A novel class of high molecular weight multifunctional antioxidants for polymers based on thiol-ene click reaction. (March 2020) - Fischer, Johannes
Abstract: Novel bifunctional antioxidants (AO) with high molecular weight were successfully synthesized by two-step free-radical thiol-ene click reaction and transesterification. The structures of the stabilizers were confirmed by 1 H NMR spectra and Fourier Transform Infrared Spectrometry (FTIR). Thermal gravimetric analysis (TGA) showed high temperature stability above 300 °C, proving suitability as potential stabilizers for standard and technical polymers. The performance of the bifunctional antioxidants was investigated through oxidation induction time (OIT) and accelerated heat aging of PP compounds in comparison to state of the art stabilizers represented through 2, 2′-thiodiethylene bis[3-(3, 5-di-tert-butyl-4-hydroxyphenyl)propionate] and a binary mixture of pentaerythritol tetrakis(3, 5-di-tert-butyl-4-hydroxyhydrocinnamate) and dioctadecyl 3, 3′-thiodipropionate. Reduced degradation and extended maintenance of mechanical values of PP stabilized through the novel antioxidants during heat aging are due to the high amount of alkyl sulfide groups. Furthermore, a low migration tendency of the high-molecular AO could be determined by FTIR mapping of heat-treated samples. Highlights: Thiol-ene reaction enables synthesis of efficient stabilizers for polyolefins under cost-effective reaction conditions. Reaction pathway bridges the gap between economic reaction conditions and at the same time variable reactant selection. Design of a simple synthesis process for complex high-molecular weight antioxidants has resulted in a new stabilizer class. Novel antioxidants show less migration tendency and superior thermo-oxidative efficiency compared to a commercial standard. Mechanical and rheological properties were maintained superior to those of the comparative example.