Method for Preparing High Molecular Weight Polybutylene Succinate

Abstract

A method for preparing high molecular weight polybutylene succinate includes: (a) using maleic anhydride (MAH) and C1-C4 alcohols to produce dialkyl maleates and water, in which dialkyl fumarate is calculated as dialkyl maleate of an equivalent mole. A reactive distillation process is used for the purification and obtains dialkyl maleates; (b) selective hydrogenation of those dialkyl maleates in the presence of high pressure hydrogen to produce the corresponding dialkyl succinates; (c) condensation of dialkyl succinates with mostly 1,4-butanediol (BDO) and other aliphatic diols to produce high molecular weight polybutylene succinates by adding catalysts. Compared with the existing technologies, the present procedure uses a new source of raw bulk feedstocks, and circumvents or overcomes problems associated with the acidic monomer's corrosiveness, excessive formation of by-products, low yields of desired products and the relatively low molecular weight of the polybutylene succinate produced by existing technologies.

Claims

1. A method for preparing high molecular weight polybutylene succinate (PBS), comprising: (a) using maleic anhydride (MAH) and C1-C4 alcohols to produce dialkyl maleates and water, in which dialkyl fumarate is calculated as dialkyl maleate of an equivalent mole, and a reactive distillation process is used for the purification and obtains dialkyl maleates; (b) selective hydrogenation of those dialkyl maleates in the presence of high pressure hydrogen to produce the corresponding dialkyl succinates; (c) condensation of dialkyl succinates with mostly 1,4-butanediol (BDO) and other aliphatic diols to produce high molecular weight PBSs by adding catalysts.

2. The method according to claim 1, wherein step a that is the production process of dialkyl maleates comprises: the aliphatic alcohols used to react with maleic anhydride (MAH) include C1-C4 alcohols such as methanol, ethanol, propanol, etc.; an esterification process in which MAH reacts with alcohols to produce dialkyl maleates and water; an esterification process that occurs at temperature 70-150° C. and absolute pressure of 20-500 kPa with a reaction time of 0.1-16 hours; the catalyst used for such a esterification process includes at least one of sulfuric acid, p-toluenesulfonic acid or sulfonic acid resin; the intermediate products after purification contain 50%-99.5% of dialkyl maleates, and the isomer dialkyl fumarate is also calculated as dialkyl maleates.

3. The method according to claim 1, wherein step b that is the production process of dialkyl succinates comprises: the reaction of dialkyl maleates with hydrogen by selective hydrogenation of the C═C bond occurs at temperature 50-350° C. and absolute pressure of 0.2-6.0 MPa; the catalyst used for such a process includes at least one of Raney nickel or supported platinum, palladium and other noble metal catalysts; the products contain at least 99.5% of dialkyl succinates.

4. The method according to claim 1, wherein step c that is the production process of PBSs comprises: the aliphatic diols used to produce high molecular weight PBSs include mostly 1,4-butanediol and also ethylene glycol, 1,6-hexanediol or other aliphatic diols.

5. The method according to claim 1, wherein step c that is the production process of high molecular weight PBSs comprises: a polymerization process which includes trans-esterification and poly-condensation processes occurring by adding catalysts, dialkyl succinates and the aliphatic diols, N.sub.2 protection, 150-200° C. for the first 2-4 hours and then 200-260° C. for the ensuing 2-5 hours under the pressure of 50-500 Pa.

6. The method according to claim 5, wherein the catalysts used for the polymerization process to produce high molecular weight PBSs include one or more compounds of p-toluene sulfonic acid, tetrabutyl titanate, nano titanium dioxide, BDO-titanium complexes and titanium silicon oxide.

7. The method according to claim 5, wherein the polymerization process to produce high molecular weight PBSs comprises: the catalysts whose weight used for the reaction is 0.1-1.0% weight of the monomers, and the molecular ratio of dialkyl succinates and alkyl diols is 1:1.0-1.5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is DSC test results of commercial PBS and PBSs in Example A1 and A2.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will be further described below in detail with reference to the accompanying drawings by embodiments.

