Method for producing thermoplastic pre-ceramic polymers

Abstract

A method for producing high-molecular weight, solid, meltable, thermoplastic, pre-ceramic polymers by converting liquid low-molecular weight polysilazanes in a solvent, in the presence of a catalyst, and a stopping reagent stopping the reaction as soon as the desired degree of polymerization is achieved. The obtained polysilazanes can be processed by conventional industrial methods, such as, for example, extrusion, injection molding, melt spinning, calendering, film and hollow body blowing, rotational molding, fluidized bed sintering, flame spraying and transfer molding (RTM and DP RTM).

Claims

1. A method for producing high molecular weight solid, meltable thermoplastic pre-ceramic polymers, having a molecular weight of at least 2000 g/mol to 2 million g/mol, comprising the step of reacting one or more liquid low molecular weight polysilazanes, having a number-average molecular weight of 150 to 150 000 glmol, in a solvent, in the presence of a catalyst by stopping the reaction with a stopping reagent as soon as the desired degree of polymerization is attained, wherein chlorides, bromides, iodides, fluorides and hydroxides of tetraalkyl-substituted ammonium salts are used as the catalyst.

2. The method as claimed in claim 1, wherein the one or more polysilazanes are of the general formula (1)
—(SiR′R″—NR′″).sub.n—  (1) where R′, R″ and R′″ are the same or different and each independently are hydrogen or an optionally substituted alkyl, aryl, vinyl or (trialkoxysilyl)alkyl radical, where n is an integer such that the polysilazane has a number-average molecular weight of 150 to 150 000 g/mol.

3. The method as claimed in claim 2, wherein R′, R″ and R′″ each independently is a radical selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, phenyl, tolyl, vinyl, 3-(triethoxysilyl)propyl and 3-(trimethoxysilylpropyl).

4. The method as claimed in claim 1, wherein the one or more polysilazanes are perhydropolysilazanes of formula (2) ##STR00004## where n is an integer such that the polysilazane has a number-average molecular weight of 150 to 150 000 g/mol.

5. The method as claimed in claim 1, wherein the concentration of the catalyst in the reaction mixture is in the range from 0.01 wt % and 10 wt %.

6. The method as claimed in claim 1, wherein the solvent comprises organic solvents containing no water and also no reactive groups.

7. The method as claimed in claim 1, wherein the concentration of the starting materials in the reaction medium is in the range of 20-80 wt %.

8. The method as claimed in claim 1, wherein the solvent comprises aliphatic or aromatic hydrocarbons.

9. A method for producing high molecular weight solid, meltable thermoplastic pre-ceramic polymers, having a molecular weight of at least 2000 g/mol to 2 million g/mol, comprising the step of reacting one or more liquid low molecular weight polysilazanes, having a number-average molecular weight of 150 to 150 000 g/mol, in a solvent, in the presence of a catalyst by stopping the reaction with a stopping reagent as soon as the desired degree of polymerization is attained, wherein hydrides of alkali and alkaline earth metals are used as the stopping reagent.

Description

EXAMPLES

Inventive Example 1

(1) 3.0 kg of KiON ML 33 and 1.5 kg of THF are admixed at room temperature, over 40 min, with a solution of 27.1 g of tetrabutylammonium fluoride (TBAF) dissolved with 513 g of THF. On completion of the admixture, the mixture is stirred for a further 30 min and then admixed with 7.5 g of Ca(BH.sub.4).sub.2 suspended in 133.5 g of THF. The mixture is stirred for a further 35 min. The THF is finally removed under elevated temperature and reduced pressure to leave 2.76 kg of a solid polysilazane having a softening point ˜90° C. and an M.sub.w of 38 000 g/mol.

Inventive Example 2

(2) 100 g of KiON ML 33 and 0.2 kg of THF are admixed at room temperature, over 40 min, with a solution of 0.26 g of TBAF dissolved with 20 g of THF. On completion of the admixture, the mixture is stirred for a further 90 min and then admixed with 0.25 g of Ca(BH.sub.4).sub.2 suspended in 5 ml of THF. The mixture is stirred for a further 30 min. The THF is finally removed under elevated temperature and reduced pressure to leave 87.9 g of a solid polysilazane having a softening point ˜50° C. and an M.sub.w of 4190 g/mol.

Inventive Example 3

(3) An argon-inertized 2 I four-neck flask equipped with stirrer, thermometer and condenser is initially charged with 0.075 kg of THF and 150 g of devolatilized KiON HTT 1800. A solution of 0.375 mg of TBAF dissolved in 27.16 ml of THF is added in the course of 30 min. After 30 min of subsequent stirring, the reaction solution is admixed with 375 mg of Ca(BH.sub.4).sub.2 in 7.5 ml of THF to stop the reaction. The solvent is removed to leave a white solid which solidifies at about 110° C. and has an M.sub.w of 116 000 g/mol.

