Radical catalyzed homopolymerization

The radical-catalyzed polymerization of furan and maleic anhydride has been reported to yield a 1 1 furan-maleic anhydride copolymer (89,91). The stmcture of the equimolar product, as shown by nmr analyses, is that of an unsaturated alternating copolymer (18) arising through homopolymerization of the intermediate excited donor—acceptor complex (91,92). 

The radical catalyzed homopolymerization of the furan-maleic anhydride (F-MAH) Diels-Alder adduct yields a saturated homopoly-mer at temperatures below 60 C, and an unsaturated equimolar alternating copolymer at elevated temperatures, due to retrograde dissociation of the adduct (10, 11). The copolymerization of monomeric furan and maleic anhydride yields the same unsaturated alternating copolymer, independent of temperature (1C)). 

In contrast, the radical catalyzed homopolymerization of the cyclopentadiene-maleic anhydride (CPD-MAH) Diels-Alder adduct yields a saturated homopolymer at temperatures as high as 220 C, while retrograde dissociation occurs at even higher temperatures. Nevertheless, the copolymerization of monomeric cyclopentadiene and maleic anhydride yields a saturated 1 2 copolymer (12-15). 

Since the F-MAH and CPD-MAH Diels-Alder adducts yield unsaturated and saturated polymers, respectively, as a result of radical catalyzed homopolymerization at elevated temperatures, it was of interest to investigate the radical catalyzed polymerization of the isomeric exo- and endo-cyclopentadiene-N-phenylmaleimide adducts, models for the norbornene end-capped polyimides whose thermal polymerization products have structures which have been diversely depicted as saturated and unsaturated, without experimental verification. 

The failure to initiate the homopolymerization of maleic anhydride (MAH) in the presence of a free radical catalyst under normal conditions was long considered evidence of the steric hindrance imposed by 1,2-disubstitution of the double bond. However, in recent years, the radical homopolymerization of MAH has been carried out under the influence of V-radiation, ultraviolet radiation in the presence of a sensitizer, and shock waves, as well as in the presence of free radical catalysts at high concentrations and/or at temperatures where they have a short half-life. These and other aspects of the polymerization of MAH have been reviewed by Gaylord, who has proposed the participation of n excited charge transfer complex and of cationic intermediates in the radical catalyzed homopolymeri zation. 

If the reaction takes place in the presence of monomer, grafting occurs in the usual manner. The fact that some homopolymerization also occurs in the redox-catalyzed grafting system can be explained by a chain-transfer mechanism (Reaction 10). The growing polymer radicals can abstract hydrogen atoms from the monomer, forming monomer radicals and thereby initiating homopolymerization. 

Hirooka (29) has proposed that copolymerizations of this type be named "complex copolymerization. Russian workers (55) have suggested that polymerizations initiated by radical catalysts in the presence of a complexing agent be called "complex-radical processes. Both polymerizations are more appropriately considered as polymerizations through activated charge transfer complexes, in which the Lewis acid or metal halide catalyzes the formation of the complex, and free radicals may or may not be necessary to initiate the homopolymerization of the complex. 

The self-condensing copper-catalyzed polymerization of macromonomer of poly(tBA) with a reactive C—Br bond (H-6) affords hyperbranched or highly branched poly(tBA).447 Copolymerization of H-1 and TV-cyclohexylmaleimide induced alternating and self-condensing vinyl polymerization.448 The residual C—Cl bond was further employed for the copper-catalyzed radical homopolymerization of styrene to give star polymers with hyperbranched structures. Hyperbranched polymers of H-1 further serve as a complex multifunctionalized macroinitiator for the copper-catalyzed polymerization of a functional monomer with polar chromophores to yield possible second-order nonlinear optical materials.325... 

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