A biodegradable copolymer, a biodegradable polymer composition, a biodegradable article, and a preparation process thereof

Abstract: Disclosed are a biodegradable copolymer, a biodegradable copolymer composition, a biodegradable article molded from a copolymer and a process for the preparation of a biodegradable lactone-carbonate random copolymer which comprises a ring-opening addition polymerization of an admixture composed of a lactone monomer and a cyclic carbonate monomer with a ring-opening initiator in the presence of an organic aluminum-based Lewis acid. The copolymers and articles of the present invention are excellent in biodegradability.

Description: FIELD OF THE INVENTION The present invention relates to a biodegradable copolymer and a biodegradable copolymer composition. Furthermore, the present invention relates to a biodegradable article molded from the copolymer or the copolymer composition. In more detail, the present invention relates to a copolymer or a composition which is capable of being applied as materials for various molded containers such as bottles, trays, box-type packages, and various molded articles, such as films for laminating the inside of paper containers, films for wrapping, films for agricultural uses, fibers, lines for fishing, ropes, nonwoven clothing, nets for construction, etc., which are substantially disposed in surroundings or circumstances in view of purposes for the use thereof. BACKROUND OF THE INVENTION Generally speaking, synthetic high polymers have been used as materials for various molded articles because of their excellence in mechanical properties and moldability, etc., and low price. However, molded articles cannot be naturally degraded even when disposed or buried, because of their durability, for example, weatherability, etc., and further, in the case when such articles are burned, these may damage incinerators because of the high-calorie energy generated in the burning thereof. Accordingly, methods for disposing of plastic wastes have recently become problematic. Therefore, there have been discovered synthetic high polymers from which compounds not adversely affecting surroundings or circumstances and living bodies are produced by biodegradation. As synthetic high polymers, poly(epsilon-caprolactone)s are known, and a demand thereof in the market has increased because of being manufactured at a relatively low price and as a safe biodegradable resin. The magazine Pratical and Biodegradable Plastics (page 42, 1992) published by CMC, Ltd., cites many references described concerning the biodegradability of a poly(e-caprolactone). In 1972, Potts et al. found that a poly(epsilon-caprolactone) having a high molecular weight (40,000) disappeared after being buried for 1 year [Am. Chem. Soc. Polymer Preprint, 13, 629 (1972)]. In 1975, Diamond et al. reported that a film prepared from a poly(epsilon-caprolactone) was degraded by Aspergillus or in soil [Int. Biodetr. Bull., 11, 127 (1975)]. In 1976, Tokiwa et al reported that a poly(epsilon-caprolactone) having a number average molecular weight of 25,000 was almost completely degraded in 12 days by a fungus of Penicillium sp. Strain 26-1 isolated from soil [J. Ferment Technol., 54, 603 (1976)]. According to unpublished data provided by the Biodegradable Plastics Study Party/Technology Meeting, as a result of field tests by burying in soil and immersion in water carried out by the Biodegradable Plastics Study Party, it is reported that disappearance of poly(epsilon-caprolactone)s began after 6 months in many places and it disappeared after 1 year in almost all places. However, the biodegradation rate is largely affected by the conditions in surroundings or circumstances, specifically, soil or types of microorganisms and living concentrations thereof, and temperatures. Accordingly, it is supposed that such a biodegradation rate in poly(epsilon-caprolactone)s is not occasionally satisfied, depending upon the uses. Furthermore, Japanese Patent Publication (Kokoku) No. 3396/1967 states that useful polymer products can be prepared by bulk polymerization, suspension polymerization, and solution polymerization using a larger mol% of a cyclic ester such as epsilon-caprolactone and a smaller mol% of a cyclic carbonate monomer such as 4,4-dimethyl-2,6-dioxacyclohexanone, and polymer products are useful for manufacturing grips for brushes, buttons, lamp stands, and toys, etc. However, Kokoku No. 3396/1967 does not state that copolymers and copolymer compositions thereof described in the present invention are biodegradable, or that biodegradable articles molded therefrom. In the meantime, Japanese Patent Unexamined Publication (Kokai) No. 294326/1990 states a process for the preparation