Example A1

[0033] (1) Synthesis of Dimethyl Maleate (DMM)

[0034] 1470 g (15 mol) of solid maleic anhydride was added in a 2500 ml three necked glass flask, together with some Φ3 mm ceramic rings and a magnetic stirrer. A thermometer, a stinger reflux glass tube and a water-cooled collection system were equipped with the glass flask. The flask was heated in an oil bath. After the inside temperature reached 55° C. when all solid maleic anhydride melted, 15 g of 98% H2SO4 was added into the flask while stirring. Then, 550 g (17.2 mol) of methanol was pumped using a peristaltic pump through a glass tube into the flask at the bottom. The reaction then vigorously occurred with a substantial amount of heat released. The reaction temperature was maintained to be 70-80° C., which was controlled by cooling reflux and methanol adding rate. After one hour, all the methanol was pumped in and the temperature was kept at 80° C. for another hour. After that, pumping of methanol was started again and the reaction temperature was raised to 120° C. During the following reaction process, a large quantity of methanol would be consumed and a large volume of the methanol-water mixture would flow out by distillation and cooling. Methanol in such a mixture could be recovered by distillation. After 3-5 hours, samples were taken periodically and analysis was done by gas chromatography. When the maleic anhydride was consumed and the remaining monomethyl maleate was less than 0.5 w %, the reaction was stopped. After cooling, the reaction mixture was poured into a 2500 ml beaker containing 500 ml of water. And that, 4 mol/L NaOH solution was added into the mixture, and the solution pH was neutralized to 6-9. Then, the stirring was stopped, and oil phase and water phase was separated. 2200 g of the oil phase was collected and analyzed with gas chromatography, and the results are shown in table 1.

[0035] (2) Synthesis of Dimethyl Succinate (DMS) in an Autoclave

[0036] 2000 g of the oil phase collected in the step 1 was added into a 2.5 L stainless steel autoclave, together with 10 g of Pd/C catalyst, in which the palladium loading was about 10%. After exchanging the headspace gas with 500 kPa of N2 for three times, the autoclave was pressurized with hydrogen to 4.0 MPa. And then, the stirring was started, and the temperature was set to 120° C. At that temperature, hydrogen was continuously fed for 12 hours. After taking samples and analysis with GC, until a point when the conversion of DMM (DFM) reached 99.7%, heating was stopped, and thus the reaction was terminated. After cooling and collecting the reaction mixture by filtering, a distillation tower was used for purification of the oil phase collected. Our GC analysis showed that we collected 1850 g of DMS with a concentration of 99.5%.

[0037] (3) Synthesis of PBS for Use as Tape Casting Films

[0038] 877 g (6 mol) of dimethyl succinate (DMS) obtained from step 2, 595 g (6.6 mol) of 1,4-butanediol (BDO) and 0.3 g of p-toluene sulfonic acid and 0.45 g of tetrabutyl titanate were added in a 316L stainless steel autoclave for polymerization reactions. This autoclave was equipped with heating, stirring, temperature controlling and vacuum components. The reaction was carried out under nitrogen atmosphere with the stirring rate set to 50 r/min. The reactor was first maintained at 140° C. and ambient pressure for 3 hours for the transesterification and the distilled methanol was collected. After that, the reaction temperature was raised to 240° C., then a vacuum of <50 Pa was applied, and the temperature was maintained for 2.5-3.5 hours. When the power of the stirring motor exceeded 75 W, the reaction was stopped. The PBS product was released to the water tank by pressurizing the autoclave under N2. After drying, 831 g of PBS was obtained. According to the analysis by gel permeation chromatography (GPC), the PBS has a Mw of 250,000 and the Mw/Mn is 2.5. The mechanical properties, melting point and melt index of the PBS obtained in this case are shown in Tables 3 and 4. Such PBS is white and has good fluidity. Even at 150° C., its melt flow index is higher than 60 g/10 min (2.16 kg load). Tests have proven that this product is suitable for manufacturing tape casting film and also for melt spinning. Such PBS can be mixed with 50% in weight of CaCO3 that endows the material with a higher rigidity.

Example A2

[0039] (1) Synthesis of Dimethyl Maleate (DMM):

[0040] The selected catalyst was 30 g of p-toluenesulfonic acid. Other conditions and steps were identical to those for DMM synthesis in Example A1.

[0041] (2) Synthesis of Dimethyl Succinate (DMS) in an Autoclave:

[0042] The selected catalyst was 50 g of Raney nickel and the reaction temperature was 180° C. Other conditions were the same as those detailed in Example A1.

