Abstract:
A methacrylimide group-containing polymer having improved moldability as well as good heat resistance and transparency is prepared by heat treating a methacrylimide group-containing polymer having imide ring structural units of the formula: ##STR1## wherein R represents a hydrogen, an alkyl, cycloalkyl, aryl, alkaryl, aralkyl or allyl group 1 to 20 carbon atoms, at a temperature of 190 to 350 C. in the presence of a tertiary amine of the formula: ##STR2## wherein R 1 , R 2  and R 3  independently represent an alkyl, aryl, aralkyl or alkaryl group having 1 to 20 carbon atoms, and two of R 1 , R 2  and R 3  may be linked to form a ring together with the nitrogen atom.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for the preparation of a methacrylimide group-containing polymer having an excellent heat resistance, transparency and moldability. 
     2. Description of the Related Art 
     A methacrylic polymer resin containing a methacrylimide group (hereinafter referred to as &#34;methacrylimide group-containing polymer&#34;) is a thermo-plastic polymer resin having a high heat distortion temperature and a high transparency, as is well-known (see Japanese Examined Patent Publication No. 60-38,404 and Japanese Unexamined Patent Publication No. 59-31,012). 
     However, a methacrylimide group-containing polymer obtained by heat-treating a methyl methacrylate polymer in the presence of an agent capable of forming a methacrylimide ring structural unit, such as a primary amine, has a poor moldability, though the polymer retains a high heat distorsion temperature and a high transparency. The term &#34;moldability&#34; used in the instant specification means particularly, the processability at the injection molding conducted at a high temperature, especially a temperature of 300° C. or more. The above-mentioned conventional methacrylimide group-containing polymer has a problem in that if the temperature is not lower than 300° C. at the melt injection molding, blowing is caused or silver streaks appear in the obtained molded article, and therefore, the polymer has a poor moldability. 
     As the means for improving the moldability of the methacrylimide group-containing polymer, there has been tried a method in which the polymerization degree of the polymer is reduced and molding is carried out at a lower temperature. 
     In this method, however, since the polymerization degree of the methacrylimide group-containing polymer is reduced, reduction of the mechanical strength of the obtained molded article cannot be avoided. 
     SUMMARY OF THE INVENTION 
     Under the above-mentioned background, we carried out research with a view to providing a methacrylimide group-containing polymer having not only an excellent heat resistance and transparency but also moldability. As the result, it has been found that if the above-mentioned methacrylimide group-containing polymer is heat-treated at a temperature of from 190 to 350 C. in the presence of a tertiary amine, this problem can be solved. 
     More specifically, in accordance with the present invention, there is provided a process for the preparation of a methacrylimide group-containing polymer, which comprises heat-treating a methacrylimide group-containing polymer having imide ring structural units represented by the following structural formula (I): ##STR3## wherein R represents a hydrogen atom, a substituted or unsubstituted alkyl, cycloalkyl, aryl, alkaryl, aralkyl or allyl group having 1 to 20 carbon atoms, at a temperature of from 190 to 350 C. in the presence of a tertiary amine having the following structural formula (II): ##STR4## wherein R 1 , R 2  and R 3  independently represent an alkyl, aryl, aralkyl or alkaryl group having 1 to 20 carbon atoms, and two of R 1 , R 2  and R 3  may be linked to form a ring together with the nitrogen atom. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The methacrylimide group-containing polymer having imide ring structural units represented by the formula (I) is advantageously prepared by a process wherein a methacrylic polymer is reacted with ammonia or a primary amine having an alkyl, cycloalkyl, aryl, aralkyl, alkaryl or allyl group having 1 to 20 carbon atoms in an inert solvent at a temperature of 150° to 350° C., preferably 200° to 330° C. A solvent capable of dissolving therein the starting methacrylic polymer and the formed methacrylimide group-containing polymer or a mixed solvent composed of two or more of such solvents is preferably used as the inert solvent. For example, there can be mentioned aromatic hydrocarbons such as benzene, toluene and xylene, and aliphatic alcohols such as methanol, ethanol and propanol. 
     In the methacrylimide ring structural units, R stands for a hydrogen atom, a substituted or unsubstituted alkyl, cycloalkyl, aryl, alkaryl, aralkyl or allyl group having 1 to 20 carbon atoms. A hydrogen atom, methyl, ,ethyl, n-butyl, n-hexyl, cyclohexyl and n-dodecyl groups are preferable as R. Accordingly, ammonia, methylamine, ethylamine, cyclohexylamine, n-butylamine, n-hexylamine and n-dodecylamine are preferably used as the methacrylimide ring structural unit-forming agent. 
     The methacrylimide group-containing polymer used in the present invention contains preferably at least 5% by weight of the imide ring structural units and more preferably at least 20% by weight of the imide ring structural units. If the content of the imide ring structural units is lower than 5% by weight, the heat distortion temperature of the polymer is low. 
