Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phosphorus-containing reactant
Reexamination Certificate
1997-05-22
2001-07-03
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phosphorus-containing reactant
C528S176000, C528S322000, C528S332000
Reexamination Certificate
active
06255448
ABSTRACT:
TECHNICAL FIELD
The invention relates to a process for the polymerization or copolymerization of at least one monomer which is polymerizable by the radical route in the presence of a stable free radical of the nitroxide family.
PRIOR ART
The presence of a stable free radical during the polymerization or copolymerization of monomers provides for control of polymerization and results in polymers of narrower polydispersity.
The quality of a polymerization or copolymerization control can also be assessed by observation of the increase in the number-average molecular mass as a function of the percentage of conversion of the monomers to polymer or copolymer. When control is good, the number-average molecular mass is linearly proportional to the percentage of conversion. The greater the departure from linearity, the less good the control.
U.S. Pat. No. 4,581,429 describes a process for the manufacture of oligomers at low temperature and with low degrees of conversion which makes use of a compound of formula ═N—O—X in the polymerization mixture.
U.S. Pat. No. 5,322,912 and U.S. Pat. No. 5,401,804 illustrate the effect of stable free radicals on the polymerization of styrene. U.S. Pat. No. 5,412,047 illustrates the effect of stable free radicals on the polymerization of acrylates. U.S. Pat. No. 5,449,724 illustrates the effect of stable free radicals on the polymerization of ethylene. The documents which have just been cited mention, as stable free radicals, cyclic molecules which have a group of low molecular mass in the position B to the nitrogen atom of the nitroxide group, which molecules have in particular the disadvantage of greatly slowing down the rate of polymerization or copolymerization, so that it is sometimes difficult, or indeed impossible, to carry out this polymerization or copolymerization at a temperature which is sufficiently low for the polydispersity of the final polymer to be sufficiently narrow.
Indeed, the greater the temperature of the mixture, the poorer the control of the polymerization or copolymerization, so that the final polymer or copolymer exhibits a higher polydispersity.
STATEMENT OF THE INVENTION
The invention overcomes the disadvantages mentioned above. The stable free radicals introduced in the context of the present invention provide excellent control of polydispersity while ensuring a better rate of polymerization or copolymerization, if they are compared with the stable free radicals made use of by the prior art.
Another advantage of the invention is to make possible the preparation of block copolymers. Indeed, the polymerization of a first monomer in the presence of a stable free radical results in a living polymer block. It is then possible to join a block of another polymer to this first block by placing the first living polymer block in a polymerization mixture of a second monomer. It is thus possible to produce block copolymers, for example copolymers comprising one or a number of polystyrene blocks and one or a number of polybutadiene blocks. The preparation of such copolymers is usually very difficult by the radical routes of the prior art and, for their preparation, copolymerization processes by the anionic route are generally resorted to.
The production of such copolymers by the radical route requires good control of the polymerization of each of the blocks. Indeed, if a termination reaction interrupts the growth by polymerization of a block, it will not be possible to join to it a block of another monomer. Termination reactions must therefore be as infrequent as possible. There are fewer termination reactions when, during polymerization, the number-average molecular mass is more linearly proportional to the percentage of conversion. The existence of termination reactions is reflected by a decrease in the rate of increase in the number-average molecular mass as a function of the percentage of conversion.
The invention relates to the polymerization or copolymerization of at least one monomer which is polymerizable in the presence of a stable free radical from the nitroxide family comprising a sequence of formula:
in which the R
L
radical has a molar mass greater than 15. The monovalent R
L
radical is said to be in the &bgr; position with respect to the nitrogen atom of the nitroxide radical. The remaining valencies of the carbon atom and of the nitrogen atom in the formula (1) can be bonded to various radicals such as a hydrogen atom or a hydrocarbon radical, such as an alkyl, aryl or aralkyl radical, comprising from 1 to 10 carbon atoms. It is not excluded for the carbon atom and the nitrogen atom in the formula (1) to be connected to one another via a bivalent radical, so as to form a ring. However, the remaining valencies of the carbon atom and of the nitrogen atom of the formula (1) are preferably bonded to monovalent radicals. The R
L
radical preferably has a molar mass greater than 30. The R
L
radical can, for example, have a molar mass of between 40 and 450. The radical R
L
can, by way of example, be a radical comprising a phosphoryl group, it being possible for the said R
L
radical to be represented by the formula:
in which R
1
and R
2
, which can be identical or different, can be chosen from alkyl, cycloalkyl, alkoxy, aryloxy, aryl, aralkyloxy, perfluoroalkyl and aralkyl radicals and can comprise from one to 20 carbon atoms. R
1
and/or R
2
can also be a halogen atom, such as a chlorine or bromine or fluorine or iodine atom. The R
L
radical can also comprise at least one aromatic ring, such as the phenyl radical or the naphthyl radical, it being possible for the latter to be substituted, for example by an alkyl radical comprising from one to four carbon atoms.
By way of example, the stable free radical can be chosen from the following list:
tert-butyl 1-phenyl-2-methylpropyl nitroxide,
tert-butyl 1-(2-naphthyl)-2-methylpropyl nitroxide,
tert-butyl 1-diethylphosphono-2,2-dimethylpropyl 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 0.005% to 5% by weight of the sum of the mass of polymerizable monomer and of stable free radical.
Within 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 medium can be a vinylaromatic monomer or an olefin or a diene or an acrylic or methacrylic monomer. The monomer can also be vinylidene difluoride or vinyl chloride.
Vinylaromatic monomer is understood to mean styrene, styrene substituted on the vinyl group by an alkyl group, such as alpha-methylstyrene, or ortho-vinyltoluene, para-vinyltoluene, ortho-ethylstyrene or 2,4-dimethylstyrene, or styrene substituted on the ring by a halogen, such as for example 2,4-dichlorostyrene, as well as vinylanthracene.
Diene is understood to mean in particular a conjugated diene comprising from 4 to 8 carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene or piperylene.
The process according to the invention is more particularly effective in the case of vinylaromatic monomers and dienes.
The polymerization or copolymerization is carried out under the usual conditions known to the person skilled in the art, taking into account the monomer or monomers under consideration, since this polymerization or copolymerization takes place by a radical mechanism, with the difference that the &bgr;-substituted stable free radical in accordance with the invention is added to the mixture. Depending on the nature of the monomer or monomers which it is desired to polymerize or copolymerize, it may be necessary to introduce a free-radical initiator into the polymerization or copolymerization mixture. The person skilled in the art knows the monomers which re
Finet Jean-Pierre
Gnanou Yves
Grimaldi Sandra
Lemoigne François
Nicol Pascal
Atofina
Boykin Terressa M.
Pennie & Edmonds LLP
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