Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1997-03-20
2003-06-10
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C508S383000, C508S383000
Reexamination Certificate
active
06576733
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a novel curable composition which comprises a reactive silicon group-containing oxypropylene polymer, an organic carboxylic acid salt of divalent tin, and an organic amine compound.
Oxypropylene polymers containing a reactive silicon group (a group which is a silicon atom-containing group with a hydroxyl group or a hydrolyzable group being bound to the silicon atom and can form a siloxane bond) can occur as liquid polymers and, upon exposure to moisture, etc., harden to give rubber-like cured substances at room temperature. Therefore these polymers are used as elastic sealants and the like for buildings. In using these polymers, they may be used in the form of compositions containing an organic carboxylic acid salt of divalent tin and an organic amine compound, which serve as curing catalysts, so that the cured products can be improved in resilience (Japanese Kokai Patent Publication No. 55-9669). The term “resilience” as used herein means the rate of recovery after 24 hours of the size of a test piece from a cured product as determined by compressing the test piece by 20%, for instance, then keeping the same in an atmosphere maintained at 40° C. in that compressed state for 24 hours and thereafter relieving the last piece from the compression. It is necessary that the resilience should be high.
The present inventors made investigations in a search for curable compositions containing a reactive silicon group-containing oxypropylene polymer and having further improved resilience and, as a result, found that resilience can be improved when the oxypropylene polymer has a narrower molecular weight distribution. This finding has now led to the present invention.
SUMMARY OF THE INVENTION
The curable composition according to the invention comprises:
(A) an oxypropylene polymer which contains, in its main polymer chain, a repeating unit of the formula
and which has at least one silicon atom-containing group (reactive silicon group) with a hydroxyl group or a hydrolyzable group being bound to the silicon atom and has an Mw/Mn (weight average molecular weight
umber average molecular weight) ratio of not more than 1.6 and a number average molecular weight (Mn) of not less than 6,000,
(B) an organic carboxylic acid salt of divalent tin, and
(C) an organic amine compound.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The reactive silicon group contained in the oxypropylene polymer, namely component (A), to be used in the practice of the invention is not limited to any particular species but may typically include, for example, groups of the following general formula (1)
In the above formula, R
1
and R
2
each is an alkyl group containing 1 to 20 carbon atoms, an aryl group containing 6 to 20 carbon atoms, an aralkyl group containing 7 to 20 carbon atoms or a triorganosiloxy group of the formula (R′)
3
SiO—. Where there are two or more R
1
or R
2
groups, they may be the same or different. R′ is a monovalent hydrocarbon group containing 1 to 20 carbon atoms. The three R′ groups may be the same or different. X is a hydroxyl group or a hydrolyzable group and, where there are two or more X groups, they may be the same or different. The number a is 0, 1, 2 or 3 and b is 0, 1 or 2. The number b may vary in the m groups of the formula
m is an integer of 0 to 19. The following condition shall be satisfied: a+&Sgr;b≧1.
The hydrolyzable group represented by the above-mentioned X is not particularly limited but may be any hydrolyzable group known in the art. More specifically, there may be mentioned a hydrogen atom, a halogen atom, an alkoxy group, an acyloxy group, a ketoximato group, an amino group, an amido group, an acid amido group, an aminoxy group, a mercapto group, an alkenyloxy group and the like. Among these, the hydrogen atom and alkoxy, acyloxy, ketoximato, amino, amido, aminoxy, mercapto and alkenyloxy groups are preferred. From the viewpoint of mild hydrolyzability and easy handling, alkoxy groups, for example methoxy, are particularly preferred.
One to three such hydrolyzable groups or hydroxyl groups may be bound to one silicon atom, and (a+&Sgr;b) is preferably equal to 1 to 5. Where there are two or more hydrolyzable groups or hydroxyl groups in the reactive silicon group, they may be the same or different.
The reactive silicon group may contain one silicon atom or two or more silicon atoms. In the case of a reactive silicon group comprising silicon atoms linked to one another via a siloxane bonding or the like, the group may contain about 20 silicon atoms.
Reactive silicon groups of the following general formula (2) are preferred because of ready availability.
In the above formula, R
2
, X and a are as defined above.
Specific examples of R
1
and R
2
appearing in the general formula (1) given hereinabove include, among others, alkyl groups, such as methyl and ethyl, cycloalkyl groups, such as cyclohexyl, aryl groups, such as phenyl, aralkyl groups, such as benzyl, and triorganosiloxy groups of the formula (R′)
3
SiO— in which R′ is methyl or phenyl. The methyl group is particularly preferred as R
1
, R
2
and/or R′.
The oxypropylene polymer should recommendably contain at least one, preferably 1.1 to 5 reactive silicon groups per molecule thereof. When the number of reactive silicon groups contained in the polymer on a per-molecule basis is less than 1, the curability becomes inadequate and good rubber elastic behavior can hardly be developed.
The reactive silicon group may be positioned terminally or internally to the molecular chain of the oxypropylene polymer. When the reactive silicon group occurs terminally to the molecular chain, the oxypropylene polymer component contained in the finally formed cured product can have an increased number of effective network chains and therefore a rubber-like cured product showing high strength, high elongation and low elasticity can readily be obtained.
The oxypropylene polymer, which constitutes the main polymer chain in the component (A) to be used in the practice of the invention, contains a repeating unit of the formula
This oxypropylene polymer may be straight-chained or branched, or a mixture of these. It may further contain another monomer unit or the like. It is preferable, however, that the polymer contains the monomer unit represented by the above formula in an amount of at least 50% by weight, more preferably at least 80% by weight.
The oxypropylene polymer that can effectively be used has a number average molecular weight (Mn) of not less than 6,000, preferably 6,000 to 30,000. Furthermore, in this oxypropylene polymer, the weight average molecular weight
umber average molecular weight ratio (Mw/Mn) is not more than 1.6, hence the molecular weight distribution is very narrow (the polymer is highly monodisperse). The value of Mw/Mn should preferably be not higher than 1.5, more preferably not higher than 1.4. The molecular weight distribution can be measured by various methods. Generally, however, the measurement method most commonly used is gel permeation chromatography (GPC). Since the molecular weight distribution is narrow in that manner despite the great number average molecular weight, the curable composition of the invention has a low viscosity before curing, hence is easy to handle and, after curing, shows a good rubber elastic behavior.
The reactive silicon group-containing oxypropylene polymer to be used as component (A) in the practice of the invention is preferably prepared by introducing a reactive silicon group into an oxypropylene polymer having a functional group.
Oxypropylene polymers having a high molecular weight with a narrow molecular weight distribution and having a functional group can hardly be obtained by the conventional method of polymerizing oxypropylene (anionic polymerization using a caustic alkali) or by the chain extension reaction method using oxypropylene polymers obtained by the conventional method as starting materials. They can be obtained, however, by such special polymerization methods
Fujita Masayuki
Homma Michihide
Wakabayashi Hiroshi
Jordan and Hamburg LLP
Kanegafuchi Chemical Industry Co. Ltd.
Moore Margaret G.
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