Polyoxalate

Degradable, synthetic polymers that are commonly known in the medical field include poly(a-hydroxy esters), poly(fi-caprolactone), poly(ortho esters), polyanhydrides, poly(3-hydroxy butyrate), polypho-sphazenes, polydioxanones, polyoxalates, and poly(amino acids). 

As an application, the polyoxalate 465 has been synthesized from dinitrite 464 using Pd-phosphine complex as a catalyst [190]. 

Four important classes of polymers from dioxane-diones and oxalates are poly(l,4-dioxane-2,5-diones), polyoxalates, poly(l,3-dioxane-2-one) and poly(l,4-dioxane-2,3-dione), and poly(p-dioxanone). Representative diagrams are given in structures 15, 16, 17, and 18, respectively. 

Secondly, a polyoxalate has been reported [80] with an ester backbone, which can be hydrolytically cleaved to produce propylene glycol and oxalic acid. The predicted degradation rate is faster than PGA owing to its lower degree of crystallinity and less hydrophobic character. 

Formation of dialkyl oxalate esters and polyoxalates ° by Pd-catalyzed carbonylation of alkyl nitrites and alkane a,heterogeneous system has been reported (Eq. 25). 

Recently, polyoxalates 6 have been synthesized from dinitrite 5 (Scheme 4).[ 5].[i6] However, TOP (mol/moIPd h) was 2-3, showing quite lower activity. In this reaction system, polyoxalate 6 is the only product under high CO pressure even in the presence of ethylene. Polysuccinate 7 can be obtained as the main product only under low CO pressure. Polyketone 8 becomes the main product under the low CO pressure combined with high ethylene pressure. 

The ability to undergo biodegradation producing nontoxic by-products is a useful property for some medical applications. Biodegradable polymers [71] have been formulated for uses such as sutures, vascular grafts, drug delivery devices, and scaffolds for tissue regeneration, artihcial skin, orthopedic implants, and others. The polymers commonly known in the medical field for such applications include poly(a-hydroxy esters), poly(e-caprolactone), poly(ortho esters), polyanhydrides, poly(3— hydroxybutyrate), polyphosphazenes, polydioxanones, and polyoxalates (see Chapter 2 of Industrial Polymers, Specialty Polymers, and Their Applications). 

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