Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1998-03-23
2000-01-04
Dawson, Robert
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524719, 528 18, C08K 534
Patent
active
060111127
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to organopolysiloxane compositions which can be stored in the absence of moisture and which cure to form elastomers in the presence of moisture at room temperature with the elimination of alcohols, said compositions being distinguished by a particularly high storage stability.
BACKGROUND OF THE INVENTION
In the context of the present invention, the term organopolysiloxanes is intended to include dimeric, oligomeric and polymeric siloxanes.
organopolysiloxane compositions which can be stored in the absence of moisture and which crosslink in the presence of moisture at room temperature with the elimination of alcohols are called RTC 1-alkoxy compositions and have been known for a long time. They consist essentially of silicone polymer with organyloxy end groups, crosslinking agent with at least three hydrolyzable groups, catalyst and, if appropriate, additives. This advantage of these RTC 1-alkoxy systems is that, in the crosslinking process, they only release odorless, neutral, non-polluting cleavage products--namely alcohols.
A substantial disadvantage of RTC 1-alkoxy compositions is the reduced storage stability compared with the corresponding acetic, oxime and amine systems. This means that although the RTC 1-alkoxy composition cures to form in elastomer in the desired manner after preparation, these curing properties usually disappear when the compositions are stored in the absence of air. After a prolonged storage time, therefore, the curing time to form elastomers is generally observed to be longer and the mechanical properties of said elastomers are markedly poorer than those of the original elastomers. In the worst case, the compositions may completely fail to cure to form elastomers after storage. The reason for this change in curing with time is often the equilibration of polymer chains with free alcohol dissolved in the composition, under catalysis by the metalorganic condensation catalyst; this generates polymer ends with an alkoxy group which are too unreactive to react further and give a network under the applied conditions (room temperature). Crosslinking does not therefore take place. The alcohol for this undesired equilibration reaction is produced from the reaction of the alkoxy crosslinking agent with water and other OH groups, e.g. silanol groups, which, in the preparation of RTC 1-alkoxy compositions, unavoidably enter the composition via the polymer, the filler and other possible additives and via the method of preparation (reaction vessel, preparation in the atmosphere). There have therefore already been numerous attempts to prevent the described change in the curing properties of RTC 1-alkoxy compositions on storage. In this connection, reference may be made, for example, to EP-A 236 042 (Dow Corning Corp.; issued on Sep. 09, 1987) and DE-A 38 01 389 (Wacker-Chemie GmbH; issued on Jul. 27 1989) or corresponding U.S. Pat. No. 4,942,211.
Furthermore U.S. Pat. No. 4,395,526 (General Electric Co.; issued on Jul. 26, 1983) claims silanes of the formula (R.sup.1 O).sub.4-a-b SiR.sup.2.sub.b X.sub.a, in which R.sup.1 and R.sup.2 are hydrocarbon radicals, X is a hydrolyzable group selected from amido, amino, carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato and ureido radicals, a is equal to 1 to 4, b is equal to 0 to 3 and a+b is equal to 1 to 4.
U.S. Pat. No. 4,417,042 (General Electric Co.; issued on Nov. 22, 1983) describes Si--N-containing compounds in crosslinkable compositions, selected from the group of silanes of the formula YR.sup.3.sub.2 Si--NR.sup.3 --SiR.sup.3.sub.2 Y, in which Y.dbd.R.sup.3 or R.sup.2.sub.2 --N--, or polymers of 3-100 mol % of R.sup.2.sub.2 N--SiR.sup.3.sub.2 --O--, R.sup.2.sub.2 N--SiR.sup.3.sub.2 --NR.sup.2 --, R.sup.2.sub.3 Si--NR.sup.2 --, --SiR.sup.3.sub.2 --NR.sup.2 --, .dbd.SiR.sup.3 --NR.sup.2 --or --Si--NR.sup.2 -- units and 0-97 mol % of R.sup.3.sub.c SiO.sub.(4-c)/2, in which c=0, 1, 2 or 3.
U.S. Pat. No. 4,467,063 (General Electric Co.; issued on Aug. 21, 1984) discloses the use of N-silyl-subst
REFERENCES:
patent: 4395526 (1983-07-01), White et al.
patent: 4417042 (1983-11-01), Dziark
patent: 4467063 (1984-08-01), Lockhart
patent: 4517337 (1985-05-01), Lockhart et al.
patent: 4797439 (1989-01-01), Peccoux
patent: 4801673 (1989-01-01), Bosch et al.
patent: 4942211 (1990-07-01), Sommer et al.
Dorsch Norman
Oberneder Stefan
Pilzweger Erich
Stepp Michael
Dawson Robert
Robertson Jeffrey B.
Wacker-Chemie GmbH
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