[0043] (3) Synthesis of General-Purpose High Molecular Weight PBS:

[0044] 1080 g (7.5 mol) of DMS obtained from step 2, 878 g (9.75 mol) of 1,4-butylene glycol (BDO), 0.5 g of tetrabutyl titanate and 0.5 g of nano titania-silica composite oxide (TiO2/SiO2 molecular ratio being 50:50) as the catalyst were added in the autoclave for polymerization reactions. This autoclave was equipped with heating, stirring, temperature controlling and vacuum components. The reaction was carried out under nitrogen atmosphere with the stirring rate set to 50 r/min. The reactor was first maintained at 180° C. and ambient pressure for 3-4 hours for the transesterification, while the distilled methanol and other side products were collected. After that, the reaction temperature was raised to 250° C., then a vacuum of <50 Pa was applied, the temperature was maintained for 4-5 hours, and low-boiling substances were distilled. When the power of the stirring motor exceeded 75 W, the stirring speed was adjusted to 25 r/min. When the stirring power reached 75 W again, the reaction was stopped. The PBS product was released to the water tank by pressurizing the autoclave under N2. After drying, 1060 g of PBS was obtained. The product yield was about 86.8%. According to the analysis by GPC, the PBS has a Mw of 285,000 and the Mw/Mn is 1.8. The mechanical properties, melting point and melt index of the PBS obtained in this case are shown in Tables 3 and 4. It should be pointed out that PBS also has very good mechanical properties with pure white color and good processability, which can be completely processed by traditional equipment, capable of replacing traditional general-purpose plastics.

Example A3

[0045] (1) Synthesis of Dimethyl Maleate (DMM):

[0046] The selected catalyst was 100 g of sulfonic acid resin. The catalyst was filtered and recovered after reaction, and the methanol content of the DMM obtained after final distillation was 50%. Other conditions and steps were identical to those for DMM synthesis described in example A1.

[0047] (2) Synthesis of Dimethyl Succinate (DMS) in an Autoclave: identical to Example A1.

[0048] (3) Synthesis of High Molecular Weight PBS for Film Blowing:

[0049] 1095 g (7.5 mol) of DMS, 540 g (6 mol) of BDO, 186 g (3.0 mol) of ethylene glycol (EG), 0.6 g of tetrabutyl titanate and 0.6 g of nano titanium dioxide were added in the autoclave for polymerization reactions. This autoclave was equipped with heating, stirring, temperature controlling and vacuum components. The reaction was carried out under nitrogen atmosphere with the stirring rate set to 50 r/min. The reactor was first maintained at 170° C. and ambient pressure for 3-4 hours for the transesterification and the distilled methanol and some side products were collected. After that, the reaction temperature was raised to 250° C. and a vacuum of <50 Pa was applied. The temperature was maintained for 4-5 hours, and low-boiling substances were distilled. When the power of the stirring motor exceeded 75 W, the stirring speed was adjusted to 25 r/min. After the stirring power reached 75 W again, the stirring speed was further decreased 12 r/min and finally, when the stirring power became 60 W, the reaction was stopped. The PBS product was released to the water tank by pressurizing the autoclave under N2. After drying, 1040 g of PBS was obtained. The product yield was about 80.6%. According to the analysis by GPC, the PBS has a Mw of 353,000 and the Mw/Mn is 1.4. The mechanical properties, melting point and melt index of the PBS obtained in this case are shown in Tables 3 and 4. It should be noted that the PBS is pure white in color and has very good mechanical properties, and its tensile strength is 38.5 MPa. In addition, the PBS has a good processability and can be processed by traditional film blowing equipment, replacing conventional non-degradable plastics in general use.

Example B1

[0050] (1) Synthesis of dimethyl maleate (DMM): identical to example A1.

[0051] (2) Hydrogenation of DMS in a Fixed-Bed Reactor:

[0052] Four different catalysts were used in the hydrogenation of the mixture of DMM and methanol in a fixed-bed microreactor. The diameter of the reactor was Φ14 mm. The amount of catalyst used was 10 g, the reaction temperature was 270° C., the liquid mass flow rate was 1.5 h-1, the reaction pressure was 4.0 MPa, and the hydrogen to DMM molar ratio was 4:1. The products were analyzed by GC, and the conversion and product selectivities were calculated. The specific product parameters obtained with different catalysts are shown in Table 2.

