Cohesive properties of Ultem and related molecules from simulations

The cohesive properties of many engineering plastics are difficult to deter mine experimentally, as the polymers are frequently insoluble, have high T( g)s, and are sometimes poorly characterized. For difficult polymers such as these, molecular modeling can provide useful information of higher quality than might be obtained by other methods. Ultem (R) is a polyether imide ha ving a very large and relatively stiff repeat unit. We have performed a ser ies of simulations on Ultem and related molecules so as to evaluate the coh esive energy density of the polymer. Small molecular fragments (N-phenylpht halimide, 2,2-diphenylpropane, and diphenylether) of the repeat unit were s tudied to get approximate bounds to be expected for values of the solubilit y parameter for the polymer. Oligomers up to 4-mers were directly simulated , and the results were used to estimate the properties of the high polymer. These methods yield a value near 22.0 MPa1/2 for the solubility parameter of the polymer, lower than has been estimated from group additivity. The in terfacial interactions between Ultem and a variety of low molecular liquids have also been evaluated in an effort to identify functional groups that m ight interact most favorably with the polymer for adhesive applications. Th ese calculations are in good agreement with expectations from solubility pa rameters. Most significantly, the calculations are fully compatible with ex perimental observations. (C) 2001 Elsevier Science Ltd. All rights reserved .