Bulk polymer degradation

Boyd, R. H. The effect of changing volume in the kinetics of bulk polymer degradation. Journal of Polymer Science 1961 49 SI. 

The second phase of polymer degradation is characterized by a decrease in the rate of chain scission (Fig. 19) and the onset of weight loss. Weight loss has been attributed to (1) the increased probability that chain scission of a low molecular weight polymer will produce a fragment small enough to diffuse out of the polymer bulk and (2) the breakup of the polymer mass to produce smaller particles with an increased probability of phagocytosis. The decrease in the rate of chain scission, as well as the increased brittleness of the polymer, is the result of an increase in the crystallinity of PCL,... 

Other methods of calibration are discussed by Zimm and by Brice and co-workers.23 Owing to difiSculties of absolute calibration, a reference standard invariably is used. This may consist of a polymer solution of constant properties (i.e., not subject to degradation) or a bulk polymer, such as that used by Debye and Bueche. ... 

Wavelengths that are non-destructive to the bulk polymer can be used. The latter is an advantage only if the sensitizer is located at the polymer surface. If it is evenly distributed in the polymer matrix it will cause degradation of the bulk polymer. There are several ways to add the sensitizer to the polymer surface. In the present work we have used ... 

In their study of branched PSA, Maniar et al. (1990) found that the molecular architecture of branched polymers affects the release kinetics in a variety of ways. They found that the branched polymers degraded faster than linear PSA of comparable molecular weight (Maniar et al., 1990). They also noted that drug (morphine) release profiles were more characteristic of bulk erosion than surface erosion An initial lag time during which very little drug was released was associated with the time required for water to swell the polymer. This was followed by a period of relatively fast release, which tapered off as the device disintegrated. The polymer matrix lost its mechanical integrity before the release experiment was complete (Maniar et al., 1990). Despite the increase... 

In contrast to bulk-eroding PLA/PLGA polymers, the polyanhydride undergoes surface erosion. The thin-disk type morphology of the wafer confers a high surface-to-volume ratio on the implant, so that the total surface area of the implant is kept almost constant over the time of polymer degradation, which facilitates a constant release of carmustine with time. 

Poly(s-caprolactone) Poly(e-caprolactone) is a semicrystalline polymer synthesized by anionic, cationic, free-radical, or ring-opening polymerization [94]. It is available in a range of molecular weights and degrades by bulk hydrolysis autocatalyzed by the carboxylic acid end groups. The presence of enzymes such as protease, amylase, and pancreatic lipase accelerates polymer degradation [95], The various methods of preparation of poly(e-caprolactone) nanoparticles include emulsion polymerization, interfacial deposition, emulsion-solvent evaporation, desolvation, and dialysis. These methods and various applications are extensively reviewed [94],... 

A detailed description of bulk polymers as hosts for geminal radical pairs and their precursors is also beyond the scope of this chapter. For general sources of information about photochemical and photophysical processes in bulk polymers, we recommend the classic book by Guillet as well as the book edited by Winnik, the journal Polymer Degradation and Stability (incorporating the defunct journal. 

Structure and mechanism in photochemical reactions. The reactions of geminal radical pairs created in bulk polymers are presented by Chesta and Weiss in Chapter 13. Of the many possible chemical reactions for such pairs, they are organized here by polymer and reaction type, and the authors provide solid rationalizations for the observed product yields in terms of cage versus escape processes. Chapter 14 contains a summary of the editor s own work on acrylic polymer degradation in solution. Forbes and Lebedeva show TREPR spectra and simulations for many main-chain acrylic polymer radicals that cannot be observed by steady-state EPR methods. A discussion of conformational dynamics and solvent effects is also included. 

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