[0053] (3) Synthesis of General-Purpose High Molecular Weight PBS:

[0054] Conditions and steps identical to those described in Example A2 were adopted and the test results of product performance were approximately the same as Example A2.

Example B2

[0055] (1) Synthesis of dimethyl maleate (DMM): identical to example A1.

[0056] (2) Hydrogenation of DMS in a Fixed-Bed Reactor:

[0057] The conditions were similar to those of Example B1, but the reaction temperature was 190° C., the liquid mass flow rate was 1.0 h-1, the reaction pressure was 3.0 MPa, and the hydrogen to DMM molar ratio was 6:1.

[0058] (3) Synthesis of General-Purpose High Molecular Weight PBS:

[0059] 1080 g (7.5 mol) of DMS obtained from step 2, 878 g (9.75 mol) of 1,4-BDO, 177 g (1.5 mol) of 1,6-hexanediol (HDO), 0.5 g of tetrabutyl titanate and 1.0 g of titanium glycolate were added in the autoclave for polymerization reactions. This autoclave was equipped with heating, stirring, temperature controlling and vacuum components. The reaction was carried out under nitrogen atmosphere with the stirring rate set to 50 r/min. The reactor was first maintained at 180° C. and ambient pressure for 3-4 hours for the transesterification and the distilled methanol and side products were collected. After that, the reaction temperature was raised to 250° C., and a vacuum of <50 Pa was applied. The reactor was maintained at 250° C. for 4-5 hours, and low-boiling substances were distilled off. When the power of the stirring motor exceeded 75 W, the stirring speed was set at 25 r/min. After the stirring power reached 75 W again, the reaction was stopped. The PBS product was released to the water tank by pressurizing the autoclave under N2. After drying, 1230 g of PBS was obtained. The test results of product performance were approximately the same as Example A2.

Example B3

[0060] (1) Synthesis of dimethyl maleate (DMM): identical to example A1.

[0061] (2) Hydrogenation of DMS in a fixed-bed reactor: identical to example B2.

[0062] (3) Synthesis of General-Purpose High Molecular Weight PBS:

[0063] 1080 g (7.5 mol) of DMS obtained from step 2, 540 g (6.0 mol) of 1,4-BDO, 102 g (1.65 mol) of ethylene glycol, 0.2 g of tetrabutyl titanate and 0.2 g of titanium glycolate were added in the autoclave for polymerization reactions. This autoclave was equipped with heating, stirring, temperature controlling and vacuum components. The reaction was carried out under nitrogen atmosphere with the stirring rate set to 50 r/min. The reactor was first maintained at 180° C. and ambient pressure for 4-10 hours for the transesterification and the distilled methanol and side products were collected. After that, the reaction temperature was raised to 250° C., and a vacuum of <50 Pa was applied. The temperature was maintained for 4-5 hours. When the power of the stirring motor exceeded 75 W, the stirring speed was adjusted to 25 r/min. When the stirring power reached 75 W again, the reaction was stopped. The PBS product was released to the water tank by pressurizing the autoclave under N2. After drying, 1030 g of PBS was obtained. The test results of product performance were approximately the same as Example A3.

Example C

[0064] (1) Synthesis of diethyl maleate (DEM): The methanol of Example A1 was replaced by ethanol, and the others were consistent with Example A1.

[0065] (2) Hydrogenation of Diethyl Maleate (DEM) in a Fixed-Bed Reactor:

[0066] Diethyl succinate (DES) was synthesized by selective hydrogenation of 99.5% diethyl maleate (DEM) in a fixed-bed microreactor using (0.25% Pt+0.25% Pd)/(Al2O3-SiO2) as the catalyst. The diameter of the reactor was Φ 14, the amount of catalyst, reaction temperature, the weight hourly space velocity of DEM, reaction pressure, the molar ratio of hydrogen to DEM were 12 g, 290° C., 1.5 h-1, 3.0 MPa and 5:1, respectively. The conversion and selectivity to diethyl maleate were 99.5% and 99.0%, respectively. After distillation, the purity of diethyl succinate was greater than 99.7%.

