Design and mediated hydrogen bonding strength of Poly(styrene-alt- N–(ethyl–4–hydroxyphenyl)maleimide) copolymer to enhance miscibility with hydrogen bonded acceptor homopolymers

In this study, the monomer N–(ethyl–4–hydroxyphenyl)maleimide (TyHPMI) was synthesized from tyramine and maleic anhydride. Subsequently, free radical copolymerization was used to prepare the poly(S–alt–TyHPMI) alternating copolymer by reacting TyHPMI with styrene. We confirmed the chemical structure using Fourier transform infrared (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR). The sequence distribution of the poly(S–alt–TyHPMI) alternating copolymer was analyzed using mass–analyzed laser desorption ionization/time–of–flight (MALDI–TOF) mass spectrometry. Differential scanning calorimetry (DSC) measurements showed a single glass transition temperature (T_g) across various weight fractions of binary blended systems containing strong hydrogen–bonded acceptors, such as poly(S–alt–TyHPMI)/poly(4–vinyl pyridine) (P4VP) and poly(vinyl pyrrolidone) PVP, implying full miscibility. The T_g values predicted by kwei equation for the poly(S–alt–TyHPMI)/P4VP and poly(S–alt–TyHPMI)/PVP blends show a positive deviation from linearity. This deviation is due to the short alkyl chain reinforcing the addition of acidic TyHPMI units, which enhances intermolecular hydrogen bonding between the pyridyl or C=O groups and the OH units of the TyHPMI segment. As a result, FTIR spectral analyses indicate that the intermolecular hydrogen bonding between pyridyl and C=O groups is stronger in the poly(S–alt–TyHPMI) copolymer compared to the poly(S–alt–HPMI) copolymer. This is supported by the larger ratio of the inter/self-association equilibrium constant (K_A/K_B) value.