GB2528814A

GB2528814A - Method for continuously preparing high molecular weight polyhydroxy acid

Info

Publication number: GB2528814A
Application number: GB1520339.1A
Authority: GB
Inventors: Qun Chen; Aijun Cui; Mingyang He; Weiyou Zhou; Shengchun Chen
Original assignee: Changzhou University
Current assignee: Changzhou University
Priority date: 2013-05-06
Filing date: 2014-04-04
Publication date: 2016-02-03
Also published as: CN103304786A; CN103304786B; WO2014180205A1; GB201520339D0

Abstract

The present invention relates to the technical field of environmentally friendly high molecular material. Disclosed is a method for continuously preparing high molecular weight polyhydroxy acid, the method comprising: employing a single-stage or multi-stage temperature-controllable screw reactor; utilizing organic or inorganic Lewis acid as a catalyzer, controlling the temperature, dosage of the catalyzer, and revolutions of the screw, and continuously feeding cyclic ester monomer and the catalyzer for polymerization reaction, the product being obtained quickly through continuous discharge; and in the middle and latter stages, directly adding antioxidizer and end-capping reagent to adjust the chromaticity of the polyhydroxy acid, and improve the stability thereof. The prepared polyhydroxy acid has advantages such as high molecular weight and low chromatic value.

Description

CONTINUOUS PROCESS FOR PREPARING HIGH

MOLECULAR WEIGHT POLYGLYCOLIDE ACID

TECHNICAL FIELD

This invention relates to a continuous process for the preparation of polyglycolide acid.

BACKGROUND ART

Traditional polymer materials generally come from the non-renewable petroleum resources, and are often difficult to degrade.

Despite their irreplaceable role in social and economic development, traditional polymer materials often lead to energy shortage and white pollution.

As a biodegradable environment-friendly polymer material, poly-hydroxy acid is preferable for its convenience to process and recycle and freedom from toxicity and pollution. Possessing the quality of superior gas barrier, excellent mechanical properties, marvelous biocompatibility and outstanding biodegradability, poly glycolic acid ( PGA) and polylactide have extensive applications to such high value-added products as absorbable surgical sutures, drug carriers, materials simulating human tissues, biodegradable polymer scaffolds, high-strength fibers (fishing line) and so on. The modified materials could be applied in the field of beverage packaging, PET composite beer bottles, films, containers, hot pressing molding cups, composite paper, single (multi) layer soft packaging materials and biodegradable agricultural films etc..

Poly-hydroxy acid is mainly prepared by virtue of ring open reaction, hydroxy acid or halogen acid solution polycondensation and melt! solid polycondensation. Melt! solid polycondensation can also produce high molecular weight PGA. However, as the solid of oligomer needs to be taken out and broken into pieces, it becomes quite difficult to ensure the continuous production, which greatly hinders its industrialization.

Chloride solution polymerization is simple and convenient, but the lower molecular weight of its PGA product results in its failure to meet the standard of application. As a relatively mature process, the lactide open loop method could yield products with high molecular weight, low chroma and wide application scope, which could generate a variety of materials with special ftinctions when modified with such material as PET composite.

U.S. Pat. No. 3,297,033 discloses a process wherein high molecular weight polyvinyl alcohol acid is prepared. The purified glycolic acid is converted into oligomer, whose depolymerization subsequently yield cyclic ester monomer containing hydroxy carboxylic acid. Finally, the cyclic ester is heated and melted in the presence of catalysts, and then the ring-opening polymerization of molten cyclic ester is carried out.

Despite its capacity of producing polyglycolic acid with high molecular weight, the method is disadvantaged by its complex process, high costs, and especially the demand of high-purity cyclic esters.

Chinese Pat. No. lOI,374,883A discloses a synthesis method for the preparation of aliphatic polyester via the ring-opening polymerisation of cyclic esters. Cyclic esters are pre-polymerized first. Then the molten materials of the pre-polymer are introduced into the twin-screw mixing device continuously. The solid phase polymerization of pulverized solid pre-polymer is further carried out. Then the polymers and stabilizers are melted together to carry on the granulation. The preparation of high molecular weight polyglycolide acid requires the solid-state polycondensation with time-consuming and discontinuous process and complicated equipments.

