Summary: Hydroxypropylcellulose has been hydrophobically modified by reaction with different amounts of palmitoyl chloride. When the degree of substitution is sufficiently high, the side chains are able to produce lateral crystallisation, which has been analysed by DSC and diffraction experiments, using both conventional and synchrotron radiation. The melting temperatures and enthalpies depend on the degree of substitution, in such a way that it is relatively easy to get melting temperatures close to that of the human body, although a rather wide melting region is obtained.
Ethyl 4'-n-undecyloxybiphenyl-4-carboxylate, 2(11)OBC, and 4'-n-undecyloxybiphenyl-4-carboxylic acid, (11)OBC, are smectic liquid crystals precursors of low molecular weight premesogens, and of potential liquid crystal macromolecules. The single-crystal X-ray study of 2(11)OBC showed that it crystallizes in a non-centrosymmetric space group with molecules stacked along the short axis [010] and [001] without significant π... π or CH... π interactions.Such an arrangement may explain its strong tendency to form smectic mesophases. Both biphenyl derivatives have a rich polymesomorphism whose phase sequences were determined by DSC, optical microscopy and diffraction profiles using synchrotron radiation. These profiles indicated quite similar phase transitions in the two samples, although very different transition temperatures.
Flat plates of poly(allyl(p-allylcarbonate) benzoate) obtained via photopolymerization and thermal polymerization have been studied by means of microindentation. The plates were about 3 mm thick. The values of microhardness (MHV)/total microhardness (MHT) have been determined. Accordingly, structural changes in the plate bulk due to the polymerization method were detected. The plates obtained by photopolymerization possess a superficial layer harder than the inner layers and its thickness is not uniform. Also, microindentention shows that the increase in the polymerization time during thermopolymerization leads to improved elasticity and resistance against plastic deformation. Microindentation data of the plates here studied shows that poor mechanical properties correspond to an unfinished network, while good mechanical properties correspond to a better crosslinked network.
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