Branched and Self-Crosslinkable Poly(methyl methacrylate)s Prepared via One-Pot Synthesis in Aqueous Emulsion

An approach to the synthesis of highly branched vinyl copolymers containing thiol and C=C crosslinking groups is proposed. This method was exemplified by the emulsion copolymerization of methyl methacrylate (MMA) and 1,6-hexanediol diacrylate (HDDA) with 2-mercaptoethyl sulfide (MES) as chain transfer agent at 70°C with 4,4′-azobis(4-cyanovaleric acid) (ACVA) as the initiator. The resulting highly branched copolymers contain both thiol and acryloyl groups. The apparent Mw (by SEC) of the resulting copolymers increased with increasing ACVA concentration, whereas the pendent acryloyl and -SH groups decreased from 6.4% to 0.8% (relative to MMA units) and 45 ×10−5 to 5 × 10−5 mol/g, respectively. The copolymers of MMA could be self-crosslinked thermally or by exposure to UV irradiation. The gel fraction of the thermally treated samples decreased from 46% to 7.2%, with the increasing of ACVA in the polymer synthesis, while the gel fraction of UV irradiated samples changed only slightly around 70%.