Editing Polymer (section)

===Morphology===
Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space. The macroscopic physical properties of a polymer are related to the interactions between the polymer chains.

{| class="wikitable floatright" style="text-align:center; font-size:90%;" width="30%"
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| [[File:Statistischer Kneul.svg|100px]]<br />Randomly oriented polymer
| [[File:Verhakungen.svg|200px]]<br />Interlocking of several polymers
|}

* '''Disordered polymers:''' In the solid state, atactic polymers, polymers with a high degree of [[Branching (polymer chemistry)|branching]] and random copolymers form [[Amorphous solid|amorphous]] (i.e. glassy structures).<ref name="MakroChem">Bernd Tieke: ''Makromolekulare Chemie.'' 3. Auflage, Wiley-VCH, Weinheim 2014, S. 295f (in German).</ref> In melt and solution, polymers tend to form a constantly changing "statistical cluster", see [[Freely Jointed Chain|freely-jointed-chain model]]. In the [[Solid|solid state]], the respective [[Protein conformation|conformations]] of the molecules are frozen. Hooking and entanglement of chain molecules lead to a "mechanical bond" between the chains. [[Intermolecular force|Intermolecular]] and intramolecular attractive forces only occur at sites where molecule segments are close enough to each other. The irregular structures of the molecules prevent a narrower arrangement.

{| class="wikitable floatright" style="text-align:center; font-size:90%;" width="30%"
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| [[File:Polyethylene-xtal-view-down-axis-3D-balls-perspective.png|180px]]<br />Polyethylene: zigzag conformation of molecules in close packed chains
| [[File:Lamellen.svg|180px]]<br /> Lamella with tie molecules
| [[File:Spherulite2de.svg|180px]]<br /> [[Spherulite (polymer physics)|Spherulite]]
|}
{| class="wikitable floatright" style="text-align:center; font-size:90%;" width="30%"
|- class="hintergrundfarbe2"
| [[File:Helix-Polypropylen.svg|100px]]<br />[[polypropylene]] [[helix]]
| [[File:P-Aramid H-Brücken.svg|200px]]<br />[[Aramide|''p''-Aramid]], red dotted: hydrogen bonds
|}

* '''Linear polymers''' with periodic structure, low branching and stereoregularity (e. g. not atactic) have a [[semi-crystalline]] structure in the solid state.<ref name="MakroChem" /> In simple polymers (such as polyethylene), the chains are present in the crystal in zigzag conformation. Several zigzag conformations form dense chain packs, called crystallites or lamellae. The lamellae are much thinner than the polymers are long (often about 10&nbsp;nm).<ref name="KunstChemIng">[[Wolfgang Kaiser (physicist)|Wolfgang Kaiser]]: ''Kunststoffchemie für Ingenieure.'' 3. Auflage, Carl Hanser, München 2011, S. 84.</ref> They are formed by more or less regular folding of one or more molecular chains. Amorphous structures exist between the lamellae. Individual molecules can lead to entanglements between the lamellae and can also be involved in the formation of two (or more) lamellae (chains than called tie molecules). Several lamellae form a superstructure, a [[Spherulite (polymer physics)|spherulite]], often with a diameter in the range of 0.05 to 1&nbsp;mm.<ref name="KunstChemIng" />
:The type and arrangement of (functional) residues of the repeat units effects or determines the crystallinity and strength of the secondary valence bonds. In isotactic polypropylene, the molecules form a helix. Like the zigzag conformation, such helices allow a dense chain packing. Particularly strong intermolecular interactions occur when the residues of the repeating units allow the formation of [[hydrogen bond]]s, as in the case of [[Aramid|''p''-aramid]]. The formation of strong intramolecular associations may produce diverse folded states of single linear chains with distinct [[circuit topology]]. Crystallinity and superstructure are always dependent on the conditions of their formation, see also: [[crystallization of polymers]]. Compared to amorphous structures, semi-crystalline structures lead to a higher stiffness, density, melting temperature and higher resistance of a polymer.

* '''Cross-linked polymers:''' Wide-meshed cross-linked polymers are [[elastomer]]s and cannot be molten (unlike [[thermoplastic]]s); heating cross-linked polymers only leads to [[Thermal decomposition|decomposition]]. [[Thermoplastic elastomer]]s, on the other hand, are reversibly "physically crosslinked" and can be molten. Block copolymers in which a hard segment of the polymer has a tendency to crystallize and a soft segment has an amorphous structure are one type of thermoplastic elastomers: the hard segments ensure wide-meshed, physical crosslinking.

{| class="wikitable centered" style="text-align:center; font-size:90%;" width="80%"
|- class="hintergrundfarbe2" valign="top"
| [[File:Polymerstruktur-weitmaschig vernetzt.svg|130px]] <br />Wide-meshed cross-linked polymer (elastomer)
| [[File:Polymerstruktur-weitmaschig vernetzt-gestreckt.svg|270px]] <br /><br />Wide-meshed cross-linked polymer (elastomer) under [[tensile stress]]
| [[File:Polymerstruktur-TPE-teilkristallin.svg|140px]] <br /> [[Crystallite]]s as "crosslinking sites": one type of [[thermoplastic elastomer]]
| [[File:Polymerstruktur-TPE-teilkristallin gestreckt.svg|250px]] <br /><br /> Semi-crystalline thermoplastic elastomer under tensile stress
|}

====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.

====Chain conformation====
The space occupied by a polymer molecule is generally expressed in terms of [[radius of gyration]], which is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of [[pervaded volume]], which is the volume spanned by the polymer chain and scales with the cube of the radius of gyration.<ref>Rubinstein, p. 13</ref> 
The simplest theoretical models for polymers in the molten, amorphous state are [[ideal chain]]s.