Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1997-11-19
2001-07-03
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C522S017000, C526S204000, C526S223000
Reexamination Certificate
active
06255422
ABSTRACT:
POLYMERIZATION IN THE PRESENCE OF A STABLE FREE RADICAL AND OF AN INIFERTER
TABLE OF CONTENTS
PAGE
1.
Background Of The Invention
2
1.1 Technical Field
2
1.2 Description Of Related Art
2
2.
Summary Of The Invention
4
3.
Description Of The Preferred Embodiments
5
4.
Claims
17
5.
Abstract Of The Disclosure
20
6.
Declaration And Power Of Attorney
21
1. BACKGROUND OF THE INVENTION
1.1 Technical Field
The present invention relates to a process for the polymerization or copolymerization of at least one monomer which can be polymerized or copolymerized by the radical route in the presence of a stable free radical and of an iniferter.
1.2 Description of Related Art
An iniferter is a molecule which generates free radicals by decomposition, wherein the said free radical is able to initiate a polymerization or copolymerization, promote transfer reactions particularly of the said iniferter, and promote termination reactions. An iniferter is characterized by the following reactions involved in polymerization:
formation of free radicals from an iniferter:
A-B→A
.
+B
.
(1)
initiation and polymerization:
A
.
+X→AX
.
, (2)
AX
.
+X→AXX., . . . ,
A(X)
n−1
X
.
+X→A(X)
n
X
.
transfer reaction involving the said iniferter:
A(X)
n
X
.
+AB→A(X)
n−1
B+A
.
(3)
termination reaction involving a free radical generated from the said iniferter:
A(X)
n
X
.
+B
.
→A(X)
n+1
B (4)
In reactions (1) to (4), A-B represents an iniferter; X represents a monomer polymerized through the radical route; n is a non-zero integer.
It is accepted by a person skilled in the art that reactions (1) to (4) characterize iniferters. Reactions (3) and (4) result in short chain formation. Therefore, according to the prior art, iniferters have been only useful in the preparation of oligomers.
When an iniferter is used in a polymerization or copolymerization reaction at a temperature where the reaction would take place and proceed to a substantial extent even in the absence of an iniferter or initiator, polymers or copolymers are obtained with broad and bimodal molecular mass distribution comprising mainly two groups of molecules distinct in molecular mass. The presence of the low molecular mass group is caused by the iniferter, and particularly, through reactions (3) and (4). The production of polymers or copolymers with a bimodal molecular mass distribution is not generally desired because of, for example, the interior heterogeneities which affect the mechanical properties of the final material.
In the prior art, for this reason, an iniferter can only be used at a temperature generally less than 100° C., at which no polymerization would take place and proceed to a substantial extent in the absence of iniferter or other polymerization initiators. Accordingly, an iniferter can only be used in the preparation of oligomers, for example, of polymers with an average molecular mass of less than 10,000. An iniferter should therefore not be confused with a conventional polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide, or dicumyl peroxide. Conventional initiators do not generate the reactions (3) and (4), and therefore, do not result in the formation of polymers or copolymers with a bimodal molecular mass distribution, even at a temperature wherein polymerization or copolymerization would take place and proceed to a substantial extent in the absence of any initiators.
Patent Application WO 94/11412 illustrates the action of stable free radicals on the polymerization of styrene. U.S. Pat. No. 5,412,047 illustrates the action of stable free radicals on the polymerization of acrylates. U.S. Pat. No. 5,449,724 illustrates the action of stable free radicals on the polymerization of ethylene. The following references may also be of interest: WO 95/26987, U.S. Pat. No. 4,581,429, EP 507 036, EP 418 118, EP 342 073 or EP 338,918.
2. SUMMARY OF THE INVENTION
The present invention relates to a process for the polymerization or copolymerization of at least one monomer which can be polymerized or copolymerized by the radical route in the presence of a stable free radical and of an iniferter.
The presence of the stable free radical greatly modifies the behavior of an iniferter during a polymerization or copolymerization so that the undesirable reactions (3) and (4) are greatly reduced, and indeed, eliminated. It is thus possible to polymerize or copolymerize rapidly and with a high yield in the presence of an iniferter. Furthermore, it is possible to result in a polymer or copolymer with monomodal molecular mass distribution and a reduced polydispersity in the presence of an iniferter, even if the polymerization or copolymerization is carried out at a temperature at which the reaction would be observed in the absence of an iniferter or initiator.
The invention is particularly advantageous in the context of the polymerization or copolymerization of methacrylates, whose polymerization or copolymerization is especially difficult as taught in WO 94/11412.
3. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described as follows.
According to the present invention, it is possible to choose an iniferter capable of splitting into two free radicals under the effect of ultraviolet radiation. For example, an iniferter comprises a single covalent bond involving two sulphur atoms (disulphide linkage), wherein the said iniferter is capable of breaking into two free radicals by the cleavage of the said bond, in accordance with the reaction (1), with each sulphur atom carrying an additional electron characteristic of the free radical state.
The iniferter can, for example, be represented by the formula
R
1
—S—S—R
2
wherein the R
1
and R
2
groups, which can be identical or different, represent radicals which can be highly varied in nature and which generally comprise at least one carbon atom. For example, the R
1
and R
2
groups can be chosen from alkyl, aryl, aralkyl or alkylaryl radicals comprising, for example, from 1 to 30 carbon atoms, thiuram radicals of formula
xanthate radicals of formula
carbamoyl radicals of formula
in which R
3
, R
4
, R
5
, R
6
and R
7
can, for example, be chosen from alkyl, aryl, aralkyl or alkylaryl radicals comprising, for example, from 1 to 30 carbon atoms.
Examples of iniferters are given in Patent Applications EP 507,036, EP 418,118, EP 342,073, and EP 338,918. The iniferter can also be chosen from the following list:
tetraethylthiuram disulphide,
tetramethylthiuram disulphide,
N,N′-diethyl-N,N′-bis(2-hydroxyethyl)thiuram disulphide,
N,N′-bis(N-(2-phthalimidoethyl)piperazine-thiuram disulphide,
diisopropyl xanthate disulphide.
The iniferter can be introduced into the polymerization or copolymerization mixture in the proportion of 0.001% to 15% of the sum of the moles of monomer and iniferter.
The process, according to the present invention, involves a stable free radical.
A stable free radical should not be confused with free radicals with a fleeting lifetime (a few milliseconds) resulting from the usual polymerization initiators such as peroxides, hydroperoxides and initiators of azo type. Free radicals of polymerization initiators tend to accelerate the polymerization. In contrast, stable free radicals generally tend to slow down the polymerization. In the present invention, a free radical is generally said to be stable if it is not a polymerization initiator and if, under the conditions of use of the present invention, its mean lifetime is at least five minutes. During this mean lifetime, the molecules of the stable free radical continually alternate between the radical state and the state of bonded in a group via a covalent bond to a polymer chain. It is preferable for the stable free radical to exhibit good stability throughout the duration of its use in the context of the present invention. Generally, a stable free radical can be isolated in the radical state at room temperature.
The family of the s
Bertin Denis
Boutevin Bernard
Nicol Pascal
Atofina
Henderson Christopher
Pennie & Edmonds LLP
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