Synthesis and characterisation of poly(2-hydroxyethyl methacrylate) polyelectrolyte complexes

Copolymerisation of charged and neutral monomers is a well-known methodology to introduce charged moieties in a polymeric chain to obtain polyelectrolytes. New polyelectrolyte complexes have been synthesised by radical copolymerisation of neutral methacrylic monomer 2-hydroxyethyl methacrylate (HEMA) with cationic 2-methacryloyloxyethyltrimethyl ammonium chloride and anionic 2-acrylamido-2-methylpropane-sulphonic acid monomers in 10:1:1 and 10:1:2 stechiometric ratio. Chemical structure of the synthesised terpolymers was confirmed by FT-IR spectroscopy, moreover, X-ray photoelectron spectroscopy showed the presence of a cationic charge excess on the 10:1:2 terpolymer surface with respect to 10:1:1 terpolymer. Swelling studies for 10:1:2 terpolymers showed a high water content in the swollen state and a "smart behaviour" upon changes in external stimuli such as pH, while, 10:1:1 terpolymer presented the behaviour of a neutral polymer. Mechanical and differential scanning calorimetry analysis confirmed that terpolymer networks were stabilised by ionic co-operative interactions. Infact, the inclusion of oppositely ionic charges in the polymeric network of p(HEMA) represent a way to achieve higher elastic modulus as they stabilise the terpolymer networks. Cytotoxicity and cytocompatibility studies demonstrated that all materials were not toxic, moreover, the presence of a cationic charge excess on 10:1:2 terpolymer surface was able to promote fibroblast adhesion.