Inventive Example 4

(4) A nitrogen-inertized 1 L single-neck flask equipped with magnetic core and condenser is initially charged at RT with 200 g of THF, 100 g of KiON HTT 1800 and 100 g of KiON ML 33. The homogeneous mixture is admixed with a solution comprising 500 mg of TBAF in 38.2 ml of THF in the course of 60 min. After 30 min of subsequent stirring, the reaction is stopped with 491 mg of Ca(BH.sub.4).sub.2 in 10 ml of THF. Distillation leaves a solid having a softening point of about 60° C. and an M.sub.w molecular weight of 10 100 g/mol.

Inventive Example 5

(5) An argon-inertized 1 l single-neck flask equipped with magnetic core and condenser is initially charged at RT with 200 g of diethyl ether and 100 g of Ceraset PSZ 20, and the initial charge is thoroughly comixed. A mixture of 1 ml of 1M TBAF/THF solution and 19 ml of diethyl ether are admixed in the course of 5 min. Following 30 min of further reaction, admixtures of 0.25 g of Ca(BH.sub.4).sub.2 in diethyl ether and a further 30 min of stirring, the solvent is removed to leave a melt which is highly viscous at 115° C. and solidifies vitreously on cooling. M.sub.w=21 300 g/mol.

Inventive Example 6

(6) An inertized 500 ml flask is charged with 80 g of toluene and 40 g of Ceraset PSZ 20. A solution of 0.4 ml of 1M tetrabutylammonium hydroxide and 7.6 ml of toluene is admixed in the course of 10 min followed by stirring for 25 min. The admixture of 2 ml of toluene with 0.1 g of Ca(BH.sub.4).sub.2 suspended therein stops the reaction completely. The solvent is removed to leave a substance which is a waxy solid at room temperature and has an M.sub.w of 20 900 g/mol.

Inventive Example 7

(7) 300 g of THF are mixed with 600 g of KiON ML 33 in a 4 I flask. 6 ml of a 1M TBAF solution diluted with 114 ml of THE are added over 30 min followed by 30 min of subsequent stirring. The reaction is stopped with 14 mmol of LiBH.sub.4 in 7 ml of THF. Following filtration and removal of the solvent, a vitreously solidified melt was obtained. The M.sub.w is 17 350 g/mol.

Inventive Example 8

(8) 0.22 ml of a 0.3M solution of tetrakis[tris(dimethylamino)phosphoranylideneamino]-phosphonium fluoride in benzene are initially charged in 40 ml of THF and admixed with 10 g of KiON HTT 1800 in the course of 10 min. The reaction is stopped with Ca(BH.sub.4).sub.2 and the solvent is removed to obtain a solid whose M.sub.w is 6200 g/mol.

Inventive Example 9

(9) 300 g of THF are mixed with 600 g of KiON ML 33 in a 4 I flask. 6 ml of a 1M TBAF solution diluted with 114 ml of THF are added over 30 min followed by 30 min of subsequent stirring. The reaction is stopped with 14 mmol of NaH in 7 ml of THF. Following filtration and removal of the solvent, a vitreously solidified melt was obtained. The M.sub.w is 28 840 g/mol.

Inventive Example 10

(10) 90 g of KiON HTT 1800 and 210 g of THF are initially charged and cooled down to 0° C. Under vigorous agitation, 15 ml of THF with 450 mg of TBAF dissolved therein are added in the course of 60 min. The mixture is subsequently stirred 60 min at 0° C. and warmed to 20° C. before the reaction is stopped with 300 mg of Ca(BH.sub.4).sub.2 in 50 ml of THF. The THF is removed by distillation to leave a waxy solid having an M.sub.w of 1650 g/mol.

Comparative Example 1

(11) 300 g of THF are mixed with 600 g of KiON ML 33 in a 4 I flask. 6 ml of a 1M TBAF solution diluted with 114 ml of THF is added in the course of 30 min and then left to stir overnight. Filtration and distillative removal of the solvent leaves an insoluble and unmeltable solid.

Comparative Example 2

(12) A nitrogen-inertized 1L single-neck flask equipped with magnetic core and condenser is initially charged at RT with 200 g of THF, 100 g of KiON HTT 1800 and 100 g of KiON ML 33. The homogeneous mixture is admixed with a solution comprising 1500 mg of TBAF in 38.2 ml of THF in the course of 45 min. After 30 min of subsequent stirring, it is possible to make out formation of a white solid, the mass of which increases rapidly. The solid is insoluble and unmeltable.

Comparative Example 3

(13) 200 g of KiON ML 33 are initially charged to a 500 ml 3 three-neck flask and admixed with 5 ml of a 1M TBAF/THF solution under vigorous agitation. A white solid is formed at the drop entry point. Completion of the admixture is followed by 60 min of stirring to obtain two-phase flask contents. The removed solid is insoluble and does not melt.