Facile synthesis of branched water-soluble poly(dimethylacrylamide)s in conventional and parallel reactors using free radical polymerisation

Water-soluble, branched dimethylacrylamide copolymers have been prepared via facile, one-step, batch solution free-radical polymerisations taken to high conversion. N,N-dimethylacrylamide has been copolymerised with different branching agents (ethylene glycol dimethacrylate, EGDMA and PEG dimethacrylates) using dodecanethiol (DDT) as a chain transfer agent to inhibit gelation. Good yields of soluble branched copolymers have been produced by carrying out individual reactions in conventional glass round-bottomed flasks and also parallel reactions in a Radley's Carousel Reactor. The products have been characterised by size exclusion chromatography and 1H NMR and FT-IR spectroscopies and interestingly though the trends in copolymer structure are similar for products prepared in the conventional glassware and those in the parallel reactor, some systematic differences arise between the two sets of products. This seems to be due in part to the slightly different scale of these reactions, and possibly also to the better sealing of the parallel reactor tubes and hence better exclusion of traces of O2. Branching seems to occur more uniformly with DAM than with the previously studied methyl methacrylate (all other parameters being identical), though the effects of the chain transfer agent, monomer concentration, monomer/chain transfer agent feed ratio and the chain length of the branching agent are similar for both monomers. Also the EGDMA/DDT ratio is at least as important in controlling branching as the absolute amount of EGDMA and DDT incorporated. Highly branched products can therefore be made with relatively low levels of EGDMA and DDT as long as the EGDMA/DDT ratio is high enough, but not so high as to favour cross-linking.