of a block copolymer composed of a lactone monomer and a cyclic carbonate monomer in which there is employed an organometallic compound such as n-BuLi, etc., as an initiator. Furthermore, there is known a process for the preparation of a lactone-carbonate block copolymer in which there is employed a trimethyl aluminum-water complex or a rare earth metal as an initiator. Still further, Y. Okamoto reports in Macromol. Chem., Symp. 42/43, 117-133 (1991), that a cationic ring-opening polymerization process for the preparation of a lactone polymer having low molecular weight in which there is employed a triethyloxonium-hexafluorophosphate as an initiator. In addition, US Patent No. 3,301,824 discloses a process for the preparation of a homopolymer of a cyclic carbonate monomer and a graft polymer of a cyclic carbonate monomer and a lactone monomer using stannous chloride or tin octylate, etc., as catalysts. In addition, Japanese Patent Unexamined Publication (Kokai) No. 502651/1991 (corresponding to W089/05664 Publication) also discloses the use of a copolymer having recurring carbonate units as bioresorbable medical devices capable of being assimilated by living bodies by degrading into biologically innocuous components after degradation or implantable and undegradable medical devices having affinity to blood and/or living bodies. In Kokai No. 502651/1991, there are employed tin salts such as stannous octoate (2-ethyl-hexanoate), etc., as catalysts for preparing the random copolymer. Also, Japanese Patent Unexamined Publication (Kokai) No. 508627/1-993 (corresponding to W091/16887 Publication) discloses the use of a random copolymer composed of trimethylene carbonate and caprolactone as a biodegradable reservoir device. Also, in Kokai No. 508627/1993, there are employed tin salts such as stannous octoate (2-ethyl-hexanoate) or stannous chloride, etc., as catalysts for preparing the random copolymer. More specifically, Kokai No. 508627/1993 discloses the use of a random copolymer composed of trimethylene carbonate and caprolactone as a biodegradable reservoir device or bioabsorbable pharmaceutical devices (e.g., a cylindrical capsule having a 2.4 mm outer diameter and a thickness of 0.1-0.3 mm) for a drug delivery system which can sustainably discharge medicines in living bodies. In view of this background, and as a result of extensive investigation, the inventor of this invention has now found that a novel copolymer prepared by the copolymerization of epsilon-caprolactone or delta-valerolactone with oxetane and copolymer composition thereof are excellent in biodegradability, and therefore articles molded therefrom are exceedingly useful as biodegradable articles, and the present invention has been now completed. SUMMARY OF THE INVENTION It is an object of the present invention to provide a biodegradable copolymer, a biodegradable copolymer composition, biodegradable molded article therefrom, and a process for the preparation of a copolymer. A first aspect of the present invention relates to a biodegradable copolymer having a number average molecular weight ranging from 1,000 to 1,000,000 which comprises (A) from 5 to 99% by mol of epsilon-caprolactone or delta-valerolactone structural units and (B) from 95 to 1% by mol of oxetane structural units, said structural units being combined in the state of a block. A second aspect of the present invention relates to a biodegradable polymer composition which comprises (D) from 60 to 95% by mol of a poly(epsilon-caprolactone) or poly(delta-valerolactone) and (E) from 40 to 5% by mol of a poly(oxetane). A third aspect of the present invention relates to a biodegradable article molded from a copolymer in the first aspect. A fourth aspect of the present invention relates to a biodegradable article molded from a copolymer composition in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 (Example 2) is a graph representing a remaining ratio of weight versus incubation time by an enzyme for degradation related to the copolymer obtained in Example 1. Figure 2 is a graph representing a remaining ratio of weight versus incubation time without an enzyme for degradation in Example 2. Figure 3 (Example 4) is a graph representing a remaining ratio of weight versus incubation time by an enzyme for degradation related to the copolymer obtained in Example 3. Figure 4 is a graph representing a remaining ratio of weight versus incubation time without an enzyme for degradation related to the polymer obtained in Example 5. Figure 5 (Example 7) is a graph representing a remaining ratio of weight versus the time of period buried in active sludge related to the polymer obtained in Example 6. Figure 6 (Example 8) is a graph representing a remaining