Antioxidants with comonomer

High-molecular-weight A-substituted maleimides have been prepared and used as polymeric food antioxidants which can achieve the desired gastrointestinal nonabsorption. A-(3,5-Di-t-Bu -hydroxyphenyl)maleimide was prepared in two steps (a) formation of 2,6-di-t-Bu-4-aminophenol either from 2,6-di-(-Bu-phenol by nitration followed by reduction, or from 4-aminophenol by alkylation, (b) amida-tion of maleic anhydride with the 2,6-di-t-Bu-4-aminophenol followed by dehydration. The nonabsorbable poly(A-(3,5-di-t-Bu-4-hydroxyphenyl)maleimide)s were prepared from the monomeric maleimides by free radical homo- and copolymerization with comonomers of alkyl vinyl ethers (Scheme 5.5) [43]. 

The use of a reactive di- or poly-functional comonomer (non-antioxidant) which can co-graft with a monofunctional polymerisable antioxidant on polymers can improve the grafting efficiency from as low as 10-40% to an excess of 80-90%. This strategy, however, presents immense challenges due to the presence of more than one polymerisable group in the comonomer which could lead to additional undesirable (competing) side reactions com-... 

Antioxidants based on 2,6-ditertiarybutyl- -vinylphenol or 2,6-ditertiarybutyl-l-isopropenylphenol are the only monomeric stabilizers that have been synthesized and studied. We have developed efficient synthetic methods for the preparation of such compounds and have polymerized them with styrene or methyl methacrylate in solution or in bulk with AIBN as the initiator. More importantly, we have developed a good emulsion polymerization of 2,6-ditertiarybutyl-4-vinylphenol and 2,6-ditertiarybutyl-4-isopropenylphenol with butadiene or isoprene. The copolymers of good molecular weights had comonomer contents between 6 mol and 20 mol of the vinyl or iso-propenyl monomer. The polymers were effective at a 0.1 weight percent level in retarding autooxidation of polybutadiene and polyiso-prene. 

The poly a-olefin/aminoolefin copolymers had lowered TmS as compared to their homopolyolefin analogues (223 °C for poly-4-methyl-l-pentene, 159—186 °C for copolymers, 115 °C for the polyamine) but showed greatly increased decomposition temperatures. With just 2.5 mol % amino comonomer present, the decomposition temperature of poly(4-methyl-l-pentene) was raised by 43 °C. This enhancement is thought to be a result of the antioxidant capabilities of the tertiary amine functionality. The copolymers can also be quaternized to give alcohol- and water-soluble polyolefins. 

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