Macromolecular packing crystallization

Within the class of polymer crystals having, ideally, long-range positional order for all the atoms, different crystalline forms (polymorphs) may arise as a result of having different almost isoenergetic macromolecular conformations (of the main chain, in most known cases) or as a result of different, almost isoenergetic modes of packing of macromolecules with identical conformations [1-3]. 

The recommendations embodied in this document are concerned with the terminology relating to the structure of crystalline polymers and the process of macromolecular crystallization. The document is limited to systems exhibiting crystallinity in the classical sense of three-dimensionally periodic regularity. The recommendations deal primarily with crystal structures that are comprised of essentially rectilinear, parallel-packed polymer chains, and secondarily, with those composed of so-called globular macromolecules. Since the latter are biological in nature, they are not covered in detail here. In general, macromolecular systems with mesophases are also omitted, but crystalline polymers with conformational disorder are included. 

Tel. 617-495-4018, fax 617-495-1792, e-mail karplus huchel.bitnet Molecular dynamics package using Chemistry at Harvard Macromolecular Mechanics force field. Extensive scripting language for molecular mechanics, simulations, solvation, electrostatics, crystal packing, vibrational analysis, free energy perturbation (FEP) calculations, quantum mechanics/molecular mechanics calculations, stochastic dynamics, and graphing data. 

The special restriction caused by tying low molecular mass liquid crystalline substances to a polymer chain was also illustrated with amphiphilic liquid crystals. A hexagonally close-packed structure of rod-like micelle cylinders of sodium 10-undecenoate with about 50% water lost during polyma-ization at 60 °C its structure and became isotropic. On cooling, a lamellar liquid crystalline structure, more suitable to accommodate the macromolecular backbone was found. Bas l on the discussions of Sect. 5.3.4 it is likely that with longer side-chain amphiphiles condis crystals could be grown in analogy to the soaps described in Sect. 5.2.3... 

The general type of crystal structure in linear macromolecular substances is essentially that also shown by the simplest long chain molecules, the paraffins. The extended chain molecules, are plane zigzag structures, lying parallel to each other, and pack like flattened rods or ribbons. 

For calculation of packing fractions see, for example, A. Bondi, "Physical Properties of Molecular Crystals, Liquids and Glasses." J. Wiley and Sons, New York, NY, 1968. For linear macromolecules, see B. Wunderlich, "Macromolecular Physics, Vol. 1" Academic Press, New York, NY, 1973. 

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