Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-06-15
2004-05-11
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S217000, C526S204000, C526S141000, C526S142000, C526S348000, C526S352000
Reexamination Certificate
active
06734269
ABSTRACT:
The present invention relates to a process for the controlled radical polymerization or copolymerization of ethylene under high pressure in the presence an initiator-controller.
The polymerization under high pressure of ethylene or its copolymerization under high pressure with comonomers which can copolymerize by the radical route results in a large variety of products which have numerous applications, among which may be mentioned bases for adhesives, in particular hot melt adhesives, bituminous binders, wrapping films, coextrusion binders, moulded items, and the like.
Processes for the polymerization of ethylene at high temperatures and pressures by means of free radical initiators have been known for a long time. Ethylene polymers are obtained by homopolymerizing ethylene or by copolymerizing it with at least one other comonomer in a polymerization system which operates continuously under pressures of the order of 50 MPa to 500 MPa and at temperatures of between 50 and 300° C. The polymerization is carried out in continuous tubular reactors or stirred autoclaves in the presence of initiators and optionally of transfer agents. The polymers are subsequently separated from the volatile substances after their departure from the reactor in separators.
It is known that the polymerization of ethylene in the presence or in the absence of comonomers can result in reaction runaways (see, for example, Chem. Eng. Proc., 1998, 37, 55-59). These runaways are reflected by a very marked rise in the temperature and in the pressure and thus by bursting of the safety devices of the plant. Consequently, the runaway must result in undesired shutdowns in production. The aim is thus to avoid these shutdowns as far as possible and one means for doing this is to carefully control the flow rates of the reactants entering the reactor, in particular the flow rate of the source of radicals, that is to say of the initiator. This is because the injection of an excessively large amount of radicals results in a localized runaway in one of the regions of the reactor, which runaway subsequently spreads very quickly to the whole of the reactor. There thus exists a content of radicals not to be exceeded in order not to result in the runaway of the polymerization.
However, it is generally known that radical polymerizations can be controlled using stable free radicals, this control making it possible in particular to obtain polymers exhibiting narrow molecular mass distributions. Thus it is that United States Patent U.S. Pat. No. 5,449,724 discloses a radical polymerization process which consists in heating, at a temperature of approximately 40° C. to approximately 500° C. and under a pressure of approximately 50 MPa to 500 MPa, a mixture composed of a free radical initiator, of a stable free radical and of ethylene, in order to form a thermoplastic resin which has a molecular mass distribution of approximately 1.0 to approximately 2.0.
Furthermore, it is known, by International Patent Application WO 99/03894, to control the radical polymerization of monomers by the use, as (co)polymerization initiators, of specific alkoxyamines, these monomers being styrene, substituted styrenes, conjugated dienes, acrolein, vinyl acetate, anhydrides of (alkyl)acrylic acids, salts of (alkyl)acrylic acids, (alkyl)acrylic esters and alkyl-acrylamides. Ethylene is not mentioned as monomer. This polymerization is carried out under low pressure and at a temperature of between 50 and 180° C., preferably between 80 and 150° C., control of the reaction no longer being possible beyond 180° C. In other words, such a process could not work for the (co)polymerization of ethylene under high pressure, in which (co)polymerization the temperature conditions generally exceed 1800° C. This process furthermore exhibits the limitation according to which the polymers obtained have low molecular masses (not exceeding 15 000 in the examples).
In seeking to improve the known process for the controlled radical (co)polymerization of ethylene under high pressure, the Applicant Company has now discovered that, if use is made in (co)polymerization of an initiator-controller capable of providing at least one initiating free radical and at least one stable free radical, more specifically a free radical which is stable under the specific temperature conditions deployed in this high-pressure (co)polymerization, the latter is controlled under particularly favourable conditions while also controlling the reaction stability. The preferred initiators-controllers of the present invention, which will be described below, constitute a family of compounds which is not recommended according to WO 99/03894. It was therefore not obvious to thus control the high pressure (co)polymerization of ethylene, with greater effectiveness than with the use of an initiator and of a stable free radical, which are introduced separately, and with the observation, also surprising, that the (co)polymerization of ethylene takes place at a markedly greater rate. Furthermore, with the process of the invention, there is no limitation on the molecular masses of the (co)polymers obtained.
In addition, another consequence of the present invention is that, in the case where the initiator-controller chosen is such that it provides an initiating free macroradical, block copolymers are produced in which at least one of the blocks comprises ethylene as constituent. In point of fact, ethylene copolymers prepared under high pressure currently have random structures and it has not been possible to date to obtain such block copolymers having an ethylene-based block. It is well known that the structure of block copolymers can result in markedly better physicochemical properties than random copolymers. The present invention thus makes it possible to achieve the production of novel materials having novel properties.
The subject-matter of the present invention is thus first a process for the radical polymerization or copolymerization of ethylene under high pressure in the presence of at least one polymerization initiating-controlling compound capable of providing, by decomposition under the polymerization or copolymerization conditions:
at least one initiating free radical (Z) which carries at least one site for initiating the (co)polymerization; and
at least one stable free radical (SFR) which carries at least one site exhibiting the stable radical state and which is stable under the polymerization conditions,
with, in total, as many initiating sites as sites exhibiting the stable radical state.
In other words, when the initiator-controller dissociates, it produces, in the medium, as many initiating sites as stable radical sites. In the simplest case, the initiator-controller is such that it dissociates to give one initiating free radical and one stable free radical, the two radicals being monofunctional. Use may also be made of initiators-controllers which dissociate to give an n-functional initiating free radical and n monofunctional stable free radicals, or vice versa. Examples of various initiators-controllers are shown below.
The growing (co)polymer is thus positioned between the “initiating” part and the “controlling” part constituted by the stable free radical SFR.
The present invention thus involves the formation of a stable free radical. A stable free radical should not be confused with free radicals with a fleeting lifetime (a few milliseconds), such as the free radicals resulting from the usual polymerization initiators, such as peroxides, hydroperoxides and initiators of the azo type. The free radicals which initiate polymerization tend to accelerate the polymerization. In contrast, stable free radicals generally tend to slow down the polymerization. It may be generally said that a free radical is stable within the meaning of the present invention if it is not a polymerization initiator and if, under the operating conditions of the present invention, the mean lifetime of the radical is at least five minutes. During this mean lifetime, the molecules of the stable free radical continually alternat
Buback Michael
Le Blevec Jean-Marc
Minaux Eric
Senninger Thierry
Atofina
Choi Ling-Siu
Jones Day
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