CS218359B1 - Process for the production of anionic polycaprolactam - Google Patents

Abstract

The invention relates to a method for producing anionic polycaprolactam with a low monomer content, increased melt viscosity stability, which does not foam during injection molding. The method is particularly suitable for continuous granulate production and is carried out in a three-stage process, i.e. prepolymerization, crystallization of the prepolymer and its postpolymerization. Prepolymerization is preferably carried out at 220 degrees Celsius for 2 to 4 minutes, crystallization at 150 to 160 °C and postpolymerization for 4 hours at 190 °C

Description

The present invention relates to the production of an anionic polycaprolactam with a low monomer content and an increased stability of the polymerization stage of the molten polymer.

After completion of the polymerization, each caprolactam polymerisate contains an equilibrium amount of polymer and starting monomer. This composition is dependent on the polymerization temperature and is, for example at about 250 ° C, about 89% of the polymer and 11% of the water-extractable substances composed of monomer and oligomers (hereinafter VEP). Towards lower polymerization temperatures, the equilibrium is shifted more to the polymer side, so that, for example, at 200 ° C the polymer content rises to 95%. The high VEP content of the polymerizate has an adverse effect on the properties of the final polycaprolactam product. Therefore, a polymer with a minimum VEP content of up to approx. 3%. A temperature of about 170 ° C corresponds to such an equilibrium content of polymer and monomer in the polymer. At conventional concentrations of a catalyst system composed of, for example, acylcaprolactam, the polymerization mixture would have to be heated for too long (more than 30 minutes), whereby the polymer solidified and could not be easily transported. This is disadvantageous for continuous production since the reactor would be too complex. While reducing the polymerization time can be achieved by increasing the concentration of the catalyst components, this results in a decrease in the stability of the polymerization stage. While the adiabatic process of anionic polymerization of caprolactam can satisfy both low VEP requirements, such a discontinuous process is economically disadvantageous to continuous production, despite the necessity of grinding larger castings in expensive investment facilities.

Therefore, ways have been sought to solve the problem of preparing a polymer with reduced VEP content. For example, according to U.S. Pat. No. 127,660, the polymerization is carried out at a temperature above the melting point of the polymer of e.g. The disadvantage of this procedure is that it requires structurally demanding elements. In addition, unwanted cyclic oligomers and volatile fumes from side reactions are contained in the recovered caprolactam; the recovered caprolactam cannot be returned to the polymer without purification. According to other methods, e.g. No. 113,971 and the like in British Patent No. 944,307, the monomer content can be substantially reduced when the polymerization is carried out at a temperature above or around the melting point of the polymer and then dopolymerizes at a lower temperature to equilibrium.

The high temperature of the polymer above the melting point of the polymer presents some disadvantages. Indeed, in each anionic polymerization, side reactions occur which are undesirable for the polymerization and the end product. Their extent is influenced by the type of catalyst components, their concentration and ratio, and in particular also by the polymer temperature. Higher temperatures reduce the life of the catalyst and the possibility of being used for dopolymerization apart from affecting the molecular weight.

A number of these disadvantages are eliminated by the method of Art. AO 177 763, however, still has the disadvantage of the possibility of foaming caused by the evolution of gases that occurs when the granulate is remelted during processing into a shaped article. Due to the lower tolerance to processing temperatures, some degree of depolymerization and polymerization degree changes may also occur.

These disadvantages can be overcome according to the invention by the three-phase anionic polymerization of caprolactam using known initiators and known activators of general formulas I-VI.

RNCO

I-n-co I I CO-N-R

R.

X χ R Ν'ίΊ

R

III

Colν col · rnhcon — co

LI —Ιχ ii ₁ I

R CO C CONHR

R *

II

IV

VI where

R = an aromatic radical of formula

R ¹ = R or alkyl of 1-4 carbon atoms

R ² = alkyl with 1-4 carbon atoms or hydrogen n = an integer from 3 to 11 x is an integer greater than 3 performed such that the first stage (prepolymerization) takes place at temperatures of 200-245 ° C, preferably 220 ° C for a maximum of 10 minutes, preferably 2-4 minutes in the presence of 0.05-0.3% / mol of initiator and at a ratio of 4.2 to 8 active groups of activator to initiator, wherein the activators of formulas I, IV, V, VI each contain one, formula II two and formula III three active groups.

