added to the vessel before during or after addition of the monomer to the polymerization vessel but during or before the addition of the catalyst the monomer or mixture of monomers is contacted with the catalytic reaction product in any conventional manner preferably by bringing the catalytic reaction product and monomer together with intimate agitation provided by suitable stirring or other means agitation can be continued during polymerization or in some instances the polymerization can be allowed to remain unstirred while the polymerization takes place in the case of more rapid reactions with more active catalysts means can be provided for refluxing monomer and solvent if any of the latter is present in order to remove the heat of reaction in any event adequate means should be provided for dissipating the exothermic heat of polymerization if desired the monomer can be brought in the vapor phase into contact with the catalytic reaction product in the presence or absence of liquid material the polymerization can be effected in the batch manner or in a continuous manner such as for example by passing the reaction mixture through an elongated reaction tube which is contacted externally with suitable cooling media to maintain the desired reaction temperature or by passing the reaction mixture through an equilibrium overflow reactor or a.