Kinetics poly degradation

Poly(vinyl chloride) has been shown to degrade thermally by a chain mechanism that is best represented by non-steady-state kinetics (NSSK). Degradations are initiated at a very few sites within a chain, and the subsequent zip reaction which accounts for substantially all of the evolved hydrogen chloride is confined to a single chain. 

Figure 7 Introducing branching into photopolymerizable poly(p-amino esters) has a dose-response effect on several physical properties of the resulting polymer, while maintaining polymerization kinetics and degradation profiles. The molar ratio of acrylates to amines was maintained at 2.4 1.

An example is poly(bis(p-carboxyphenoxy)propane) (PCPP) which has been prepared as a copolymer with various levels of sebacic anhydride (SA). Injection molded samples of poly (anhydride) / dmg mixtures display 2ero-order kinetics in both polymer erosion and dmg release. Degradation of these polymers simply releases the dicarboxyhc acid monomers (54). Preliminary toxicological evaluations showed that the polymers and degradation products had acceptable biocompatibiUty and did not exhibit cytotoxicity or mutagenicity (55). 

Recently, Brich and coworkers (40) reported the synthesis of lactide/glycolide polymers branched with different polyols. Polyvinyl-alcohol and dextran acetate were used to afford polymers exhibiting degradation profiles significantly different from that of linear poly-lactides. The biphasic release profile often observed with the linear polyesters was smoothened somewhat to a monophasic profile. Further, the overall degradation rate is accelerated. It was speculated that these polymers can potentially afford more uniform drug release kinetics. This potential has not yet been fully demonstrated. 

The in vitro degradation profiles of several TDI poly(phosphoester-ure thanes) are shown in Figure 2. It is not possible from this study to correlate the decomposition kinetics with the chemical structure, except for the fact that biodegradability is demonstrated. The in vitro release of 5-FU from PPU-7 is shown in Figure 3. After an initial burst, a reasonably steady and sustained release followed. The UV spectrum of the released 5-FU was identical to that of pure 5-FU, suggesting the chemical integrity of the drug. 

Table 1. Kinetic parameters of some bacterial poly(3HB) synthesizing and degrading enzymes (values in mmol 1 )... 

Recently Madras et al. [17], studying the degradation of styrene and poly(vinyl acetate) in chlorobenzene have analysed their data using a continuous distribution kinetics model. 

Peng S, An Y, Chen C, Fei B, Zhuang Y, Dong L (2003) Thermal degradation kinetics of uncapped and end-capped poly(propylene carbonate). Polym Degrad Stab 80 141-147... 

Liu Q, Zou Y, Bei Y, Qi G, Meng Y (2008) Mechanic properties and thermal degradation kinetics of terpolymer poly (propylene cyclohexene carbonates). Mater Lett 62 3294—3296... 

Following route A (Fig. 1), Yan Xiao et al. reported the chemoenzymatic synthesis of poly(8-caprolactone) (PCL) and chiral poly(4-methyl-8-caprolactone) (PMCL) microparticles [5]. The telechelic polymer diol precursors were obtained by enzymatic polymerization of the corresponding monomers in the presence of hexanediol. Enzymatic kinetic resolution polymerization directly yielded the (R)-and (S )-enriched chiral polymers. After acrylation using acryloylchloride, the chiral and nonchiral particles were obtained by crosslinking in an oil-in-water emulsion photopolymerization. Preliminary degradation experiments showed that the stereoselectivity of CALB is retained in the degradation of the chiral microparticles (Fig. 2). 

Another study of stent-based paclitaxel delivery, which also used a degradable polymer [poly(lactide-co-Scaprolactone)] to control the drug-release kinetics, demonstrated sustained reduction in neointimal hyperplasia in the rabbit iliac model (Fg. I I) (56). 

Holland, B. J. and Hay, J. N. The kinetics and mechanisms of the thermal degradation of poly(methyl methacrylate) studied by thermal analysis-Fourier transform infrared spectroscopy. Polymer 2001 42 4825. 

The formation of halohydrins can be promoted by peroxidase catalysts.465 Recently 466 it has been shown that photocatalysis reactions of hydrogen peroxide decomposition in the presence of titanium tetrachloride can produce halohydrins. The workers believe that titanium(IV) peroxide complexes are formed in situ, which act as the photocatalysts for hydrogen peroxide degradation and for the synthesis of the chlorohydrins from the olefins. The kinetics of chlorohydrin formation were studied, along with oxygen formation. The quantum yield was found to be dependent upon the olefin concentration. The mechanism is believed to involve short-lived di- or poly-meric titanium(IV) complexes. 

Park,T. G., Lu, W., and Crotts, G. (1995), Importance of in vitro experimental conditions on protein release kinetics, stability and polymer degradation in protein encapsulated poly(D,L-lactic acid-co-glycolic acid) microspheres,/. Controlled Release, 33,211-222. 

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