2- methyl-7-oxabicyclo 2,2,1 heptane polymerization

Fig. 1. Enthalpy change for the polymerization and depolymerization of exo- and endo-2-methyl-7-oxabicyclo[2.2. l]heptanes...

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

Thus, according to Plesch et al. 25,54) enthalpies of polymerization determined from the heats of combustion of 7-oxabicyclo 2,2,l heptane and its 2-methyl derivatives are considerably higher than those for unsubstituted and substituted 5-membered rings (Table 2.10). 

The stereochemistry of the ring-opening polymerization of 1, -bridged bicyclic ethers derived from cyclohexane have been studied. The endo- and exo-2-methyl-T oxabicyclo[2.2.l]heptane (5) were found to polymerize exclusively through nucleophilic attack at the bridge head carbon in the Sj 2 propagation step leading... 

Two dimethyl substituted derivatives have been studied that is endo,exo- and exo,exo-2,6-dimethyl-7-oxabicyclo[2.2.1]heptane. Only the former monomer yielded a polymer. The exo,exo-isomer (6) will not polymerize since the conformational forms of the repeat unit are unfavourable. In the two chair conformations two substituents will be in axial positions and in one form a l,3 diaxial interaction will exist between the methyl groups ... 

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