[0067] (3) Synthesis of High Molecular Weight PBS for Injection Molding:

[0068] 1305 g (6 mol) of DES obtained from step 2, 540 g (6.0 mol) of 1,4-BDO, 186 g (3.0 mol) of ethylene glycol (EG), 0.6 g of tetramethylene titanate and 0.6 g of titanium butanediolate were added into the autoclave for polymerization reactions. This autoclave was equipped with heating, stirring, temperature controlling and vacuum components. The reaction was carried out under nitrogen atmosphere with the stirring rate set to 50 r/min. The reactor was first maintained at 150° C. and ambient pressure for 3 hours for transesterification and the distilled ethanol and side products were collected. After that, the reaction temperature was raised to 250° C., and a vacuum of <50 Pa was applied. The temperature was maintained for 3.5-5 hours, and the low-boiling substance was steamed. When the power of the stirring motor exceeded 75 W, the stirring speed was set at 25 r/min. When the stirring power reached 75 W again, the reaction was stopped. The PBS product was released to the water tank by pressurizing the autoclave under N2. After drying, 1088 g of PBS was obtained. The product yield was about 85%. GPC analysis showed that its weight-average Mw value was 303,000, and its Mw/Mn value was 1.6. The test results of product performance were approximately the same as Example A2.

[0069] Performance Testing and Analysis:

[0070] (1) The high molecular weight PBS obtained from example A, B and C was crushed by a Φ 45 mm twin-screw granulation, showing its good granulation processing performance. Part of the material also was also used for filler mixed granulation. The high molecular weight PBS after granulation was used to conduct injection molding tests on an injection molding machine. PBS obtained in example A3 after granulation was also used to attempt at film blowing on a film-blowing machine. And it was subjected to twin-screw extrusion granulation, put on an injection molding machine for injection experiment, and a trial film-blowing of PBS was conducted on the film-blowing machine. The subsequent mechanical performance test results proved that the high molecular weight PBS produced by the process in this invention has excellent processing performance, mixing modification performance and excellent mechanical properties

[0071] (2) For comparison, DSC tests were also performed with a certain commercial PBS material sold in a domestic market (molecular weight 110,000) and with our synthesized high molecular weight PBS; in both cases, the sample amount was 26 mg. The specific test results are shown in FIG. 1. PBS1 is the sample after granulation of example A1, and PBS2 is the sample after granulation of example A2. It can be seen that the melting point of our synthesized high molecular weight PBS was nearly 10° C. higher than the commercial PBS, which means a better heat resistance of our high molecular weight PBS material.

TABLE-US-00001 TABLE 1 Example A1 Contents of the compounds used to synthesize the reaction intermediate DMM dimethyl dimethyl methanol fumarate maleate Other Components (MeOH) (DMF) (DMM) impurities Content (w %) 10 3.20 86.0 0.8

TABLE-US-00002 TABLE 2 DMM conversion and DMS selectivity obtained with different catalysts used DMM (DMF) Selectivity conversion to DMS Catalysts (%) (%) 0.5%Pt/Al.sub.2O.sub.3 99.5 99.0 0.3%Pd/Al.sub.2O.sub.3 98.6 99.5 (0.25%Pt + 0.25%Pd)/Al.sub.2O.sub.3 99.5 99.4 (0.25%Pt + 0.25%Pd)/(Al.sub.2O.sub.3—SiO.sub.2) 99.5 99.0

TABLE-US-00003 TABLE 3 Mechanical properties of the PBS products Notched Tensile Elongation Elastic Izod strength, at break modulus, Impact, PBS samples/performance (MPa) (%) MPa kJ/m.sup.2 PBS described in Example 27.2 450 295 9 A1 PBS of Example 17.7 30 588 6 Al + 50%CaCO.sub.3 PBS described in Example 37.5 320 286 12 A2 PBS described in Example 38.5 340 386 12 A3 PBS described in Example 40.2 300 305 14 C

TABLE-US-00004 TABLE 4 Melting point and melt index of the PBS products (2.16 kg load) Melting point Melt index, g/10 min PBS samples/Performance (° C.) 130° C. 150° C. 190° C. PBS described in Example 110-115 11.0 >60 — A1 PBS of Example 110-115 8.17 20.1 — A1 + 50%CaCO.sub.3 PBS described in Example 110-120 6.0 12.5 26.6 A2 PBS described in Example 115-130 1.18 4.20 7.16 A3 PBS described in Example 112-125 3.75 6.79 14.2 C