Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1997-05-09
2002-02-12
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S227000, C526S232000, C526S347000, C526S347100
Reexamination Certificate
active
06346589
ABSTRACT:
1. BACKGROUND OF THE INVENTION
1.1 Technical Field
The invention relates to a process for the polymerization of at least one polymerizable or copolymerizable monomer by the radical route in the presence of (1) a stable free radical and (2) a polymerization initiator.
1.2 Description of the Related Art
The presence of a stable free radical in a polymerization mixture makes it possible to control the growth of the polymer chains and generally to result in a polymer of low polydispersity, indeed with a polydispersity of approximately one, as is possible in anionic polymerization. However, the presence of the stable free radical is disadvantageous because it greatly slows down the reaction rate and makes it difficult, if not impossible, to obtain polymers with a high weight-average molecular weight, for example greater than 50,000 g/mol.
It is possible to attempt to overcome this disadvantage by adding a polymerization initiator to the polymerization. However, to date, the initiators used in mixtures comprising a polymerizable monomer and a stable free radical cause side reactions reflected by the partial destruction of the stable free radical and of the initiator itself. An additional difficulty is the formation of impurities which damage, in particular, the appearance of the final polymer. Due to these side reactions, the initiator has little effectiveness, lengthening the reaction time and making it difficult to obtain polymers with a high molecular weight. Moreover, the final polymer is colored and often opaque.
PCT Patent WO 94/11412 describes a polymerization process in the presence of a stable free radical and benzoyl peroxide as polymerization initiator. The polymers thus obtained exhibit a number-average molecular weight of less than 60,000 g/mol and a weight-average molecular weight of less than 70,000 g/mol and moreover exhibit a high yellowing index.
U.S. Pat. No. 4,581,429 describes a polymerization process which confers control on the formation of the growing polymer chains. This process requires the preparation of an alkoxyamine and results in oligomers with a molecular weight of less than 10,000 g/mol. This process also exhibits low rates of conversion of monomer to polymer.
The following references also disclose stable free radical and polymerization initiator systems: WO 95/26987, U.S. Pat. No. 5,412,047, U.S. Pat. No. 5,449,724 and BR 9400671. In these patent documents, the polymerization initiator is not regarded as an essential factor. In contrast, in the process according to the invention, the polymerization initiator is one of the novel features of the invention.
It has now been found that the use of a specific family of polymerization initiators makes it possible to overcome the above-mentioned disadvantages. The process according to the invention is fast, allows the initiator to act more effectively and results in polymers or copolymers exhibiting a low yellowing index, as determined according to ASTM standard D 1925.
2. DESCRIPTION OF THE INVENTION
The invention relates to a process comprising a stage of polymerization or copolymerization of at least one polymerizable or copolymerizable monomer by a radical route or mechanism in the presence of a stable free radical and of an initiator of formula:
R
1
——O—O—R
2
in which R
1
and R
2
, which can be identical or different, represent hydrocarbon radicals comprising alkyl, such as aliphatics (straight and branched chain) and cycloaliphatics (substituted by alkyl and unsubstituted); aryl, such as aromatics; alkylaryl or aralkyl, i.e., mixed character groups. R
1
and R
2
, independently, preferably comprise from 1 to 20 carbon atoms.
Preferably, at least one radical from R
1
and R
2
comprises an aromatic ring. The initiator preferably exhibits a half-life of one hour at a temperature of between 80° C. and 150° C. and, preferably, between 100° C. and 130° C.
Mention may be made, by way of example, of the following initiators:
di-tert-butyl peroxide,
tert-butyl cumyl peroxide,
dicumyl peroxide. Dicumyl peroxide is a particularly suitable initiator.
The initiator can be introduced into the polymerization or copolymerization mixture in the proportion of about 50 ppm to about 50,000 ppm by weight based on the total monomer weight.
The stable free radical should not be confused with free radicals with fleeting lifetimes (a few milliseconds), such as the free radicals resulting from the usual polymerization initiators, e.g., peroxides, hydroperoxides and initiators of azo type. Free radicals which are polymerization initiators tend to accelerate the polymerization. In contrast, stable free radicals generally tend to slow down the polymerization. Within the meaning of the present invention, a stable free radical is not a polymerization initiator and the mean lifetime of the stable free radical is at least five minutes under the conditions of use of the present invention. While not wishing to be bound by any particular theory, it is thought that during this mean lifetime, the molecules of the stable free radical continually alternate between the radical state and the state of a group bonded via a covalent bond to a polymer chain. Of course, 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 stable free radical materials includes compounds acting as radical polymerization inhibitors and stable nitroxide radicals, i.e., comprising the ═N−O
•
group, such as the radicals represented by the following formulae:
in which R
1
, R
2
, R
3
, R
4
, R′
1
and R′
2
which can be identical or different, represent a halogen atom, such as chlorine, bromine or iodine; a saturated or unsaturated, linear, branched or cyclic hydrocarbon group, such as an alkyl or phenyl radical; an ester group; an alkoxy group; a phosphonate group; or a polymer chain which can be, for example, a poly(methyl methacrylate) chain, a polybutadiene chain, a polyolefin chain, such as a polyethylene or polypropylene chain, but which is preferably a polystyrene chain, and in which R
5
, R
6
, R
7
, R
8
, R
9
and R
10
, which can be identical or different, can be chosen from the same classes of groups just described for R
1
, R
2
, R
3
, R
4
, R′
1
and R′
2
, and can furthermore represent a hydrogen atom; a hydroxyl group —OH; or an acid group such as —COOH, —PO(OH)
2
or —SO
3
H, and in which n is preferably from 2 to 10 inclusive.
In particular, the stable free radical can be 2,2,5,5-tetramethyl-1-pyrrolidyloxy, sold under the trade name Proxyl, or 2,2,6,6-tetramethyl-1-piperidinyloxy, generally sold under the name Tempo.
The stable free radical can also be chosen from the following materials:
tert-butyl 1-phenyl-2-methylpropyl nitroxide,
tert-butyl 1-(2-naphthyl)-2-methylpropyl nitroxide,
tert-butyl 1-diethylphosphono-2,2-dimethyl propyl nitroxide,
tert-butyl 1-dibenzylphosphono-2,2-dimethylpropyl nitroxide,
phenyl 1-diethylphosphono-2,2-dimethylpropyl nitroxide,
phenyl 1-diethylphosphono-1-methylethyl nitroxide,
1-phenyl-2-methylpropyl 1-diethylphosphono-1-methylethyl nitroxide.
The stable free radical can be introduced into the polymerization or copolymerization mixture in the proportion of about 0.005% to about 5% by weight based on the sum of the weights of polymerizable monomer and of stable free radical.
The molar ratio of the stable free radical to the initiator is preferably between about 1.5 and about 2.5 and, more preferably, approximately 2.
In the context of the present invention, any monomer exhibiting a carbon-carbon double bond capable of polymerizing or copolymerizing by the radical route can be used.
At least one monomer present in the polymerization or copolymerization mixture can be a vinylaromatic monomer, an olefin, a diene, an acrylic monomer or a methacrylic monomer. The monomer can also be vinylidene difluoride or vinyl chloride.
The term “vinylaromatic monomer” is understood to include sty
Bertin Denis
Boutevin Bernard
Nicol Pascal
Elf Atochem S.A.
Pennie & Edmonds LLP
Zitomer Fred
LandOfFree
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