Helfand-type motions, poly

Figure 1. Helfand-type motions about three bonds (6). The segments represented here correspond to the —OCH2CD2CD2CH20— portion of the poly (butylene terephthalate) hard segments. These motions are consistent with the solid state deuterium NMR data for poly(butylene terephthalate) (5).

The results presented here show that there are two distinct motional environments for the "central" deuterons of poly (butylene terephthalate) in the segmented copolyesters containing poly (butylene terephthalate) as the hard segment. One of the motional environments is identical to that observed in the poly (butylene terephthalate) homopolymer, in which Helfand-type motions (6) about three bonds occur with a correlation time of 7 x 10-6 s at 20 °C. The Tj for these deuterons is ca. 60 ms at 20 °C. Approximately 90% of the hard segments reside in these organized lamellar environments in the segmented copolymer with 0.87 mole fraction hard segments. 

Many NMR dynamics studies attempt to correlate the observed data with models of molecular motion. Some of the more successful are the Hall-Helfand [189,190], the Dejean-Laupretre-Monnerie (DEM) [189,191, 192], and the Williams-Watts [189,194,195] models. They predict the relaxation times and NOEs expected from specific types of motion such as unrestricted diffusion or discrete jumps. Very often, distinct parts of the molecule are be best modeled by different functions. For a poly(isobutyl methacrylate) solu-... 

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