xy)ethyl methacrylate (MTSHEMA) with methyl methacrylate (MM-A). The highly branched polymethacrylates were characterized by multidetector SEC and NMR . Kinetic measurements show that cyclization, i.e., the intramolecular reac tion of an active center with the vinyl group of the polymer, limits the mo lecular weights and lowers the polydispersity. Depending on the comonomer r atio, gamma = [MMA](0)/[MTSHEMA](0), molecular weights up to M-w, = 240 000 at a polydispersity of M-w/M-n approximate to 3 could be obtained. The Mar k-Houwink exponent of these branched copolymers depends on the comonomer ra tio and is significantly lower (0.45 greater than or equal to alpha greater than or equal to 0.23) than linear PMMA (alpha = 0.69). Only 4% of inimer are necessary to lower the Mark-Houwink exponent to half the value of linea r PMMA. Using slow addition of the comonomer mixture to the monofunctional initiator 1-methoxy-3-(trimethylsilyloxy)-2-methyl-1-propene (MTS) enables control of the molecular weights and decreases the polydispersity to M-w/M- n approximate to 1.6. Copolymerization of MTSHEMA with tert-butyl methacryl ate followed by acid-catalyzed hydrolysis of the tert-butyl groups yields h ighly branched poly(meth acrylic acid).