Carbon chain structures, polymer glass

The most common backbone structure found in commercial polymers is the saturated carbon-carbon structure. Polymers with saturated carbon-carbon backbones, such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyacrylates, are produced using chain-growth polymerizations. The saturated carbon-carbon backbone of polyethylene with no side groups is a relatively flexible polymer chain. The glass transition temperature is low at -20°C for high-density polyethylene. Side groups on the carbon-carbon backbone influence thermal transitions, solubility, and other polymer properties. 

The availability of soluble polymers has permitted measurements of molecular weight, as discussed below. The glass transition temperatures are quite low, from 145 °C for polymethylthiophene to 41 °C for polybutylthiophene. X-ray diffraction shows a broad peak which has been interpreted by different groups as showing a structure which is either partly crystalline or is amorphous. The temperature of fusion decreases from 280 °C to 80 °C as the length of the alkyl chain increases from 4 to 22 carbons 263). 

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