Comparison of the thermal and light stabilising action of novel aromatic phosphites substituted with 2-hydroxybenzophenone and hindered piperidine moieties in polyolefins

Abstract

Three novel phosphite stabilisers have been synthesised and characterised and their thermal and photochemical effectiveness examined in polyethylene and polypropylene films. Two structures are based on a bis-hindered phenolic moiety coupled to a 2-hydroxybenzophenone (2) and a 4-amino-tetramethylpiperidine (3) chromophore. The third is a tris-2-hydroxybenzophenone based phosphite (4). Thermal oven aging and thermal analysis on the polymer films showed that the hindered piperidine phosphite is an effective primary and secondary antioxidant compared with the 2-hydroxybenzophenone derivatives. These results are consistent with its ability to inhibit the formation of hydroperoxides during thermal aging. The 4-aminopiperidine phosphite compound is also an effective light stabiliser for polypropylene. The 2-hydroxybenzophenone derivative (2) was ineffective as a light stabiliser in all cases and antagonised the effectiveness of a commercial polymeric hindered piperidine stabiliser (Chimassorb 944). The tris-2-hydroxybenzophenone phosphite compound (4), however, was more effective as a light stabiliser in polypropylene than in polyethylene. Both mass spectrometry and thermal analysis indicated initial fragmentation resulting in the loss of the 2-hydroxybenzophenone and 4-aminopiperidine stabiliser moieties from the phosphorus atom. the importance of combining different stabiliser moieties within the same structure in terms of performance is discussed.