Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-10-30
2003-10-14
Zalukaeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S064000, C526S065000, C526S066000, C526S317100, C526S318100, C526S258000, C526S328000
Reexamination Certificate
active
06632907
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for the continuous production of methacrylic polymers by bulk polymerization.
BACKGROUND ART
The continuous polymerization of polymethyl methacrylate (PMMA) by bulk polymerization has for long been intensively investigated for the reasons that it has more excellent productivity as compared with batchwise suspension polymerization, that the resulting polymer has very high transparency because no dispersant or other assistant is required, that it does not require the separation of the reaction solvent as contrasted with solution polymerization, that the resulting polymer has very high transparency because no residual solvent is present in the polymer after the removal of volatile matter, and that it yields a polymer having excellent thermal decomposition resistance because the amount of radical initiator supplied to the reaction zone may be very small.
On the other hand, solution polymerization has for long been investigated for the reason that, although it yields a polymer having poorer thermal decomposition resistance and poorer moldability as compared with bulk polymerization, it facilitates the control of polymerization.
For example, JP-B 52-32665 discloses a process in which the half-life at the polymerization temperature of the radical initiator used and the amount of radical initiator added are specified, and polymerization is carried out at 130-160° C. in one perfect mixing type reactor so as to give a degree of monomer conversion of 50 to 70%.
Moreover, JP-A 3-111408 discloses a process in which, using a short-lived radical initiator having a half-life period of 0.5 to 120 seconds at the polymerization temperature, polymerization is carried out at 130-160° C. in one perfect mixing type reactor so as to give a degree of monomer conversion of 45 to 70%.
Generally, it is known that, in the bulk polymerization of methyl methacrylate, the gel effect causes the reaction rate to be accelerated as the degree of conversion becomes higher. Consequently, when bulk polymerization is carried out by using one perfect mixing type reactor, a critical degree of conversion up to which operation can be carried out under stable control over the reaction exists for each polymerization temperature. Accordingly, in both of the processes described in the aforementioned JP-B 52-32665 and JP-A 3-111408, the polymerization reaction must unavoidably be carried out at or below such a critical degree of conversion. When it is desired to achieve high productivity preferentially under this limitation, there is employed a method for maintaining a high degree of conversion by raising the polymerization temperature.
However, in order to improve polymer properties desired for molding materials, it is necessary to carry out polymerization at a low temperature which can decrease the contents of dimers and terminal double bonds. To this end, the polymerization temperature must be lowered. This will produce a problem in that a lower polymerization temperature reduces the degree of conversion and hence detracts from productivity.
Moreover, in JP-A 54-90284, there is described a bulk polymerization process comprising the steps of effecting polymerization in an intimate agitation type reactor at a temperature of 120 to 200° C. to a degree of conversion of 30 to 80% by weight, and subsequently effecting polymerization in a plug flow type reactor at a temperature of 120 to 200° C. to a degree of conversion of not less than 90% by weight. In practice, however, our investigation on the continuous bulk polymerization of methyl methacrylate has revealed that it is extremely difficult to produce a polymer stably in a plug flow type reactor at a degree of conversion of not less than 90% and, moreover, it is very difficult to produce a polymer having excellent quality with good productivity.
Moreover, in JP-B 59-21325 and JP-B 1-49295, there are described processes for producing a methyl methacrylate-based syrup continuously by using one perfect mixing type reactor and a succeeding plug flow type reactor. The processes described in these publications are ones for producing a syrup which is a precursor for the formation of sheets by casting and polymerization. In these processes, the plug flow type reactor is installed for the purpose of decomposing the residual initiator present in the syrup leaving the first-stage perfect mixing type reactor and thereby producing a stable syrup which does not undergo postpolymerization. Thus, the object of the processes described in these publications is to produce a syrup containing no residual initiator and having good fluidity in an economical manner. Accordingly, the second-stage in plug flow type reactor does not involve the supply of an additional radical initiator, and the final degree of conversion is as low as 40% by weight or less. If a methacrylic polymer is produced according to the teachings of these publications and used as a molding material, the resulting polymer will have a high terminal double bond content and hence markedly poor thermal decomposition resistance because the polymerization time is extremely short and the amount of radical initiator used is extremely large. Thus, this polymer is disadvantageous from the viewpoint of properties.
As to continuous solution polymerization, processes for carrying out continuous polymerization in a perfect mixing type reactor by using 10 to 25% by weight of an inert solvent are described in JP-A 63-57613 and JP-A 1-79209; processes for carrying out polymerization in one perfect mixing type reactor and a succeeding perfect mixing type reactor or plug flow type reactor by using 5 to 29% by weight of an inert solvent are described in JP-A 7-206906 and JP-A 8-253507; a process for carrying out continuous polymerization in two or more reactors by using not less than 40% by weight of an inert solvent is described in JP-A 1-172401; and a process for the production of methacrylic polymers by using a perfect mixing tank and a plug flow type reactor connected in series therewith and by carrying out continuous polymerization in the presence of 10 to 40% by weight of a solvent is described in JP-B 40-22200. In all of the processes described in these publications, at least 5% by weight, mostly not less than 10% by weight, of a solvent is used to suppress the gel effect and thereby facilitate the control of the reaction. However, the processes using not less than 5% by weight of a solvent involve various problems in that they have low productivity owing to a slow polymerization rate and are hence disadvantageous from an economic point of view, that a radical initiator is used in large amounts to cause an increase in the terminal double bond content of the polymer and hence a reduction in thermal decomposition resistance, and that the separation and recovery of a large amount of solvent is required to impose a heavy burden on the volatile matter separation step.
Furthermore, JP-A 58-132002 discloses a process for carrying out continuous polymerization in a special reactor formed by the integration of a perfect mixing type reactor with a plug flow type reactor, while using 1 to 30% by weight of methyl isobutyrate as an inert solvent. However, this process requires the use of a special screw agitator in the plug flow type reactor and is hence disadvantageous from an economic point of view. Moreover, it is difficult to increase the capacity of this process to an industrial scale.
DISCLOSURE OF THE INVENTION
The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a process for producing methacrylic polymers having excellent moldability with good productivity.
The present invention relates to a process for production of methacrylic polymers wherein a homopolymer of methyl methacrylate or a copolymer containing methyl methacrylate units and alkyl acrylate units or alkyl methacrylate units (exclusive of methyl methacrylate units) is produced by using one perfect mixing type reactor, a plug flow type reactor and a volatile m
Ishizaka Kouzi
Mizota Hirotoshi
Murakami Tomonari
Sasaki Shigeaki
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Zalukaeva Tatyana
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