Polymerization of siloxanes

Details Polymerization of siloxanes Polymerization of siloxanes

1999-12-09

2002-03-05

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S021000, C528S037000

Reexamination Certificate

active

06353075

ABSTRACT:

FIELD OF INVENTION
This invention relates to the polymerization of siloxanes catalyzed by certain phosphazene bases.
BACKGROUND OF INVENTION
In EP0860461-A, there is described a process for the ring-opening polymerization of cyclosiloxanes, which comprises contacting a cyclosiloxane with 1 to 500 ppm of a phosphazene base, by weight of cyclosiloxane, in the presence of water. In GB 2311994, there is described a method of effecting polycondensing which comprises contacting at a temperature of from 0 to 200° C. and a pressure up to 350 torr, a silanol-containing organosiloxane with an amount of a peralkylated phosphazene base which is effective for polycondensation of said organosiloxane. The preferred peralkylated phosphazene base has the formula
wherein R
#
is a C
1-4
alkyl radical, R* is a C
1-10
alkyl radical and n is 2 or 3. GB 2279945 discloses that short chain linear acidic phosphazenes of the formulae OCl
2
P(NPCl
2
)
n
NPCl
2
OH, OCl
2
P(NPCl
2
)
n
N(H)PCl
2
O or OCl
2
P(NPCl
2
)
n
NPCl
3
as well as products of their reaction with water, alcohols and organosiloxanes are active catalysts for polycondensation and redistribution of organosiloxane polymers. U.S. Pat. No. 5,380,902 discloses a process for the condensation and/or equilibration of organosilicon compounds in the presence of oxygen-containing phosphazenes of the formula Cl
3
P═N(—PCl
2
═N)
n
—PCl
2
O or HO—PCl
2
═N(—PCl
2
═N)
n
—PCl
2
O.
SUMMARY OF INVENTION
This invention is a process for polymerizing siloxanes comprising mixing a first siloxane having silicon-bonded groups R′, wherein R′ is selected from the group consisting of hydroxyl and a hydrocarbonoxy group having 1 to 8 carbon atoms, and a second siloxane having no silicon-bonded groups R′ together with a phosphazene base catalyst and allowing the siloxanes to polymerize so that the siloxane having silicon-bonded groups R′ condenses and the cyclic or linear siloxane having no silicon-bonded R′ groups polymerizes by equilibration.
We have surprisingly found that phosphazene bases are at least as effective as catalysts for the combined polymerization via condensation and polymerization by equilibration, when carried out simultaneously. This is unexpected as there is usually a substantial difference in catalytic rate between both reactions.
The speed of polymerization via equilibration seems to be substantially faster than for the condensation reaction described in this application. It was therefore surprising to find that the same catalyst can be used for combined polymerization via condensation and equilibration by mere mixture of the siloxane materials used for condensation polymerization, with cyclic siloxanes or certain linear siloxanes as described below, which are suitable for polymerization by equilibration. The combined reaction did not seem to favor one polymerization reaction to the detriment of the other.
DETAILED DESCRIPTION OF THE INVENTION
A process according to the invention for polymerizing siloxanes using a phosphazene catalyst comprises mixing a first siloxane having silicon-bonded groups R′, where R′ denotes a hydroxyl group or a hydrocarbonoxy group having 1 to 8 carbon atoms, and a second siloxane, either cyclic or linear, having no silicon-bonded groups R′, together with a phosphazene base catalyst and allowing the siloxane having silicon-bonded groups R′ to condense and the cyclic and linear siloxanes having no silicon-bonded R′ groups to polymerize by equilibration.
In principle, any non-ionic phosphazene base is suitable for use in the present invention. Phosphazene bases generally include the following core structure P═N—P═N, in which free N valencies are linked to hydrogen or hydrocarbon, i.e. form amino groups, and free P valencies are linked to amino groups.
Phosphazene bases and routes for their synthesis have been described in the literature, for example in Schwesinger et al., Liebigs Ann. 1996, 1055-1081. Some phosphazene bases are commercially available e.g. from Fluka Chemie AG, Switzerland.
The phosphazene bases preferably have at least 3 P-atoms. Preferred phosphazene bases are non-ionic phosphazenes of the following general formulae:
((R
1
2
N)
3
P═N—)
x
(R
1
2
N)
3−x
P═NR
2
in which R
1
, which may be the same or different in each position, is hydrogen or an optionally substituted hydrocarbon group, preferably a C
1
-C
4
alkyl group, or in which two R
1
groups bonded to the same N atom may be linked to complete a heterocyclic ring, preferably a 5- or 6-membered ring; R
2
is hydrogen or an optionally substituted hydrocarbon group, preferably a C
1
-C
20
alkyl group, more preferably a C
1
-C
10
alkyl group and x is 1, 2 or 3, preferably 2 or 3. Particularly suitable compounds are those where R
1
is methyl, R
2
is tertiary butyl or tertiary octyl and x is 3.
The phosphazene base is found to be a very powerful catalyst for the polymerization, and can therefore be present in a relatively low proportion, for example from 2 to 200 ppm by weight, based on the weight of siloxanes. The proportion of catalyst actually used will be selected depending on the speed of polymerization that is sought.
The process can be carried out in the presence of water, a silanol or an alcohol, or in the absence of any of these compounds. It is surprising that there is neither any need to have water present, nor is there any need to eliminate water prior to the commencement of the polymerization. Water may be present in the reaction, preferably at least 0.5 or 1 up to 10 mols per mol of the phosphazene base. The silanol, for example a trialkyl silanol, or alcohol, for example an alkanol having 1 to 8 carbon atoms, can be used in similar amounts. It is possible to use higher proportions of water, and this can have the benefit of enabling greater control over the polymerization reaction, as described in more detail below. It is however preferred to carry out the reaction with conditions where water will be removed during the process, e.g. by working in a system which encourages a large liquid gas interface.
The polymerization can be carried out in bulk or in the presence of a solvent. Suitable solvents are liquid hydrocarbons or silicone fluids. The phosphazene base catalyst can be diluted in a hydrocarbon solvent, such as hexane or heptane, or dispersed in a silicone fluid such as polydiorganosiloxanes. Where the phosphazene base catalyst is initially in a solvent such as hexane, the hexane can be removed by evaporation under vacuum, and the catalyst dispersed in a silicone fluid to give a stable clear solution. When this silicone dissolved catalyst is used for polymerization reactions, the catalyst disperses evenly and gives reproducible results. The catalyst can also be dissolved in water, and this has the advantage of moderating and enabling greater control over the polymerization reaction, as described below.
The polymerization reaction can be carried out at ambient temperature or under heating at a temperature as high as 250° C. or even 300° C. or higher. Heating, for example to 100° C. or higher, is appropriate when the catalyst activity has been moderated as described below. The preferred temperature range may be from 50 to 170° C. The time taken for polymerization will depend on the activity of the catalyst in the chosen system, and on the desired polymer product. In the absence of moderation, the phosphazene base catalysts are sufficiently active to convert siloxanes to high molecular weight polysiloxane gums within a short time frame.
The siloxanes having silicon-bonded groups R′ are for example, organosiloxanes having the general formula (3):
In formula (3), R
3
is a hydrogen or an alkyl or aryl group having up to 8 carbon atoms, each R
4
is the same or different and denotes a monovalent hydrocarbon group preferably having 1 to 18 carbon atoms or halogenated hydrocarbon group preferably having 1 to 18 carbon atoms and t is an integer having a value of from at least 2.
Preferably R
4
denotes an alkyl group h

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