RING-OPENING LAUROLACTAM POLYMERIZATION WITH LATENT INITIATORS

Abstract

The present invention relates to a rapid and innovative mechanism for initiating anionic ring-opening polymerization of laurolactam by means of latent initiators on the basis of thermally activatable N-heterocyclic carbene compounds, such as, more particularly, N-heterocyclic carbene-CO.sub.2 compounds and carbene-metal compounds (NHCs). With the new initiation mechanism it is possible accordingly to realize molecular weights (M.sub.w) of from 2000 up to more than 30,000 g/mol, and narrow polydispersities. The polymerizations may be carried out both in bulk and in solution in a suitable solvent. Compounds of this type are thermally latent and on heating initiate a polymerization to polylaurolactam in high yields, up to a quantitative conversion, whereas at room temperature there is no reaction. Polydispersity and molecular weight of the polylaurolactam can be adjusted through the choice of the initiator and of the reaction conditions.

Claims

1. A method for initiating a polymerization of laurolactam, characterized in that the laurolactam-comprising monomer mixture or monomer solution is admixed with a protected N-heterocyclic carbene, which has a pKa of at least 24 as determined in anhydrous DMSO, and the polymerization is commenced by the raising of the temperature to an onset temperature, which is at least 60° C. and in the case of a bulk polymerization is above the melting temperature of the monomer mixture.

2. The method as claimed in claim 1, characterized in that the protected N-heterocyclic carbene is a compound having one of the two formulae (I) or (II) ##STR00010## where R.sub.1 is a CH.sub.2, C.sub.2H.sub.4, C.sub.3H.sub.6 or a corresponding substituted radical, R.sub.2 and R.sub.3, identically or in each case differently with respect to one another, are a cyclic, branched or linear alkyl radical having 1 to 20 carbon atoms and optionally containing heteroatoms, or are a substituted or unsubstituted aromatic radical, R.sub.4 and R.sub.5, identically or in each case differently relative to one another, are hydrogen, a cyclic, branched or linear alkyl radical having 1 to 20 carbon atoms and optionally containing heteroatoms, or are a substituted or unsubstituted aromatic radical, and X is CO.sub.2, ZnX′.sub.2, BiX′.sub.3, SnX′.sub.2 or MgX′.sub.2, where X′ is a halogen or a pseudohalogen.

3. The method as claimed in claim 1, characterized in that the protected N-heterocyclic carbene is a compound having one of the two formulae (III) or (IV) ##STR00011## where R.sub.1 is a CH.sub.2, C.sub.2H.sub.4, C.sub.3H.sub.6 or a corresponding substituted radical, R.sub.2 and R.sub.3, identically or in each case differently with respect to one another, are a cyclic, branched or linear alkyl radical having 1 to 20 carbon atoms and optionally containing heteroatoms, or are a substituted or unsubstituted aromatic radical, R.sub.4 and R.sub.5, identically or in each case differently relative to one another, are hydrogen, a cyclic, branched or linear alkyl radical having 1 to 20 carbon atoms and optionally containing heteroatoms, or are a substituted or unsubstituted aromatic radical, and Y is a CF.sub.3, C.sub.6F.sub.4, C.sub.6F.sub.5, CCl.sub.3, or OR.sub.4 radical, with R.sub.4 as an alkyl radical having 1 to 10 carbon atoms, ZnX′.sub.2, BiX′.sub.3, SnX′.sub.2 or MgX′.sub.2, where X′ is a halogen or a pseudohalogen.

4. The method as claimed in at least one of claims 1 to 3, characterized in that the polymer obtained from the method has a weight-average molecular weight, in a GPC measurement against a polystyrene standard, of between 5000 and 50,000 g/mol.

5. The method as claimed in at least one of claims 1 to 4, characterized in that the polymerization is a bulk polymerization and in that the onset temperature is between 150° C. and 220° C.

6. The method as claimed in at least one of claims 1 to 5, characterized in that the protected N-heterocyclic carbenes have a pKa of between 25 and 30.

7. The method as claimed in at least one of claims 1 to 6, characterized in that the protected N-heterocyclic carbenes are six-membered N-heterocycles of the formula (I) with R.sub.1═C.sub.2H.sub.4.

8. The method as claimed in at least one of claims 1 to 7, characterized in that the monomer mixture or monomer solution comprises not only laurolactam but also c-caprolactone and/or one or more lactones.

9. The method as claimed in at least one of claims 1 to 8, characterized in that prior to the polymerization a carrier material in fibre form is impregnated with a composition comprising laurolactam, optional comonomers and protected N-heterocyclic carbenes and then the temperature is raised to the onset temperature.

10. The method as claimed in at least one of claims 1 to 8, characterized in that a composition comprising laurolactam, optional comonomers and protected N-heterocyclic carbenes is poured or injected into a mould and the polymerization is initiated in this mould by an increase in temperature to the onset temperature.

11. A composite material characterized in that it is producible by means of a method as claimed in claim 9.

12. A moulding characterized in that it is producible by means of a method as claimed in claim 10.

Description

EXAMPLES

[0050] General Polymerization Procedure

[0051] For the polymerization, laurolactam, the initiator, optionally benzyl alcohol and optionally a solvent, such as DMSO, DMF or toluene, for example, were weighed out together and transferred to a glove box under an argon atmosphere. The laurolactam was used in technical grade (98% purity) without particular purification. In the case of a solution polymerization, dried DMSO was used as solvent and a Schlenk flask was used as the reaction vessel. After the end of the reaction time, reaction was terminated by addition of m-cresol and the product was dissolved in m-cresol at a temperature of 190° C. The product was subsequently precipitated from an acetone solution which had been cooled beforehand, and was isolated by filtration and washed three times with acetone. The yield was determined by weighing the product after drying under a high vacuum.

[0052] The precise amounts and the nature of the initiators and any further components used can be seen from Table 1.

[0053] Table 1 contains initial results of a bulk polymerization of laurolactam (monomer).

TABLE-US-00001 TABLE 1 Temper- Molar ratio ature Time NHC/ Yield M.sub.w (PDI) Example NHC [° C.] [h] monomer [%] [g/mol] 1  (2) 180 45 1:100 82 24 300 (2.9) 2 (12) 180 45 1:100 100 18 900 (2.6) 3 (12) 180 45 1:200 100 n.d. 4 (13) 180 45 1:100 93 15 400 (2.3) 5  (6) 180 45 1:100 71 21 000 (2.8) 6 (14) 180 45 1:100 96 18 300 (2.6) CE1 — 180 45 — — — CE2 (13) 20 45 1:100 — — CE3  (5) 180 45 1:100 — — CE4 (18) 180 45 1:100 — —

[0054] The conversion, the onset temperature and the molecular weight can be set through the choice of initiators and the polymerization temperature. It is also apparent that even quantitative conversions are achievable within very short polymerization times.

[0055] Table 1 also includes comparative examples (CE). CE1 shows that the same system without addition of the inventive initiator does not exhibit polymerization activity. CE2 shows that in accordance with the invention there is no polymerization, or no significant polymerization, at room temperature. The systems are therefore latent.

[0056] CE3 and CE4 show that protected N-heterocyclic carbenes with a low basicity, i.e. with a pKa of less than 24, do not initiate polymerization at 180° C.