Chinese Pat. l,544,503A discloses a technology for producing polyvinyl alcohol acid, which is prepared by using low boiling point solvents capable of dissolving chlorine and alkaline reagent as catalysts and maintaining appropriate reaction concentration, temperature, reaction time and washing condition. The lower molecular weight of the polymer obtained by this method can not meet the standard of practical application.

The intense toxicity and corrosion of the raw material chioroacetic acid could serve as another disadvantage.

Yamane (JP-A 2009-185065) discloses a process wherein water solution of industrial ethanol acid with the concentration of 70% is charged into the stirred reaction under ordinary pressure at 170 200°C for 2 hours before distillation. The reaction continues under the pressure of 5kPa at 200°C for another 2 hours until the unreacted reagents with low-boiling point are removed and PGA oligomers with high yield, whose molecular weight lies in the range from 20,000 to 100,000, are obtained.

According to Takahashi (Polymer, 2000,41(24):8725-8728) , mixed with the catalyst zinc acetate dehydrate, glycolic acid is stirred under the pressure of 2OkPa at 190°C for one hour, then continuously react under 2OkPa at 190°C for 1 hour, then continuously reacted for 4 hours under 4kPa. The solid product of Mw 91,000, similar to that prepared by ring open polymerization, was obtained after melting at 230°C and quickly cooling to 190°C.

According to Nanjo Kazunari (JP-A 2006-182017), 20 kg glycolic acid was stirred at 170°C for 4 hours with 4g SnCI4 as catalyst under N2 atmosphere, then the solid product was crushed into 3mm granules and dried at 150°C under 0.lkPa for 24 hours. At last the polymer was obtained with Tm 228°C, melt viscosity (250°C, 100s1) 2200Pas, and could be used to prepare film by biaxial tension technology.

In summary, currently polyglycolide acid is mainly synthesized by virtue of the reaction kettle intermittent preparation method or other partially continuous preparation process, hut completely continuous production is far from being achieved. This situation leads to such adverse conditions for industrial production as the longer polymerization reaction time, the darker color of the product, the difficult removal of material from the reaction system and so on. Therefore, the invention proposes that the raw material cyclic ester should be charged directly into the screw type reactor for the continuous and rapid preparation of polyglycolide acid, which is superior in its shorter reaction time and brighter color. Antioxygen and end blocking agent can be added in the middle and rear section of the extruder in order to adjust the color of the polyglycolide acid and to improve its stability.The continuous process of the invention makes it adaptable to large-scale production.

DISCLOSURE OF INVENTION

4, An object of the present invention is to overcome the shortcomings of the above existing techniques, and provide a fast method for preparing the polyglycolide acid via chemical synthesis.

Process for the preparation of high molecular weight polyglycolide acid is carried out continuously in accordance with the following steps.

(1) Under the protection of inert gases (nitrogen or argon), the annular lipid monomers and the catalysts are continuously and uniformly added into the screw extruder provided with heating segments the temperature of which can be regulated to carry on the polymerisation.

With basically the same charging and discharging speed, products are obtained in a rapid and continuous way. (2) Mixed with hydroxy acid, antioxygen and end blocking agents are added directly in the middle and rear section of the extruder in order to adjust the color of the polyglycolide acid and to improve its stability.

Cyclic ester monomers described in this invention are selected mainly from the group: glycolide, lactide, Ding gamma lactone, Delta valerolactone, epsilon caprolactone and mixture of two or more of these monomers, preferably glycolide and lactide, whose mass fraction accounts for no less than 90% in mixed cyclic esters.

Catalysts described in the present invention are Lewis acids, and are specifically guanidinium salt, organic ammonium salts, calcium acetate, zinc acetate, zinc acetate dihydrate, Sb2S3, Ge02, Sb203, SnCl2, SnCI2H20, stannous octoate, SnCl4, SnO, Cr203, Ti02, complex titanium catalyst, preferably zinc acetate dihydrate, Sb203, SnCl2H20, or any two or more composite catalysts.

Catalysts described in the present invention are the oxides or metal salts of zinc, antimony, germanium, tin and titanium.

