Formation of soluble hyperbranched polymer through the initiator-fragment incorporation radical copolymerization of ethylene glycol dimethacrylate with N-methylmethacrylamide

Abstract

The copolymerization of ethylene glycol dimethacrylate (EGDMA) as a divinyl monomer with N-methylmethacrylamide (NMMAm) as a water-soluble monomer was carried out at 70 and 80°C in N,N-dimethylformamide (DMF) using dimethyl 2,2′-azobisisobutyrate (MAIB) of high concentrations as initiator. When the concentrations of EGDMA, NMMAm and MAIB were 0.15, 0.50 and 0.35mol/l, the copolymerization proceeded homogeneously with no gelation at 80°C to give soluble copolymer in a yield of 50%. EGDMA was polymerized more rapidly than NMMAm as shown by Fourier-transform near infrared spectroscopy. The copolymer formed for 8h consisted of 20mol% of EGDMA unit, 47mol% of NMMA unit and 33mol% of methoxycarbonylpropyl group unit as MAIB-fragment. The copolymer formed at 80°C for 30min showed an upper critical solution temperature (34°C on cooling) in methanol. The intrinsic viscosity of the copolymer formed for 2h was very low (0.11dl/g) at 30°C in DMF despite high weight-average molecular weight [3.1×l06 by multi-angle laser light scattering (MALLS)]. The copolymer exhibited a very low second virial coefficient (4.2×l0−6) as determined at 25°C in DMF by MALLS. The individual copolymer molecules were observed as nanoparticles of 7–20nm diameter by a transmission electron microscope. These results show that the resulting copolymers are of hyperbranched structure.