Molecular dynamics simulations of PNIPAM- co-PEGMA copolymer hydrophilic to hydrophobic transition in NaCl solution.

Classical molecular dynamics simulations were carried out to investigate the hydrophilic to hydrophobic transition of PNIPAM- co-PEGMA close to its lower critical solution temperature (LCST) in 1 M NaCl solution. PNIPAM- co-PEGMA is a copolymer of poly( N-isopropylacrylamide) (PNIPAM) and poly(ethylene glycol) methacrylate (PEGMA). The copolymer consists of 38 monomer units of NIPAM with two PEGMA chains attached to the PNIAPM backbone. The PNIPAM- co-PEGMA was observed to go through the hydrophilic−hydrophobic conformational change for simulations at temperature slightly above its LCST. Na+ ions were found to bind strongly and directly with amide O, even more strongly with the O atoms on PEGAMS chains, whereas Cl− ions only exhibit weak interaction with the polymer. Significantly a novel caged stable metal-organic complex involving a Na+ ion coordinated by six O atoms from the copolymer was observed after the PNIPAM- co-PEGMA copolymer went through conformational transition to form a hydrophobic folded structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 [ABSTRACT FROM AUTHOR]