Crosslinking agents Degradable

Novolac network degradation mechanisms vary from tiiose of resole networks due to differences in crosslinking metiiods. Nitrogen-containing linkages must also be considered when HMTA (or other crosslinking agent) was used to cure novolac networks. For example, tribenzylamines, formed in HMTA-cured novolac networks, decompose to cresols and azomethines (Fig. 7.50). 

Cortisone acetate has been incorporated into several polyanhydrides (15). The rates of release of cortisone acetate from microcapsules of poly(terephthaUc acid), poly(terephthaUc acid-sebacic acid) 50 50, and poly(carboxyphenoxypropane-sebacic acid) 50 50 are shown in Fig. 8. These microcapsules were produced by an interfacial condensation of a diacyl chloride in methylene chloride with the appropriate dicarboxylic acid in water, with or without the crosslinking agent trimesoyl chloride. This process produces irregular microcapsules with a rough surface. The release rates of cortisone acetate from these microcapsules varied correspondingly with the rate of degradation of the respective polyanhydrides. It can be expected that the duration of release of cortisone acetate from solid microspheres, such as those produced by the hot-melt process, would be considerably longer. 

A crosslinked starch was described as a fluid loss additive for drilling fluids [632,1626]. The additive resists degradation and functions satisfactorily after exposure to temperatures of 250° F for periods of up to 32 hours. To obtain crosslinked starch, a crosslinking agent is reacted with granular starch in an aqueous slurry. The crosslinking reaction is controlled by a Brabender... 

The main commerdally useftil methods for aosslinking use agents whose sole purpose is to promote free-radical processes that essentially initiate polyethylene degradation. This ultimately aeates bonds direcdy between carbon atoms on adjacent polymer chains. Some crosslinking agents, such as silanes, integrate themselves between polymers to form intermediate "bridging" links that connect one chain to another. 

The mechanical and physical properties of PLA are severely degraded when subjected to electron beam irradiation [89], because the dissipated energy from the irradiation easily causes chain scission of the backbone chain of PLA and forms free radicals. Additional additives, such as a crosslinking agent, are therefore... 

He, S., Timmer, M. D., Yaszemski, M. J., Yasko, A. W., Engel, P. S. Mikos, A. G. (2001) Synthesis of biodegradable poly(propylene fumarate) networks with poly(propylene fumarate)-diacrylate macromers as crosslinking agents and characterization of their degradation products. Polymer, 42, 1251-1260. 

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