Polymerizable antioxidants

The use of a reactive di- or poly-functional comonomer (nonantioxidant), which can co-graft with a monofunc-tional polymerizable antioxidant on polymers, can improve the grafting efficiency from as low as 10-40% to an excess of 80-90%. This strategy, however. 

The resulting copolymers are good antioxidants for their parent polymers at copolymer compositions of only 10 to 15 mol% of polymerizable antioxidant. 

The incorporation of comonomers into the rubber substrate can be useful in achieving specialized performance of the final ABS polymer, such as adjusting the refractive index of the rubber phase to better match the continuous SAN phase to achieve a clear or more translucent ABS product (92). The incorporation of polymerizable antioxidants or uv stabilizers has also been reported (93). Typically, these modifications increase the cost of ABS and are only employed for specialized applications. 

Oxazines with an olefinic substituent were suggested as polymerizable monomers.307-309 1,3-Oxazines were claimed as plasticizers for cellulose acetate,309 tanning agents,19 and corrosion inhibitors.310 N-Oxides of 1,3-oxazines were reported to be antioxidants and polymerization inhibitors.34... 

There are a few examples of polymers based on vinylbenzofurans. Vinyldibenzofuran 324 has been patented for use in copolymer formulations with other vinyl arenes, used to prepare light-emitting devices <2004USP6803124>. Benzofuran 325 was developed as one of four polymerizable monomers that contain a built-in antioxidant. The polymerization process was transition metal catalyzed <2003MM8346>. Benzofuran 326 also contains the styrene substructure, but there are few examples of its polymerization. Poly(2,3-benzofuran) films were synthesized by anodic oxidation on stainless steel in the presence of boron trifluoride etherate. The films had good thermal stability and conductivity of lO Scm <2005MI1654>. 

In general, reactive antioxidants are compounds that contain one or more antioxidant functions (the antioxidant, AO component) and one or more chemical functions that are capable of reacting either with monomers (same or different) or with polymers (the reactive, Rv, component). The AO function is based on any antioxidant moiety (see examples A-D in Scheme 7), whereas the reactive moiety can either be a polymerizable (e.g., Rv functions 1-4) or nonpoly-merizable (e.g., Rv functions 5-7) groups, and may or may not contain a spacer (an inert flexible and short chemical link connecting the antioxidant moiety to the reactive function). 

The use of polymerizable monofunctional antioxidants with one reactive group per antioxidant molecule is... 

Non-polymerizable monofunctional antioxidants were subsequently used to avoid the problem of homopolymerization of the antioxidant. For example, melt grafting of the two maleated antioxidants, BPM and APM (see below), on PP was shown to lead to high grafting efficiencies (up to 75% in the former and >90% in the latter), which were attributed to the nonpolymerizable nature of the maleate (maleimide) functions.The performance of these antioxidants, especially under extractive organic solvent conditions, was also shown to far exceed that of conventional antioxidants with similar antioxidant function. 

Other polymerizable ultraviolet stabilizers and antioxidants have also been synthesized and incorporated into polymeric structures. 

In the case of synthetic elastomers formed by free radical emulsion techniques, monomers that contain both an antioxidant moiety and a polymerizable function can be copolymerized (6). A series of esters and amides containing the 4-anilinophenyl group or the 3,5-di- er -butyl-4-hydroxyphenol group and a polymerizable a, /3-unsaturated acyl group such as acryloyl or methacryloyl were incorporated into the polymer. 

Copolymerization during Polymer Manufacture. Extensive work has been documented on the synthesis and successful copolymerization of a large number of polymerizable UVA containing one or two UVA functions (see Scheme 24 for selected examples) (163,164). However, the use of such antioxidants has been beset by high ssmthetic costs. 

The use of phenolic and amino-based antioxidants (ie, thermal stabilizers) by this approach has been limited because they inhibit the free-radical polymerization process (polymerization inhibitor) leading to lower efficiency. One of the few commercial products produced is based on the polymerizable chain breaking antioxidant (AO 12b, Table 3), designed for NBR rubbers (Chemigum HR 665) that has been shown to offer superior antioxidant performance, especially imder aggressive (hot oil/high temperature) conditions, compared to low molecular mass conventional aromatic amine antioxidants (165). In spite of the successful synthesis and copoljmierization of a large number of reactive antioxidants, there is a lack of major commercial development and production of antioxidant systems... 

Vogt is Professor in the Department of Pol3rmer Science and Engineering, University of Massachusetts, Amherst, MA. He is a member of the National Academy of Sciences and is recognized inter-nationally in the field of pol)rmers. His research Interests are synthesis of polymerizable absorbers and antioxidants and development of synthetic polymeric drugs. He is a prolific author and has many research publications to his credit. 

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