International Union of Crystallography Monographs on Crystal #17: Crystallography of the Polymethylene Chain: An Inquiry Into the Structure of Waxes

By considering the solid state packing of linear chain wax components, this book aims at understanding three things: firstly, which modifications of molecular components are allowed for maintaining stable solid solutions; secondly, what happens when stability conditions are traversed and fractionation begins and thirdly, the structure of fractionated arrays. The co-compatibility of molecular ingredients is considered in terms of their shapes and relative sizes, following an approach originally proposed by Kitaigorodskii. As demonstrated profusely by the crystal structures of pure component types (e. g. alkanes, fatty alcohols, fatty acids, long chain esters, cholesteryl esters) and insertion of functional groups (e. g. chain branches, unsaturation, heteroatoms), characteristic molecular packing arrays provide important geometric information for understanding the co-packing of different molecules in mixtures. Single crystal and spectroscopic data from polydisperse arrays can then be evaluated to arrive at plausible structures of solid solutions and fractionated systems. The resultant structures are not only relevant to the understanding of so-called waxes but also include certain classes of polymers. The ramifications of this work extend into any solid state array of polymethylene chains, including lipid foodstuffs.

A researcher for a major petroleum corporation, Dorset takes the waxes as a case study for investigating the solid state of multi-component linear chain assemblies, which also include polymers, lipid arrays, detergents, and edible fats. The wax molecules themselves are not very complex, he explains, so the rules for their association in the solid state can be uncovered from the geometric rules governing the assembly of van der Waals surfaces. He overviews the scientific literature on solidified waxes as thoroughly as he can up to April 2004, especially evaluating the model for wax chain assemblies proposed by Le Roux and Loubser in 1980, but also considering newer studies that take advantage of electron crystallography.
Annotation ©2004 Book News, Inc., Portland, OR (booknews.com)

Douglas L. Dorset is Senior Research Associate at ExxonMobil Research & Engineering Company in Annandale, New Jersey.

1. Polydispersity of the paraffin chain--statement of the problem

2. Layer packing of polymethylene chains

3. Crystal structures and phase transitions of the paraffins

4. Thermotropic disorder in n-paraffin crystals

5. Binary and multicomponent solids of n-paraffins

6. Some functional substitutions in n-paraffins

7. Lipid alcohols

8. The fatty acids

9. Linear fatty acid esters

10. The cholesteryl esters

11. From waxes to polymers--the crystallography of polydisperse arrays