Abstract
The anionic polymerization of acrylonitrile by cyclopentadienyl sodium in tetrahydrofuran was studied. The effects of the concentration of monomer, catalyst, temperature, and added cyclopentadiene on the polymerization were investigated. Contrary to previously studied anionic polymerizations, the molecular weight was found to increase with monomer concentration as a result of the cyclopentadiene radical acting as a polyfunctional catalyst due to the following equilibrium:
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The cyclopentadienyl polymer anions thus formed (which have 5 resonance structures) initiate polymerization especially at high monomer concentration leading to increase in molecular weight as a result of the formation of several polymeric chains attached to the same cyclopentadienyl radical. Proof for the existence of such polymers was obtained on treatment of the polymers with ozone which caused considerable lowering of the molecular weight due to scission of polymer side chains as a result of the opening of the cyclopentadiene rings. Xβray diffraction diagrams of the branched polymers showed no strong reflection band at 5.3 A. which is associated with hydrogen bonding between chains of polyacrylonitrile. The molecular weight was independent of catalyst concentration and increased with lowering in temperature. Polymerization in the presence of free cyclopentadiene led to lowering in molecular weight due to termination by the acidic hydrogen of cyclopentadiene; plot of molecular weight against the reciprocal of the cyclopentadiene concentration gave a straight line. The polyacrylonitriles, having cyclopentadiene end groups, were utilized to introduce different end groups by the Diels Alder Reaction with dienophiles. Thus the adduct of the polymer with maleic anhydride gave an amide on reaction with amine.