Aromatic-aliphatic block copolyesters

Aromatic-Aliphatic Block Copolyesters Based on AA/BB Polymers and Poly(lactic acid)... 

On the other hand, it has been established that aliphatic-aromatic copolyesters are indeed biodegradable and that the biodegradability of these copolyesters is related to the length of the aromatic sequence. Block copolyesters with relatively long aromatic sequences are not rapidly degraded by microorganisms. 

TPEs associating both rigid and soft polyester blocks have also been described. They cannot be obtained by the melt polyesterification used for polyesterether TPEs, since interchange reactions would yield random—rather than block — copolyesters. The preferred method involves the reaction of OH-terminated aliphatic and aromatic-aliphatic polyesters with chain extenders such as diisocyanates and results in copoly(ester-ester-urethane)s. 

In 1994, Witt and co-workers [5] first reported a microbial degradation of a block-copolyester [poly(trimethylene decanoate)-block-(trimethylene terephthalate)] with 50 mol% of terephthalic acid in the acid component. In a mineral medimn inoculated with sewage sludge, Witt and co-workers observed a weight loss in polyester films of about 9% within four weeks. In 1995 the same authors published data about the degradation of random aliphatic-aromatic copolyesters from terephthalic acid, 1,3-propanediol and adipic acid or sebacic acid (30 mol% of terephthalic acid content) in a soil burial experiment... 

Thermoplastic copolyester elastomers are generally block copolymers produced from short-chain aliphatic diols, aromatic diacids, and polyalkylene ether-diols. They are often called polyesterether or polyester elastomers. The most significant commercial product is the copolymer from butane-1,4-diol, dimethyl terephthalate, and polytetramethylene ether glycol [25190-06-1/, which produces a segmented block copolyesterether with the following structure. 

Tokiwa, Y., and Suzuki, T., 1981, Hydrolysis of copolyesters containing aromatic and aliphatic ester blocks by lipase. J. Appl. Polym. Sci. 26 441>448. 

To check the influence of the length of the aliphatic and aromatic sequences in the chains, we synthesised copolyesters of different structure, such as (blends), block copolymers, random copolymers and alternating BTA copolyester, all with the same fraction of terephthalic acid (50 mol % of the total acid components) (Fig 5). 

Aliphatic/aromatic copolyesters can be prepared either as random copolymers or block copolymers. Random copolymers are more readily biodegraded than copolymers with long aromatic blocks. 

Aliphatic/aromatic copolyesters may be prepared either as random copolymers or block copolymers. Random copolymers are more readily biodegraded than copolymers with long aromatic blocks. Generally, copolyesters with about 35-55 mol% aromatic component (in reference to the total amount of acid components) are in an optimal range that guarantees biodegradability and suitable mechanical and physical properties [51]. 

Payne and Rader [28] cite three generic classes of TPEs. In the first class they put the block copolymers. These include the styrene-butadiene-styrene triblocks, copolyesters, polyurethanes, and polyamides. The latter result when aromatic diamines are used in the hard segments and aliphatic diamines are used in the soft segments, both in combination with aliphatic dicarboxylic acids. The mechanical properties, processing conditions, and solvent resistance differ for the various copolymers. Within each type, a spectrum of hardness values is obtainable by variation of the size and chemical composition of the segments. 

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