SOLID POLYMERS DOPED WITH RARE-EARTH-METAL COMPOUNDS .3. FORMATION AND STABILITY OF MACROMOLECULAR COMPLEXES COMPRISING NEODYMIUM NITRATE AND DIPIVALOYLMETHANE IN POLY(ETHYLENE OXIDE)

The solubility, complexation, and morphology in the Nd (NO3)3-PEO and Nd (Dpm)3-PEO systems were investigated using the FTIR, DSC, TGA, WAXD , and SAXS techniques. In both systems, dissolution was verified by th e absence of features characteristic of the bulkphase dopants detectab le with WAXD and DSC, and complexation was evident from the FTIR spect ral shifts involving the stretching motions of the EO unit. The extent of the Nd3+-EO interaction was found to be much stronger with Nd(NO3) 3 than Nd(Dpm)3. As a consequence, a T(g) elevation from 222K in pure PEO to 335K at an EO/Nd3+ ratio (defined as n) of between 4.0 and 5.6 was observed in the Nd (NO3)3-PEO system. Moreover, completely dry and amorphous complexes were obtained at n greater-than-or-equal-to 5.6, while residual moisture accompanying complexes at n less-than-or-equal -to 4 was found to persist upon prolonged vacuum drying. Being intrins ically hygroscopic at all doping levels, the Nd (NO3)3-PEO system was found to absorb moisture from the atmosphere resulting in wet amorphou s complexes, although precipitation of Nd (NO3)3 . 6H2O was observed a t n less-than-or-equal-to 4. It was proposed that moisture present in the Nd(NO3)3-PEO system be classified into two categories. One is tigh tly bound to Nd3+ to satisfy its coordination requirement, which was d etermined to be 11. The other is loosely bound, which is capable of be ing removed by heating and returning upon exposure to the atmosphere. It is the latter that can be readily quantified by the TGA technique a nd that lowers T(g) via plasticization. In addition to the observed mi nor FTIR spectral shifts, a relatively weak Nd3+-EO interaction in the Nd(Dpm)3-PEO system resulted in a lack of the T(g) elevation for PEO, persistence of the crystalline portion of PEO at all doping levels, a nd the formation of new crystalline phases as revealed by the WAXD pat terns and the DSC thermograms. The short-range order in PEO does not a ppear to be perturbed, but the SAXS data suggest that the long range-o rder is disrupted by the presence of Nd(Dpm)3 at an extremely low dopi ng level (i.e., n > 60). (C) 1994 John Wiley & Sons, Inc.