The synthesis and living cationic ring-opening polymerization of 2-[3,4-bis(n-alkan-1-yloxy)phenyl]-2-oxazolines with alkan being tetradecan and pentadecan, i.e., (3,4)nG1-Oxz with n = 14 and 15, is described. The structural analysis of the resulting polymers with well-defined molecular weights and narrow molecular weight distribution was carried out by a combination of techniques, including differential scanning calorimetry (DSC), thermal optical polarized microscopy (TOPM), and X-ray diffraction (XRD). At low molecular weights both polymers self-assemble into spherical supramolecules that self-organize into a Pm3n 3-D lattice while at high molecular weights they form cylindrical macromolecules that self-organize into a p6mm 2-D hexagonal columnar lattice. Both polymers exhibit a 3-D shape change as a function of their degree of polymerization as was reported for the first time in a previous publication from our laboratory (Percec, V.; Ahn, C.-H; Ungar, G.; Yeardley, D. J. P.; Möller, M.; Sheiko, S. S. Nature (London) 1998, 391, 161). Since these polymers can be obtained via a living polymerization, a detailed mechanistic investigation of the influence of the degree of polymerization and molecular weight distribution on the formation of a 3-D spherical macromolecule from a single polymer chain, i.e., a tertiary structure, was possible. The experimental results have demonstrated that the synthesis of nonbiological macromolecules exhibiting tertiary structure is possible in at most a few percent of all macromolecules via living polymerization. This is the case even when macromolecules with very narrow molecular weight distributions and well-defined molecular weights are used. Therefore, the design of synthetic macromolecules with tertiary structure requires not only chains with well-defined molecular weight but also, in particular, macromolecules with no distribution of their chain length.

The effect of high-energy radiation on n-alkanes and polyethylene (PE) are reviewed. The article includes a description of (a) primary radiation events, formation, spatial distribution and decay of free radicals and radical migration mechanisms, (b) formation of cross-lin ks and other sta ble products, (c) the effects of crystal linity, crystalline modifications and morphology on radiation cross-linking, and (d) radiation-induced changes in the crystal lattice and the destruction of crystallinity at high irradiation doses.An attempt is made to bring together conflicting views on various unsolved problems of the radiation physics and chemistry of these important and much studied substances. Long-chain paraffins are given considerable attention since their radiation behaviour often provides a link between that of PE and its short-chain analogues.

Savitz • Semor _ce Ihe,qdent Southwest Re,,carch Inshlule D_rectur Itomeqake Mmmg Company P.(). l)ra'_er 28510 Garrett Ceramic Components 651) ('ahfornm Slreet San Antonio. TX 78284 Divi-,ton San Ft'ant_t,,co. ('A 9410g Allied-Signal Aerospace Co. l)r. Ronald M. Latarnsmn

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