Mechanisms and Activities of Organophosphites

摘要

Organophosphites can undergo a number of reactions during the stabilization of polymers. The reactions are dependent upon the structure of both the polymer and the organophosphite. In polyolefins two desired properties are high activity at decomposing peroxides and good hydrolytic stability. In this paper it was shown that a phosphite could be designed to meet both of these requirements. In PVC it was found that the phosphite had several functions. Oxidation of both alkyl and aryl phosphites was shown to occur during processing. The peroxide decomposition mechanism was significant, and may be of benefit to extend the process window. Trialkyl phosphites were more active than triaryl phosphites, which could partly explain their better stabilizing effects in PVC. Also, alkyl phosphites, because of their ability to undergo the Arbuzov rearrangement, were shown to react with ZnCl_2, HCl and labile chlorines. The reaction with ZnCl_2 happened rapidly and explains how an alkyl phosphite can deactivate ZnCl_2. The ability of alkyl phosphites to act as a primary stabilizer in the presence of zinc explains the benefits to early and mid-term color. Aryl phosphites offered the benefit of improved hydrolytic stability and remained in the polymer for longer periods of time. A mixed alkyl-aryl system offers the advantages of both classes of phosphites.