Catalysts described in the present invention added to the cyclic ester monomer is 20-2000ppm, preferably 50-1000 ppm, which enables the molecular weight of the polymer and characteristic viscosity to reach more than 200,000 and more than 1 respectively. At the same time, the amount of the catalysts has a significant effect on the color of the polyglycolide acid, When the amount of catalysts is lower than l000ppm, the yellowness index of polyglycolide acid stays below 50.

According to this invention, catalysts and monomers are crushed into evenly mixed powder, molded into granules, or evenly mixed in the melt pump before entering the reactor.

According to this invention, the reaction temperature in each segment of the reactor is preferably in the range between 160°C and 260°C, particularly between 190°C and 230°C, which could effectively regulate the molecular weight and yellowness index of polyglycolide acid.

The reaction temperature can be regulated according to the characteristics of the product. The molecular weight of the polymers ranges from 50,000 to 1,000,000, while their yellowness index is in the range between 2 and 50.

In the process of this invention, screw extruders with 2-10 segments are preferable, particularly those with 6 segments. Each segment is heated up to the reaction temperature by means of electric heating or oil bath heating; the single-screw or twin-screw reactor contains a semi-closed device capable of controlling both the reaction time and the screw speed.

Being vital to the mass and heat transfer of the reagents, the rotational speed of the reactor also exerts a certain effect on the even distribution of the polymer's.molecular weight. The rotational speed is preferably maintained at 5-150 revolutions per minute, particularly 20-80 revolutions per minute, adjusted according to the quality of products.

Molecular weight distribution, represented by the weight-average molecular weight I number-average molecular weight (Mw/Mn) ratio, ranges from 0.8 to 3.0.

The reaction time of the invention has a greater effect on the properties of the polymers. With the increase of reaction time, the intrinsic viscosity of the polymer increases and then decreases within a range, e.g. when the catalyst is SOOppm, the intrinsic viscosity of polyglycolide acid reaches its maximum 0.9ldL/g after 8 minutes at 20000; and subsequently with the increase of reaction time, the intrinsic viscosity begins to fall. The intrinsic viscosity declines to 0.66dL/g when the dwell time is 40 minutes. Therefore the reaction time is preferably in the range between 1 and 100 minutes, particularly between 3 and 30 minutes.

In order to reduce the chroma of polyglycolide acid, an antioxygen charging opening is added in the middle and rear section of the screw extruder, so that mixture of phosphate esters or phosphite antioxygen can be added into the extruder so as to prevent the further coloration of the polyglycolide acid in the discharging and subsequent processing period. The preferable antioxygen include BIS eighteen alkyl phosphate, Didodecyl phosphate, Double 2,4-tert butyl phenyl phosphate, Eighteen alkyl phosphate, Twelve alkyl phosphate, Three phenyl phosphate, Three (2,4-dibutyl) phenyl phosphite, etc. The antioxygen preferably accounts for 0.1-5% of amount of the cyclic esters, particularly between 0.5% and 2%.

In order to obtain polymers with stable molecular weight, an charging opening for carboxyl end-blocking agents is added in the middle and rear section of the screw extruder so as to meet the different requirements concerning the water resistant capacity of the polymers. The preferable carboxyl end blocking agents are N, N- 2,6-diisopropylcarbodi imide, N, N-dicyclohexylcarbodiimide, 2-phenyl-2-oxazoline, carbonyl cyclohexene etc. The carboxyl end blocking agents preferably account for 0.01-2% of the amount of cyclic esters, particularly between 0.1% and 1%.

In order to obtain a polymer with fewer residual monomers, prepared polyglycolide acid goes through the solid phase polymerization under lower pressure at 120-180°C so as to pump out the unreacted residual monomers and narrow down the molecular weight distribution of the polymers. The preferable pressure is 0.01 -5Kpa, particularly 0.1-1 Kpa.

The preferable time limit for the solid phase polymerization is 1-50 hours, particularly 2-10 hours.

At 180-240°C, the prepared polyglycolide acid possesses a stable melt viscosity. Its retention of melt viscosity, defined by the proportion of viscosity (6O) measured after a 60-minute retention at 250°C to the initial viscosity (i-jO) measured after 5-minute preheating at 250 °C [(i60/0) xlOOI, is at least 45%. Consequently polyglycolide acid possesses better durability and superior outside shape retention.

