Sorption and diffusion of organic solvents through interpenetrating polymer networks (IPNs) based on polyurethane and unsaturated polyester

The equilibrium swelling experiments of interpenetrating polymer networks (IPNs) based on castor oil based polyurethanes (PU) and unsaturated polyester (UPE) were performed in various solvents, in order to calculate their solubility parameter. The kinetics of swelling and sorption have also been studied in chlorobenzene at 25°C. IPNs with various weight composition of PU and UPE (80:20, 50:50, 20:80), and also having various crosslink density (NCO/OH ratio) viz. 1.2, 1.5 and 2.0 were employed in the study. The results are found to vary with the weight composition of the components and crosslink density of the samples. The sorption behavior is also found to vary with the hydroxyl number (molecular weight) of the polyol employed in the preparation of PU. Studies revealed that, the sorption is anomalous in nature in all the cases. Diffusion coefficient (D) is found to increase with both increase in NCO/OH ratio and UPE content, whereas sorption coefficient (S) shows a reverse trend in all the samples studied. From the swelling studies, the molecular weight between two crosslinks (Mc) and hence the number of chains per unit volume (N) and degree of crosslinking (ν) were also calculated. The results obtained were compared with that of the homopolymer networks.