Editing Polymer (section)

====Crystallinity====
When applied to polymers, the term ''crystalline'' has a somewhat ambiguous usage. In some cases, the term ''crystalline'' finds identical usage to that used in conventional [[crystallography]]. For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for [[x-ray crystallography]], may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of [[angstrom]]s or more. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers.<ref>{{cite book|last1=Allcock|first1=Harry R.|last2=Lampe|first2=Frederick W.|last3=Mark|first3=James E.|title=Contemporary Polymer Chemistry|publisher=Pearson Education|edition=3|year=2003|page=546|isbn=978-0-13-065056-6}}</ref> Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For many polymers, crystallinity may also be associated with decreased transparency.