The polyglycolide acid prepared in this invention is characterized in: (1) a weight-average molecular weight (Mw) in the range of 10,000 to 1,000,000; (2) a molecular weight distribution in the range of 0.8 to 3.0 as defined by the weight-average molecular weight-to-number-average molecular weight ratio(Mw/Mn), and (3) a yellowness index (Yl) of up to 50 as measured using a sheet obtained by press molding and crystallization; (4) a retention of melt viscosity of at least 45% as defined by the proportion of viscosity (60) measured after a 60-minute retention at 250°C to the initial viscosity (DO) measured after 5-minute preheating at 250°C [(i601n0) xlOO].

The polyglycolide acid is preferably glycolic acid, polylactic acid or their copolymers.

The invention relates to a continuous process for the preparation of polyglycolide acid. With appropriate reaction conditions, the polymers with excellent melt stability can be obtained. Characterizing in the higher viscosity, better intensity and shape retention and the lighter color, the polymers can be used directly as degradable plastics. With the advantages of higher production rate and continuous reacting process, the method for preparing polyglycolide acid mentioned in this invention is suitable for industrial production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the infrared spectra of the prepared polyglycolic acid in

Example 1;

FIG. 2 is the HNMR spectra of the prepared polyglycolic acid in

Example 1;

FIG. 3 is the DSC curve of the prepared polyglycolic acid in

Example 1;

FIG. 4 is the XRD spectra of the prepared polyglycolic acid in

Example 1;

FIG. 5 is the polymerization chart of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described more specifically based on Examples and Comparative Examples with glycolide and lactide as raw materials polymerized in 6 zones twin-screw extruder ( Haake Reomex OS PTW16 System).

In the following descriptions, "%" and "ppm" refer to weight unless otherwise noted specifically.

H All the materials (or reagents) and instruments could be bought from market.

The physical properties (values) are based on values measured according to the following methods: FT-JR spectra were obtained by using Fourier transform infrared Spectrometer in ICBr.

H NIVIR spectra were recorded in CF3COOD at ambient temperature, and NIvIR chemical shifts are expressed relative to TMS as the internal standard.

X-ray diffraction is measured under Cu Ka irradiation at 30 mA with slit DSSS1°, RS=0.3mm, and the scan range is between 5° and 80° at the scan rate of 10°/mm.

The degree of crystallization (Xc) was also evaluated according to the intensity of the crystalline peak area and the overall intensity for both the amorphous and crystalline areas by equation (a).

Xc =Ac/(Ac+Aa)* 100% (a) Ac -crystalline peak area Aa -amorphous peak area Differential scanning calorimetry (DSC) scans were performed using a Perkin-Elmer 8500. Samples were heated from 50°C to 250°C at the rate of 20°C/mm, after holding for 1.0mm, and were cooled to 50°C at the rate of 10CC 7mm under nitrogen flow of 4OmL/min.

Intrinsic viscosity was measured at 25°C by using a Ubbelohde viscosimeter (internal diameter 0.5-0.6mm) after 25mg polymer dissolving in hexafluoroisopropanol (HFJP) with the concentration of 5mM. The time of pure HFIP and polymer solvent flowing through Ubbelohde viscosimeter is to and t respectively. The following equation was used to calculate the intrinsic viscosity: [i]=[2( ?7-ln Jlr)I 2ic (b) qr-tlto Relative viscosity; mr q-1 Specific viscosity Each sample will be measured for 3 times, and the average value of time (t) is obtained for calculating i.

Measurement of weight-average molecular weight and its distribution: The sample was dissolved in a solution with 5mM of sodium trifluoroacetate dissolved in hexafluoroisopropanol (HFIP) to prepare a ijL of solution, whose mass fraction ranged from 0.05-0.3%.; After the sample solution was filtered through a membrane filter, it was charged into a gel permeation chromatograph (GPC) to measure its molecular weight. Five standard PMIMAs having different molecular weights were used for molecular weight calibration.

