GB2096155A

GB2096155A - Multi-stage anionic polymerisation of caprolactam

Info

Publication number: GB2096155A
Application number: GB8110797A
Authority: GB
Original assignee: Chemopetrol AS
Current assignee: Chemopetrol AS
Priority date: 1981-04-07
Filing date: 1981-04-07
Publication date: 1982-10-13
Also published as: GB2096155B; DE3115602C2; DE3115602A1

Abstract

A process for producing polyamides or copolyamides based on 6-caprolactam, optionally on its mixtures with lactams of omega -amino acids with 4 to 13 carbon atoms and their modified types, by continuous activated anionic polymerization of lactams above melting temperature of the mixture of monomer and polymer under adiabatic and quasi-isothermal conditions and for final polymerization below the melting temperature of the polymer. The process is carried out in four stages. In the first stage the lactam is dehydrated usually in a wiped-film evaporator, in the second stage prepolymerization and degassing of the reaction mixture are realized under mixing, after finishing the polymerization again in stirred device in the third stage, final polymerization of solid polymer takes place below its melting temperature in the last stage.

Description

SPECIFICATION A process for producing polyamides or copolyamides based on 6-caprolactam, optionally on its mixtures with lactams of w-amino acids with 4 to 13 carbon atoms and their modified types This invention relates to a process for producing polyamides or copolyamides on the basis of 6-caprolactam.

-A common feature of previously proposed processes is the fact that they were mostly onestage processes operated below the melting point of polymer or they were at most two-stage operating only above melting temperature of the mixture of monomer and polymer author's certificate 127 660. The main disadvantage of one-stage processes is that the polymer obtained contains equilibrious residual monomer which changes for the worse physical and chemical properties of the product. The disadvantage of a two-stage process operating above the melting point of polymer is the fact that residual content of monomer is so high that it is necessary to remove it together with volatile oligomers and residual catalyst from the polymer in the aqueous phase by the so-called "demonomeration" either in vacuum or by expansion of melt.These systems are difficult to control operationally, volatile fractions choke the parts of device for gaseous and liquid fractions offtake and granulation is complicated.

An object of the present invention is to obviate or mitigate the aforesaid disadvantages of these processes.

According to the present invention there is provided a process for producing polyamides or copolyamides based on 6-caprolactam by continuous activated anionic polymedz,ation above the melting temperature of the mixture of monomer and polymer under adiabatic or quasiisothermal conditions followed by final polymerization below the melting temperature of the polymer wherein the process comprises the following four stages: (a) dehyodration of lactam starting material in a wiped-film-type evaporator; (b) prepolymerization with simultaneous degassing of a mixture of dehydrated lactam and catalyst components in a stirred polymerator at 10 to 40% delay of the total polymerization time; (c) polymerization of the prepolymerized mixture in a stirred vessel to form a solid polymer; and (d) fina! polymerization of the solid polymer at a temperature below its melting point.

Preferably the copolyamides based on 6-caprolactam are formed from mixtures thereof with lactams of a)-amino acids with from 4 to 13 carbon atoms.

In a preferred embodiment of the process lactam starting material is dehydrated in a filmtype evaporator with internal wiper to produce a thin layer of concentrated lactam, in the second stage prepolymerization occurs after addition of catalysts to the concentrate to form a reaction mixture with degassing of the reaction mixture in a stirred polymerator at 10 to 40% delay of the total polymerization time, in the third stage the polymerization is completed in a stirred device e.g.

a screw agitator, ribbon mixer or leaf agitator and in the fourth stage final polymerization of solid polymer taking place below its melting point at 413 to 483 K (140-1 500C). The first stage of the production proceeds e.g. in a film evaporator with an internal facility to provide a wiped film of lactam whereby the lactam is cleared of residual content of water by the most economical way. The optimum content of water is at most 0.02% by weight. The evaporator operates on the principle of differential contact of phases. In the second stage of production mixing of monomer with activator and initiator takes place at elevated temperature 453 to 485 K (180-21 20C). The volatile fractions originating from catalytic system are simultaneously removed.It is possible to control the degree of prepolymerization at given time of delay by properly chosen temperature and thus to utilize in the highest degree polymerizing heat in the third stage. An advantage of this invention is the possibility of producing modified polyamides, e.g. self-extinguishing and additive ones. Compatibility of modification component with catalytic system is a condition of successful result of modification. Additives containing moisture are added in the first stage, dry substances can be added in the second stage.

Prepolymerization of the reaction mixture in the second stage substantially facilitates the process in the third stage from the point of view of machine performance (processing of a liquid with high viscosity). A horizontal two-screw system appears to be the most suitable one.

