Two polymer gel systems have been studied : (1) Poly(N-isopropylacrylamide) (NIPA) and (2) Poly(N-methyl-N(1,3-dioxoran-2-ermethyl)acrylamide) (NOMA). For system (1), an extensive proton NMR chemical shift and relaxation studies have revealed how various chemical groups of NIPA behave below and above the phase transition temperatures (32 - 37 C). We have extended this work by studying gels of NIPA-D7 (all protons in the N-isopropyl group are deuterated), in order to elucidate their dynamic behaviors more clearly than those measured for the corresponding proton-only analogs.The study of system (2) (NOMA gels) has revealed the role of liquid component in polymer gel systems. The polymer component (not gel) of NOMA dissolved in water exhibited an interesting behavior around low critical solution temperature (LCST) (50.0 q 2' C). The peaks assigned to the CH2 protons of dioxoran ring forms a doublet at temperatures 2-3' below LCST change to a quartet at temperatures 2-3' above LCST. This transformation between doublet and quartet is a reversible and kinetically rapid process. By taking spectra around LCST at both 360 and 500 MHz, it was confirmed that this transformation arises from appearance and disappearance of peaks differentiated by chemical shift, not by spin-spin coupling. Spectral changs near the LCST must be related to aggregation and dispersion of polymers. Apperance of another peak just few degrees above LCST is probably caused by slowing down of molecular (particualrly of the dioxoran ring) motions due to molecular aggregation. One may estimate an approxiamte rate of this process to be slower than splitting (about 100 - 150 Hz). Transforming a quartet to a doublet (again) with rising temperature (above LCST) must be attributed to faster thermal motions. A similar behavior may be expected in ethanol environment because LCST is observed to be quite sharp at 52' C.
NIH ExPorter
NIH ExPorter