Thermoresponsive behavior of poly(DEGMA)-based copolymers. NMR and dynamic light scattering study of aqueous solutions

Abstract

We studied temperature behavior of diblock copolymers of poly[2-(2-methoxyethoxy)ethyl methacrylate] (PDEGMA) with poly(N-(2-hydroxypropyl)methacrylamide and a statistical copolymer PDEGMA-co-N-propargylmethacrylamide in aqueous solutions. NMR spectra and dynamic light scattering showed that the copolymers exhibit a reversible phase transition which depends on the composition of the block copolymer and slightly on polymer concentration. In contrast to statistical copolymer, different behavior of proton groups in polymer backbone (and in the nearest side chain OCH2 group) on the one hand and in other side chain groups of the PDEGMA on the other hand was observed for diblock copolymers. Additionally, two types of water molecules were detected in solutions of the diblock copolymers above the phase transition –“free” with long and “bound” with short spin-spin relaxation times T2. NOESY spectra indicate that a core- to- shell morphology is unlikely in these block copolymers. This report emphasizes the importance of understanding of the self-association of copolymers in solution on the molecular level and provides important information for the design of “smart” thermoresponsive polymer-based drug delivery systems.