Thermodynamics of interactions and structural peculiarities of interpenetrating polymer networks based on polyurethane and copolymer of 2-hydroxyethyl methacrylate with methacryloyloxyethylphosphorylcholine

Abstract

Interpenetrating polymer networks based on biocompatible components – polyurethane and copolymer of 2-hydroxyethyl methacrylate with methacryloyloxyethylyphosphorylcholine (HEMA-MPC) were synthesized and thermodynamic parameters of interactions in the system and morphology were investigated. The thermodynamic parameters of interactions between polymer components of the IPNs were calculated based on sorption isotherms of methylene chloride vapors by samples of the created polymer systems. It is shown that MPC plays the role of a compatibilizer in the system, increasing the thermodynamic compatibility between polyurethane and the HEMA-MPC copolymer at small amounts of the copolymer in the IPNs. As the amount of copolymer HEMA-MPC in the IPNs increases, the value of the free energy of the polyurethane and copolymer mixing shifts to the positive value, which is associated with the formation of ionic clusters of MPC. This may mean that with an increasing amount of the MPC in the system, interactions between the negatively charged phosphoryl groups and the positively charged nitrogen atom of various MPC polymer chains occur, i.e., the part of intermolecular interactions (polyurethane and copolymer) decreases, while the part of intramolecular interactions (between different groups of MPC) increases. The results of the morphology investigations of the IPN samples are consistent with the data of the thermodynamic compatibility study of polymers during the formation of the IPNs. With a significant increase in the positive values of the free energy of the polyurethane and copolymer mixing in the IPNs with 41 % and 51 % of the copolymer content, a significant phase separation is observed in the IPNs, with phase inclusions ranging from 1 to 5 mm.