DE4423617A1 - Poly:acetal(s) prodn. from cyclic formaldehyde oligomers - Google Patents

Abstract

The continuous prodn. of end gp.-stabilised co-polyoxymethylene in a homogeneous phase, as in DE4327245.2, comprises (1) polymerising cyclic formaldehyde oligomers in the presence of 0.005-500 ppm protic acid initiator (I) in a tubular reactor contg. static mixing elements, with a residence time of 0.1-10 mins., (2) immediately deactivating (I) and stabilising the chain ends in the presence of residual monomer, so that there is a fluid transition between polymerisation and deactivation zones which is marked only by the addn. of deactivator, and (3) removing volatiles in a downstream degassing system. The novelty is that stage 2 is carried out at 175-250 deg C in the absence of water.

Description

The invention relates to a process for the continuous production of End group-stable copolyoxymethylenes in a homogeneous phase, in which a tubular reactor with static mixing elements cyclic Formaldehyde oligomers in the presence of protonic acids as initiators in Amounts from 0.005 to 500 ppm in one polymerization zone in a first Process step are polymerized, the residence time of the Reaction components in this zone is 0.1 to 10 min and deactivation of the initiator second immediately after the polymerization Process step follows, with a smooth transition between Polymerization and deactivator zone consists only of the addition of the deactivator is set, and wherein in addition to the deactivation Stabilization of the chain ends in the presence of residual monomers is what the volatile in a downstream degassing unit Components are removed from the reaction mixture after Patent application P 43 27 245.2.

In this way it is possible to carry out both the polymerization and the tube reactor of polyoxymethylenes as well as the deactivation of the initiator and stabilize the chain ends.

The invention has for its object the method according to the main patent not only to improve, but also to make it more economical.

This object is achieved with the method according to the invention in that that the second step, d. H. deactivation and stabilization the chain ends at temperatures from 175 ° C to 250 ° C, preferably 175 ° C  up to 200 ° C in the absence of water.

The process is divided into two process steps, the one in a tubular reactor expire. The first process step, the polymerization, is the usual one Temperatures and pressures are made and correspond to those in practice known as z. B. are described in EP-B-0 080 656, to the hereby Reference is made. The remaining criteria of the first step and the second process step in the deactivator and Stabilization zone correspond to the information in the patent application P 43 27 245.2 with the exception of the temperature range and absence of water in the deactivation.

Due to the faster course of the degradation of the unstable chain ends, one Improvement of the process and thus greater economy guaranteed.

Examples

The monomer mixture, consisting of trioxane and dioxolane, was in one tempered storage kettle (80 ° C). The was via a dosing pump Monomer mixture at the reactor head in the polymerization reactor (tubular reactor equipped with static mixing elements). A solution to the Initiator is injected into the monomer stream in the reactor head. In the The premix section was intimately mixed with the two mixtures. The polymerization took place in the following section of the reactor. Subsequently the deactivator solution was injected into the polymer melt and over static mixer incorporated homogeneously. The deactivation took place in the as Dwell time designed third zone of the reactor instead. The pressure in The reactor was set via a throttle valve at the reactor outlet. The Product was released to atmospheric pressure and via this throttle valve froze spontaneously. Most of the residual monomers evaporated.  

table

Examples 1V to 4V represent comparative examples.

From the table it can be seen that the procedure according to Invention at temperatures above 175 ° C in the absence of water much lower final concentration of the unstable end groups occurs.

To determine the unstable end groups, this is from the tubular reactor resulting polyacetal in an alkaline methanol-water solution at 170 ° C treated to break down the unstable chain ends.

The alkaline methanol-water solution is made up of 400 ml demineralized water, 600 ml of methanol and 3.4 ml of 25% ammonia.

From the polyacetal sample to be analyzed are 20 to 1000 mg in one Weighed in 150 ml of small autoclaves and 40 ml of the alkaline methanol  Water solution added. The sample is treated at 170 ° C for one hour. It is then cooled and filtered. The one during treatment cleaved formaldehyde is present in the solution and is Method (T. Nash, Biochem. J., Vol. 55, 416 (1953)). He's on the Weighted and is a measure of the unstable chain ends.

Claims (2)

1. Process for the continuous production of end group-stable copolyoxymethylenes in a homogeneous phase, in which cyclic formaldehyde oligomers are polymerized in a tubular reactor with static mixing elements in the presence of protonic acids as initiators in amounts of 0.005 to 500 ppm in a polymerization zone in a first process step, the residence time of Reaction components in this zone is 0.1 to 10 min and the polymerization is immediately followed by deactivation of the initiator as a second process step, there being a smooth transition between the polymerization and deactivator zones, which is determined only by the addition of the deactivator, and in addition to the deactivation, the chain ends are stabilized in the presence of residual monomers, whereupon the volatile constituents are removed from the reaction mixture in a downstream degassing unit, according to patent application P 43 27 245 .2, characterized in that the second process step is carried out at temperatures of 175 ° C to 250 ° C in the absence of water. 2. The method according to claim 1, characterized in that the temperature 175 ° C to 200 ° C.