Local Segmental Dynamics of Poly(2-hydroxyethyl Methacrylate) in Methanolic Solution by Spin Label X-Band ESR

Abstract

A copolymer of 2-hydroxyethyl methacrylate (HEMA) with spin-labeled methacrylic acid units distributed randomly along the main chain (∼3 mol %) was synthesized. ESR spectra of methanolic solutions of the copolymer at concentrations ranging from 2 to 50 wt % were measured at X-band (9 GHz) over a broad temperature range. Temperature dependence of the parameter RS, characterizing the local segmental dynamics in PHEMA chain, and of the other parameters characterizing local dynamics and conformation of the copolymer were determined by fitting experimental ESR spectra to the theoretical spectra calculated using the MOMD model. Arrhenius plots of the rotational parameters exhibit atypical nonlinear behavior characterized by two breaks at particular temperatures in the RS plot. It is concluded that, similarly to PMMA in a number of solvents, PHEMA in methanol undergoes a conformational transition from a less compact to more compact conformation of the polymer chain when the temperature increases in a particular ...