SSP of Poly butylene terephthalate

Poly(butylene terephthalate) (PBT) closely resembles PET, the difference being that 1,4 butandiol (BD) is used instead of ethylene glycol in its manufacture. PBT 

Molecular weights (number average) in the range of 20 000 to 35 000 [88] are achieved in the melt phase and are used for fibre and engineering plastics applications. For some injection moulding and extrusion applications, molecular weights above 40 000 [88] are required. Such high valves are best achieved by SSP. 

PBT has two crystal modifications [91]. The a-form is stable, while the ( -form is reversibly formed by stretching [92], The amorphous density is given as 1.26 g/cm3 [88] and that of 100% crystalline in the range from 1.394 to 1.406 g/cm3 [93], The melting point is 225 °C [43] and the heat of fusion values for crystalline PBT reported are generally in the range of 31 to 32kJ/mol [93], 

The manufacture of polyethylene naphthalate) (PEN) is carried out using dimethyl 2,6-naphthalene dicarboxylate (NDC) and EG and is similar to the manufacture of PET from DMT. The IV after the melt is typically in the range of 0.5 

PEN has two crystal modifications [99], Both forms have a triclinic structure and can be obtained under crystallization conditions. Their densities are 1.407 and 1.439 g/cm3, compared to 1.326 g/cm3 for amorphous material. 

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