Semi- and fully interpentrating polymer networks based on polyurethane–polyacrylate systems. IV. Grafted semi-1-interpenetrating polymer networks

A series of semi-1-IPNs containing 40% polyurethane and 60% polymethyl acrylate was synthesized using Adiprene L-100, trimethylol propane, and polybutadiene diol. This diol was chosen to yield polyurethanes with a large number of potential graft sites for the methyl acrylate which was polymerized after the polyurethane network had been formed. A series of linear polyurethane–polymethyl acrylate blends, covering a range of compositions, was also prepared. The polyurethane for these polyblends was synthesized from Adiprene L-100 and butane-1,4-diol. Both sets of materials were investigated by dynamic mechanical analysis. On the basis of a comparison of solubility parameters, the polyurethanes and polymethyl acrylate would be expected to be incompatible. In the dynamic loss modulus-temperature plots of the polyblends there was a significant shift of the polyurethane T_g to higher temperature, but the polymethyl acrylate transition did not shift. The polyurethane transitions of the semi-1-IPNs were also shifted, but considerably more than in the case of the polyblends. For both systems, it was postulated that grafting had occured to a significant extent. With the semi-1-IPNs, it was found that as M?_c decreased the extent of grafting apparently increased. This was rationalized on the grounds that as the network chain lengths decrease, a higher proportion of the methyl acrylate monomer, prior to polymerization, was close to polyurethane segments and that this is a situation likely to lead to more grafting.