Measurement of melt viscosity: Ten (10) grams of polyglycolide acid ester sandwiched between aluminum sheets were placed on a press machine preheated to 240°C. After a 30-second preheating, the acid was pressed at 5 Mpa for 15 seconds, after which it was rapidly cooled to make a sheet. The thus obtained amorphous sheet was heated at 150°C. in an oven for 15 minutes for crystallization. The weight of the melt viscosity-measuring sample was 7 grams. This sample was put into a cylinder having an inside diameter of 9.55 mm in Capirograph 3C made by Toyo Seiki Co., Ltd., said cylinder being set at 240°C. Then the sample was preheated for 5 minutes, after which the resin was extruded out of a die of 1 mm in inside diameter and 1 mm in length at a shear rate of 122/second, and the melt viscosity (Pas) of the sample was found from the then stress.

Measurement of per cent loss in weight: Using TG5O made by Melter Co., Ltd. in a nitrogen atmosphere wherein nitrogen prevails at a flow rate of lOml!min., polyglycolic acid was heated from 50°C. at a heating rate of 2°C! mm to measure the per cent loss in weight. The temperature at which the weight (W50) at 50°C of polyglycolic acid shows a 1% loss was precisely read out.

Measurement of residual monomers: Ca. 300mg of the sample was dissolved in ca 6mg of a dimethyl sulfoxide (DM50) solution containing 4-chlorobenzophenone and acetone under heating at 150°C for ca. 10 mm., followed by cooling to room temperature and filtration. 2 jil of the filtrate liquid was injected into a GC apparatus. From values obtained in the measurement, a glycolide content (wt. % in the polymer) was calculated. The GC analysis conditions are as follows: Apparatus: "GC-2010" made by K. K. Shimadzu Seisakusho.

Column: "TC -17".

Column temperature: Held at 50°C. for 5 mm., heated at 270°C. at a rate of 20 C.! mm. and then held at 270°C. for 4 mm.

Gasification chamber temperature: 200°C.

Detector: FID (hydrogen flame ionization detector) at 300°C.

Measurement of Yellowness Index (Yl): Ten (10) grams of polyglycolic acid were placed on a press machine preheated to 240°C to make a 0.5 mm sheet, which was heated at 100°C for crystallization.

Using Color Analyzer SF 600 made by Plus CT Ca, Ltd., the yellowness index (Yl) of the crystallized sheet was determined. Three measurements were obtained under the conditions of field of view of 2°C, standard light C, and measurement of reflected light to calculate their average defining the yellowness index (Yl) of the sample.

EXAMPLE 1

l000g of glycolide and 5Oppm SnCIv2H2O were mixed by grinder, and fed continuously via a shaking trough to a twin-screw extruder having six heating zones (Fig. 5). The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 10 rpm; Temperature settings: zone 1-2 = 200°C; zone 3-4 = 210°C; zone 5-6 = 190°C; Residence time: 10mm. The polymer had a molecular weight of 180,000(Mw), molecular weight distribution of 2.5; yellowness index of 25.6; melt viscosity of 500Pas.

EXAMPLE 2

l000g of glycolide and SOOppm SnCIv2H2O were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 30 rpm; Temperature settings: zone 1-2 = 210°C; zone 3-4 = 220°C; zone 5-6 = 190°C; Residence time: 3mm. The polymer had a molecular weight of 250,000(Mw), molecular weight distribution of 1.8; yellowness index of 28.8; melt viscosity of 620Pas.

EXAMPLE 3

l000g of glycolide and 2000ppm SnCl22H20 were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 80 rpm; Temperature settings: zone 1-2 = 2 10°C; zone 3-4 = 220°C; zone 5-6 = 190°C; Residence time: 1.0mm. The polymer had a molecular weight of 245,000(Mw), molecular weight distribution of 2.0; yellowness index of 47.1; melt viscosity of 61 OPa s.

EXAMPLE 4

l000g of glycolide and 200ppm SnClv2H2O were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 5 rpm; Temperature settings: zone 1-2 = 200°C; zone 3-4 = 210°C; zone 5-6 = 190°C; Residence time: 30mm. The polymer had a molecular weight of 160,000(Mw), molecular weight distribution of 2.1; yellowness index of 43.6; melt viscosity of 480Pas.

