Poly degradation mechanism

Poly(lactide-coglycolide). Mixtures of lactide and glycolide monomers have been copolymerised in an effort to extend the range of polymer properties and rates of in vivo absorption. Poly(lactide- (9-glycolide) polymers undergo a simple hydrolysis degradation mechanism, which is sensitive to both pH and the presence of ensymes (32). 

Cheng et al. [116] reported that the structure of primaquine phosphate irradiated with 0.7—10 Mrad remained unchanged. The energy transfer action of the quinolyl group was considerable due to its resonance stabilization. Radiation-induced degradation of polyl(vinyl alcohol) decreased in the presence of primaquine phosphate but the degradation mechanism was unaffected. The content of primaquine phosphate showed linear relationship with degradation parameters of poly(vinyl alcohol). 

Liu B, Zhang M, Yu A, Chen L (2004) Degradation mechanism of poly (propylene carbonate) polyols. Gongcheng 20 76-79... 

Sakai K, Hamada N, Watanabe Y (1986) Degradation mechanism of poly(vinyl alcohol) by successive reactions of secondary alcohol oxidase and [l-diketone hydrolase from Pseudomonas sp. Agric Biol Chem 50 989-996... 

Poly(vinyl chloride) prepared at -78°C, and containing no branches, was compared to PVC prepared at 50°C and having the highest branch content. Similar comparisons were made for polymers prepared with intermediate branch content. No differences were observed in the ESR spectra on irradiation and measurement at LNT. Even for the 50°C case the number of branches are only four per thousand repeat units (13). Therefore, even if radicals are formed at (or near) these branch sites, their effects will be overshadowed by the unbranched radicals if they do not significantly alter the degradation mechanism. 

B. Rimez, H. Rahier, G. Van Assche, T. Arttoos, M. Biesemans, and B. Van Mele, The thermal degradation of poly(vinyl acetate) and poly(ethylene-co-vinyl acetate), Part I Experimental study of the degradation mechanism, Polym. Degrad. Stab., 93, 800-810 (2008). 

Liquid chlorinated paraffins are the main halogen-containing fire-retardant additives used for poly(vinyl chloride) often in combination with a phosphate ester. In this case, the chlorinated paraffins have the secondary function of plasticizers. The thermal degradation mechanism of chlorinated paraffins is similar to that of poly(vinyl chloride), so in this case poly(vinyl chloride) stabilizers have also the secondary function to stabilize chlorinated paraffins. 

Previous investigations have shown that polyisobutene and poly(isobutene-co-iso-prene), i. e. butyl rubber, are unable to cross-link in the presence of free radicals, since extensive chain scissions occur and thus low molecular weight products are formed The degradation mechanism proposed by Loan involves, in the case of polyisobutene, the H abstraction from methyl groups followed by chain scission. Apparently, the formation of secondary alkyl radicals, which are believed to be responsible of polyolefin radical curing is prevented for steric reasons by the presence of two adjacent dimethyl substituted carbon atoms and hence j3 scission reactions prevail. 

The influence of molecular structure on the degradation mechanism of degradable polymers of poly(tri-methylene carbonate), poly (trimethylene carbonate-co-caprolactone), and poly(adipic anhydride) was explored by Albertsson and Eklund [7]. Measuring the change of the mass and the molecular weight for the... 

One of the most important degradation mechanisms of SLM is an emulsification ofthe membrane phase due to lateral shear forces. Therefore, formation of barrier layers on the membrane surface by physical deposition [98] or by interfacial polymerization could prevent instability [99, 100]. A polysulfone support with N-methylpyiTolidone as a solvent was coated by a poly(ether ketone) layer as the outside layer and gave a specific composite membrane support. Such composite hoUow-fiber membranes showed significant improvement in stabUity in copper ions permeation. 

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