     A homopolymer of methyl methacrylate and a copolymer of methyl methacrylate with an ethylenically unsaturated monomer copolymerizable therewith such as other methacrylic acid ester, an acrylic acid ester, styrene or α-methylstyrene can be used as the methacrylic resin for the production of the methacrylimide group-containing polymer. 
     As the methacrylic acid ester, there can be mentioned, for example, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate and benzyl methacrylate. As the acrylic acid ester, there can be mentioned, for example, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, and benzyl acrylate. 
     A homopolymer of methyl methacrylate, a methyl methacrylate/methyl acrylate copolymer and a methyl methacrylate/styrene copolymer are especially preferred as the methacrylic resin to be used for the production of the methacrylimide group-containing polymer. In the above-mentioned copolymers, the methyl methacrylate unit content is not particularly critical, but it is generally preferred that the methyl methacrylate unit content be at least 70% by weight. 
     The methacrylimide group-containing polymer having imide ring structural units represented by the formula (I) is heat-treated in the presence of the tertiary amine represented by the structural formula (II). As the tertiary amine of the structural formula (II) to be used in the present invention, there can be mentioned, for example, trimethylamine, triethylamine, methyldiethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-octylamine, dimethylaniline, triphenylamine, N-methylpyrrolidine, N-ethylpyrrolidine, N,N&#39;-dimethylpiperazine, N-methylpiperidine, N-ethylpiperidine, N,N&#39;-dimethylethanolamine and triallylamine. Trimethylamine and triethylamine are especially useful. 
     The heat treatment of the methacrylimide group-containing polymer in the presence of a tertiary amine as described above is preferably performed according to a method in which the polymer is heated in the presence of the tertiary amine in a kneader, an extruder where kneading is possible, or an autoclave in which stirring is possible. A solvent capable of dissolving therein the methacrylimide group-containing polymer can be used as a diluent at the heat treatment. Preferably, the heat treatment temperature is 190° to 350° C., especially 200° to 350° C. If the heat treatment temperature is lower than 190° C., attainment of a sufficient effect cannot be expected, and if the heat treatment temperature is higher than 350° C., thermal decomposition of the methacrylimide group-containing polymer is readily caused. The heating time depends on the temperature, but generally, the heating time is from 1 minute to 120 minutes. As the diluent, there can be used aromatic hydrocarbons such as benzene, toluene and xylene. 
     The amount of the tertiary amine used differs according to the molecular weight thereof, but it is generally preferred that the tertiary amine be used in an amount of at least 1 part by weight per 100 parts by weight of the methacrylimide group-containing polymer. The tertiary amine may be used in an amount larger than the amount of the methacrylimide group-containing polymer. 
     The methacrylimide group-containing polymer of the present invention obtained by the above-mentioned heat treatment can be mixed with a phosphite type, sulfur type or hindered phenol type antioxidant, an ultraviolet absorber, a lubricant, a fiber reinforcer, a colorant or a pigment according to the intended use. 
     The present invention will now be described in detail with reference to the following examples. 
     The following measurement methods were adopted in the following examples. 
     Heat distortion temperature: 
     The heat distortion temperature was measured according to the method of ASTM D-648-56. 
     Tensile strength and elongation: 
     The tensile strength and elongation were determined according to the method of ASTM D-638-61T. 
     Flexural strength and flexural modulus: 
     The flexural strength and flexural elastic modulus were measured according to the method of ASTM D790-63. 
     Moldability: 
     Twenty samples were molded by using a spiral mold, and the moldability was evaluated based on the molded resin temperature at which blowing was observed at the end of the flow. Note, the higher the molded resin temperature, the better the moldability. The injection molding was carried out under the following conditions. 
     Injection molding machine: 
     Model SJ-35A (supplied by Meiki Co., Ltd.), 5 ounces 
     Injection pressure: 78 kg/cm 2   
     Screw rotation number: 80 rpm 
     Back pressure, 60 kg/cm 2   
     Cycle: 60 seconds 
     Mold temperature: 80° C. 
     Mold specification: 2 mm in thickness, spiral mold 
     Referential Example 
     The preparation of a methacrylimide group-containing polymer is illustrated in this example. 
     An autoclave was charged with 100 parts by weight of the dried methyl methacrylate polymer having a weight average molecular weight of 100,000 together with 100 parts by weight of toluene, 10 parts by weight of methanol and a primary amine shown in Table 1, and reaction was carried out at 250° C. for 3 hours with stirring. The properties of the obtained methacrylimide group-containing polymer are shown in Table 1. 
     