ratio of weight versus incubation time by an enzyme for degradation related to the copolymer obtained in Example 6. Figure 7 is a graph representing a remaining ratio of weight versus incubation time without an enzyme for degradation in Example 8. Figure 8 (Example 9) is a graph representing a remaining ratio of weight versus incubation time by the enzyme Lipase B for degradation related to the copolymer obtained in Example 6. Figure 9 (Example 9) is a graph representing a remaining ratio of weight versus incubation time by the enzyme Rhizopus delmer Lipase for degradation related to the copolymer obtained in Example 6. Figure 10 (A) is an 1H-NMR chart related to the components produced by degradation in Example 8, and Figure 10 (B) is an 1H-NMR chart related to the caprolactone homopolymer (CL). Figure 11 (Example 12 and Comparative Example 13) is a graph representing a remaining ratio of weight versus incubation time by the enzyme for degradation related to the dimethyltrimethylene carbonate (DTC) homopolymer (Comparative Example 6), the valerolactone-dimethyltrimethylene carbonate (VL/DTC) block copolymer (Example 11), and the valerolactone (VL) homopolymer (Comparative Example 12). DETAILED DESCRIPTION OF THE INVENTION The present invention will be described hereinafter in more detail. According to a first aspect of the present invention, there is provided a biodegradable copolymer having a number average molecular weight ranging from 1,000 to 1,000,000 which comprises (A) from 5 to 99% by mol of epsilon-caprolactone or a delta-valerolactone structural unit and (B) from 95 to 1% by mol of an oxetane structural unit, said structural units being combined in the state of a block. According to a second aspect of the present invention, there is provided a biodegradable polymer composition which comprises (D) from 60 to 95% by mol of a poly(epsilon-caprolactone) or a poly(delta-valerolactone) and (E) from 40 to 5% by mol of a poly(oxetane). According to a third aspect of the present invention, there is provided a biodegradable article molded from a copolymer having a number average molecular weight ranging from 1,000 to 1,000,000 which comprises (A) from 5 to 99% by mol of epsilon-caprolactone or delta-valerolactone structural unit and (B) from 95 to 1% by mol of an oxetane structural unit, said structural units being combined in the state of a block. According to a fourth aspect of the present invention, there is provided a biodegradable article molded from a biodegradable copolymer composition which comprises (D) from 60 to 95% by mol of a poly(epsilon-caprolactone) or poly(delta-valerolactone) and (E) from 40 to 5% by mol of a poly(oxetane). Monomers to be employed in the biodegradable copolymers or composition, and the biodegradable articles of the present invention include epsilon-caprolactone, delta-valerolactone, and oxetane (another name for this is trimethylene oxide or 1,3-epoxypropane), which are essential structural units, respectively. The biodegradable copolymer which is the first aspect of the present invention is an epsilon-caprolactone-oxetane copolymer of delta-valerolactone oxetane copolymer which is a block type. The block copolymers are not particularly limited in the type of their block structures, which include a random block type, diblock type, triblock type, etc., which types include a linear chain type, a branch chain type, and a radial chain type. The above-described block copolymers essentially have a number average molecular weight ranging from 1,000 to 1,000,000, preferably from 10,000 to 500,000, more preferably from 30,000 to 300,000 based on a standard polystyrene measured by a GPC. In the case when the number average molecular weight is less than 1,000, the copolymers are frequently in liquid states at ordinary temperatures, unpreferably resulting in being incapable of using as molded articles. In contrast, in the case when it exceeds 1,000,000, it is substantially difficult to prepare the copolymers, and the biodegradability thereof would occasionally unpreferably lower. In the case when there are molded the above-described block copolymers alone or a mixed composition containing more than 50% by weight of the copolymers, the number average molecular weight preferably ranges from 30,000 to 300,000, more preferably from 50,000 to 200,000, from a viewpoint of a balance between mechanical properties, moldability, biodegradability, etc. The content of the epsilon-caprolactone structural unit of delta-valerolactone structural unit in the above-described block copolymers generally ranges from 5 to 99% by mol, preferably from 50 to 98% by mol, more preferably from 70 to 95% by mol, based on the total contents containing the oxetane