Homopolymerization cyclopentadiene adducts

Diels-Alder synthesis, 112 homopolymerization, 353, 660 MA-cyclopentadiene adduct, 353 1, r-Bicyclohex-2,2-ene, MA copolymerization, 359 l,r-Bicyclohexenyl, MA Diels-Alder adduct, 109 Bicyclo[2.2.2]-5-octene-2,3-dicarboxylic anhydride, Diels-Alder synthesis, 115 l,r-Bicyclopenta-2,2-ene, MA copolymerization, 359... 

The mechanism of the crosslinking reaction has been postulated as (a) dissociation of the terminal cyclopentadiene-N-arylma1-eimide Diels-Alder adduct to the monomeric precursors, which immediately react to form an adduct which initiates the homopolymerization of the undissociated terminal norbornene rings to form a saturated polymer (j>). 

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. 

It has previously been proposed that the saturated products from the homopolymerization of norbornene (17) and the CPD-MAH Diels-Alder adduct (12-15), and probably from the furan-maleic anhydride Diels-Alder adduct (11), have rearranged structures. An analogous structure would arise from the homopolymerization of the cyclopentadiene-N-phenylmaleimide CPD-NPMI adduct, as follows ... 

In the absence of radical initiators, cyclopentadiene and MA form a 1 1 Diels-Alder adduct, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride (see Chapter 4). The Jo-adduct formed below 170°C, undergoes isomerization above 170°C to the exo-adduct/ " Both the endo- and oxo-adducts undergo homopolymerization to yield polymer containing equimolar amounts of the two monomers/ " Copolymerization occurs in the presence of radical initiators at a temperature where the initiator has a short half-life. For example, heating molten adduct with 6.6 mol % crr-butylhydroperoxide for 1 h at 240°C gives 83% copolymer. Heating the exo-adduct with 10 mol % /-butyl peracetate in chlorobenzene for 1 h gives a 72% yield of copolymer. 

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