Amphiphilic polymethacrylate model co-networks: Synthesis by RAFT radical polymerization and characterization of the swelling behavior

Reversible addition - fragmentation chain transfer (RAFT) controlled radical polymerization was employed, for the first time, to prepare well-defined (model) amphiphilic polymer co-networks based on n-butyl methacrylate (BuMA, hydrophobic monomer) and 2-(dimethylamino)ethyl methacrylate (DMAEMA, hydrophilic ionizable monomer) cross-linked with ethylene glycol dimethacrylate (EGDMA) and bearing elastic chains having the following comonomer distributions: BuMA-b-DMAEMA-b-BuMA and DMAEMA-b-BuMA-b-DMAEMA triblock and BuMA-co-DMAEMA statistical copolymers. Two randomly cross-linked (not model) amphiphilic co-networks were also synthesized, the one by RAFT and the other by conventional free radical polymerization. The amphiphilic triblock copolymer-based model co-networks were obtained by stepwise synthesis in three stages: (1) the synthesis of linear homopolyrners bearing two active ends by using a bifunctional chain transfer agent (CTA), (2) the sequential addition of the second monomer on the macro-CTAs (homopolymers) to yield linear ABA or BAB triblock copolymers, and (3) the inter-linking of the linear copolymer chains at both ends using EGDMA cross-linker to form the final model co-networks. The homopolymer and copolymer precursors to the networks were characterized using gel permeation chromatography and H-1 NMR spectroscopy. The swelling behavior of the networks was investigated in tetrahydrofuran and water. The co-networks swelled more in acidic than in neutral water due to the ionization of their DMAEMA units. The low pH aqueous swelling of the statistical co-network was higher than those of its triblock counterparts due to the lack of microphase separation with the statistical copolymer chains.