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...
Reexamination Certificate
2003-04-04
2004-05-18
Szekely, Peter (Department: 1714)
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...
C525S342000, C528S024000, C528S025000
Reexamination Certificate
active
06737470
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally directed to a curable sealant composition. It is more specifically directed to a poly(conjugated diene) curable sealant composition.
Polymers, such as polyisobutylene, have found applications in building sealants due to inherent moisture impermeability. To function as a sealant, a curable group is usually combined with the isobutylene units, resulting in, for example, alkoxy-silane functionalized polyisobutylene. Current polyisobutylene building sealants are often formed using a two-step process. The polymer backbone is formed and endcapped with a reactive functional group. The reactive functional group is then reacted, often in the presence of a metal catalyst, resulting in the presence of a curable group on the polymer backbone. In one specific example, the polymer is endcapped with allyl groups through the use of allyltrimethylsilane. Then, the allyl group is hydrosilylated using a platinum catalyst and an appropriate silane. In another method, the reactive functional groups are dispersed throughout the polymer backbone, followed by the reaction of the functional groups to form curable siloxane groups within the polymer backbone. This two-step process is both expensive and cumbersome.
Accordingly, polyisobutylene-based sealants may suffer from several drawbacks. Moreover, such sealants are (i) often expensive to prepare and (ii) strongly influenced by the relatively high cost of isobutylene monomer. Furthermore, they are often limited to use as a two-part building sealant, requiring combination of the sealant with a catalyst immediately prior to use. If the catalyst is added to the sealant too soon, premature curing may occur, resulting in difficult, and inconsistent, application of the sealant. The requirement for end-user mixing may also result in inconsistencies in the building sealants due to carelessness on the part of the end-user.
It would be desirable to have available a less expensive, more efficient process to directly prepare alkoxysilane functionalized sealant compositions with low polydispersity.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, a curable sealant composition is provided. The composition includes a polymer including at least conjugated diene contributed monomer units in a backbone of the polymer and terminal groups including silicon. The composition further includes additional curable sealant ingredients selected from the group consisting of plasticizers, fillers, reinforcing agents, modifiers, curing catalysts/hardeners, stabilizers, and mixtures thereof.
In a second embodiment of the present invention, a process for forming a curable sealant is provided. The process comprises initiating a living polymerization of conjugated diene monomer units with a multifunctional substituted initiator, and terminating the polymerization with a tetra-substituted silicon group.
In another embodiment of the present invention, a curable sealant is provided. The curable sealant includes a poly(conjugated diene) backbone having a M
w
between about 5,000 and 60,000, and at least one alkoxysilane end group. The composition further includes additional curable sealant ingredients selected from the group consisting of plasticizers, fillers, reinforcing agents, modifiers, curing catalysts/hardeners, stabilizers, and mixtures thereof.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The present invention is directed to a curable sealant comprised of polymers with conjugated diene monomer units and curing groups. The curing groups may be terminal groups, resulting in a telechelic polymer composition. The polymer compositions of the present invention preferably have a polydispersity ratio less than about 1.8, more preferably less than about 1.7, and most preferably less than about 1.6. The polydispersity ratio is represented by the ratio of M
w
to M
n
, with a ratio of about one representing a composition that is substantially monodisperse. If the polydispersity is too high, the resultant sealants may demonstrate poor tensile properties and poor workability. “Workability” refers to the rate at which the viscosity of the sealant increases as it begins to cure.
The polymer composition of the present invention includes a polymer backbone with monomer units selected from the group consisting of C
4
-C
8
conjugated dienes, and mixtures thereof. Preferred conjugated dienes include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 1,3-hexadiene, 2-methyl-1,3-pentadiene, 3,4-dimethyl-1,3-hexadiene 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, phenyl-1,3-butadiene, and mixtures thereof. An especially preferred conjugated diene is 1,3-butadiene.
The conjugated diene backbone preferably has a weight average molecular weight (M
w
) between about 5,000 and 60,000, more preferably between about 10,000 and 35,000. While the backbone is preferably linear, it may be crosslinked to form branched structures.
The polymer composition may also include additional monomer units in the polymer backbone. Suitable additional monomer units may include vinyl aromatic hydrocarbon monomers, ethylene oxide, propylene oxide, styrene oxide, ethylene sulfide, propylene sulfide, styrene sulfide, acetaldehyde, propionaldehyde, isobutyraldehyde, n-caproaldehyde, acetthioaldehyde, propionthioaldehyde, isbutyrthioaldehyde, n-caprothioaldehyde, 3-dimethyl-oxycyclobutane, 3-diethyloxycyclobutane, 3-methylethyl-oxycyclobutane, 3-diemethylthiocycylobutane, 3-diethyl-thiocyclobutane, 3-methylethylthiocyclobutane, methylethyl thioketone, methyl isopropyl thioketone and diethyl thioketone, heterocyclic nitrogen containing monomers, and mixtures thereof Exemplary vinyl aromatic hydrocarbon monomers for use in the present invention include one or more of styrene, &agr;-methyl styrene, 1-vinyl naphthalene, 2-vinyl naphthalene, 1-&agr;-methyl vinyl naphthalene, 2-&agr;-methyl vinyl naphthalene, as well as alkyl, cycloalkyl, aryl, alkaryl, and aralkyl derivatives thereof, in which the total number of carbon atoms in the combined hydrocarbon is not greater than about 18, and mixtures thereof. Exemplary heterocyclic nitrogen containing monomers include pyridine and quinoline derivatives containing at least 1 vinyl or alphamethylvinyl group such as 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 3-ethyl-5-vinylpyridine, 3-methyl-5-vinylpyridine, 3,5-diethyl-4-vinylpyridine and similar mono- and di-substituted alkenyl pyridines and like quinolines such as 2-vinylquinoline, 3-vinylquinoline, 4-vinylquinoline and mixtures thereof.
In the event additional monomer units are employed, the polymer composition preferably includes between about 1 and 99 wt % conjugated diene contributed monomer units, more preferably between about 50 and 99 wt %, and most preferably between about 70 and 99 wt %. The polymer composition further preferably includes between about 1 and 99 wt % additional 20 contributed monomer units, e.g., vinyl aromatic hydrocarbon, more preferably between about 1 and 50 wt %, most preferably between about 1 and 30 wt %.
The sealant can be formed by any polymerization technique known to the skilled artisan. Preferably, the polymerization is initiated via addition of anionic initiators that are known in the art as useful in the polymerization of diene monomers and/or copolymerization of diene monomers and vinyl aromatic hydrocarbons. A multi-functionalized lithium initiator may be used to initiate the preferred living polymerization reaction. Lithium initiators with two or more active initiation sites will initiate a living polymerization with at least two living polymerization sites on each living polymer chain. The polymer backbone may have an initiator residue derived from the multi- or di-functional lithium initiator remaining at the initiation site. Especially preferred initiators include 1,3-bis(1-lithio-1,3-dimethylpentyl)benzene, 1,3-phenylenebis(3-methyl-1-phenylpentylidene)dilithium, 1,3-phyenylenebis[3-methyl-1(methylphenyl)pentylidene]dilithium, initiators derived from reaction of two mola
Poulton Jason T.
Yako Takayuki
Yan Yuan-Yong
Bridgestone Corporation
McCollister Scott A.
Palmer Meredith E.
Szekely Peter
LandOfFree
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