Control of transesterification in polyester blends

Abstract

Polyester blends may undergo transesterification during processing, resulting in molecular rearrangements, transient properties, and eventually, degradation. To suppress transesterifcation, the use of organophosphites has been suggested in the patent and technical literature. The effectiveness of organophosphites, however, is variable and sometimes inconsistent. Our recent studies suggest a clue to the inconsistent behavior and provide a simple way to enhance the effectiveness of these stabilizers. Using solid state 31P NMR it was shown that for bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite a conversion of the phosphite group to a phosphonate, via hydrolysis, is a prerequisite for a n effective inhibition of transesterification. This conversion occurs readily during melt compounding if the polymers are not completely dry. However, if rigorous drying is employed and phosphite conversion does not occur, then transesterification is not arrested. It was also found that over a period of time the conversion of the phosphite to a phosphonate may take place at room temperature as well. After aging for about a year in the laboratory, the originally ineffective compound, has become a very effective inhibitor of transesterification in blends containing poly(ethy1ene terephthalate), poly(buty1ene terephthalate), polycarbonate, and polyarylate. Thus, a simple way to enhance the phosphite effectiveness is to expose it to a humid environment prior to blending.

Degradation and Recyclability of Poly (Ethylene Terephthalate)

“…It is reported that phosphoric acid interact with the polycondensation catalysts thereby modifying the catalyst [30][31][32][33]. Since the same catalyst catalyses the thermal degradation addition of phosphoric acid mitigates degradation reactions.…”

Processing characteristics of PET/PEN blends, part 1: Extrusion and transesterification reaction kinetics

“…Melt-phase blending of PET with PEN causes transesterification reactions to occur between the two polymers, which result in the formation of block copolymers that become more random as the reactions proceed. [7][8][9][10][11][12] Studies conducted by Porter and Wang 13 have shown that both PET and PEN are immiscible; however, transesterification reactions increased the blend miscibility through the formation of copolymers. Good mixing was necessary before the blends became transparent.…”

Polymer Blends

“…This holds particularly for the PETP and PBT blends. The ester interchange reaction does not need to be stopped in PAr -PCHT blends due to its complete miscibility [104][105][106][107].…”