structural units. In the case when the content is less than 5% by mol or exceeds 99% by mol, biodegradability thereof is unpreferably poor. In the biodegradable copolymer which is the first aspect of the present invention, a copolymer having a number average molecular weight ranging from 30,000 to 300,000, an epsilon-caprolactone structural unit or a delta-valerolactone structural unit ranging from 70 to 95% by mol and oxetane structural unit ranging from 30 to 5% by mol exhibits mechanical properties, thermal stability, and moldability, etc., equal to an epsilon-caprolactone or delta-valerolactone homopolymer, and it is particularly excellent also in biodegradability. The bond between the epsilon-caprolactone structural unit and the oxetane structural unit is represented by -CO-(CH 2 ) 5 -O-(CH 2 ) 3 -O-, and similarly, the bond between the delta-valerolactone structural unit and the oxetane structural unit is represented by -CO-(CH 2 ) 4 -O-(CH 2 ) 3 -O- which essentially constitutes the biodegradable copolymer which is the first aspect of the present invention. The biodegradable copolymers which are the first aspect of the present invention can be prepared without particular limitations, that is, the copolymers are prepared by any processes in which epsilon-caprolactone or delta-valerolactone can be copolymerized with oxetane. Specifically, there are preferred processes using an organometallic compound which is an initiator. As examples of the organometallic compound, there are specifically exemplified trialkylaluminum-water based complexes, zinc dialkylate-water based complexes, alkyl lithiums, organic potassium compounds, and organic sodium compounds. Of those, trialkylaluminum-water based complexes, more specifically, triethyl aluminum-water based complexes are preferably employed. In the above-described complexes, although a polymerization activity becomes maximum in the case when the molar ratio is 1/1, the molar ratio of water/ trialkylaluminum ranges preferably from 0.7 to 1.1. It is to be noted that there is no known copolymerization process between epsilon-caprolactone or delta-valerolactone and oxetane using the triethyl aluminum-water based complexes which is an initiator. In the case that the copolymer of the first aspect is prepared, oxetane is not readily copolymerized with epsilon-caprolactone due to the difference of the copolymerization rate between oxetane and epsilon-caprolactone. Accordingly, there is preferably carried out a process that oxetane alone is partially or totally polymerized using a triethyl aluminum-water-based complex as an initiator at a temperature ranging from -20 to 40°C, and then epsilon-caprolactone is charged to copolymerize with the resulting oxetane homopolymer at a temperature ranging from 0 to 180 C, preferably from 50 to 150°C. On the other hand, oxetane can be copolymerized with delta-valerolactone due to a similar copolymerization rate between oxetane and delta-valerolactone. Accordingly, there is preferably carried out a process in which oxetane and delta-valerolactone can be simultaneously charged to copolymerize using a triethyl aluminum-water-based complex as an initiator at a temperature ranging from 0 to 180°C. In the case when the copolymerization is carried out beyond the above-described temperature range, the content of block type polymer would be unpreferably lowered. The biodegradable copolymers of the first aspect of the present invention can be prepared without any limitations using popular polymerization procedures and equipment for the preparation. As commonly used procedures, there are exemplified bulk polymerization, solution polymerization, and sedimentation polymerization. As the solvents in the above-described solution polymerization, there are employed aromatic hydrocarbons such as benzene, toluene, xylene, etc., ethers such as diethylether, etc. Also, the solvents can be mixed with aliphatic hydrocarbons such as hexane, heptane, cyclohexane, etc., in a range capable of dissolving the resulting polymers. As commonly used equipment for the preparation, there can be employed a continuous, semicontinuous, and batch-type equipment without any problem. Particularly, a Sultzer-mixer type or an extruder type continuous-polymerization equipment is preferably employed in bulk polymerization, in view of the capability of economically manufacturing the biodegradable copolymer of the present invention on a large scale. In the above-described bulk polymerization and procedures for the preparation, polymerization are preferably carried out in a temperature ranging from 40 to 180°C, and preferably from 100 to 170°C. In the case when the temperature is below 40°C, the viscosity of copolymers is too high, resulting