Ester group hydrolysis, poly degradation

Poly(ortho esters) (POE) eontain ortho ester groups along the chain an ortho ester is a funetional group eontaining three alkoxy groups attached to one earbon atom. Degradation results from a hydrolysis mechanism. These polymers ean be formulated in order to obtain a surfaee erosion degradation. 

In marked contrast to enzymatic degradation, the position of the ester group (chain end or within the chain) does not affect the hydrolytic degradability of PLA-based materials, as long as the polymers are composed of one monomer unit. An exception is the report on the acidic hydrolysis of amorphous poly(DL-lactide) (poly(DL-lactic acid) (PDLLA)) in the solid state by Shih [110,111], where the ester group adj acent to the chain terminal is more susceptible to hydrolytic degradation than that in the middle of the chain. Degradation at the chain end and in the middle of the chain is, respectively, called exo-... 

In Europe, interest has centered particularly on polyhydroxybutyr ate, which can be made into films for packaging as well as into molded items. The polymer degrades within 4 weeks in landfills, both by ester hydrolysis and by an elimination reaction of the oxygen atom (i to the carbonyl group. This elimination is similar to what occurs during the dehydration step in an aldol reaction (Section 23.4). The use of poly-hydroxybutyrate is limited at present, however, by its cost—about four times as much as polypropylene. 

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