Synthesis of novel hindered amine light stabilizers (HALS) and their copolymerization with ethylene or propylene over both soluble and supported metallocene catalyst systems

Novel polymerizable hindered amine light stabilizers (HALS) such 1-(but-3-enyl)-2,2,6,6-tetramethylpiperidine (1), 1-(undec-10-enyl)-2,2,6,6-tetramethylpiperidine (2), 4-(but-3-enyl)-1,2,2,6,6-pentamethyl-3, 3,4-dehydropiperidine (3), 2-(but-3-enyl)-2,6,6-trimethylpiperidine (4), 4-(but-3-enyl)-1,2,2,6,6-pentamethyl-4-piperidyl ether (5), 4-(undec-10-enylamide)-1,2,2,6,6-pentamethylpiperdine (6), 4-((N-n-butyl)-undec-10-enylamide)-1,2,2,6,6-pen (7), and bis(N-n-butyl-N-2,2,6,6-tetramethyl- piperidine)-N-n-butyl-N-allyltriazine (8) were synthesized. All the aforementioned HALS monomers except for 5 and 8 were successfully copolymerized in fair to high yields with ethylene or propylene over eight different group 4 metallocene catalysts using methylalumoxane (MAO) as cocatalyst. Copolymerizations were also performed over a supported metallocene/SiO2/MAOtriisobutylaluminum(TIBA) catalyst system. The silica-supported metallocene catalyst system readily promoted copolymerization of the sterically hindered monomer 2 with ethylene, however, copolymerizations using either 6 or 7 as comonomer failed. Moreover, a catalyst derived from the reaction of rac-[dimethylsilylenebis(1-indenyl)]zirconium dichloride (CA1) with triethylaluminum and trityl tetra(perfluorophenyl)borate (TRI-FABA) afforded HALS copolymers in high yields. Surprisingly, it was found that TRI-FABA, a strong Lewis acid, could impede the Lewis base activity of HALS monomers such as 2, 6 and 7 provided a sufficient relative amount of TRI-FABA was employed. Thus, once an equilibrium concentration between TRI-FABA and HALS monomer was established, the presence of HALS monomer no longer affected the rate of polymerization. Normally, metallocene catalysts are severely poisoned when traces of polar monomers (Lewis bases) are present, due to the Lewis acidic nature of the catalyst. Furthermore, a series of standard ethylene homopolymerizations over rac-[dimethylsilylenebis(4,5,6,7-tetrahydro-1-indenyl)]zirconium dichloride (CA2)/MAO catalyst system was performed in the presence of different sterically hindered amine model compounds such as 1-(1-methylene-2,6-di-tert-butylphenol)-2,2,6,6-tetramethylpiperidine (A), N,N-diisopropylaniline (B), 1-octyl-2,2,6,6-tetramethylpiperidine (C), 1-benzyl-2,2,6,6-tetramethylpiperidine (D), 2,2,6,6-tetramethylpiperidine (E), 1,2,2,6,6-pentamethylpiperidine (F), diisopropylethylamine (G), 1,2,2,6,6-pentamethyl-4-oxopiperidine (H), 2,2,6,6-tetramethylpiperidine-1-oxyl (I), 1-propargyl-2,2,6,6-tetramethylpiperidine (J), 4-N,N-bis(n-butylamino)-2,2,6,6-tetramethylpiperidine (K), tris(N-butyl-N-2,2,6,6-tetramethylpiperidineamino)triazine (L) and tris(dibutylamino)triazine (M). The results show that some of the amine model compounds are highly reactive and deactivating whereas others are less so. Much preferred are those HALS structures which have a sterically demanding substituent attached on nitrogen and no additional heteroatoms in I-position of the piperidine ring in terms of metallocene/MAO catalyst activity. C-13 NMR analyses revealed that the produced materials are random copolymers containing isolated HALS branches and that the prepared propylene copolymers have highly stereoregular microstructures. According to size exclusion chromatography, the prepared copolymers have molecular weight distributions close to 2, which are characteristic for polymers produced over single-site catalysts. The prepared copolymers contained from 0.2 to 14.1 wt % of HALS units and exhibited high ultraviolet and thermooxidative stabilities even after exhaustive extraction with a mixture of refluxing (50:50) cyclohexanc/2-propanol. For example, the poly(ethylene-co-4) copolymer with a HALS content of 0.2 wt % exhibited considerable improved thermooxidative stability in comparison to unstabilized polyethylene, i.e., for the copolymer the carbonyl peak had not appeared after one year of oven aging at 115 degrees C, whereas unstabilized polyethylene shows a strong increase in the carbonyl index within 2 days.