Process for preparation of oxymethylene polymers, selected polymers, and their use

A process for preparation of oxymethylene copolymers containing the structural units of the formula II and III, and also end groups of the formula IV

• or containing the structural units of the formula II and V, and optionally formula IV, and also end groups of the formula IV
• in which R1 is an alkyl radical,
• m is a whole number from 1 to 1000,
• o is a whole number from 2 to 6,
• p is a whole number from 3 to 6, and
• R3 is a p-valent organic radical
• encompassing the following measures:
• i) heterogeneous polymerization of a monomer which forms —CH2—O— units and simultaneously of a monomer which forms —O—CoH2o— units, in the presence of an acetal of formaldehyde and of an initiator for cationic polymerization, or heterogeneous polymerization of a monomer which forms —CH2—O— units and simultaneously of a monomer which forms —O—(R3—O)p— units and, optionally simultaneously of a monomer which forms —O—CoH2o— units, in the presence of an acetal of formaldehyde and of an initiator for cationic polymerization, wherein the heterogeneous polymerization is a precipitation polymerization conducted at a temperature from 70 to 120° C. and a pressure from 0 to 10 bar, and
• ii) deactivation of the initiator and/or of the active polymer chains by using an aprotic solvent which is basic and/or which comprises a dissolved base, the aprotic solvent added in an amount of at least 10% by weight, for treatment in a homogeneous phase of the polymer prepared in step i), wherein deactivation is conducted at a temperature from 130 to 160° C.