A method for producing saturated polyester

Abstract: A method for producing a high molecular weight saturated polyester comprising adding to an saturated polyester with the terminal group being substantially hydroxyl group, having a number average molecular weight of 5,000 or more and being in the molten state, diisocyanate containing isocyanate group the amount of which corresponds to 1/10 to 2 equivalents of the amount of the hydroxyl group.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for producing a polyester useful for various applications, comprising further polymerizing a polymeric saturated polyester with the terminal group being substantially a hydroxyl group. Description of the Related Art It has been well known that saturated polyesters, in particular those containing terephthalate as one component, have been utilized as film, molded articles and glass fiber reinforced plastics for applications in various fields. They are also useful as base resins for adhesives and paints, so their development has also been progressing recently. The present invention relates to a method for imparting satisfactory practical properties to polyesters such as those with relatively low melting points to be used as paints and adhesives and aliphatic polyesters not sufficiently provided with film forming properties, etc. by increasing the molecular weights thereof rather than polyesters with relatively high melting points such as polyethylene terephthalate. As has been well known, the method for synthesizing a polyester of a high molecular weight (the term "high-molecular weight" means a number average molecular weight of about 10,000 or more) depends on the deglycol reaction of the terminal hydroxyl group of a low-molecular polyester. Hence, the concentration of the terminal group decreases remarkably as the molecular weight increases. Furthermore, a decomposition reaction additionally occurs due to the temperature during the ester exchange, so a limitation is imposed on the molecular weight. Such a tendency can be distinctively observed in aliphatic polyesters in particular. When a conventional deglycol reaction in reduced pressure is employed for producing a high-molecular saturated polyester as is shown in Fig.1, for example, it is observed that the molecular weight begins to decrease once the molecular weight reaches the maximum. In such case, it is very hard to produce an aliphatic polyester with a molecular weight satisfactory for forming tough film by means of the conventional deglycol reaction. In other words, it may be concluded that a film with mechanical properties for practical use cannot be formed from the molecular weights which have been realized by aliphatic polyesters. Polyesters with aromatic structures also induce similar situations, for example, when the polyesters are to be used as a base resin of an adhesive. The unsatisfactory molecular weights thereof appear as insufficient mechanical properties. US-A- 2999851 discloses rubbery polyether glycols formed by reacting a dihydroxy terminated polyester of formula H-(RO)n-H having a molecular weight from 10,000 to 20,000 with a diisocyanate. n in the above formula may have a value of from 1 to 50 but the only example shown has a value of n greater than 1 so comprising a polyether. Thus, the present inventors, as a result of various studies aimed at increasing the molecular weight of such polyesters with lower thermal decomposition temperatures, as much as possible, have found that a high-molecular polyester can be unexpectedly synthesised in a smooth manner without a risk of gelation, by adding to a saturated polyester with the terminal group being substantially a hydroxyl group and being in the molten state at a temperature not less than the melting point thereof, a diisocyanate containing isocyanate group the amount of which corresponds to 1/10 to 2 equivalents of the amount of the hydroxyl group to thus achieve the present invention. Accordingly the present invention provides a method for producing a high molecular weight saturated polyester comprising adding a diisocyanate to a molten saturated polyester having a terminal hydroxyl group, characterised in that :- i) said saturated aliphatic polyester is obtained by the reaction of:- a) succinic acid and butanediol 1, 4 b) succinic acid, adipic acid, and butanediol 1, 4 or c) succinic acid and ethylene glycol ii) said saturated aliphatic polyester has a number average molecular weight of 10,000 or more iii) said diisocyanate has an isocyanate group the amount of which corresponds to from 1/10 to 2 equivalents of the amount of the hydroxyl group of the saturated aliphatic polyester and iv) said high molecular weight saturated polyester is capable of forming film. Although according to technical common view, gelation cannot be avoided in the process of reacting isocyanate with polymers at higher temperatures, the present invention is significant in that the increase in the molecular weight of a polyester can be realised without the risk of gelation, by setting the molecular weight of the polyester and the amount of isocyanate, at 10,000 or more and 1/10 to 2 equivalents of the amount of the hydroxyl group, respectively. The amount of diisocyanate to be used is preferably 0.3 to 1.5 equivalents, more preferably 0.5 to 1.2 equivalents. If the amount of diisocyanate to be used is represented as the equivalent of the hydroxyl group of isocyanate group and is less than 1/10 equivalent of the hydroxyl group, the effect on the increase in the molecular weight is poor; if the amount is above 2 equivalents, the risk of gelation gets higher. In terms of melting point, film forming property and cost, two combinations, namely the combination of succinic acid and ethylene glycol and the combination of succinic acid and butanediol 1,4 are preferable. In this case, a part of the succinic acid can be substituted with adipic acid, and the substituted proportion is preferably 50 mol % or less. For polyester production, esterification is effected up to a desirable acid number (10 or less generally) in the excess of polyhydric alcohol, followed by deglycol reaction in the presence of a reaction catalyst such as a tetraalkyl titanium compound under vacuo. Said reaction catalyst may be added at the outset of esterification reaction. A desired amount of diisocyanate is added in the stage where a required molecular weight is achieved. No limitation is imposed on the types of diisocyanate to be used in the present invention, and commercially available ones may be used as they are. Their examples include 2,4-tolylenediisocyanate, a mixture of 2,4-tolylenediisocyanate and 2,6-tolylenediisocyanate, diphenylmethane diisocyanate, p,p'-diphenyl diisocyanate, 1,6-naphthylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. The reaction proceeds simultaneously on the addition of diisocyanate, and the reaction is then completed in a few minutes. The saturated polyester with the increased molecular weight by means of diisocyanate in accordance with the present invention can be subjected to the applications mainly as adhesives, sticking agents, molded articles, films and the like. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a graph representing the relation of the reaction time and the distribution of molecular weights in the process of producing a high-molecular saturate polyester according to the conventional reaction in reduced pressure. Fig.2-A is a graph representing the results of the GPC measurement of of the molecular weight of Polyester A in Example 1. Fig.2-B is a graph representing the results of the GPC measurement of the molecular weight of Polyester B in Example 1. Fig.3-A is a graph representing the results of the GPC measurement of the molecular weight of Polyester G in Example 4. Fig.3-B is a graph representing the results of the GPC measurement of the molecular weight of Polyester H in Example 4. DESCRIPTION OF THE PREFERRED EMBODIMENTS Methods of the present invention are illustrated with reference to the following examples, but the invention is not intended to be limited only to these following examples. EXAMPLE .1 In a 1 liter separable flask equipped with a stirrer, a fractionation condenser, a gas introduction tube, and a thermometer, were placed 206 g of butanediol 1,4 and 236 g of succinic acid, followed by esterification in a nitrogen stream at 210 to 220 °C to render the acid number of the mixture to 7.9. Subsequently, 1.2 g of tetrabutyl titanate was added prior to the exchange of the condenser. Deglycol reaction was effected about five hours initially in a reduced pressure of 3.5 Torr and finally in a reduced pressure of 0.6 Torr. The number average molecular weight measured by GPC was 16,200 (see Fig.2-A, Polyester A). To the resulting reaction mixture was added 4 g of hexamethylene diisocyanate (OH/NCO = 1/0.8) at a temperature of 190 °C. The number average molecular weight of the high-molecular polyester after 10-min reaction was 45,800 (see Fig.2-B, Polyester B), but gelation did not occur. The high-molecular polyester thus obtained had a melting point of about 120 °C, being capable of forming film, and was stretched into a tough film four times the original size by biaxial orientation, with the tensile strength of the film being 13.4 - 16.1 kg/mm 2 . EXAMPLE 2 Into a 1 liter separable flask equipped with a stirrer, a fractionation condenser, a gas introducing tube, and a thermometer, were placed 202 g of succinic acid, 216 g of butanediol 1,4 and 29 g of adipic acid, followed by esterification at 200 to 210 °C to render the acid number of the mixture to 9.1. The condenser was subsequently exchanged before adding 1 g of tetraisopropyl titanate at 210 to 220 °C in a final reduced pressure of 0.7 Torr, to synthesize a polyester C of a number average molecular weight of 10,200. The temperature was continuously lowered to 190 °C, followed by addition of 5 g of hexamethylene diisocyanate, and reacted for 15 minutes. The ratio OH/NCO was about 1/1. Gelation did not occur. The polyester D obtained was of a number average molecular weight of 48,900, melting point of about 106 °C and slightly yellowish white in wax-like form, and was observed to become a tough film. EXAMPLE 3 In a 1 liter separable flask equipped with a stirrer, a fractionation condenser, a gas introducing tube, and a thermometer, were placed 150 g of ethylene glycol and 236 g of succinic acid, followed by esterification in nitrogen gas stream at 195 to 210 °C to render the acid number of the mixture to 7.9. Subsequently, 1 g of tetrabutyl titanate was added after the exchange of the condenser. The atmosphere was at a temperature of 210 to 220 °C and a finally reduced pressure of 0.7 Torr, to synthesize a polyester E of a number average molecular weight of 11,800. Then, the temperature was lowered to 190 °C, followed by addition of 5.5 g of diphenylmethane diisocyanate (OH/NCO = 1/0.85) for reaction for 10 minutes. The number average molecular weight was about 40,000 and no gelation occurred. The polyester F obtained was slightly yellowish brown in wax-like form, and was observed to have a melting point of about 105 °C and to make tough films.

