Polyester chain cleavage

This reaction can be catalysed by both acids or bases. Also, the reaction product, RCOOH, is able to accelerate ester hydrolysis according to a phenomenon named autocatalysis. In the case of aliphatic polyesters, chain cleavage at ester bond level is autocatalysed by carboxyl end groups initially present or generated by the degradation reaction ... 

More definitive evidence of enzymatic attack was obtained with 1 1 copolymers of e-caprolactone and 6-valerolactone crosslinked with varying amounts of a dilactone (98,99). The use of a 1 1 mixture of comonomers suppressed crystallization and, together with the crosslinks, resulted in a low-modulus elastomer. Under in vitro conditions, random hydrolytic chain cleavage, measured by the change in tensile properties, occurred throughout the bulk of the samples at a rate comparable to that experienced by the other polyesters no weight loss was observed. However, when these elastomers were implanted in rabbits, the bulk hydrolytic process was accompanied by very rapid surface erosion. Weight loss was continuous, confined to the... 

Imaging via Main-chain Cleavage of Polycarbonates. Polyesters and Polvethers. 

Scheme 1 shows the reaction which occurs when an aromatic polyester such as [I] is subjected to UV irradiation (5). The polymer first undergoes main-chain cleavage with subsequent rearrangement to polymer [II] which is photostable and can be used as a thin coating to protect efficiently other substrates which are normally photodegradable. 

In the case of polyamides and polyesters the most important photolytic reactions are the Norrish I and II reactions (see Scheme 1). The Norrish I reaction leads to chain cleavage and radicals that might initiate oxidation, the Norrish II reaction only leads to chain cleavage. The main question for these polymers is What is the relative importance of photolysis and photo-oxidation ... 

Pitt, G.G. Gu, Z.W. Modification of the rates of chain cleavage of poly(e-caprolactone) and related polyesters in the solid state. J. Controlled Release 1987, 283 (4), 283-291. 

The cleavage of polyester chains is known to be catalyzed by the carboxyl end groups, and its rate is proportional to the concentrations of water, and ester bonds those on the initial stage of hydrolysis are constant... 

Crystallinity has a significant effect on the degradation rate of aliphatic polyesters because it determines how easily water molecules can access the ester linkages to cause chain cleavage. 

Poly(p-dioxanone) is a polyester which degjrades by chemical hydrolysis in the body there is no etddence of chain cleavage by enzymatic degradation. 

Other groups focused on the nature of the biodegradation products and investigated the hydrolytic pathway of PU chain cleavage. A number of reports described the generation of potentially carcinogenic aromatic diamines from polyester urethanes (PEUs) that had been used in the Meme breast implant [16,17]. 

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