in difficulty of manufacture, and, on the contrary, in the case when the temperature exceeds 180°C, there is caused the problem that a polymer unpreferably changes colors, and the content of the block type polymers is lowered. In solution polymerization of sedimentation polymerization, it is preferably carried out in a temperature ranging from -20°C to the boiling points of solvents. In the case when the temperature is below -20°C, the content of a block-type polymer would be unpreferably lowered, and polymerization rate would be unpreferably slow. On the contrary, in the case when the temperature exceeds the boiling points of the solvents, the polymerization stystem would be unpreferably maintained at compressed conditions. In the biodegradable copolymers of the first aspect in the present invention, other copolymerizable monomers can be employed together with epsilon-caprolactone, delta-valerolactone, and oxetane. Examples of other copolymerizable monomers include ethylene oxide, propylene oxide, tetrahydrofran, cyclic ethers such as dioxane or trioxane, beta-propiolactone, methylated caprolactone, lactones other than epsilon-caprolactone or delta-valerolactone, lactide which is a dimer of lactic acid, glicolides, cyclic carbonates such as trimethylene carbonate and methyltrimethylene carbonate, etc. Furthermore, the biodegradable copolymers of the first aspect in the present invention can be also mixed with each other, and further with other biodegradable or unbiodegradable thermoplastics in any mixing ratio. Specific examples of other biodegradable thermoplastics include a polylactic acid, a polyglicolide, an aliphatic polyester, polylactones such as a poly(epsilon-caprolactone) or a poly(delta-valerolactone), starch, celluloses, and hydroxyethyl celluloses, etc. The biodegradable polymer composition of the second aspect in the present invention is a mixed composition composed of poly(epsilon-caprolactone) homopolymer or a poly(delta-valerolactone) homopolymer and a poly(oxetane) homopolymer. In the biodegradable polymer composition, the poly(oxetane) homopolymer is employed in an amount ranging from 5 to 40 mol% based on the total amount. In the case when the amount exceeds 40 mol% by mol or it is below 5 mol% by mol, biodegradability is unpreferably poor in the copolymer composition. It is to be noted that the above-described "mol%" shows the content of oxetane units based on 100 mol% of each monomer unit in the homopolymers. Number average molecular weight in all of the homopolymers to be mixed ranges from 20,000 to 1,000,000, preferably from 30,000 to 500,000, and more preferably from 50,000 to 200,000. In the case when number average molecular weight is below 20,000, moldability is poor because of a low melt viscosity of the homopolymer. In the case when number average molecular weight exceeds 1,000,000, it is practically difficult to prepare the homopolymers, and biodegradability unpreferably tends to become poor. The biodegradable polymer composition of the second aspect in the present invention also includes a three-homopolymer admixture composed of a poly(epsilon-caprolactone) homopolymer, a poly(delta-valerolactone) homopolymer, and a poly(oxetane) homopolymer. A process for mixing the homopolymers is not limited, a conventional melt kneader such as an extruder can be preferably employed in an industrial fashion. The biodegradable copolymers of the first aspect and the biodegradable polymer composition of the second aspect in the present invention can provide the biodegradable articles of the third and fourth aspect, respectively. The biodegradable articles can be molded from biodegradable copolymers and the biodegradable polymer composition. Biodegradable articles include all products which are usually left consciously or unconsciously in living circumstances from the viewpoint of usage. Hitherto, there has been a problem that the products molded from resins were generally left in our living circumstances or surroundings without degradation for a long period after uses. The products include, for example, materials for agricultural uses such as films or nonwoven clothing, textiles, ropes, materials such as films or nonwoven clothes for engineering works, materials such as nets for construction use, materials such as oil spill blotters for protecting the environment, materials such as lines or nets for fishing, various foam materials (for example, life preservers, materials for cushions, buoys or markers for fishing nets, etc.), coatings for ships (coatings for bottom of ships), films for protecting bottom of boats, bottles, trays, various containers such as box-type packages, internal films for laminating on paper containers, wrapping films for waste