Composition for anionic lactam polymerization

Abstract

A composition comprising a) at least one aliphatic or cycloaliphatic isocyanate compound having at least two isocyanate groups and b) at least one lactone, containing 4 to 7 carbon atoms and use of the composition as an activator for anionic lactam polymerization to obtain polyamides.

Description

FIELD OF THE INVENTION[0001]This invention relates to a composition for the preparation of polyamides by activated anionic polymerization of lactams.BACKGROUND OF THE INVENTION[0002]The activated anionic polymerization of lactams is used in numerous different processes for the manufacture of polyimide shaped products. Unproblematic polymerization and the quality of the polyamides prepared by the various processes depend not only on the catalyst but to a large extent also on the nature of the activator used.[0003]Numerous compounds have been used as activators for the anionic polymerization of lactams, i.e. acyl lactams (EP1449865), oxazolines (EP0786482), ethylenebisamides (US2010 / 0113661), isocyanates and the corresponding masked isocyanate compounds.[0004]Polyisocyanates or isocyanates, particularly diisocyanates, are frequently used as activators. Hexamethylene diisocyanate is particular preferred since it is a highly mobile liquid and as such affords considerable advantage, part...

AI Technical Summary

Benefits of technology

[0025]Mechanical properties of the resulting polyamide obtained by the anionic lactam polymerization are substantially improved when using the composition of the present invention. During a cast polymerization process of the lactam to polyamide, the lactone contained in the composition of the present invention is statistically inserted into the polyamide chain and so generating defects in the macromolecular section of the polyamide preventing the entire crystallization of the cast polyamide. These macromolecular defects may be determined by DSC-analysis of the obtained polyamide. The obtained polyamide shows substantially improved elastic modulus and impact strength.

[0026]It was surprisingly found that the obtained polyamides show improved impact strength when using the composition of the present invention as a liquid activator even without the addition of any impact modifiers, which simplifies the polymerization process.

[0029]Contrary to the problems described in connection with the prior art disclosure (coagulation with conventional liquid activator compositions) no detrimental effect can be seen on the compositions in accordance with the present invention, so that these impact modifiers surprisingly may be employed together with the other essential components of the activator compositions disclosed herein. While it is possible to obtain storage stable compositions when mixing components a) and b) with polyamide impact modifiers, it is nevertheless preferred to mix such impact modifiers with the activator system in accordance with the present invention only shortly before addition to the polymerization system. Nevertheless, in view of the fact that these components may be added to a polymerization system together without detrimental effect, the overall process is facilitated since no separate addition means is required for the impact modifier.

[0049]Method Analysis BRGC 206 is used to determine the reactivity of catalysts for the anionic polymerization of caprolactam in a short time test.

Problems solved by technology

Unproblematic polymerization and the quality of the polyamides prepared by the various processes depend not only on the catalyst but to a large extent also on the nature of the activator used.

One serious disadvantage of the use of hexamethylene diisocyanate, however is its toxicity which is due to its high vapor pressure and which necessitates special safety measures.

One serious disadvantage of pyrrolidones, however, is their toxicity.

However, conventional liquid activator systems coagulate when supplied together with such impact modifiers in the reaction container.

To overcome this problem, separate addition means are required, which complicates the polymerization process.

Sometimes the impact modifiers are mixed with the polymerization catalyst before the addition to the lactam melt which unavoidably leads to a decrease of the catalyst activity, since polymerization catalysts for anionic lactam polymerization are highly hygroscopic.