                                           TABLE 1__________________________________________________________________________Methacrylimide   Primary Amine    Imide Ring                          HeatGroup-           Amount Added                    Structure                          DistortionContaining       (parts by                    Content (%                          TemperaturePolymer Kind     weight) by weight)                          (°C.)__________________________________________________________________________M-1     Methylamine            15      45    125M-2     Methylamine            20      69    138M-3     Methylamine            25      80    145M-4     Cyclohexylamine            50      52    140__________________________________________________________________________ 
    
     Examples 1 through 4 
     An autoclave having a capacity of 1.5 liters was charged with 100 parts by weight of the methacrylimide group-containing polymer prepared in Referential Example together with 100 parts by weight of toluene, and 35 parts by weight of trimethylamine was added. The heat treatment of the mixture was carried out at 250° C. for 30 minutes with stirring. 
     The obtained polymer was dried and pelletized by an extruder. The obtained pellet was dried at 90° C. a whole day and night and was then subjected to spiral molding at a resin temperature shown in Table 2 by an injection molding machine. The blowing state was observed and the moldability was evaluated. The obtained results are shown in Table 2. 
     A test piece for the measurement of the heat distortion temperature and a test piece for the measurement of the tensile and flexural characteristics were prepared at a resin temperature of 290° C., and the characteristics were determined. The results are shown in Table 2. 
     Comparative Examples 1 through 4 
     The methacrylimide group-containing polymer prepared in Referential Example was dried, pelletized by an extruder, dried at 90° C. a whole day and night and injection-molded in the same manner as described in Examples 1 through 4, and the moldability and characteristics were evaluated. The results are shown in Table 2. 
     
                                           TABLE 2__________________________________________________________________________Starting       HeatMetha-  Heat   Distor-crylimide   Treatment in          tion Mechanical CharacteristicsGroup-  Presence of          Temper-               Tensile                    Elon-                        Flexural                             Flexural                                  Moldability (blowing in spirals)Containing   Trimethyl-          ature               Strength                    gation                        modulus                             Strength                                  Resin temperature in injection                                  molding machinePolymer amine  (°C.)               (kg/cm.sup.2)                    (%) (kg/cm.sup.2)                             (kg/cm.sup.2)                                  290° C.                                      300° C.                                          310° C.                                              320° C.                                                  330°                                                      340°__________________________________________________________________________                                                      C.ExampleNo.1    M-1   conducted          126  850  4.7 39000                             1270 not not not not slight                                                      observed2    M-2   conducted          138  850  4.8 40000                             1300 not not not not not slight3    M-3   conducted          145  870  5.0 42000                             1330 not not not not not slight4    M-4   conducted          141  800  4.0 37000                             1120 not not not not slight                                                      ob-                                                      servedCompar-ativeExampleNo.1    M-1   --     125  850  4.7 39000                             1270 slight                                      ob- ob- ob- ob- ob-                                      served                                          served                                              served                                                  served                                                      served2    M-2   --     138  850  4.8 40000                             1300 not slight                                          ob- ob- ob- ob-                                          served                                              served                                                  served                                                      served3    M-3   --     145  870  5.0 42000                             1330 not slight                                          ob- ob- ob- ob-                                          served                                              served                                                  served                                                      served4    M-4   --     140  800  3.9 37000                             1130 slight                                      ob- ob- ob- ob- ob-                                      served                                          served                                              served                                                  served                                                      served__________________________________________________________________________ 
    
     Examples 5 through 14 
     An autoclave having a capacity of 1.5 liters was charged with 100 parts by weight of the methacrylimide group-containing polymer prepared in Referential Example and 100 parts by weight of toluene, and a tertiary amine shown in Table 3 were added. Then, the heat treatment was carried out at 250° C. for 30 minutes with stirring. 
     The moldability of the obtained polymer was evaluated in the same manner as described in Example 1. The results are shown in Table 3. 
     
                                           TABLE 3__________________________________________________________________________StartingMetha-crylimide   Tertiary AmineGroup-                AmountContaining            (Parts by                      Resin Temperature in Injection Molding                      MachinePolymer Kind          weight                      300° C.                          310° C.                              320° C.                                  330° C.                                       340° C.                                            350° C.__________________________________________________________________________ExampleNo.5    M-3   triethylamine 30   not not not not  slight                                            observed6    &#34;  tributylamine 20   not not not slight                                       observed                                            --7    &#34;  trioctylamine 15   not not slight                                  observed                                       --   --8    &#34;  N-methylpiperidine                 30   not not not slight                                       observed                                            --9    &#34;  N-ethylpiperidine                 30   not not not slight                                       observed                                            --10   &#34;  N-methylpyrrolidine                 30   not not not slight                                       observed                                            --11   &#34;  N,N&#39;-dimethylpiperazine                 30   not not not slight                                       observed                                            --12   &#34;  N,N&#39;-dimethylethanolamine                 30   not not not slight                                       observed                                            --13   &#34;  triallylamine 30   not not not slight                                       observed                                            --14   &#34;  trimethylamine                 30   not not not not  slight                                            observed__________________________________________________________________________ 
    
     As is shown in the examples, the methacrylimide group-containing polymer obtained according to the process of the present invention has an excellent moldability and the polymer retains the good heat resistance, transparency and mechanical characteristics of the starting methacrylimide group-containing polymer.