or shopping, cushion materials or protective films for goods to be exported (electrical appliances, precision parts, large-scale equipments), etc. The above-described products molded from biodegradable copolymers or polymer compositions can be biologically degraded by being left in our living circumstances or surroundings, resulting in their being useful from the viewpoint of environmental protection. The present invention is illustrated below by Examples. <Example 1 : Preparation of a poly(epsilon-caprolactone-oxetane) block copolymer> According to the ratio for charging as described in Table 1, oxetane (referred to as ox in the Table) was firstly polymerized in a bulk state at 0°C for 12 hours using 0.2% by mol of a a triethylaluminum-water (1/C.75) based complex as an initiator based on the total amount of the monomers. Successively, epsilon-caprolactone (referred to as CL in the Table) and 20% by weight of toluene based on the total amount of the monomers were added, followed by stirring at 60°C for 24 hours to obtain a block copolymer. There are combinedly shown a yield, results measured with GPC [Number average molecular weight : Mn, molecular weight distribution : Weight average molecular weight (Mw)/Number average molecular weight (Mn)], and monomer ratio analyzed with an 1 H-NMR analyzer concerning the block copolymer in the Table 1. <Comparative Example 1> For reference, an oxetane homopolymer and an epsilon-caprolactone homopolymer were prepared and analyzed according to the same conditions as in Example 1, and the results are shown in Table 1. A B C D E F G H Comparative Example 1-1 100/0 1.0 0 24 65.6 12.1 2.61 100/0 Example 1-1 70/30 0.2 0-60 12-24 47.6 14.6 3.05 33.67 1-2 60/40 0.2 0-60 12-24 60.2 14.5 2.53 27/73 1-3 50/50 0.2 0-60 12-24 82.1 7.06 4.68 28/72 1-4 40/60 0.2 0-60 12-24 84.2 14.0 2.85 20/80 1-5 30/70 0.2 0-60 12-24 79.4 16.3 2.15 9/91 Comparative Example 1-2 0/100 0.2 60 24 81.7 6.33 2.53 0/100 Comparative Example 1-3 0/100 1.0 60 24 89.2 4.39 1.89 0/100 In the Table 1, the abbreviation A-H shows polymerization conditions or properties in polymers as described below. A : charging ratio of oxetane/caprolactone (% by mol) B : catalyst concentration (% by mol) C : polymerization temperature (°C) D : polymerization period (hour) E : yield (% by weight) F : Number average molecular weight (X10 4 ) G : Weight average molecular weight/Number average molecular weight H : composition ratio of oxetane/caprolactone in the copolymer analyzed with 1 H-NMR analyzer (% by mol). In the Table 1, 0-60 in the polymerization temperature and 12-24 in the polymerization period show that oxetane was polymerized at 0°C for 12 hours, and then caprolactone was added to obtain a block copolymer at 60°C for 24 hours, respectively. <Example 2, Comparative Example 2> Films having 1 cm X 1 cm X 500 µm were prepared from the copolymers and the homopolymers obtained in Example 1 and Comparative Example 1, and then the films were placed in a sample bottle filled with 10 milliliter of a buffer solution (pH 7.2) composed of phosphoric acid having 0.1M, and then there was added 8µg of Cholesterol esterase which is an enzyme for degradation. Successively, the sample bottle was warmed at 37°C and pH 7.2 for 200-300 hours in an incubator, and remained films were taken out, followed by measuring the remaining ratio of the weight after washing with water and freezedly drying. The results are shown in Figure 1. Figure 1 shows that biological degradation rate is high in the two samples prepared from the block copolymers having 9 mol% and 20 mol% of oxetane contents (hereinafter, referred to as oxetane/CL in Figures) compared to the poly(epsilon-caprolactone) homopolymers. It is to be noted that the weight values in all samples do not almost change in the same tests as in Example 2 carried out without any enzymes for degradation as shown in Figure 2. <Example 3 : Preparation of a poly(delta-varelolactone-oxetane) block copolymer> According to the ratio for charging as described in Table 2, oxetane and delta-valerolactone (referred to as VL in Table and Figure) were mixed, and polymerized in a bulk state at 60°C for 24 hours using 0.2% by mol of a triethylaluminum-water (1/0.75) based complex as an initiator based on the total amount of the monomers. There are combinedly shown a yield, results measured with GPC, and monomer ratio analyzed with an 1 H-NMR analyzer concerning the block copolymer in the Table 2. <comparative Example 3> For reference, a delta-valerolactone homopolymer was prepared in toluene using 1.0% by mol of a diethylzinc-hydrogen complex as an initiator at 60°C for 15 days while stirring, and analyzed according to the same conditions as in Example 3, and the results