Process for producing oxymethylene polymers

Abstract

The present invention relates to an improved process for the preparation of oxymethylene polymers, comprising the steps of: a) heterogeneous polymerization of a mixture at the existence of a chain transfer agent and an initiator used for cationic polymerization, wherein the mixture comprises a-1) at least one monomer forming a -CH2-O- unit, and a-2) optionally, at least one comonomer copolymerized with the monomer forming a -CH2-O- unit and provided with at least one C-C bond; b) increasing the temperature to be high enough to enable basically-homogeneous polymer melt besides residual monomers at the end of a polymerization reaction before passivation; c) passivating basically-homogeneous active polymer through supplying a passivant to the polymer and monomer mixture; d) supplying the passivated homogeneous polymer mixture prepared in the steps a) and c) to a hydrolyzation area, wherein the hydrolyzation area is used as a hydrolyzation mixture comprising one or more protic solvents, and the polymer mixture is hydrolyzed at the presence of the protic solvents under a temperature higher than the melting point temperature of the polymer mixture prepared in the steps a) and c); and e) precipitating a hydrolyzed formaldehyde polymer from the solution prepared by the step d). the present invention also relates to the formaldehyde polymer obtained therefrom and the use thereof.

Description

technical field [0001] The present invention relates to an improved process for the preparation of oxymethylene polymers, to the oxymethylene polymers thus obtained and to their use. Background technique [0002] The preparation of polyoxymethylene polymers is known per se. Polymerization can be carried out in bulk or in solution as precipitation polymerization, at atmospheric or superatmospheric pressure. Chain transfer agents, such as formals, are also known for the preparation of oxymethylene polymers. [0003] The cationic initiator variant of the polymerization reaction uses a cationic initiator. A disadvantage of using cationic initiators is that they also catalyze the reverse reaction, ie, POM degradation to formaldehyde. The reaction mixture must therefore be deactivated after the polymerization. [0004] A considerable number of methods for the passivation of reaction mixtures have been disclosed previously. These methods can be divided into methods in which a ...

AI Technical Summary

Problems solved by technology

Although the amount of residual monomers can be significantly reduced by efficient polymerization and quenching processes as taught in US 7812110 and WO-Al-2009 / 127386, the melt hydrolysis described here results in significant reduction in oligomers, remaining residual Limitations in removal effectiveness of monomers and formaldehyde originating from unstable end groups

Images