Abstract
A mixed aqueous solution of hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(acrylic acid) (PAAc) becomes cloudy under acidic conditions at room temperature. The pendant carboxylic acid groups in PAAc form hydrogen bonds with the ester and phosphate groups in PMPC. While the polymers aggregate under acidic conditions, neither one associate under basic conditions because of the deprotonation of the pendant carboxy groups in PAAc. We observed that the interpolymer complex formed from PMPC, and PAAc was dissociated in aqueous solutions with increasing temperature, which is an upper critical solution temperature behavior. With increasing temperature, the molecular motion increased to dissociate the interpolymer complex. The phase transition temperature increased with increasing polymer and salt concentrations, and with decreasing pH.
Highlights
Stimuli-responsive polymers can change their physical and/or chemical properties on exposure to external conditions, such as temperature, pH, salt concentration, light, and magnetic fields [1,2,3,4]
The degrees of polymerization (DP)(NMR) for poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) was 98, which was calculated from the integral intensity ratio of the pendant methylene protons at 3.7 ppm and the terminal phenyl protons attributed to chain transfer agent (CTA) at 7.4–8.2 ppm
PMPC and poly(acrylic acid) (PAAc) were prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization
Summary
Stimuli-responsive polymers can change their physical and/or chemical properties on exposure to external conditions, such as temperature, pH, salt concentration, light, and magnetic fields [1,2,3,4]. (PNIPAM), has been found to become insoluble in water owing to dehydration above the lower critical solution temperature (LCST) [5]. The Tp of PNIPAM increases and decreases to copolymerize hydrophilic and hydrophobic monomers, respectively [9]. It is well-known that another class of thermo-responsive polymers with the upper critical solution temperature (UCST) shows phase separation below the UCST. Far, only a few UCST water-soluble polymers have been reported, compared to LCST polymers [10]. UCSTtype phase separation behavior in aqueous media can be observed by electrostatic [11]
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