Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-07-11
2003-06-03
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S014000, C528S020000, C528S032000, C528S033000, C528S037000, C525S477000
Reexamination Certificate
active
06573355
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel method for the preparation of an organopolysiloxane having a branched molecular structure as a class of silicone products, which is useful in a great variety of industrial application fields.
Among the great variety of silicone products, as is well known, those organopolysiloxanes prepared by utilizing the so-called hydrosilation reaction are particularly important and have usefulness in a wide field of applications. The above mentioned hydrosilation reaction is conducted usually between an alkenyl group-containing organopolysiloxane and an organohydrogenpolysiloxane having hydrogen atoms directly bonded to the silicon atoms in the presence of a catalytic amount of a platinum compound to promote the addition reaction.
The alkenyl group-containing organopolysiloxane pertaining to the hydrosilation reaction is not particularly limitative relative to the molecular structure depending on the desired products. When an alkenyl group-containing organopolysiloxane having a branched molecular structure is used, a product organopolysiloxane of good reactivity containing a controlled amount of the alkenyl groups at the molecular chain ends to comply with the requirements in different applications can be prepared by adequately selecting the number of branches in the starting alkenyl group-containing organopolysiloxane (see Japanese Patent Publication 3-19267 and Japanese Patent 2965231). However, only very few reports are available on the method for the preparation of such an alkenyl-terminated organopolysiloxane of a branched molecular structure and the only methods thus far disclosed are each very complicated to inhibit practical application of the method.
For example, Japanese Patent Publication 3-19267 proposes a method in which an alkyl trimethoxy silane and octamethyl cyclotetrasiloxane are subjected to a polymerization reaction in the presence of an alkaline catalyst and then this polymer is subjected to a hydrolysis-condensation reaction with tetramethyl divinyl disiloxane under an acidic condition and a method in which an alkyl trimethoxy silane is subjected to hydrolysis-condensation with tetramethyl divinyl disiloxane under an acidic condition followed by a polymerization reaction thereof with octamethyl cyclotetrasiloxane in the presence of an alkaline catalyst. These methods, however, are disadvantageous because, in addition to complicacy of the method as an industrial process, the viscosity of the final product can hardly be controlled with a large variation as a consequence of the alkaline polymerization in the presence of a large amount of the alkoxy groups and the reaction mixture is sometimes under a danger of bumping due to the water and/or alcohol contained therein.
SUMMARY OF THE INVENTION
The present invention accordingly has an object to provide, in view of the above described problems and disadvantages in the prior art methods, a novel and efficient industrial method for the preparation of an organopolysiloxane having a branched molecular structure from starting materials of good availability.
Thus, the present invention provides a method for the preparation of an organopolysiloxane having a branched molecular structure which comprises the steps of:
(A) Mixing
(A1) from 1 to 100 parts by weight of a first organopolysiloxane represented by the average unit formula
(R
1
3
SiO
½
)
m
(R
1
SiO
{fraction (3/2)}
)
n
[R
1
(R
2
O)SiO]
q
, (I)
in which R
1
is, each independently from the others, a monovalent hydrocarbon group having 1 to 8 carbon atoms selected from the group consisting of alkenyl groups, alkyl groups and phenyl group, R
2
is a hydrogen atom, methyl group or ethyl group and the subscripts n, and q are each 0 or a positive number with the proviso that (n+q)/m is in the range from 0.6 to 1.5 and q/(m+n) is 0 or a positive number not larger than 0.05;
(A2) from 1 to 100 parts by weight of a cyclic dialkylsiloxane oligomer, and
(A3) from 1 to 100 parts by weight of a polydiorganosiloxane represented by the structural formula
R
3
3
Si—O—(SiR
3
2
—O)
r
—SiR
3
3
, (II)
In which R
3
is, each independently from the others, a monovalent hydrocarbon group having 1 to 8 carbon atoms selected from the group consisting of alkenyl groups, alkyl groups and phenyl group and the subscript r is 0 or a positive integer not exceeding 100, to give a siloxane mixture;
(B) admixing the siloxane mixture with an alkaline compound; and
(C) heating the siloxane mixture to effect siloxane rearrangement polymerization of the organopolysiloxanes (A1), (A2) and (A3).
In particular, it is preferable that at least one of the three R
1
groups in one of the siloxane units (R
1
3
SiO
½
) in the organopolysiloxane (A1) is an alkenyl group.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The starting material in the method of the present invention is a combination of three kinds of organopolysiloxanes (A1), (A2) and (A3) mixed together in a specified mixing proportion to give a siloxane mixture. The organopolysiloxane (A1) is represented by the average unit formula (I) given above, in which each R
1
is, independently from the others, a monovalent hydrocarbon group having 1 to 8 carbon atoms selected from the group consisting of alkenyl groups such as vinyl, allyl, butenyl and pentenyl groups, alkyl groups such as methyl and ethyl groups and phenyl group and the subscripts m, n and q are each 0 or a positive number with the proviso that (n+q)/m is in the range from 0.6 to 1.5 and q/(m+n) is 0 or a positive number not larger than 0.05.
When the value of (n+q)/m is smaller than 0.6, the number of the branching points in the branched-structure organopolysiloxane prepared by using such a starting organopolysiloxane is undesirably limited to 3 or less to cause a decrease in the usefulness of the product in applications. When the value of (n+q)/m is larger than 1.5, the molar proportion of the units R
1
SiO
{fraction (3/2)}
is so large as to cause a difficulty in the preparation of the product organopolysiloxane. When the value of q/(m+n) is larger than 0.05, the organopolysiloxane has a too large number of remaining alkoxy groups to cause instability or uncontrollability of the viscosity thereof.
The organopolysiloxane (A1) can be prepared by subjecting a mixture of a trialkoxy methyl silane, dialkenyl tetramethyl disiloxane and hexamethyl disiloxane in an alcoholic solution to a cohydrolysis reaction in the presence of an acidic catalyst followed by neutralization of the catalyst, removal of the by-product alcohol, washing with water and stripping of the unreacted reactants.
The second organopolysiloxane reactant (A2) pertaining to the reaction of the inventive method is a cyclic dialkylsiloxane oligomer including those represented by the general formulas [Me
2
SiO]
t
, [EtMe-SiO]
t
and [PrMeSiO]
t
, in which Me is a methyl group, Et is an ethyl group, Pr is a propyl group and the subscript t is a positive integer of 3 to 10. These cyclic dialkylsiloxane oligomers can be used either singly or as a combination of two kinds or more.
The third organopolysiloxane reactant (A3) pertaining to the reaction of the inventive method is a diorganopolysiloxane having a linear molecular structure as represented by the above given general formula (II), in which each R
3
is, independently from the others, a monovalent hydrocarbon group having 1 to 8 carbon atoms exemplified by alkenyl groups such as vinyl, allyl, butenyl and pentenyl groups, alkyl groups such as methyl and ethyl groups and aryl groups such as phenyl group and the subscript r is 0 or a positive integer not exceeding 100.
The mixing proportion of the three organopolysiloxane reactants (A1), (A2) and (A3) is selected depending on several parameters characterizing the desired organopolysiloxane product having a branched molecular structure such as the average degree of polymerization and number of the branching points in a molecule to meet the intended application
Irifune Shinji
Ogawa Masahiko
Dawson Robert
Millen White Zelano & Branigan P.C.
Robertson Jeffrey B.
Shin-Etsu Chemical Co. , Ltd.
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