EXAMPLE 5

1 000g of glycolide and 200ppm SnC12 2H20 were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 45 rpm; Temperature settings: zone 1-2 = 220°C; zone 3-4 = 210°C; zone 5-6 = 190°C; Residence time: 3.0mm. The polymer had a molecular weight of 355,000(Mw), molecular weight distribution of 2.2; yellowness index of 21.6; melt viscosity of78OPas.

EXAMPLE 6

l000g of glycolide and 200ppm SnClv2H2O were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 150 rpm; Temperature settings: zone 1-2 = 220°C; zone 3-4 = 2 10°C; zone 5-6 = 190°C; Residence time: 1.0mm. The polymer had a molecular weight of 235,000(Mw), molecular weight distribution of 1.5; yellowness index of 20.3; melt viscosity of 600Pws.

EXAMPLE 7

l000g of glycolide and SOOppin SnC1v2H2O were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 50 rpm; Temperature settings: zone 1-2 = 240°C; zone 3-4 = 210°C; zone 5-6 = 160°C; Residence time: 2.0mm. The polymer had a molecular weight of 265,000(Mw), molecular weight distribution of 2.4; yellowness index of 16.3; melt viscosity of660Pas.

EXAMPLE 8

1 000g of lactide and 3 O0ppm SnC12 2H20 were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 40 rpm; Temperature settings: zone 1-2 = 220°C; zone 3-4 = 220°C; zone 5-6 = 200°C; Residence time: 2.4mm. The polymer had a molecular weight of 305,000(Mw), molecular weight distribution of 2.2; yellowness index of 24.2; melt viscosity of 750Pa s.

EXAMPLE 9

500g of glycolide, 500g of lactide and 600ppm SnC122H20 were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 130 rpm; Temperature settings: zone 1-2 = 180°C; zone 3-4 = 190°C; zone 5-6 = 170°C; Residence time: 1.6mm. The polymer had a molecular weight of 195,000(Mw), molecular weight distribution of 2.1; yellowness index of 33.1; melt viscosity of48OPas.

EXAMPLE 10

l000g of glycolide, 50g of s-caprolactorte and 600ppm SnCIv2H2O were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder. The reaction condition was: Feeding speed: 1kg/h; Rotational speed of extruder: 30 rpm; Temperature settings: zone 1-2 = 220°C; zone 3-4 = 2 10°C; zone 5-6 = 190°C; Residence time: 3.0mm. The polymer had a molecular weight of 295,000(Mw), molecular weight distribution of 2.8; yellowness index of 28.2; melt viscosity of 720Pas.

EXAMPLE 11

1 000g of glycolide and óOOppm SnC12' 2H20 were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder.

I OOg masterbatch containing 10%(mass percent) antioxygen of triphenyl phosphate was added to the 5th segment of the reactor.The reaction condition was: Feeding speed of glycolide: 1kg/h; Feeding speed of antioxygen: 1 OOg/h Rotational speed of extruder: 30 rpm; Temperature settings: zone 1-2 = 220°C; zone 3-4 = 2 10°C; zone 5-6 = 190°C; Residence time: 3.0mm. The polymer had a molecular weight of 225,000(Mw), molecular weight distribution of 2.3; yellowness index of 18.2; melt viscosity of65OPas.

EXAMPLE 12

l000g of glycolide and 600ppm SnClr2H2O were mixed by grinder, and fed continuously via a shaking trough to the twin-screw extruder.

1 OOg toluene solvent containing 10% (mass percent) N, N-dicyclohexylcarbodiimide was added to the 5th segment of the reactor.The reaction condition was: Feeding speed of glycolide: 1kg/h; Feeding speed of end blocking agent: lOOg/h Rotational speed of extruder: 30 rpm; Temperature settings: zone 1-2 = 220°C; zone 3-4 = 210°C; zone 5-6 = 190°C; Residence time: 3.0mm. The polymer had a molecular weight of 252,000(Mw), molecular weight distribution of 2.0; yellowness index of 23.5; melt viscosity of68OPas.

EXAMPLE 13

l000g polymer prepared in example 13 was sealed and stirred continuously in high pressure reaction kettle at 160°C for 5 hours under the pressure of 2Mpa. Then the pressure was reduced to lkPa, and polymer with molecular weight of 552,000 (Mw), molecular weight distribution of 2.3, yellowness index of 33.5, melt viscosity of 880Pas.

was obtained after 2 hours.

