Synthesis, Characterization and Thermolysis of Hyperbranched Homo- and Amphiphilic Co-Polymers Prepared Using an Inimer Bearing a Thermolyzable Acylal Group

Degradable hyperbranched polymers were synthesized via self-condensing atom transfer radical copolymerization of methyl methacrylate (MMA) with a novel inimer bearing a thermolyzable acylal group. This inimer was 1-(2-bromoisobutyryloxyl)ethyl methacrylate (BIB1EMA) and was synthesized in a one-step reaction between 2-bromoisobutyric acid and vinyl methacrylate at 40% yield. The inimer was subsequently used for the preparation of three degradable hyperbranched homopolymers of MMA (monomer conversion similar to 80%) with molecular weights in the range from 36 000 to 51 000 g mol(-1) synthesized using initial MMA-to-inimer molar ratios between 25 and 100. The inimer was also used for the preparation of two degradable hyperbranched amphiphilic copolymers of MMA and 2-(dimethylamino)ethyl methacrylate (DMAEMA) with an MMA hydrophobic hyperbranched core and different compositions, 10 and 38 mol % DMAEMA, afforded by changing the relative loadings in the two comonomers. Both hyperbranched amphiphilic copolymers were soluble in THF: water mixtures with up to 50% w/w water content, whereas they precipitated at higher water contents. All hyperbranched (co)polymers were thermolyzed in a vacuum oven at 200 degrees C within 24-56 h. The molecular weights of the thermolysis products were consistent with the inimer content and the complete thermolysis of the hyperbranched (co)polymers. Hyperbranched polymers of MMA, also prepared in this investigation, but using a nondegradable inimer, isomeric to BIB1EMA, 2-(2-bromoisobutyryloxyl)ethyl methacrylate (BIB2EMA), did not present any reduction in their molecular weight when subjected to the same thermolysis conditions as those applied for the degradable hyperbranched polymers (200 degrees C, similar to 24 h).