SYNTHESIS AND CHARACTERIZATION OF NEW HINDERED AMINE LIGHT STABILIZERS

Abstract

New polymerizable monomers containing hindered amine moiety were synthesized and studied. 2,2,6,6-tetramethylpiperidinyl methacrylate (I) was prepared by an ester exchange reaction between methyl methacrylate (MMA) and 2,2,6,6-tetramethyl-4-piperidinol (TMP). 1,2,2,6,6-Pentamethyl-4-piperidinyl m-isopropenyl-?,?- dimethylbenzyl carbamate (II) was synthesized by direct addition of 1,2,2,6,6-pentamethyl-4-piperidinol (PMP) to m-isopropenyl-?,?-dimethylbenzyl isocyanate (m-TMI) in the presence of dibutyltin dilaurate (DBTDL) catalyst at elevated temperature. For a comparison study, the tetramethyl analog of II (II') was also prepared. 4-(2-naphthylamino)phenyl m-isopropenyl-?,?-dimethylbenzyl carbamate (III) was synthesized by reacting 4-(2-naphthylamino)phenol (NAP) with m-TMI. Compound IV, a higher molecular weight product of the addition reaction between II and methyltris(dimethyl siloxy)silane (T3H), was made. The catalyst employed was a platinum divinyl tetramethylsiloxane complex. The monomers were characterized by IR, 1H-NMR, MS and elemental analysis. Their thermal stability and UV absorptivity were also determined. Copolymers of monomers I and II with styrene (S) and with methyl methacrylate (MMA), separately, were prepared using ?,?' -azobis-(isobutyronitrile) (AIBN) as initiator. Monomer reactivity ratios and structures of the copolymers were determined. The light stabilizing effectiveness of monomer II and its corresponding copolymers as HALS in polypropylene film was evaluated through photo-oxidation and liquid extraction experiments. A comparison study on the photostabilizing effectiveness between monomeric and their corresponding polymeric HALS revealed that monomeric HALS are more effective. Photo-oxidation experiments indicated that monomer II, which carrys a tertiary hindered amine, exhibited higher photostabilizing effectiveness than monomer II', a secondary hindered amine. Of all the HALS tested, HALS of low molecular weight showed a high extractibility while HALS of high molecular weight showed a high resistance to liquid extraction. The monomers also showed a much lower thermostability than their copolymers.