pH response of model diblock and triblock copolymer networks containing polystyrene and poly(2-hydroxyethyl methacrylate-co-2-(dimethylamino)ethyl methacrylate)

We investigated the swelling behavior of lamella-forming diblock and triblock copolymers of polystyrene, PS, and poly (2-hydroxyethyl methacrylate-co-2-(dimethylamino)ethyl methacrylate), PHD, with varying 2-(dimethylamino)ethyl methacrylate (DMAEMA) content. In phosphate buffer solutions of varying pH's, these model networks swell like cationic hydrogels; their swelling characteristics are tunable through the DMAEMA content within the PHD block. While glassy PS domains within PS/PHD/PS can serve as physical cross-links in triblock copolymer networks, the PS domains are not effective anchors in diblock copolymer networks. PS/PHD with high DMAEMA content thus macroscopically disintegrate upon protonation of DMAEMA. The lamellar microdomains within these networks, however, continue to swell with decreasing pH. By reducing the DMAEMA content in PS/PHD, we have been able to create a diblock copolymer network that is macroscopically stable upon protonation of DMAEMA, as its water uptake cannot induce sufficient osmotic pressure to break up the sample. The swelling characteristics of this particular network mirror those of physically cross-linked PS/PHD/PS networks with comparable DMAEMA content.