Functional biodegradable polyesters

The concept of transesterifications was used for polymerization reactions by Hedrick and colleagues [76]. Various biodegradable polyesters were synthesized with the l,3-dimethylimidazol-2-ylidene carbene in THF at 25 °C. Polymers such as poly(e-caprolactone) were obtained with no need of organometallic catalysts, as in classical methods. Poly(ethylene terephthalate) (PET) 97 was synthesized in the ionic liquid 98, which functions as the reaction medium and, at the same time, as a precatalyst that is activated (99) with KOt-Bu. Dimethyl terephthalate (DMT) 100 was condensed with an excess of ethylene glycol 101 to generate 102. The melt condensation of 102 was performed under vacuum using a heating ramp to 280 °C. 

Synthetic biodegradable polyesters are used mainly as specialty materials for paper coating, fibres, and garbage bags and sacks. They are also showing up in thermoformed packaging as functional adjuncts to lower-cost biodegradable materials. 

Most of the commonly used degradable polymer scaffolds are mechanically strong, but for certain applications such as engineering muscles and tendons, which require considerable elasticity, these polymers are not optimal. Novel biodegradable polyesters have been developed with superior elasticity and strength that resemble vulcanized rubber and are hence termed as biorubber. Scaffolds made with these mechanically functional materials may be useful especially in engineering elastic tissue such as muscular-skeletal tissues and blood vessels. 

It is surprising that relatively little work has been published on the use of unmodified castor oils in the synthesis of polyesters compared with studies involving several of its preliminary chemical modifications, as discussed below. A noteworthy excursion into incorporation of castor oil in biodegradable polyesters destined to function as drug carriers [11,12] describes the melt co-polycondensation of the oil with mannitol, as well as different aliphatic di-and tri-acids. Use of comonomers sebacic acid and citric acid is shown in Scheme 3.6. 

He M, Chu C. A new family of functional biodegradable arginine-based polyester urea urethanes synthesis, chracterization and biodegradation. Polymer 2013 54(16) 4112-25. 

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