ESR spin‐label study of poly(styrene‐co‐methacrylic acid)/poly(ε‐caprolactone) semi‐interpenetrating polymer networks with controlled hydrogen‐bond interactions

Abstract

The morphology and miscibility of semi-interpenetrating polymer networks (semi-IPN) prepared with poly(styrene-co-methacrylic acid) [P(S-co-MAA)] of different carboxylic acid contents and poly(epsilon-caprolactone) (PCL) have been studied by ESR spin-label method. The ESR spectra of spin-labeled PCL showed one motional component at any specific temperature. It indicated that the spin-labeled molecules were located in one type of environment. The coexistence of two motional components in the ESR spectra of all semi-IPN samples was observed over a certain temperature range. This phenomenon suggested that the semi-IPNs were not compatible systems; they contained two microphases, a PCL-rich microdomain and a P(S-co-MAA)-rich microdomain. The miscibility could be improved by increasing the carboxylic acid content, which could enhance the hydrogen-bonding interactions between the ester groups of PCL and carboxylic acid groups in P(S-co-MAA). It was also found that the intracomponent cross-linking of the semi-IPNs was not in favor of the miscibility. The microphase separation occurred in all semi-IPNs, even in the samples having strong hydrogen-bonding interactions. With increasing cross-linking density, the microphase separation became more remarkable.

ESR Spectroscopy of Multiphase Polymer Systems

“…The miscibility can be improved by increasing the carboxylic acid content, which could enhance the hydrogenbonding interactions between the ester groups of PCL and carboxylic acid groups in P(S-co-MAA). It was also found that the microphase separation became more remarkable with increasing intracomponent crosslinking of the SIPNs [82].…”