Cyclopolymerization. IV. Structure of polymethacrylic anhydride and kinetics of polymerization of methacrylic anhydride

The cyclopolymerization of methacrylic anhydride at 36.6°C. produces a polymer whose structure has been examined by infrared spectrometry and bromometric analysis. This polymer contains mainly hexaatomic rings of the A type (absorption bands at 1800 and 1760 cm. −1 ) and open anhydride units with unsaturated side‐groups, the content of which varies only slightly with the monomer concentration. Polymerization at 100°C. produces some syndiotactic hexaatomic rings (1730 cm. −1 ). Chemical analysis of the polymers obtained at 36.6°C. for different monomer concentrations permitted the ratio of the rate constants of vinyl propagation to that of cyclization to be evaluated. This ratio is 0.022 l./mole, compared to 0.17 l./mole for acrylic anhydride. From a plot of the reciprocal of the degree of cyclization against the monomer concentration the values of the ordinate intercepts are interpreted on the basis of chain transfer reaction with monomer and intramolecular isomerization. From a kinetic point of view, the order of reaction at 36.6°C. with respect to the concentration of initiator varies from 0.66 to 0.58 for monomer concentrations of 0.656 and 3.282 mole/l., respectively. With respect to the monomer concentration, the order of reaction is one up to a concentration of 3 mole/l.; above this concentration, the order increases progressively. This behavior can be easily explained by the progressive insolubilization of the polymer and the increasing viscosity of the solution.