OBSERVATION OF HETEROGENEOUS TRACE (0.4-PERCENT W/W) WATER-UPTAKE IN BISPHENOL A POLYCARBONATE BY NMR IMAGING

The uptake of water by injection-molded bars of bisphenol A polycarbonate (Lexan 121 resin) has been monitored by a combination of one-dimensional proton NMR spectroscopy, relaxation time (T1 and T2) measurements, and microscopic imaging techniques. The bulk of the water absorbed in the initial stages (20-24 h) of 100-degrees-C water exposure is uniformly distributed throughout the polymer with a trace amount of the water found in clusters of 200-300-mu-m in size. The water that has aggregated to form these clusters is more mobile, having a T2 relaxation time 20 times longer than that found for the uniformly distributed water. At longer exposure times (30-40 days) the number of clusters is observed to increase. Although the total amount of water adsorbed is considerably less than 1 % w/w, good-quality images are obtained, demonstrating that the NMR microimaging technique can successfully monitor even trace levels of solvent if the molecules are relatively mobile.