Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-09-14
2002-08-06
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S173000, C526S180000, C526S181000, C526S183000, C502S153000, C502S155000, C502S156000, C502S157000
Reexamination Certificate
active
06429273
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a vinyl polymer preparation process, vinyl monomer polymerization initiator and styrene resin compositions. According to the process of the present invention, living polymerization can be carried out in a controllable temperature range without causing self-accelerated reaction due to generation of heat in the polymerization reaction, transfer reaction and termination despite high monomer concentration and high temperature reaction conditions in comparison with the conventional anionic polymerization.
BACKGROUND ART
Styrene polymers, a typical example of which is polystyrene, have been industrially produced for a long time by means of radical polymerization. However, radical polymerization, as is well known, causes reaction termination due to recombinations of growing radicals, etc. or radical transfer reactions to the solvent or monomer, so that it was difficult to achieve structural control of the polymer, such as control of molecular weight distribution or the structures of the polymer chain ends. Also, since radical polymerization is not living polymerization, it was not possible to produce block polymers or radial polymers.
Living anionic polymerization of monomers such as styrene and butadiene has been proposed as a solution to the above problems. For instance, in anionic polymerization of styrene using butyl lithium which is a general-purpose initiator, there can be obtained a polymer with very narrow molecular weight distribution since, in this case, living polymerization free of transfer reactions and reaction termination can proceed. Also, by taking advantage of reactivity of the propagating species of the living polymer, it is possible to obtain various well-defined polymers which have been unobtainable with the conventional radical polymerization, such as styrene/butadiene block polymers. However, the living anionic polymerization of styrene, despite its potential in producing very attractive resin materials, has not been industrially utilized except for some specific cases. This is attributable, for one thing, to low production yield because living anionic polymerization is a type of solution polymerization and to high production cost as compared with conventional radical polymerization, resulting in little industrial utilization, because of the necessity of a large-scale solvent recovery process. Therefore, there has been no other way but to resort to the conventional solution polymerization techniques for the production of specific polymers such as styrene/butadiene block polymers.
For reducing the production cost in living anionic polymerization, it is necessary to decrease the amount of the solvent used for the polymerization, to enhance productivity and to minimize the load for solvent recovery. However, reduction of the amount of the solvent invites a sharp rise of viscosity of the polymerization solution, necessitating elevation of the polymerization temperature to a remarkably higher level than required in conventional solution polymerization.
When styrene is polymerized by using, for example, butyl lithium under these conditions according to the conventional art, there arise the following problems, which make such polymerization impractical.
{circle around (1)} Since the polymerization initiation reaction and propagation reaction take place very rapidly, polymerization reaction heat is generated quickly, often resulting in unsatisfactory release of heat from the polymerization system to cause a steep rise of temperature in the system, which tends to initiate a self-acclerated reaction, the so-called “runaway” reaction (a situation where control of the reaction rate is impossible).
{circle around (2)} At a high temperature such as 100° C. or more, carbonic anions at the propagating species of the polymer become unstable to cause frequent occurrence of transfer reactions to the solvent or polymer backbone or reaction termination due to the &bgr;-elimination, resulting in a remarkable reduction of activity of the living polymer.
In the conventional polymerization using an organic alkali metal such as butyl lithium as initiator, the above problem {circle around (1)} can be solved by controlling the polymerization rate by decreasing the amount of the initiator, but this gives rise to the problem that a polymer having a high molecular weight is only obtained. The number-average molecular weight Mn of a polymer obtained by anionic polymerization using an organic alkali metal depends upon the ratio of the monomer to the alkali metal according to the following equation:
Mn
=
[
monomer
]
/
[
organic
alkali
metal
]
×
(
molecular
weight
of
monomer
)
(
[
]
:
molar
concentration
)
Therefore, when the amount of the initiator is small, the produced polymer is correspondingly high in molecular weight, which means that a large amount of initiator is necessary for obtaining a polymer of low molecular weight. It has thus been difficult with the prior art to freely obtain a polymer of a desired molecular weight because of the operational restrictions required for preventing the runaway reaction.
It is also notable that when a conventional organic alkali metal is used, the initiation reaction proceeds very rapidly as against the propagation reaction, so that in many cases the produced polymer has a very narrow molecular weight distribution. However, the narrow molecular weight distribution is sometimes detrimental to the balance of moldability and physical properties of the resin material. Therefore, in order to have a broad molecular weight distribution, it has been essential to add an initiator gradually or to carry out polymerization in a continuous reactor having a specific retention time profile. Thus, discovery of a living anionic polymerization system capable of freely controlling the molecular weight distribution without a complicated polymerization reaction has been desired.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a novel process for producing vinyl polymers with a controlled molecular weight distribution, according to which anionic polymerization of vinyl monomers is carried out under the high monomer concentration and high temperature conditions to allow the polymerization reaction to proceed at a controllable rate without causing a runaway reaction due to self-induced reaction heat, making it possible to conduct living polymerization free of transfer reactions and reaction termination even when conducted at a high temperature, which has never been achievable with the prior art. Another object of the present invention is to provide a styrene resin composition having excellent moldability and minimized in production of styrene monomers due to thermal decomposition.
In the course of studies aimed at these objects, the present inventor found that when anionic polymerization of a vinyl monomer such as styrene or butadiene is carried out using an initiator comprising an organic magnesium compound and a specific alkyl metal compound, quite surprisingly living polymerization proceeds at a reaction rate which enables control of heat release without causing a runaway reaction or extremely slow polymerization rate even under the conditions of high monomer concentration and high temperature. As a result, control of the molecular weight distribution is made possible. It was further found that the thus obtained styrene resin composition is lower in decomposition rate under heat retention and less in monomer formation than the resin compositions obtained by using the conventional anionic polymerization initiators. The present invention has been attained on the basis of these findings.
The present invention relates to a vinyl polymer preparation process which comprises carrying out anionic polymerization under the condition in which the polymerization temperature is not lower than 45° C. and not higher than 250° C. and the concentration of the vinyl monomer based on the polymerizati
Asahi Kasei Kabushiki Kaisha
Teskin Fred
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