Claims: A method for producing a high molecular weight saturated polyester comprising adding a diisocyanate to a molten saturated polyester having a terminal hydroxyl group, characterised in that :- i) said saturated aliphatic polyester is obtained by the reaction of:- a) succinic acid and butanediol 1, 4 b) succinic acid, adipic acid, and butanediol 1, 4 or c) succinic acid and ethylene glycol ii) said saturated aliphatic polyester has a number average molecular weight of 10,000 or more iii) said diisocyanate has an isocyanate group the amount of which corresponds to from 1/10 to 2 equivalents of the amount of the hydroxyl group of the saturated aliphatic polyester and iv) said high molecular weight saturated polyester is capable of forming film. A method as claimed in claim 1, wherein the amount of diisocyanate containing isocyanate group added corresponds to 0.3 to 1.5 equivalents of the hydroxyl group. A method as claimed in claim 2, wherein the amount of diisocyanate containing isocyanate group added corresponds to 0.5 to 1.2 equivalents of the hydroxyl group.

Inventors: HATANO YOSHITAKA, NIIKURA ISAMU, TAKIYAMA EIICHIRO, HATANO, YOSHITAKA, NIIKURA, ISAMU, TAKIYAMA, EIICHIRO
Applicants: SHOWA HIGHPOLYMER, SHOWA HIGHPOLYMER CO., LTD.
Application year: 1991
Main classification: C08G18
IPC codes: C08G63, C08G18