Curable compositions based on functional polysiloxanes

Details Curable compositions based on functional polysiloxanes Curable compositions based on functional polysiloxanes

1999-05-11

2001-02-13

Wu, David W. (Department: 1713)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S474000, C528S026000, C528S041000

Reexamination Certificate

active

06187863

ABSTRACT:

BACKGROUND OF THE INVENTION
Polysiloxane polyols are well known in the art. Japanese Patent Publication 48-19941 describes polysiloxane polyols which are obtained by the dehydrogenation reaction between a polysiloxane hydride and an aliphatic polyhydric alcohol or polyoxyalkylene alcohol to introduce the alcoholic hydroxy groups onto the polysiloxane backbone. In practice, however, it is difficult to obtain an industrially significant yield of such polysiloxane polyols because such a hydrosilylation reaction readily gels. Another problem encountered with this hydrosilylation reaction is the difficulty in obtaining a solvent capable of dissolving both reactants. Strongly hydrophilic alcohols such as polyglycerols are highly soluble in alcohols and water, but insoluble in hydrocarbon solvents. Polysiloxanes, however, are generally only soluble in hydrocarbon solvents such as toluene or n-hexane.
U.S. Pat. No. 4,431,789 to Okazaki et al. discloses a polysiloxane polyol which is obtained by the hydrosilylation reaction between a polysiloxane containing silicon hydride and a polyglycerol compound having an aliphatically unsaturated linkage in the molecule. Examples of such polyglycerol compounds are those obtained by the reaction of allyl alcohol and glycidol or by the reaction of diglycerin and allyl glycidyl ether. This reaction, a so-called hydrosilylation reaction, is the addition reaction between an organosilicon compound having a hydrogen atom directly bonded to the silicon atom, i.e., a polysiloxane hydride, and an organic compound having aliphatic unsaturation in the molecule carried out in the presence of a catalytic amount of a Group VIII noble metal. The hydrosilylation reaction can proceed readily in the presence of an alcoholic solvent which can dissolve both reactants. The resulting polysiloxane polyols are useful as non-ionic surface active agents. However, the polysiloxane polyols have limited compatibility with organic resins and solvents which restricts their use in solvent-borne coatings.
U.S. Pat. No. 5,260,469 discloses butoxylated polysiloxane polyols which are disclosed as being useful in cosmetics. U.S. Pat. No. 5,248,789 discloses epoxy functional polysiloxanes which are formed by reacting a polysiloxane-containing silicon hydride with allyl glycidyl ether.
The prior art references do not teach further reacting the hydroxyl groups of the polysiloxane polyols with other groups to provide various reactive functional groups pendant from the polysiloxane backbone. Such reactive functional groups allow incorporation of the polysiloxane moiety into curable compositions which can contain a variety of reactive components, including a variety of curing agents. There is no indication in the references of using either the polysiloxane polyols or their derivatives as major components in curable compositions.
SUMMARY OF THE INVENTION
The present invention relates to curable compositions comprising an organic polysiloxane which can contain a variety of reactive functional groups and a curing agent which contains functional groups reactive with the functional groups of the polysiloxanes. Such curable compositions are particularly useful in coating compositions which are curable at both ambient and thermal cure conditions where they provide such excellent properties as increased pot-life, improved tack-time, adhesion, mar resistance and acid etch resistance.
The curable composition of the present invention comprises an organic polysiloxane containing reactive functional groups, said polysiloxane having the following general structure:
where m is at least 1; m′ is 0 to 50; n is 0 to 50; R is selected from the group consisting of HOH and monovalent hydrocarbon groups connected to the silicon atoms; R
a
has the following structure:
R
1
—O—X  (IV)
wherein R
1
is alkylene, oxyalkylene or alkylene aryl; and X is a moiety containing a functional group selected from the group consisting of OH, COOH, NCO, carboxylate such as ester, carbonate and anhydride, primary amine, secondary amine, amide, carbamate and epoxy functional groups; and a component which contains functional groups reactive with the functional groups of the organic polysiloxane.
Preferably, the curable composition comprises:
(a) an organic polysiloxane containing reactive functional groups, the polysiloxane having the formula (II) or (III), where m, m′, n, R, R
a
and X are as described above;
(b) a polymer or oligomer which contains reactive functional groups; and
(c) a curing agent containing functional groups which are reactive with the functional groups of (a) and (b). In one preferred embodiment n+m and n+m′ is 2 or 3.
DETAILED DESCRIPTION OF THE INVENTION
Generally, the curable composition of the present invention comprises:
(a) an organic polysiloxane containing reactive functional groups, the polysiloxane having the formula (II) or (III), where m, m′, n, R, R
a
and X are as described above; and
(b) a curing agent which contains functional groups reactive with the functional groups of (a).
It should be appreciated that the various R groups can be the same or different, and it is usually the case that the R groups will be mixed groups or entirely monovalent hydrocarbon groups.
By monovalent hydrocarbon groups is meant organic groups containing essentially carbon and hydrogen. The hydrocarbon groups may be aliphatic, aromatic, cyclic or acyclic and may contain from 1 to 24 (in the case of aromatic from 3 to 24) carbon atoms. Optionally, the hydrocarbon groups may be substituted with heteroatoms, typically oxygen. Examples of such monovalent hydrocarbon groups are alkyl, alkoxy, aryl, alkaryl or alkoxyaryl groups.
By alkylene is meant acyclic or cyclic alkylene groups having a carbon chain length of from C
2
to C
25
. Examples of suitable alkylene groups are those derived from propene, butene, pentene, 1-decene, isoprene, myrcene and 1-heneicosene. By oxyalkylene is meant an alkylene group containing at least one ether oxygen atom and having a carbon chain length of from C
2
to C
25
, preferably of from C
2
to C
4
. Examples of suitable oxyalkylene groups are those associated with trimethylolpropane monoallylether, pentaerythritol monoallylether, trimethylolpropane diallylether, polyethoxylated allyl alcohol and polypropoxylated allyl alcohol. By alkylene aryl is meant an acyclic alkylene group containing at least one aryl group, preferably phenyl, and having an alkylene carbon chain length of from C
2
to C
25
. The aryl group may optionally be substituted. Suitable substituent groups may include hydroxyl, benzyl, carboxylic acid and aliphatic groups. Examples of suitable alkylene aryl groups include styrene and 3-isopropenyl-&agr;, &agr;-dimethylbenzyl isocyanate.
Formulae (II) and (III) are diagrammatic, and it is not intended to imply that the parenthetical portions are necessarily blocks, although blocks may be used where desired. In many cases the compound is more or less random, especially when more than a few siloxane units are employed and when mixtures are used. In those instances where more than a few siloxane units are used and it is desired to form blocks, oligomers are first formed and then these are joined to form the block compound. By judicious choice of reactants, compounds having an alternating structure or blocks of alternating structure may be used.
Preferably, the curable composition comprises:
(a) an organic polysiloxane containing reactive functional groups, the polysiloxane having the formula (II) or (III), where m, m′, n, R, R
a
and X are as described above;
(b) a polymer which contains reactive functional groups; and
(c) a curing agent containing functional groups which are reactive with the functional groups of (a) and (b). In one preferred embodiment n+m and n+m′ is 2 or 3.
It should be mentioned that when both (a) and (b) are present, the reactive functional groups of (a) and (b) can be the same or different, but both must be reactive with the functional groups of the curing agent. Examples of such reactive

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