Search

The nanoporous crystalline phase of a cheap commercial polymer shows, already at room temperature, large uptake of gas molecules (e.g., butadiene and carbon dioxide) leading to polymer/gas clathrate phases. These clathrate phases have been characterized by X-ray diffraction and infrared linear dichroism measurements. Gas release kinetics are strongly reduced as a consequence of clathrate formation and can be further reduced by (010) orientation of the host phase, i.e., by placing the ac layers of close-packed enantiomorphous polymer helices nearly parallel to the film plane. The reported results indicate that this robust and easy-to-process polymeric crystalline framework is suitable for gas storage and controlled release.

Cosyndiotactic random copolymers of styrene/p-chlorostyrene (S/p-CS) have been prepared for the entire composition range. Their polymorphic behavior has been studied by means of wide-angle X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, and ultraviolet spectroscopy. For all samples, the possible formation of clathrate structures has been investigated. A new clathrate phase, being colored and comprising trans planar chains, has been obtained for copolymers with high chlorinated comonomer unit content in the presence of the p-chlorostyrene guest. Both colored and trans-planar clathrates are unprecedented for styrene-based syndiotactic homopolymers and copolymers. A phase diagram of this copolymer system in the presence of the p-chlorostyrene guest has been reported.

The crystalline structure of isotactic poly(vinylcyclobutane), claimed to be tetragonal, has been revised on the basis of fiber diffraction spectra. The chain symmetry is 41, as already assessed, but the conformation is different (the identity period is 6.91 A and not 6.60 A). The space group is the orthorhombic P212121 with lattice constants a = 17.14 A, b = 8.99 A, and c = 6.91 A. The excellent quality of the oriented samples allowed a full structure analysis and refinement. Integrated diffraction intensities, from a stretched fiber, measured with a Fuji image plate detector, have been utilized in a constrained refinement (the helix was assumed strictly of 41 symmetry and the C−C bond lengths were set to 1.54 A) obtaining a final R index of 15%. The refined chain bond angles are 103 and 107°, and the chain torsion angles are 165 and 273°.

A preliminary model for the crystal structure of form III of isotactic poly(4-methylpentene-1) is suggested on the basis of structure factor calculations. Chains in 4(1) helical conformations are packed in a tetragonal unit cell with axes a = 19.38 angstrom and c = 6.98 angstrom; the space group is I4(1). The polymorphic behavior of poly(4-methylpentene-1) is discussed on the basis of conformational energy calculations on the isolated chain. The presence of different modifications is in accordance with energy minima present in the conformational energy map.