Inter/intramolecular hydrogen bonding mediate miscible blend formation between near-perfect alternating Poly(styrene-alt- hydroxyphenylmaleimide) copolymers and Poly(vinyl pyrrolidone)

Abstract

In this study we synthesized two isomeric hydroxyphenylmaleimide (HPMI) monomers, with para (pHPMI) or ortho (oHPMI) OH groups, and subjected them to free radical copolymerization with styrene to form the near-perfect alternating copolymers poly(S-alt-pHPMI) and poly(S-alt-oHPMI), respectively. We used nuclear magnetic resonance and Fourier transform infrared (FTIR) spectroscopy, MALDI-TOF mass spectrometry, and quantum chemical calculations to characterize the chemical structures, hydrogen bonding interactions, and alternating sequence distributions of the two HPMI-based copolymers. Poly(S-alt-pHPMI) and poly(S-alt-oHPMI) formed miscible blends with the homopolymer poly(vinyl pyrrolidone) (PVP) due to strong intermolecular hydrogen bonding between the OH groups of the copolymers and the CO groups of PVP, as revealed from FTIR spectral analysis and quantum chemical calculations. Because the ortho OH groups of the phenolic units of oHPMI experienced additional intramolecular hydrogen bonding with the CO groups of the maleimide units, their intermolecular interactions were limited and weaker than those of the para OH groups of pHPMI. These differences in hydrogen bonding ultimately affected the thermal properties of the copolymers and their blends with PVP.