Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-07-19
2003-03-04
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S105000, C525S106000, C525S276000, C526S279000
Reexamination Certificate
active
06528585
ABSTRACT:
The invention relates to crosslinkable polymers which contain hydrolyzable silane groups and also a process for their preparation by means of a grafting reaction. The invention further relates to a process for producing moldings by shaping and crosslinking the crosslinkable polymers. The invention finally relates to the moldings produced in this way.
1. PRIOR ART
Moldings made of crosslinked polymers have, inter alia, good mechanical properties, high thermal stability and good resistance to chemical and physical influences. Such moldings are produced starting from a crosslinkable polymer which is brought to the desired shape and crosslinked. A known process uses standard polymers which are crosslinked by electron beams after shaping. This process is costly in terms of apparatus and requires comprehensive radiation protection measures. Standard polymers can also be crosslinked by heating with a free-radical initiator. This process is energy-intensive and allows only low output rates.
Another process which has become known under the name SIOPLAS is described in U.S. Pat. No. 3,646,155. In a first stage of this process, polyolefins are reacted with an unsaturated hydrolyzable silane (i.e. a silane containing at least two hydrolyzable substituents), advantageously in a screw extruder, at a temperature of >140° C. in the presence of a free-radical initiator. This forms a grafted polyolefin having hydrolyzable silane groups located on side chains. In a second stage, the hydrolyzable silane groups are hydrolyzed by means of water and the silanol groups formed are condensed in the presence of a catalyst. According to the patent, the condensation catalyst can be added, before, during or after the grafting reaction. The catalyst is preferably added to the crosslinkable polyolefin immediately before shaping, advantageously in the form of a masterbatch comprising the unmodified polyolefin and the catalyst which is homogenized with the crosslinkable polyolefins. This procedure enables the production of the crosslinkable polyolefin to be carried out by the raw materials manufacturer and the mixing with the catalyst to be carried out by the producer of the moldings.
The MONOSIL process which has become known from U.S. Pat. No. 4,117,195 corresponds to a large extent to the SIOPLAS process of U.S. Pat. No. 3,646,155, but the condensation catalyst is added during the grafting reaction and the crosslinkable polymer catalyzed in this way is then immediately shaped and crosslinked to produce a molding. This process is carried out completely by the producer of the moldings.
In the COPO process of Jap. Kokai Tokkyo Koho 80 155.040 (Mitsubishi Petrochemical), the crosslinkable silane groups are not introduced by grafting but instead an olefin and an olefinically unsaturated hydrolyzable silane are polymerized in the presence of a free-radical initiator and a silane condensation catalyst to form a crosslinkable copolymer. The crosslinkable silane groups are located on the main polymer chain. Crosslinking again occurs by hydrolysis and subsequent catalyzed silanol condensation.
According to EP-B1-0 351 241, EP-A2-0 245 938 and WO 90/07542, premature crosslinking can occur in all three processes during the preparation of the polymer containing silane groups and before the planned crosslinking reaction. This premature crosslinking leads, according to the first two of the abovementioned documents, to difficulties in the production of moldings or to moldings having unsatisfactory physical and mechanical properties. The premature crosslinking is said to be particularly disadvantageous in the production of wire and cable insulation. According to the first of the 3 publications mentioned, the premature crosslinking can be countered by adding an ester of dipentaerythritol with one or more C
4
-C
8
-carboxylic acids and an organometallic silanol condensation catalyst to the crosslinkable polymer. The second of the publications mentioned describes the addition of at least 2% by weight of a filler and of one or more water-binding substances, namely an organic ortho ester, an organic ketal or acetal or a siloxane (inappropriately referred to as “silane”) of the formula
R
9
R
10
R
11
—Si—[OSiR
12
R
13
]R
14
,
where R
9
, R
10
, R
11
, R
12
, R
13
and R
14
are identical or different and are each hydrogen, a hydrocarbon radical or an oxyhydrocarbon radical.
According to the abovementioned publication WO 90/07542, premature crosslinking leads to gelling and adhesion of the gel to the surfaces of the apparatus. Sticky deposits are formed, with the risk of a blockage so that mechanical and therefore time-consuming cleaning of the extruder becomes necessary after a relatively short time. If the crosslinkable polymer is used for producing cables by sheathing wires, the crosslinked polymer adheres relatively strongly to the metal so that the sheathing cannot be stripped off easily, which is a disadvantage, for example, when making connections. A further disadvantage caused by premature crosslinking is that gel particles form lumps in the molding, which in the case of thin layers, e.g. films, results in the product being unusable in most cases. WO 90/07542 proposes that premature crosslinking be countered by additionally using a silane of the formula
R
1
(SiR
2
n
X
3−n
)
m
.
In the formula,
R
1
is a monovalent hydrocarbon radical having from 13 to 30 carbon atoms or a divalent hydrocarbon radical having from 4 to 24 carbon atoms,
R
2
are identical or different hydrocarbon radicals having from 1 to 10 carbon atoms,
X are identical or different hydrolyzable radicals,
n is 0, 1 or 2 and
m is 1 or 2.
The crosslinkable polymer can be a copolymer or graft polymer containing hydrolyzable silane groups. The silane of the formula I can be solid or liquid and is in each case mixed into the finished crosslinkable polymer. In the case of a solid, this can be achieved by dispersing it homogeneously, e.g. in an extruder. In the case of liquids, incorporation by impregnation is a further possibility.
2. SUMMARY OF THE INVENTION
The invention provides a process for preparing crosslinkable polymers containing silane groups having at least one hydrolyzable radical by free-radical-initiated grafting of the base polymers with an olefinically unsaturated silane having at least one hydrolyzable radical, wherein the grafting is carried out in the presence of
(a) an alkylsilane of the formula I,
R
1
(SiR
2
n
X
3−n
)
m
, (I)
where
R
1
is a monovalent hydrocarbon radical having from 1 to 33 carbon atoms or a divalent hydrocarbon radical having from 4 to 24 carbon atoms,
R
2
is a hydrocarbon radical having from 1 to 10 carbon atoms,
X are identical or different hydrolyzable radicals,
n is 0, 1 or 2 and
m is 1 or 2 and/or
(b) a fluoroalkylsilane of the formula
R
3
x
SiR
4
y
X
z
, (II)
where
R
3
is a fluoroalkyl radical,
R
4
is an alkyl radical and
X is a hydrolyzable radical,
x is an integer from 1 to 3,
y is 0, 1 or 2 and
z is an integer from 1 to 3,
with the proviso that the sum x+y+z=4.
The invention also provides the crosslinkable polymers which contain silane groups having at least one hydrolyzable radical and also an alkylsilane (a) and/or a fluoroalkylsilane (b) and are obtainable by the process of the invention.
The invention further provides a process for producing moldings based on polymers crosslinked via siloxane bridges (—Si—O—Si—), in which process the crosslinkable polymers containing silane groups having at least one hydrolyzable radical of the invention which have been brought to the desired shape are treated with water.
The invention finally provides the moldings obtainable in this way.
3. ADVANTAGES OF THE INVENTION
In contrast to the teachings of WO 90/07542, the alkylsilane I and/or the fluoroalkylsilane II are not mixed afterwards into the preformed crosslinkable polymer containing silane groups having at least one hydrolyzable radical, but instead are added during the preparation of the latter. This saves a process step and significantly
Edelmann Roland
Frings Albert-Johannes
Horn Michael
Jenkner Peter
Laven Ralf
Asinovsky Olga
Degussa - AG
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seidleck James J.
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