GB2243370A

GB2243370A - Silethynyl-siloxane copolymers

Info

Publication number: GB2243370A
Application number: GB9108591A
Authority: GB
Inventors: Toshio Suzuki
Original assignee: Dow Corning Ltd; Dow Corning Corp
Current assignee: Dow Silicones UK Ltd; Dow Silicones Corp
Priority date: 1990-04-26
Filing date: 1991-04-22
Publication date: 1991-10-30
Also published as: GB9108591D0; GB9009410D0

Abstract

A method of making siloxane silethynyl copolymers of the general formula <IMAGE> comprises reacting together a lithiated silane of the general formula RnSi(C IDENTICAL CLi)4-n with a cyclic siloxane polymer of the formula [R2SiO)x, followed by reaction with a silane of the formula R''nR3-nSiX or with a Bronsted acid to provide the group R'. The method allows making copolymers in which the acetylenic unit is in a predetermined position. In the formulae: R is C1-16 hydrocarbyl, preferably methyl; n is 1-3, preferably 3; R' is hydrogen or a silyl end group, preferably trimethylsilyl or dimethylmethacryloxypropylsilyl.

Description

METHOD OF MAKING SILETHYNYL-SILOXANE COPOLYMERS This invention relates to a method of making silethynyl siloxane copolymers and, more specifically, to a method of making those polymers in which the ethynyl groups are located at one end of a polysiloxane block in the copolymers.

In pending British patent application 8917329.8 there are provided silethynyl-siloxane copolymers of the general formula R'R2Si-[OSi(R)2]a~[C~CSi(R)2]b-R' wherein each R independently denotes a hydrogen atom, a hydrocarbon group or a substituted hydrocarbon group having up to 16 carbon atoms, R' denotes a group -CECH or a group R and a and b are integers each having a value of at least I. The patent specification also provides a method of making these copolymers which comprises ring-opening copolymerisation of cyclic siloxanes of the formula [R2SiO] and cyclic polymers of the formula [R2SiCEC] m wherein n and m denote integers with a value of at least 3 in die presence of a catalytic amount of a lithium compound. The resulting copolymers of the general formula described above have siloxane units and silethynyl units which are randomly distributed throughout the copolymer.

We have now found a method of making siloxane silethynyl copolymers in which the ethynyl group is in a predetermined position.

According to the invention there is provided a method of making siloxane silethynyl copolymers of the general formula

which comprises (I) reacting together a lithiated silane of the general formula RnSi(C~CLi)4 with a cyclic siloxane polymer of the formula [R2SiO] followed by (II) the reaction of the product of (I) with a silane of the formula R"nR3 SiX or with a Bronsted acid, wherein R denotes a hydrocarbon or a substituted hydrocarbon group having up to 16 carbon atoms, R' denotes a hydrogen atom or a group of the formula Si(R)3 nR"n wherein R" denotes an organic group n n having C, H and one or more 0 atoms present, X denotes a halogen atom, m is an integer with a value of at least 1, n has a value of from 0 to 3 and x has a value of from 3 to 6.

The reagents for step (I) of the method of the invention are well known materials and may be easily derived from many commercially available silanes of the formula Rn Si (CECH)4 -n Such silanes have been described for example in Journal of Organometallic Chemistry, 21 (1970), 83-90, as is a method for making them. It is preferred for most applications that the value of n is 3 providing a silane witil only one ethynyl group per molecule. The group R denotes a hydrocarbon or substituted hydrocarbon having up to 16 carbon atoms and includes alkyl, aryl, arylalkyl, alkylaryl, alkenyl and substituted alkyl, aryl, arylalkyl, alkylaryl and alkenyl groups.

Examples of such groups ar methyl, methyl, propypl hexyl, dodecyl, phenyl, tolyl, phenylediyl, vinyl, allyl, hexenyl, trifluoropropyl and chloromediyl. It is preferred that die group R denotes a lower alkyl or an aryl group, preferably methyl or phenyl. The lithiated silanes are prepared by reacting the silane with a lithium compound which may be an organolithium compound or lithium metal. This lithiation step may be carried out immediately prior to Step (I) of the method of the invention. Preferred organolidiium materials are butyl lithium and methyl lithium. The cyclic siloxane polymer is also well known and commercially available.The value of x may be 3, 4, 5 or 6 but it is preferred to use a cylcotrisiloxane, most preferably hexamethylcyclotrisiloxane.

