MOLEC DYNAMIC & INTERMOLECULAR INTERACTIONS OF POLYMER & SOLVENT COMPONENTS

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A study of the macroscopic properties of thermo-sensitive poly(DIOMMA) revealed a reversed temperature dependence in water versus alcohols. Gels made of the cross-linked analog also showed the same reversed trend between both solvents. We have studied the role of solvent in molecular processes of the polymer aggregations (PA) and the volume phase transitions (VPT) of gels in water or alcohols. We have completed extensive temperature dependence studies of 1H NMR spectra and some relaxation times for poly(DIOMMA) and its cross-linked analog (systems A and B) at both 360 and 500 MHz. Based on these molecular level data, we can deduce the relative strength and nature of the polymer-polymer, polymer-solvent and solvent-solvent interactions. Volumes of gel bead systems (these were created by cross-linking poly(NIPA), poly)NNPA), poly(NIPMA) and poly(NNPMA) with water) shrink at temperatures above the phase transition temperature (ph. tr.T). Spectral changes in 1H NMR (360 MHz) have recently been analyzed from 3 to 65 *C. These data have revealed details of differences in the molecular processes of the VPT among these gel systems. Spectra at temperatures below ph. tr. T (swollen state) consist of several peaks representing various chemical groups of the polymer. The linewidths of all peaks in the spectra suddenly broaden just above the ph. tr. T. These broadenings increase with rising temperature and, at the same time, a broad peak emerges near the HOD peak. Eventually all peaks coalesce to this new broad peak, except in the poly(NNPMA) system where the linewidths of all peaks become rather narrow again at high temperatures. Determination of the ph. tr. T. is usually defined as the onset of volume contractionexpansion measured by certain macroscopic methods. However, the IH NMR spectra indicate that significant spectral changes of the polymer component certainly begin within a narrow temperature range around the ph. tr. T., though gradual changes still continue for 10 to 30* C above the ph. tr. T. These results suggest that molecular processes in the VPT occur rather gradually by manifesting various conformational changes in the polymer chain with changing temperature. Our recent measurements of the temperature dependence of density of various gels demonstrated that onset of volume contractionexpansion corresponds to losing or gaining solvent molecules to or from the bulk liquid phase. Therefore, broadening of NMR linewidths in the collapsed state can be attributed to close proximity of various chemical groups caused by the loss of water and thus increasing the nuclear magnetic dipolar interactions between protons.