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Polyesteramides based on PET

Engineering plastics have good mechanical, thermal and electrical properties, and can be easily processed. Typical engineering plastics include polyamides (PA6,6, PA6, PA4,6) and polyesters (PBT, PET). Compared to polyesters of a similar structure, polyamides have a high glass transition (Tg) and melting temperature (Tm) and crystallize more rapidly. The disadvantage of polyamides is that they have a high water absorption (up to 15 wt%). Thus it would be of interest to combine the good properties of both the polyesters and polyamides into copolyesteramides. Copolyesteramides which combine these desirable properties, are alternating polyesteramides and polyesteramides with amide segments of uniform length. A random copolyesteramide has properties that are inferior to the homopolymers, due to a lowering of the chain order. 
Poly(ethylene terephthalate) (PET) is a semi-crystalline polyester with a relatively high Tg of 85oC and a Tm of 255oC. The major drawback for its use in injection molding applications is its slow rate of crystallization. Nylon 2,T is a semi-crystalline polyamide with a Tg of approximately 200oC and a Tm of 455oC. For applications requiring a high temperature dimensional stability, a polymer should have a high Tm. Thus it is of interest to modify PET to a polymer with a Tm of approximately 280oC. Therefore T2T (a one-and-a-half repeating unit of nylon 2,T) is incorporated in PET to obtain a rapidly crystallizing polyesteramide with an improved dimensional stability whilst maintaining a low water absorption. In order to obtain a uniform amide segment length, the pre-formed bisesterdiamide T2T-dimethyl is used as starting material in the polymerization reaction.