Process for preparing polyorganosiloxanes which comprise substan

Details Process for preparing polyorganosiloxanes which comprise substan Process for preparing polyorganosiloxanes which comprise substan

1997-08-15

1999-07-06

Marquis, Melvyn I.

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

Synthetic resins

From silicon reactant having at least one...

528 23, 528 16, 528 18, C08G 7706

Patent

active

059198834

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to a process for preparing polyorganosiloxanes which comprise substantially no cyclic components and have process molcular weight distribution by reacting organosilicon compounds which have no condensable groups in the presence of a catalyst which exclusively promotes equilibration and suppresses formation of cyclic components. The resulting polyorganosiloxanes have a linear or branched structure. They can either be used immediately, for example in silicone rubbers and silicone greases, as components in release agents, in impregnating agents, in antifoams, etc., or are starting compounds for preparing organofunctionally modified polysiloxanes which are obtained by hydrosilylation of the polyorganosiloxanes with hydrocarbons and/or organic polymers.


PRIOR ART

A common process for preparing polyorganosioxanes is the ring-opening polymerization of oligomeric cyclic siloxanes. This process can be accelerated by means, for example, of basic catalysts. Examples thereof are tetramethylammonium hydroxides (EP 492 662; Spinu, M. et al.: J. Polym. Sci. A, Polym. Chem. 29 657 (1991)), cesium hydroxides (DE 26 19 187) or sodium or potassium hydroxide (U.S. Pat. No. 4,122,247; Fish, D. et al.: Makromol. Chem. Macromol. Symp. 32 241 (1990)) and also the siloxanolates and silanolates derived from these hydroxides. In this process, from 10 to 15% by weight of the cyclic starting materials remain in the end product as a result of the thermodynamic equilibrium which is established. To prepare pure polyorganosiloxanes, therefore, a laborious vacuum distillation is required which, especially in the case of highly viscous products, gives rise to considerable technical problems.
When acidic catalysts are used for the ring-opening polymerization, equilibrium cyclic compounds again remain in the product. Examples of customary acidic catalysts are acidic ion exchangers and acid-activated bleaching earths (U.S. Pat. No. 4,831,174), trifluoromethanesulfonic acid (Penczek, S. et al.: Adv. Polym. Sci. 68/69 216 (1986)), and phenyldimethylsilyl perchlorate (U.S. Pat. No. 5,196,559). Even if the polymerization is initiated by an entirely different mechanism, by means of gamma rays (Sigwalt, P. et al.: Makromol. Chem. Macromol. Symp. 32 217 (1990)), because of the cyclic compounds which remain it is impossible to do without a distillation step.
The position of this equilibrium is independent of the catalyst used (Kendrick, T. C. et al. in "The Chemistry of Organosilicon Compounds" ed. by S. Patai and Z. Rappaport, J. Wiley & Sons Ltd 1989, p.1289), of the concentration of catalyst and also of the temperature (Penczek, S. et al.: Adv. Polym. Sci. 68/69 216 (1986)).
Equilibrium cyclic compounds can be regarded as unavoidable, and their formation is known to the skilled worker (Demby, D. H.: Chem. Ind. (Dekker) 1993 43 183). The underlying scientific laws have been investigated both theoretically by the Nmobel prizewinner P. Flory (J. Am. Chem. Soc. 88 3209 (966)) and practically (Brown, J. F. et al. ibid 87 931 (1965)).
Where the intention is to prepare polyorganosiloxanes containing no volatile by-products or unreacted starting materials, then the reaction must be carried out such that the thermodynamic equilibrium is not reached but instead the product composition is controlled kinetically.
It is known that the polycondensation of hydroxy-terminated polyorganosiloxanes can be carried out with kinetic control. Typical catalysts for this reaction are alkylsulfonic acids (EP 314 315), trifluoromethanesulfonic acid (U.S. Pat. No. 4,696,970), alkali metal borates (EP 382 367) and phosphorus nitride halides (DE 12 62 020, DE 22 29 514). These processes require the presence of condensable groups and the removal of volatile by-products of the condensation (e.g. water). However, if the process regime is inappropriate (excessive duration of action of the catalyst), here again there is the risk of the formation of cyclic oligomeric siloxanes (DE 12 62 020).
The polymerization of cyclotrisiloxanes, which bec

REFERENCES:
patent: 3715334 (1973-02-01), Karstedt
patent: 5110969 (1992-05-01), Dittrich et al.
patent: 5270424 (1993-12-01), Drake
patent: 5540221 (1995-05-01), Razzano
Chemical Abstracts, vol. 116, AN-84454a, JP 3-221 530, Sep. 30, 1991.
Derwent Abstracts, AN 74-34821V/19, FR 2 203 821, Jul. 21, 1974.
Derwent Abstracts, AN 82-06448E/04, GB 2 079764, Jan 27, 1982.

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