Corrosion-resistance Crystalline polymer

Chlorination of natural rubber, involving both addition and substitution (with some cyclization), yields a product with improved chemical and corrosion resistance. Chlorination of polyethylene in the presence of sulfur dioxide results in substituting both chloride and sulfonyl chloride groups into the polymer. A commercially useful material is one which contains about 12 chlorides and one sulfonyl chloride per 40-45 repeating units. This extensive substitution converts the polyethylene, a plastic, into an elastomer by destroying crystallinity. 

The oxacyclobutane derivative, 3,3-bischloromethyloxacyclobutane, is polymerized (structure 5.26) using cationic ROP giving a water-insoluble, crystalline, corrosion-resistant polymer sold under the trade name of Penton. 

Because protein and cellulosic fibers are buried in contact with copper metal objects, a chemical microsystem is established whereby the degradation of the fiber and the corrosion of the metal interact physically and chemically. As the corrosion solution impregnates and swells the fibers, polymer molecules in amorphous areas are spread apart but are prevented from complete dissolution by the resistant crystalline segments. Copper ion from the corrosion solution is bound to the polymers (Figure 5). As the fiber degrades and more end groups are formed, more copper is bound. Polymers expand further apart as interchain forces are reduced. 

PTFE is a crystalline polymer consisting of twisted zigzag spirals with at least 13 repeating units per turn. This nonpolar polymer has a solubility parameter of 6.2 H, a high (327 C), and a heat deflection temperature of 121 C PTFE is a tough, flexible polymer which retains its ductility at extremely low temperatures (-269 0. The coefficient of friction of ptfe is the lowest of any known solid material (see Table 13.4). Films of ptfe can be bonded by adhesives to other surfaces if the polymer surface is treated with sodium. It also bonds to diamonds and graphite whose surfaces have been fluorinated. Liquid sodium removes fluoride ions from the surface and leaves free radicals on the polymer surface, ptfe is resistant to almost all corrosives and solvents, but it can be dissolved in hot perfluorinated kerosene, ptfe is difficult to mold or extrude. 

In recent years silicon-based polymers were investigated as precursors for SiC and Si3N4 ceramics, as well as for crystalline or amorphous Si/C/N and SiC/Si3N4 composite materials [1, 2]. This is due to the very interesting chemical and thermomechanical properties of silicon carbonitrides, such as high hardness, toughness and corrosion resistance. In most of these studies polycarbosilanes, polysilazanes and polycarbosilazanes were applied [3]. 

Because of the presence of the larger chlorine atom on the backbone which reduces intermolecular forces and the degree of crystallinity, this polymer is more readily processed and has a lower Tm than polytetrafluoroe thylene (ptfe). Thin films of pctfe are transparent and are resistant to corrosives and solvents. The coefficient of friction of pctfe is low but somewhat higher than that of ptfe ... 

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