are shown in Table 2. A B C D E F G H Comparative Example 3-1 100/0 0.2 0 24 65.6 12.1 2.61 100/0 Example 3-1 60/40 0.2 60 24 28.0 5.11 2.65 19/81 3-2 50/50 0.2 60 24 40.2 5.06 2.51 14/86 3-3 40/60 0.2 60 24 54.3 3.71 1.59 12/88 3-4 30/70 0.2 60 24 57.3 4.02 2.00 6/94 3-5 20/80 0.2 60 24 78.2 2.83 1.59 5/95 Comparative Example 3-2 0/100 1.0 60 15 days 60.3 3.30 1.57 0/100 In the Table 2, the abbreviation A-H shows polymerization conditions or properties in polymers as described below. A : charging ratio ; oxetane/delta-valerolactone (% by mol) B : catalyst concentration (% by mol) C : polymerization temperature (°C) D : polymerization period (hour) E : yield (% by weight) F : Number average molecular weight (X10 4 ) G: Weight average molecular weight/Number average molecular weight H : composition ratio of oxetane/delta-valerolactone in the copolymer (% by mol) <Example 4, Comparative Example 4> According to the same procedures as in Example 2, biodegradability was evaluated concerning the copolymer, the homopolymer, and the oxetane homopolymer obtained in Example 3, Comparative Example 3, and Comparative Example 1, respectively. The results obtained are shown in Figure 3. <Example 5, Comparative Example 5> The epsilon-caprolactone homopolymer and oxetane homopolymer obtained in Comparative Example 1 were mixed according to the molar ratio as described in Figure 4, followed by dissolving into chloroform and evaporating chloroform to obtain a film composed of the mixed polymers. The film was employed to evaluate biodegradability according to the same procedures as in Example 2. The results obtained are shown in Figure 4. It was confirmed that even a blended polymer composed of the epsilon-caprolactone homopolymer and oxetane homopolymer exhibits a better biodegradability than the respective homopolymers depending upon blend ratio. <Example 6, Comparative Example 6 : Preparation of a random block copolymer composed of epsilon-caprolactone and dimethyltrimethylene carbonate> Epsilon-caprolactone, dimethyltrimethylene carbonate (referred to as DTC in Table and Figure), and toluene were mixed and copolymerized at 60°C for 4 hours using 0.2% by mol of a triethylaluminum-water (1/0.75) based complex as an initiator based on the total amount of the monomers. The monomer ratio and number average molecular weight measured with an 1 H-NMR concerning the copolymer obtained are shown in Table 3. Furthermore, an epsilon-caprolactone homopolymer and a dimethyltrimethylene carbonate homopolymer were prepared according to the same conditions as in Example 6. Molecular weight values of the homopolymers are shown in Table 3. A E F G Comparative Example 6-1 100/0 94.5 230 1.55 Example 6-1 87/13 87.2 131 1.52 6-2 70/30 97.2 196 1.71 6-3 55/45 97.5 211 1.52 6-4 46/54 92.8 86.9 1.49 6-5 27/73 64.4 347 2.06 6-6 16/84 67.3 364 1.70 Comparative Example 6-2 0/100 60.6 131 1.83 In the Table 3, the abbreviation A-G shows polymerization conditions or properties in polymers as described below. A: caprolactone/dimethyltrimethylene carbonate in the copolymer analyzed with 1 H-NMR analyzer (% by mol) E : yield (% by weight) F : Number average molecular weight (X10 3 ) G: Weight average molecular weight/Number average molecular weight <Example 7, Comparative Example 7> Films prepared from the copolymers and the epsilon-caprolactone homopolymer obtained in Example 6 and Comparative Example 6 were buried in an active sludge for 200 days. The films were taken out at fixed time lapses, followed by washing with water and freezedly drying to measure remaining ratio of the weight. The results obtained are shown in Figure 5. All the copolymers exhibit a better biodegradability than the epsilon-caprolactone homopolymer. <Example 8, Comparative Example 8> The copolymers and the epsilon-caprolactone homopolymers obtained in Example 6 and Comparative Example 6, respectively, were employed to evaluate a biodegradability according to the same conditions as described in Example 2. The results obtained are shown in Figure 6. Furthermore, the same tests were carried out without any enzymes. As shown in Figure 7, weight loss was almost no observed in all the samples. <Example 9, Comparative Example 9, Example 10, Comparative Example 10> Example 8 was repeated except that the copolymers and the homopolymers obtained in Example 6 and Comparative Example 6, respectively, were employed, and the enzyme Rhizopus delemer Lipase B (pH 9.0, 37°C) for degradation was employed in place of the enzyme Cholesterol esterase (pH 7.2). The results obtained are shown in Figures 7 and 8, respectively. <Reference Example 1> By the analysis results with 1 H-NMR concerning degradation components generated from the epsilon-caprolactone