End-linked poly[2-(dimethylamino)ethyl methacrylate]-poly(methacrylic acid) polyampholyte conetworks: Synthesis by sequential RAFT polymerization and swelling and SANS characterization

Abstract

Four well-defined end-linked triblock polyampholyte conetworks composed of positively ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA) repeating units and negatively ionizable methacrylic acid (MAA) repeating units were synthesized using one-pot, sequential reversible addition-fragmentation chain transfer (RAFT) polymerization, by employing 1,4-bis[2-(thiobenzoylthio)prop-2- yl]benzene (1,4-BTBTPB) as the chain transfer agent, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. From the four end-linked conetworks, three were based on ABA triblock polyampholytes with polyDMAEMA midblocks with a constant degree of polymerization (DP) and polyMAA end-blocks of different DPs. The fourth end-linked polyampholytic conetwork was based on an equimolar BAB triblock polyampholyte with a polyMAA midblock. Furthermore, two polyampholyte networks were also prepared: one based on an end-linked equimolar statistical polyampholyte, and one with a randomly cross-linked, rather than an end-linked, architecture. Finally, the two homopolymer networks based on the DMAEMA and the MAA monomers were also synthesized. The MAA units were introduced in the (co)networks via the polymerization of 2-tetrahydropyranyl methacrylate (THPMA) followed by its acid hydrolysis after (co)network formation. The linear precursors to the (co)networks were found to have molecular weights and compositions close to the expected values, whereas the extractables from the (co)networks were determined to be lower than 30%. In water, the degrees of swelling (DS) of all the polyampholyte (co)networks presented a characteristic minimum at intermediate pH values, around the (co)network isoelectric point (pI), while they increased at acidic and basic pHs. The pI values of the ampholytic (co)networks were estimated as the midpoints of the regions of reduced swelling and ranged between 5.3 and 6.8, decreasing with the increase of the MAA content in the (co)networks. Finally, small-angle neutron scattering (SANS) studies of the polyampholyte (co)networks swollen in D2O provided SANS profiles without any peaks but broad shoulders whose location was consistent with the spacing of the cross-linking cores. © 2011 American Chemical Society.