ELSEVIER PolymerDegradationand Stability46 (1994) 85-91 Q 1994 ElsevierScience Limited Printed in Northern Ireland. All rights reserved 0141-3910/94/$07.00 Comparison of the thermal and light stabilising action of novel imine and piperazine based hindered piperidine stabilisers in polyolefins N. S. Allen,* R. Acosta Ortiz,t G. J. Anderson Chemistry Department, Faculty of Science and Engineering, Manchester Metropolitan University, Chester Street, Manchester, UK, M1 5GD I. Sideridou & E. Malamidou Laboratory of Organic Chemical Technology, Aristotle University of Thessaloniki, Thessaloniki, Greece 54006 (Received 5 May 1994; accepted 23 May 1994) A novel imine stabiliser based on 2-hydroxybenzophenone and a 4-amino-tetra- methylpiperidine structure has been synthesised and characterised, as have two novel mono and bis-alkylated esters of tetramethylpiperidine with piperazine. Using FTIR spectroscopy, rates of polymer oxidation were measured by carbonyl index. Hydroperoxide formation was also measured. All three structures are shown to be highly effective thermal and light stabilisers for polyethylene and polypropylene. In all cases their thermal and light stabilising activities are consistent and follow their ability to inhibit hydroperoxide formation during thermal aging. The ability of the stabilisers to operate as effective radical scavengers is discussed and related to the effects of some commercial thermal and light stabilisers. INTRODUCTION Absorbers based on the 2-hydroxybenzophenone chromophore are known to operate through a weak sacrificial antioxidant mechanism, ~.2 i.e. they behave as weak chain-breaking donors for hydroxyl and alkoxy radicals. On this basis we recently examined methods of improving the thermal and photochemical stabilising action of these types of stabilisers in polyolefins by substituting a tertiary amine functionality in the 2-hydroxybenzophenone chromophore. 3 Amines are well-known scavengers of oxygen and free radicals and this is borne out by the efficiency of the hindered piperidine light stabilisers, espe- cially with regard to their protective effect on * To whom correspondence should be addressed. t Research student on leave of absence from CIQA, Saltillo, Mexico. 85 2-hydroxybenzophenones. 4-'° In this case, sub- stitution of simple aliphatic tertiary amine groups in the meta positions of the benzophenone imparted weak thermal antioxidant behaviour. 3 On this basis further work was undertaken to examine the effect of substituting alicyclic amine groups in the para position of the benzophenone chromophore. 1°'~I Here, the effect of substituting a hindered piperidine molecule was compared with that of simpler amine structural types. Of the compounds studied, substitution of a 4-butoxy-4-amino-2,2,6,6-tetramethylpiperidine group was found to produce a highly effective photothermal antioxidant. 12 In this same work we also synthesised bis-2-hydroxybenzophenone de- rivatives of piperazine 1° and found them to be weak photothermal antioxidants. In this paper we extend our previous work on the stabilising activity of substituting a 4-butoxy-