Figure 1 is the FT-JR spectra of PGA in example 1. 1 746cm1 is the peak of C0 stretching vibration. 1154 cm1 and 1089cm' are the peaks of C-O-C absorbtion. 3515 cm1 is the peak of-OH at the end of polymer chain. 2993 cm1 is the peak of C-H stretching vibration. 1419 cm1 is the peak of CH2 absorbtion. Therefore, the prepared polymer was confirmed to be PGA.

Figure 2 is the 1JJNR spectra of PGA in example 1. The simple structure of PGA is characterized in this figure: 811.5 is the source of CF3COOD solvent, and 85.160 is the peak of hydrogen in (OCH2CO).

Figure 3 is the X-ray diffraction spectra of PGA. It is shown in this picture that PGA is half crystallization polymer, and the degree of crystallinity is 63.33% with 20 at 22.2° and 29.10.

Figure 4 is the DSC curve of PGA. In this figure, glass transition temperature is 36.4°C; crystallization temperature is 175.1°C; melt point is 219.7°C.

Figure 5 is the diagram for preparing PGA. The adding part could be continuous feeding funnel or melt pump; the reactor is tube type charged with screw mixter, and the reaction temperature could be controlled on different zones. In the middle or end of the reactor, antioxygen and end blocking agent could be added, then the product can be pelleted after being dried by solvent or air cooling.

Claims

We claim: 1. Process for the preparation of high molecular weight polyglycolide acid, characterised in that the polyrnerisation process is carried out continuously in accordance with the following steps.(1) Under the protection of nitrogen or argon, annular lipid monomers and catalysts are continuously and uniformly added into the screw extruder provided with heating segments, the temperature of which can be regulated to carry on the polymerisation. With basically the same charging and discharging speed, products are obtained in a rapid and continuous way. (2) Mixed with polyglycolide acid, antioxygen and end blocking agents are added directly in the middle and rear section of the extruder in order to adjust the color of the polyglycolide acid and to improve its stability.
2. Process according to claim 1, characterised by a cyclic ester monomer selected mainly from the group: glycolide, lactide, Ding gamma lactone, Delta valerolactone, epsilon caprolactone and mixture of two or more of these monomers, preferably glycolide and lactide, whose mass fraction accounts for no less than 90% in mixed cyclic esters.
3. Process according to claim 1, characterised by a catalyst selected from the group: guanidinium salt, organic ammonium salts, calcium acetate, zinc acetate, zinc acetate dihydrate, Sb2S3, 0e02, Sb203, SnCI2, SnCI2H20, stannous octoate, SnCI4, SnO, Cr203, Ti02, complex titanium catalyst, preferably zinc acetate dihydrate, Sb203, SnC1vH2O, or any two or more composite catalysts.
4. Process according to claim 1, characterised by a catalyst selected from the oxides or metal salts of zinc, antimony, germanium, tin and titanium.
5. Process according to claim I, characterised in that the amount of the catalysts added to the cyclic ester monomers is 20-2000ppm, preferably 50-l000ppm, which enables the molecular weight of the polymer and characteristic viscosity to reach more than 200,000 and no less than I respectively
6. Process according to claim 1, characterised in that catalysts and monomers are crushed into evenly mixed powder, molded into granules, or evenly mixed in the melt pump before entering the reactor.
7. Process according to claim 1, characterised in that the screw extruders with 2-10 segments are preferable, those with 6 segments being the best.
8. Process according to claim 1, characterised in that the rotational speed of the extruder is maintained at 5-150 revolutions per minute, preferably 20-80 revolutions per minute, adjusted according to the quality of products. Molecular weight distribution, represented by the weight-average molecular weight I number-average molecular weight (Mw/Mn) ratio, ranges from 0.8 to 3.0.
9. Process according to claim I, characterised in that the reaction time is preferably in the range between I and 100 minutes, particularly between 3 and 30 minutes; antioxygen and end blocking agent can be added in the middle and rear section of the extruder in order to adjust the color of the poly hydroxy acid and to improve its stability.