Association in aqueous solutions of a thermoresponsive PVCL-g-C11EO42 copolymer

Thermoresponsive associations in aqueous solution of poly(N-vinylcaprolactam) chains grafted with omega-methoxy poly(ethylene oxide) undecyl alpha-methacrylate (PVCL-g-C11EO42) at different copolymer concentrations have been investigated with the aid of various experimental methods. Turbidity measurements reveal that the cloud point (CP) decreases with increasing polymer concentration, and this effect is more pronounced in the semidilute concentration regime. Small-angle neutron scattering (SANS) results at large scattering wavevectors suggest a gradual conformational transition from random coils to contracted coils in the dilute concentration regime as the temperature rises. The rheological experiments disclose a strong temperature-induced contraction of the molecules in the dilute concentration regime, and the results in the semidilute regime indicate that the polymer chains are unentangled even at high concentrations. Dynamic light scattering results on solutions at temperatures up to the CP show the existence of a bimodal relaxation process; one mode is associated with the diffusion of individual polymer coils, or small clusters of molecules, and the other one is ascribed to interchain aggregation and the formation of aggregates at higher concentrations. At low concentrations, the intrachain species exhibit a temperature-induced compression, whereas at higher concentrations a temperature rise generates intermolecular aggregates. At a low constant temperature, an increase in polymer concentration leads to poorer thermodynamic conditions of the system, and shrinkage of the polymer coils is observed. At temperatures slightly above CP, the decay of the correlation function is characterized by a narrow unimodal relaxation mode. At this stage, most of the intrachain structures have been consumed in the formation of more compact particles.