Step (I) of the method of die invention may be carried out in the presence of a solvent which is preferably an ether or a hydrocarbon solvent, e.g. dimethyl ether, tetrahydrofuran, hexane, toluene or xylene. It is.

preferred that the solvent is of a more polar nature. Tie reaction is preferably carried out at or below room temperature, i.e. around 0 to 300C. However, elevated temperatures are also acceptable. It is believed that the reaction product of Step (I) of the method of the invention is a compound of die general formula

It will depend on the ratio of the two organosilicon reagents how large the organosiloxane part of the reaction product will be. There is, in theory, no limit to this as long as at least one siloxane unit is present in each molecule. It is, however, preferred that the ratio of -SiOunits to -SiCEC- units is at least 3/1 resulting from the reaction of one cyclotrisiloxane molecule with every silicon-bonded ethynyl group. Much higher ratios are even more preferred.These can range up to about 5000/1, preferably 600/1, most preferably 75/1.

TEle reagents for Step (II) of the method of the invention are the reaction product of Step (I) and a Bronsted acid or triorganosilyl endblocker. Ale latter is preferred and is a silane of the general formula RT?nR3nSiX In the simplest case n has a value of 0 and all R groups are the same. X is preferably a chlorine atom as these silanes are generally commercially more easily available. The groups R and their preferred definitions are as outlined above for the ethynyl silanes. The group R" may be any organic group which contains carbon, hydrogen and oxygen atoms.Examples of such organic groups include those containing ether groups, e.g. oxyalkylene and polyoxyalkylene groups, ester groups, epoxy groups, carbinol groups, ketones, aldehydes, acrylates which may be linked to silicon via a Si-C or Si-O-C bond. The group R" may also be a R group which is linked to the silicon atom via a Si-O-C bond, e.g. alkoxy groups, alkoxyalkoxy groups, aryloxy groups and alkylaryloxy groups. It is preferred that the silanes which are used in Step (II) of the invention are either those in which n has a value of 0 or in which n has a value of 1 where R" denotes an acrylate or methacrylate group. The two silicon-bonded R groups in these silanes are preferably alkyl groups or aryl groups, most preferably methyl or phenyl groups.In the case where n has a value of 0 it is preferred that either all R groups are alkyl or aryl groups or that one of the R groups is a group with aliphatic unsaturation, e.g. vinyl, allyl, hexenyl or styryl while the other R groups are alkyl or aryl groups. Suitable Bronsted acids are any proton donor acids, e.g. HCl, H2S04, H3PO4 or HF. In die case where a Bronsted acid is used the group R' will be a hydrogen atom.

Step (II) is preferably carried out in the presence of a solvent which may conveniently be the solvent in which Step (I) has been carried out.

The copolymer made by the method of the invention may be recovered by standard methods including washing, distidistillation, precipitation and filtration. ile copolymers tend to be liquid polymers of which tile viscosity will depend on the value of m. In cases where m is very high the compounds may be gumlike or solid materials. The copolymers which are made by the method of the invention can be used e.g. in the case where R" is an olefinically unsaturated group for copolymerisation with organic groups having olefinic unsaturation, e.g. styrene groups. They may also be useful for inhibiting metal catalysis due to the presence of the acetylenic unsaturation.

There now follow a number of examples which illustrate the invention wherein all parts and percentages are expressed by weight, unless otherwise stated.

Example 1 6g of trimethylsilylacetylene, which had been distilled over calcium hydride, was dissolved in 10ml of tetrahydrofuran which had been dried over sodium and distilled from potassium- benzophenone. The solution was placed under dry nitrogen and cooled to -78 C. To this 22.5ml of a 2.88 molar solution of n-butyl lithium in hexane was added under stirring.The mixture was allowed to warm up to room temperature at which point 28g of hexamethylcyclotrisiloxane and 32ml of tetrahydrofuran were added. The mixture was stirred for a further 40 minutes at 20"C. The reaction was dien terminated by adding 8g of trimethylchlorosilane. The reaction mixture was distilled under reduced pressure and die residue was filtered.

Fractional distillation at 3.3mbar at 700C yielded (CH3)3SiCEC-[(CH3)25i0]3-Si(CH3)3 at 76% of the theoretical value. The compound was characterised by gas chromatography, mass spectrometry and nuclear magnetic resonance.

