Studies in Cyclocopolymerization. VIII. Solvent Effects in Cyclocopolymerization of Maleic Anhydride with Divinyl Ether

Abstract

Abstract Solvent effects in the cyclopolymerization of maleic anhydride (MA) with divinyl ether (DVE) were systematically studied. Evidence is presented which supports a charge-transfer (CT) complex formed between the comonomers as the active species in the cyclocopolymerization. The equilibrium constants (K) of CT complexation with MA was measured in n-heptane by UV spectrophotometry for tetra-hydrofuran, ethyl vinyl ether, DVE, furan, and dihydropyran. K-values increased in the above order. K of the MA-DVE pair was measured by UV and NMR in polyhaloalkanes as solvents. K-values decreased with increase of the dielectric constant of the solvent. The rate of copolymerization and number-average molecular weights decreased in more polar solvents. The initial rate was about 100 times faster in CHCl3 than in DMF. In dilute solution, [M1 + M2]=0.57 mole/liter, the initial overall rate of copolymerization was maximum in DVE-rich feed in CHC13, CH2C12, and DMF. Kinetical derivation failed to explain the rate profile. Though still open to question, strong solvation of MA by the solvent has been proposed as an explanation. The overall rate of copolymerization was proportional to one-half order of AIBN concentration in DMF. The overall energy of activation was 27 kcal/mole in CHC13 and in DMF. Thermal autopolymerization, photopolymerization, and γ-ray polymerization of the MA-DVE pair in bulk gave the same 2:1 (= [MA]:[DVE]) copolymer. Retardation of rate by hydroquinone was observed in thermal autopolymerization. The dative state of the CT complex was considered to be the initiating species.