Degassing of reaction mixture by prepolymerization substantially improves the outlet of the melt of polymer from the reactor and it facilitates further treatment of the melt after transformation into solid stage. In comparison with extraction removal of volatile fractions the final polymerization of polyamides in solid state below its melting point by prolongation of heat action has the advantage of better utilization of the initial raw material at minimum volatized amount and it brings significant energy savings by elimination of drying of washed polymer. Likewise the difficulties with regeneration of removed monomer and oligomers with maintenance of the device which appear with demonomeration.

The invention will now be described by way of the following Examples: EXAMPLE 1 6-caprolactam with an initial water content of 0.05% by weight was dehydrated in a film evaporator to 0.01% by weight of water at 358 to 361 K (85 to 880C) and 666 and 1333 Pa. After preheating melt to 468K (195"C), 0.25 molar % of sodium bis-(2-methoxyethoxy)-di-aluminium hydride and 0.5 molar % of the cyclic trimer of phenyl isocyanate were added and after mixing for 60 seconds the mixture was fed to a double-screw Werner-Pfleiderer ZSK where the polymerizing process took place under a thermal profile of 493 to 503 K (220--2300C) at the inlet, 503 to 513 K (230--2400C) in the middle and 488 to 498 K (21 5-2250C) at the outlet.After driving-out and cooling of melt of the polymer in the form of a band at 413 to 433 K (140-1 600C) the band was cut into granules which were further exposed to final polymerization at 433 to 453 K (160-1 800C) for 3 hours in a fluidized bed reactor. The polymer was then allowed to cool in reservoirs under inert gas. The polymer obtained contained 1.7% by weight of water-extractible fractions; viscosity polymerizing degree Pn = 220 in m-cresol was achieved.

EXAMPLE 2 A mixture of 95% by weight of 6-caprolactam and 5% by weight of 12-laurolactam was dehydrated at 1333 to 1 600 Pa and at 363 to 368 K (90--950C) in a film evaporator to a water content of 0.003% by weight, preheated to 473 K (2000C) and mixed with 0.20 molar % of sodium bis-(2-methoxyethoxy)-dicaprolactam aluminate and with 0.7 molar % of the cyclic trimer of phenyl isocyanate. For 45 seconds the mixture was fed through a double-screw Werner-Pfleiderer ZSK where the polymerization was completed under a thermal profile of 493 to 503 K (200-2300C) at the iniet, 508 to 518 K (235-2450C) in the middle and 483 to 488 K (210--2150C) at the outlet.After cooling on a metallic band under inert gas the strings of polymer having a temperature of 413 to 423 K (240-2500C) were cut into a granulated product. Final polymerization was performed in a reactor with moving bed at 443 to 458 K (270--2850C) for the time of 1 to 3.5 hours. The resulting copolymer contained 1.8% by weight of water-extractible fractions and itsP= 177.

EXAMPLE 3 A process carried out in an analogous fashion to that in Example 1 above with the difference that 0.3 molar % of catalyst and 0.8 molar % of activator have been used. In addition to these 0.5% by weight of red phosphorus in homogeneous mixture with lactam was added simultaneously with the addition of both components of catalytic system to the dehydrated 6-caprolactam. The resulting product contained approximately 2% by weight of water-extractible fractions and its P= 165. A product having a flame-proof finish was achieved.

Claims

1. A process for producing polyamides or copolyamides based on 6-caprolactam by continuous activated anionic polymerization above the melting temperature of the mixture of monomer and polymer under adiabatic or quasiisothermal conditions followed by final polymerization below the melting temperature of the polymer wherein the process comprises the following four stages: (a) dehydration of lactam starting material in a wiped-film-type evaporator; (b) prepolymerization with simultaneous degassing of a mixture of dehydrated lactam and catalyst components in a stirred polymerator at 10 to 40% delay of the total polymerization time; (c) polymerization of the prepolymerized mixture in a stirred vessel to form a solid polymer; and (d) final polymerization of the solid polymer at a temperature below its melting point.

2. A process according to claim 1 wherein the copolyamides based on 6-caprolactam are formed from mixtures thereof with lactams of cs-amino acids with from 4 to 1 3 carbon atoms.

3. A process according to claim 1 or claim 2 wherein a modifier is added to the mixture of dehydrated lactam and catalyst components.

4. A process according to claim 3 wherein the modifier is red phosphorus.

5. A process according to any one of the preceding claims wherein the lactam starting material is evaporated to 0.02% by weight of water.

6. A process according to any one of the preceding claims wherein polymerization of the solid polymer is carried out at a temperature of from 413 to 483 K (140210 C).

7. A process for producing polyamides or copolyamides based on 6-caprolactam according to any one of the Examples 1-3 hereinbefore.

8. Polyamides and copolyamides based on 6-caprolactam whenever prepared by a method according to any one of the preceding claims.