Examples 2 - 4 The procedure of Example 1 was repeated except that respectively 12.8g, 26.6g and 12.8g of trimethylsilylacetylene, 569g, 1627g and 1391g of hexamethylcyclotrisiloxane and 23.8g, 36.8g and 20.5g of trimethylchloro silane were used and in that die reaction time was 65, 230 and 155 minutes respectively for Examples 2, 3 and 4. The resulting copolymer according to tie invention was obtained with conversion of respectively 90, 80 and 87% of the total amount of cyclotrisiloxane used in the reaction. The reaction yield was about 90 to 98% in each case. The polymers which had the general structure (CH)3Si-C-C-[(CH3)2SiO]n-Si(CH3)3 were characterised by Si nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), vapour pressure osmometry (VPO) and UV spectroscopy.Tile results of number average molecular weight and theoretical values (Mth) are given in Table I as well as the ratio of mass average molecular weight over number average molecular weight (Mw/Mn).

TABLE I Example Mdi GPC UV NMR VPO Mw/Mn 2 2180 2790 2200 2540 2100 1.21 3 2580 3460 2870 3360 2760 1.25 4 4830 5800 5610 5430 5480 1.17 The results show that the structure of die polymers are consistent, which indicates that the copolymers are not random polymers but have the silethynyl group in consistent positions.

Example 5 The procedure of Example 1 was followed except that 19.7g of trimethylsilylacetylene, 800g of hexamethylcyclo- trisiloxane and 57g of dimethylmethacryloxypropylchloro- silane were used. The resulting copolymer according to the invention was obtained with 81% conversion of the cyclotrisiloxane used in the reaction mixture. The polymer had the general structure (CH3)3Si-CEC-(CH3) SiO] -(CH3)2Si(CH2)30C(O)C(CH3)CH2 and was characterised 5129 nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and vapour pressure osmometry (VPO). The number molecular weight was 1900 (Mth), 2590 (GPC), 2060 (NMR) and 2000 (VPO) and the ratio Mw/Mn was 1.22.

Claims

1. A method of making siloxane silethynyl copolymers of the general formula

which comprises (I) reacting together a lithiated silane of tile general formula RnSi(C--CLi)4 n with a cyclic siloxane polymer of the formula [R2SiO]x, followed by (II) the reaction of the product of (I) with a silane of the formula R" R"n R3-n or with a Bronsted acid wherein R denotes a hydrocarbon or a substituted hydrocarbon group having up to 16 carbon atoms, R' denotes a hydrogen atom or a group of the formula Si(R) nR"n wherein R" denotes an organic group having C, H and one or more 0 atoms present, X denotes a halogen atom, m is an integer with a value of at least 3, n has a value of from 0 to 3 and x has a value of from 3 to 6.

2. A method of making siloxane silethynyl copolymers according to Claim 1 wherein n in RnSi(C ECLi)4n has a value of 3.

3. A method of making siloxane silethynyl copolymers according to Claim 1 or Claim 2 wherein R in RnSi(C=CLi)4 and in [R2SiO]x denotes a lower alkyl or aryl group.

4. A method of making siloxane silethynyl copolymers according to any one of the preceding claims wherein R in RnSi(C-CLi)4 n and in [R2SiO] x denotes methyl or phenyl.

5. A method of making siloxane siletnyl copolymers according to any one of the preceding claims wherein x has a value of 3.

6. A method of making siloxane silethynyl copolymers according to any one of the preceding claims wherein Step (I) is carried out in die presence of an ether or hydrocarbon solvent.

7. A method of making siloxane silethynyl copolymers according to any one of die preceding claims wherein the ratio of -SiOunits to -SiCEC- units in the copolymer is at least 3.

8. A method of making siloxane silethynyl copolymers according to any one of the preceding claims wherein the ratio of -SiOunits to -SiCEC- units in the copolymer is up to 75.

9. A method of making siloxane silethynyl copolymers according to any one of the preceding claims wherein n in R"nR3 SiX has a value of 0.

10. A method of making siloxane silethynyl copolymers according to any one of Claims 1 to 8 wherein n in R"nR3 SiX has a value of 1 and R" is an acrylate or methacrylate group.

11. A method of making siloxane silethynyl copolymers according to any one of the preceding claims wherein Step (II) is carried out in a solvent in which Step (I) was carried out.