homopolymer and the epsilon-caprolactone-dimethyltrimethylene carbonate block copolymer in Example 8, it was confirmed that 6-hydroxycaproic acid is produced. Figure 10(A) is an 1 H-NMR chart. Furthermore, Figure 10(B) is an 1 H-NMR chart concerning degradation components generated from the epsilon-caprolactone homopolymer. <Example 11, Comparative Example 11 : Preparation of a delta-valerolactonedimethyltrimethylene carbonate block copolymer> Delta-valerolactone, dimethyltrimethylene carbonate, and toluene were mixed and copolymerized at 60°C for 4 hours using 0.2% by mol of a triethylaluminum-water (1/0.75) based complex as in initiator based on the total amount of the monomers. The monomer ratio and number average molecular weight measured with an 1 H-NMR concerning the copolymer obtained are shown in Table 4. A E F G Comparative Example 11-1 100/0 99.0 224 1.89 Example 11-1 93/7 99.0 211 2.07 11-2 75/25 79.9 233 1.42 11-3 57/43 59.2 116 1.69 11-4 47/53 78.6 112 1.96 11-5 33/67 75.9 135 1.66 Comparative Example 11-2 0/100 60.6 128 1.58 In the Table 4, the abbreviation A-G shows polymerization conditions or properties in polymers as described below. A: delta-valerolactone/dimethyltrimethylene carbonate in the copolymer (% by mol) E : yield (% by weight) F : Number average molecular weight (X10 3 ) G: Weight average molecular weight/Number average molecular weight <Comparative Example 12 : Preparation of a delta-valerolactone homopolymer> A delta-valerolactone homopolymer was prepared according to the same conditions as in Example 6. Molecular weight of the homopolymer is shown in Table 4. <Example 12, Comparative Example 13> Example 2 was repeated except that the copolymers and the homopolymers obtained in Comparative Example 6, Example 11, and Comparative Example 12, respectively, were employed to evaluate biodegradability. The results obtained are shown in Figure 11. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

Claims: A biodegradable copolymer having a number average molecular weight ranging from 1,000 to 1,000,000 which comprises (A) from 5 to 99% by mol of epsilon-caprolactone or delta-valerolactone structural units and (B) from 95 to 1% by mol of oxetane structural units, said structural units being combined in the state of a block. The biodegradable copolymer as set forth in claim 1, wherein said number average molecular weight ranges from 30,000 to 300,000, said epsilon-caprolactone or delta-valerolactone structural units range from 5 to 99% by mol, and said oxetane structural units range from 95 to 1% by mol. The biodegradable copolymer according to claim 1 or 2, wherein said oxetane structural units are admixed with carbonate structural units, in particular dimethyltrimethylene carbonate structural units, said structural units being combined in the state of a block. A biodegradable polymer composition which comprises (D) from 60 to 95% by mol of a poly(epsilon-caprolactone) or poly(delta-valerolactone) and (E) from 40 to 5% by mol of a poly(oxetane). A biodegradable polymer composition which comprises (D) from 60 to 95% by mol of a poly(epsilon-caprolactone), a poly(delta-valerolactone) homopolymer, and a poly(oxetane)homopolymer. A method of preparation of a biodegradable copolymer according to claim 1 or 2 wherein epsilon-caprolactone is used, wherein oxetane is partially or totally polymerized using a triethyl aluminum-water-based complex as an initiator at a temperature ranging from -20 to 40°C, and epsilon-caprolactone is charged to co-polymerise with the resulting oxetane homopolymer at a temperature ranging from 0 to 180°C, preferably from 50-150°C. A method of preparation of a biodegradable copolymer according to claim 1 or 2 wherein delta-valerolactone is used, wherein oxetane and delta-valerolactone are simultaneously charged to co-polymerise using a triethyl aluminum-water-based complex as an initiator at a temperature ranging from 0 to 180°C. A method of preparation of a biodegradable copolymer according to claim 3, wherein epsilon-caprolactone or delta-valerolactone is co-polymerised with oxetane and a carbonate, preferably dimethyl trimethylene carbonate, by mixing these with each other, followed by feeding a triethyl aluminum-water-based complex as an initiator, at a temperature ranging from 0 to 180°C. Use of a copolymer according to any one of claims 1 to 3 for the manufacture of a biodegradable molded article. Use of a biodegradable polymer composition according to claim 4 for the manufacture of a biodegradable molded article.

Inventors: WATANABE KAZUSHI, YASUDA HAJIME, WATANABE, KAZUSHI, YASUDA, HAJIME
Applicants: DAICEL CHEM, DAICEL CHEMICAL INDUSTRIES, LTD.
Application year: 1995
Main classification: C08G63
IPC codes: C08G63