The method according to the invention is characterized by a number of advantages over the method according to U.S. Pat. A. O. 177 763, such as in the reduction of foaming under thermal stress, as is the case with remelting during processing. Another important advantage of this process is the increase in the stability of the polymerization stage over the process of US. A. 0.177 763 and hence melt viscosity stability. Therefore, polycaprolactam produced by the process of the present invention is particularly suitable for injection molding and extrusion processing. In addition, the process according to the invention is economically advantageous since it also enables production on high-capacity devices with high hourly output. Examples

Examples 1-5

Activator (N-phenylcarbamoylcaprolactam and 1,3,5-triphenyltriazine-2,4,6-trione) and the initiator Synhydride, ie benzene solution, were gradually dissolved in 11.3 g of molten 6-caprolactam at 80-100 ° C. sodium di- (2-methoxyethoxy) dihydroaluminate) and the resulting polymerization mixture was filled into glass vials with an internal diameter of 5 mm and after sealing, the vials were placed in thermostats in which the polymerization mixture was polymerized for a selected period of time. and then doped. After the operations were completed, the water extractable fraction (VEP) and the polymerization degree of the products were determined. The concentrations of the catalyst components (in mol% active groups) and the reaction temperatures and times are given in the table; FK denotes N-phenylcarbamoylcaprolactam, F 1,3,5-triphenyltriazine-2,4,6-trione, with S denotes Synhydride.

Example Activator ³ ) kind mol% Initiator kind mol% Polymerization Dopolymerization VEP% T% min. T. ° C rt.

HaHCOlM co c \ T c \ T co co ψ a v ¹ rl ooooo CT) CT) 00 CD CD H rl rl Η H what ie co ooooo rl CO rl rl rl 00 OO OO OO OO rl rl NW CO θ 'θ 'θ' θ 'θ' co c / ό ω co c / o

Os tx CD CO o 'θ' rH r? τ-Γ

For fa b fe rH (N CO 31IO a

tí ω

tí

C 1 H 2 H 3

Example 6

A reaction mixture of 11.3 g containing 27.8 mg of 1,3,5-triphenyltriazine-2,4,6-trione, i.e. 0.7 mol% of active groups, was prepared as described in Examples 1-5. 1 mole why. Synhydride and 0.2 mol% acetanilide. This mixture was then subjected to the same operations as described for Example 1. The product obtained contained 2.8% VEP and had a polymerization degree of 173. The product of Example 1 (prepared under the same conditions but without acetanilide) had a polymerization degree of 249. After remelting 250 ° C / 5 min the product of Example 1 showed a degree of polymerization of 252 and the product of Example 6 had a degree of polymerization of 176 after remelting.

Example 7 “w &t;

In the laboratory apparatus shown in Scheme 1, continuous polymerization, crystalline polymer strand formation, and dopolymerization were performed. In tray 1, a solution of 3.808 g (i.e. 32 mol active groups) of 1,3,5-triphenyltrlazine-2,4,6-trione in 226 g of molten anhydrous 6-caprolactam was prepared and the resulting solution was heated to 120 ° C. In container 2, 7 mmol of Synhydride as a 70% benzene solution was added to 226 grams of anhydrous 6-caprolactam at 80 ° C. Co-powered pumps 3 and 4 were pumped solutions from reservoirs 1 and 2 into mixer 5 and the resulting mixture was fed by gear pump 6 (0.6 ml / rev) heated to 220 ° C to reactor 7 maintained at 220 ° C; the total residence time in the gear pump and reactor was in the range of 3-4 minutes. The viscous polymerizate flowing through a 2 mm nozzle was cooled on a stainless steel continuous web 8 to an average temperature of 150 ° C, the resulting string of crystalline polymerizate was cut into sections of 5-8 cm and immediately fed to the dopolymerizer 9 where they were in an inert atmosphere ( dry argon) maintained at 190 ° C for 4 hours. The product contained 2.9% water extracts and had a polymerization degree of 270 (after remelting at 250 ° C / 5 minutes, the polymerization degree increased to 273).

Claims (3)

1. A process for the preparation of anionic polycaprolactam by a three-phase process using known basic initiators and known activators of general formula I-VI R RNCO AND R-N-CO-CO-N-R II ° ύ ^ν υ ° R 1 ^R O -v ^l r rnhcon— co ^L (CHJ ^j i. n v /// R2 RtCO-C-CONHR R ² where R = aromatic residue R ¹ = R or C 1-4 alkyl; R 2 = C 1-4 alkyl; or a hydrogen atom% n = an integer of 3-11 x = an integer greater than 3, characterized in that the first phase, prepolymerization, is carried out at 200-245 ° C, preferably at 220 ° C for a maximum of 10 minutes, preferably 2-4 min in the presence of 0.05-0.3 mol% of initiator and at a ratio of 4.2-8 activator groups to initiator, the second phase, crystallization and granulation, is carried out at 130-180 ° C, preferably 150-80 ° C. 160 ° C and the third phase, dopolymerization, at 160-200 ° C for 0.5-24 h, preferably 4 h at 190 ° C. 2. A process according to claim 1, wherein the polymerization mixture comprises known additives for influencing properties, i.e., molecular weight regulators, flame retardants, antioxidants, fillers. 3. Method according to claim 1, characterized in that the individual production phases are carried out continuously.