Synthesis of Hyperbranched and Highly Branched Methacrylates by Self-Condensing Group Transfer Copolymerization

Abstract

We report a study of the self-condensing group transfer copolymerization of the initiator−monomer (“inimer”) 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate (MTSHEMA) with methyl methacrylate (MMA). The highly branched polymethacrylates were characterized by multidetector SEC and NMR. Kinetic measurements show that cyclization, i.e., the intramolecular reaction of an active center with the vinyl group of the polymer, limits the molecular weights and lowers the polydispersity. Depending on the comonomer ratio, γ = [MMA]0/[MTSHEMA]0, molecular weights up to Mw = 240 000 at a polydispersity of Mw/Mn ≈ 3 could be obtained. The Mark−Houwink exponent of these branched copolymers depends on the comonomer ratio and is significantly lower (0.45 ≥ α ≥ 0.23) than linear PMMA (α = 0.69). Only 4% of inimer are necessary to lower the Mark−Houwink exponent to half the value of linear 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 Mw/Mn ≈ 1.6. Copolymerization of MTSHEMA with tert-butyl methacrylate followed by acid-catalyzed hydrolysis of the tert-butyl groups yields highly branched poly(methacrylic acid).