X-ray methods are used to investigate the structure of melt-spun fibers of p-hydroxybenzoate/ethylene terephthalate copolymers, by analogy with the electron diffraction patterns obtained from single crystals of homopoly(p-hydroxybenzoate) [systematic name: poly(l,4-oxybenzoyl)]. The fiber diagrams of copolymers containing 60-80% p-hydroxybenzoate are very similar to the electron diffraction patterns of homopolymer single crystals that have been heat treated at 360 °C. These observations indicate that the fibers contain oriented, ordered regions with the same basic structure as the high-temperature form of the homopolymer. These regions probably consist of copolymer sequences rich in hydroxybenzoate, in which some ethylene terephthalate units are present as defects. The data also define the orientation of the chains with respect to the homopolymer crystal morphology. Both the X-ray and electron diffraction data show that the poly(p-hydroxybenzoate) chain has a stiff, extended 2X helical conformation, with two monomer units repeating in ~12.4 ± 0.2 A, for which a stereochemically acceptable model is presented.
Surface-active N-alkylpyridinium salts and N,Nf-dialky1-4,4'-bipyridinium salts were synthesized carrying long aliphatic chains with a diacetylene unit in the midchain position. All compounds polymerized in the solid state, when exposed to UV and y-irradiation. In the case of the N-alkylpyridinium salts a complete conversion to polymer was obtained. X-ray structure studies revealed a head-head-tail-tail arrangement of the amphiphiles. During polymerization the structure was completely retained. Some of the N-alkylpyridinium salts formed polymers, which were soluble in a 1:l mixture of chloroform and methanol. Monomeric crystals of the bipyridinium salts showed solid-to-solid and solid-to-liquid crystalline phase transitions, which disappeared upon the polymerization process. Monolayers of the amphiphiles at the air-water interface were of low stability and could be transferred onto substrates only in mixtures with cadmium arachidate. UV irradiation of the mixed multilayers caused a solid-state polymerization of the diacetylene amphiphiles on the substrate. Aqueous suspensions of the monomeric N-alkylpyridinium salts turned into clear, micellar solutions at temperatures above 46.5 "C. Sonication of aqueous dispersions resulted in the formation of translucent, slightly opaque solutions in which the amphiphiles formed spherical aggregates of diameters between 100 and 250 nm. Micellar solutions as well as dispersions of the spherical aggregates were completely photoinactive in UV light. However, the spherical aggregates rapidly rearranged into thin particles of oval or polygonal shape of more than 1 Km in diameter (multilamellar layers), which were highly photoreactive. The polymerized amphiphile dispersions neither disintegrated into micelles at elevated temperature nor precipitated within several weeks.
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