Introduction.Recently, syndiotactic polypropylene (sPP) with high stereoregularity was synthesized by Ewen et al. 1 Whereas early investigations carried out by using less syndiotactic samples had difficulties in precise characterization, the success of highly stereoregular polymerization made the detailed analysis of the crystal structure possible. A large number of investigations on the molecular chain conformation and molecular packing in crystals have also been reported for sPP. As for the polymorphs, four crystalline forms are known: the planar zigzag, 2-5 t 2 g 2 t 6 g 2 , 6-8 and two forms with the t 2 g 2 conformation. 9-22 Of these, the crystals with the planar zigzag conformation have been believed to be formed only by cold drawing after quenching from the melt into an ice-water mixture. [2][3][4][5] Very recently, we have found that the crystallization of the planar zigzag form is spontaneously induced at 0 °C without any mechanical stress, although the growth rate is very slow. In this communication, we report briefly the first results to confirm such spontaneous crystallization of the form at 0 °C, which have been obtained by CP/MAS 13 C NMR and wide-angle X-ray scattering methods.Experimental Section. A highly syndiotactic polypropylene sample with an rr fraction of 0.96, provided by Sumitomo Chemical Co. Ltd., was used without further purification. CP/MAS 13 C NMR spectra were measured at room temperature on a Bruker MSL 200 spectrometer under a static magnetic field of 4.7 T. Magic angle spinning at 3 kHz was achieved with the double air bearing system. The contact time for the cross polarization process was 1 ms and the pulse delay time was 4 s. 13 C chemical shifts were expressed as values relative to tetramethylsilane (Me 4 Si) by using the CO carbon line at 176.03 ppm of glycine crystals as an external reference. Wide-angle X-ray diffraction patterns were obtained at room temperature on an automatic RIGAKU diffractometer with Ni-filtered Cu KR radiation.Results and Discussion. Figure 1 shows CP/MAS 13 C NMR spectra of sPP films quenched in ice-water from the melt at 170 °C, which were measured at room temperature. The times shown in this figure indicate the periods for which each film was kept in ice-water. As shown in Figure 1a, the film taken out immediately after quenching in ice-water gives a spectrum similar to the previously reported one; 23 two resonance lines assignable to the methylene carbons clearly appear at 47.7 and 39.1 ppm. Although the downfield line at 47.7 ppm seems to be composed of multiple components

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Kratky functions (µ) were calculated for scattering points consisting of (i) all eight protons, (ii) six methyl protons, (iii) two methylene protons, (iv) all four carbon atoms, and (v) only the substituted carbons in the monomer unit. These five functions differ appreciably for larger values of µ, indicating the importance of a proper choice of scattering points when calculations are compared with experimental curves. The first function (i) was compared with the experimental neutron scattering curves for PIB-H in the PIB-d8 matrix and in the -solvent, the second (ii) with that observed in the PIB-d6 matrix, and the fourth (iv) with the X-ray scattering curve observed in solution. Close agreement throughout the range of µ covered by the experiments confirms the conformational analysis of PIB and demonstrates randomness of configurations in the bulk down to distances of ca. 10 Á.

Cellulose gels were prepared from cellulose in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solution. When the cellulose concentration in the solution is above the one at which cellulose molecules overlap, cellulose gels were formed. While the gel prepared by the addition of water was turbid, the one prepared by the ion exchange was colorless, transparent, and optically anisotropic. In order to explain this gelation behavior of cellulose, small-angle X-ray scattering (SAXS) measurements of the cellulose solutions and the gels were performed. The SAXS profiles of the cellulose solutions and the gels suggested that the large-scale fluctuation of the molecular chain density in the solution can be the origin of the molecular aggregates formed in the gel. Furthermore, the differences in the structure of the gels at the macroscopic and the molecular level were discussed in terms of the phase separation and the molecular association.

The scattering function was measured for four samples of atactic oligo-and poly(methyl methacrylate)s (a-PMMA), each with the fraction of racemic diads ft = 0.79, in the range of weight-average molecular weight Afw from 1.10 X 103 to 1.19 X 106 in acetonitrile at 44.0 °C ( ) for the magnitude k of the scattering vector smaller than 1 A™1 by the use of a point-focusing small-angle X-ray scattering (SAXS) camera.Supplementary measurements were also carried out on the sample with Mw = 1.19 x 10s in benzene (good solvent) at 25.0 °C in order to examine the solvent effect. The Kratky plot of the present data for the high-molecular-weight samples in the solvent exhibits the first maximum and minimum as observed by Kirste and Wunderlich for syndiotactic PMMA (with /, 0.9). However, in the range of larger k, the former exhibits only a slight inflection, while the latter exhibits strong oscillation. A comparison is made of the present SAXS data with literature data for small-angle neutron scattering for a-PMMA in the bulk. It is found that the Kratky plots of these two kinds of data are in good agreement with each other in the range of small k but the latter plot deviates downward from the former for larger k because of the difference in the distribution of scatterers. A comparison of the present SAXS data with the helical wormlike (HW) chain theory shows that it may reproduce the data quantitatively in the range of rather small k but only qualitatively in the range of large k. A comparison is also made of the present data for a-PMMA with the previous data for atactic polystyrene in cyclohexane at 34.5 °C ( ). It is then found that the HW theory may well explain the difference in the Kratky plot between the two polymer chains in the range of small k arising from that in the local conformation.