Eray Cavus 030060022 11th Week Part2

 Polyacetals (Material)

Polyacetals (old)

There is no old definition.

Polyacetals (new) (better)

The term “polyacetal” is commonly used in the area of biomaterials and it means “polyoxymethylene homopolymer” (hPOM) or copolymer of trioxane with dioxolane or ethylene oxide (also denoted as cPOM). In this paper, the names “poly-acetal” and “POM” will be used alternatively. Polyoxymetylene has the general formula (-OCH₂-)_n and its linear backbone structure is similar to that of PE. Properties that arise from this structure are: high-impact strength, stiffness, resiliency, toughness and high yield stress; low friction coefficient; low gas and vapour permeability; exceptional dimensional stability and dielectric properties; high fatigue strength; and good retention of properties at elevated temperature. POM shows an ultrahigh Young`s modulus, which is caused by the presence of extended-chain crystals, whereby a part of the polymer could still appear as chain-folded lamellae. Extended chains can be obtained in topotactic polymerization or during processing, when the melting region is approached and a cooperative process throughout crystals becomes dominating. The POM copolymer usually contains cyclic ether segments (e.g. ethylene oxide), which provide increased resistance to unzipping degradation of the polymer chain. The copolymer form of polyacetalhas slightlysuperior resistance to unzipping to monomer (formaldehyde), but is mechanical properties are generally inferior to those of the homopolymer.

(Biopolymers: Lignin, Proteins, Bioactive Nanocomposites, Yazar: Shirō Kobayashi, page124)

Polystyrenes (Material)

Polystyrenes (old)

There is no old definition.

Polystyrenes (new) (better)

Polystrene (PS), CAS# 9003-53-6, is typically found in atactic and amorphous form. Isostatic and syndiotatic polystyrenes can be synthesized, but they are not used in practice since there are few advantages in properties compared to the atactic form. The reticulation of the carbon chains in polystyrene is frequently done using in the polymerization process a certain proportion of 1,4-divinylbenzene or less often of 1,3-divinylbenzene. The resulting polymer in the case of crosslinking with 1,4-divinylbenzene has the idealized structure shown below:

The general formula [-CH(C₅H₅)-CH₂-]_n commonly used for PS corresponds to tail polymer (H-T), which is morecommon than head to head form (H-H). However,H-H polystyrene is known also, and in commercial products a certain proportion of H-H polymer can be present. Pure H-H polymer can be obtained using specific synthetic procedures.

(Analytical Pyrolysis Of Synthetic Organic Polymers, Yazar: Șerban Moldoveanu, page: 238-239)