Synthesis of Novel-dl-α-Tocopherol-Based and Sterically-Hindered-Phenol-Based Monomers and Their Utilization in Copolymerizations over Metallocene/MAO Catalyst Systems: A Strategy To Remove Concerns about Additive Compatibility and Migration

In this paper we present an initial study on various synthetic routes to novel polymerizable dl-α-tocopherol derivatives and to a styrenic sterically hindered phenol which was stimulated by our desire to conduct copolymerization with these monomers with α-olefins over different metallocene/methylalumoxane (MAO) catalyst systems. The syntheses of 6-hydroxyl-2,5,7,8-tetramethyl-2-(but-3-enyl)chroman (1) and 5,7,8-trimethyl-3-(hex-5-enyl)benzofuran-6-ol (2) were achieved by cyclocondensation of trimethylhydroquinone (TMHQ) with 3-methylhept-1,6-dien-3-ol and 2,7-octadienol, respectively. However, the latter tocopherol compound (2) could only be obtained in low yields, and all our attempts to isolate the product from its ring-opened isomers failed. This can be attributed to the fact that the reaction between TMHQ and 2,7-octadienol gave rise to a highly complex reaction mixture. Compound 3, 6-hydroxyl-2,2,8,9-tetramethyl-6-allylchroman, was prepared from the corresponding allylchromanoxy ether via Claisen rearrangement. In addition facile synthetic pathways to 4-methylene(3,5-di-tert-butyl-4-phenoxy)styrene (4) and its trimethylsilylated derivative 5, i.e., 4-methylene(3,5-di-tert-butyl-4-trimethylsiloxyphenyl)styrene, were successfully developed. The chromanol 1 was copolymerized with ethylene over a rac-[dimethylsilylenebis(4,5,6,7-tetrahydro-1-indenyl)]zirconium dichloride/MAO catalyst system, and monomers 4 and 5 were copolymerized with styrene over an (η⁵-indenyl)trichlorotitanium (IndTiCl3)/MAO catalyst system. The copolymers contained from 2.3 to 6.8 wt % functional units and exhibit enhanced thermooxidative stabilities in comparison to the corresponding homopolymers as determined by TGA and DSC analysis.