ENZYMATIC SYNTHESIS

Abstract: A process for producing a polyester comprising as repeated units: (i) residues of at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; or (ii) residues of (a) at least one aliphatic dicarboxylic acid or a carboxylic acid derivative thereof, (b) at least one aliphatic diol or polyol, and optionally (c) at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; which process comprises reacting the components defined in (i) or components defined in (ii) in the presence of a lipase and optionally in the presence of water such that the molar ratio of acid groups to hydroxyl groups in the reactants is 1:1 to 1:1.1 and wherein bound enzyme is removed from the reaction mixture and is then used in a further polymerisation of components defined in (i) or (ii).

Description: ENZYMATIC SYNTHESIS The present invention relates to a process for producing polyesters by enzyme catalysed reaction of monomers and to polyesters obtained by that process . Polyesters are well known industrial products finding applications principally as moulded articles m, for instance, the car industry. They are also of interest as the intermediates m the production of polyurethanes , which are also used to form moulded articles. Polyesters are reacted with isocyanates to form polyurethanes. The characteristics of the resulting polyurethane depend at least m part on those of the polyester. Polyesters are typically produced by chemically catalysed reactions using elevated temperatures, strong acids and long reaction times. Competition between esterification, transesterification and hydrolysis limits the molecular weight of the products. Moreover these processes are accompanied by the formation of quantities of unwanted by-products, such as cyclic esters, and have the added disadvantage that the catalyst is difficult to remove. Polyesters produced by conventional processes generally contain at least 0.5% or more, for instance up to 1.5% or more by weight of cyclic diester impurities such as the cyclic ester 1,6- dιoxacyclododecane-7 , 12-dιone . Furthermore, it is necessary to remove the water produced by the reaction m order to force the equilibrium towards products. If the presence of byproducts and residual catalyst is not to degrade the properties of the desired material, complex arrangements are required to prevent their formation or remove them after the main reaction (see e.g. EP-A-0425201) . The present invention seeks to overcome the difficulties of chemically catalysed reactions by use of lipase enzymes. Whilst lipases have been known for some time for simple esteπfication and transesterification reactions (see, e.g. EP-A-0383 405) and stereoselective oligomerisations (see, e.g. Margolin A. L. et al . , Tet . Letters, 28 ; 1607-1610, (1987)), only limited use has been made of lipases m polyesteπfication. In particular Wallace and Morrow, J. Polymer Science Part A, 27, 2553-2562 (1989) and Gutman, Mat. Res. Soc . Symp. Proc . , 174, 217-222 (1990) have succeeded m forming polyesters of high weight average molecular weight starting from dicarboxylic acid diesters where the ester moiety is highly activated (2 , 2 , 2-trιchloroethyl esters) or from esters of hydroxycarboxylic acids and diesters of hydroxy dicarboxylic acids. GB-A-2 272 904 discloses the use of a lipase to make polyesters m the presence of an organic solvent. GB-A-2 286 401 discloses a solvent free process for obtaining polyesters having desirable properties. Enzymatic processes of the older prior art would prove costly and inefficient to perform on a commercial scale. The products of the processes of the more immediate prior art are prone to hydrolysis particularly when subjected to heat and moisture. This is of particular concern where the polyester is used portion-wise from a bulk quantity and extraction of a useable portion requires melting the solid polyester m non- anhydrous conditions. In this case marked deterioration in the quality of the polyester is observed particularly m regard to the molecular weight and distribution of the polyester. It is known in the art that conventionally produced polyesters, in the presence of suitable catalysts, undergo transesterification and hydrolysis under the control of thermodynamic equilibrium. This promotes the classical Poiseuille distribution of molecular weights producing broad dispersity characteristics. It is known that the process of polyester formation using a lipase can be considered as proceeding in two stages, the first stage being the oligomerisation stage and the second being the conversion of the resulting oligomers to a polyester. It is also known to use supported lipase in such a process and that the lipase can be removed from the reaction mixture at the end of either stage. In the case where the supported lipase is removed at the end of the oligomerisation stage the subsequent conversion of oligomer to high molecular weight polyester was thought originally to be due to a self assembly process as all of the enzyme catalyst was believed to have been removed at the previous stage. Surprisingly, it has been found that, contrary to previous understanding, lipase becomes detached from the support and leaches into the polymerisation stage of the process and thus into the finished product. Research has shown that the residual enzyme m the finished product makes the polyester susceptible to hydrolysis. Also, the leaching of the enzyme from the support renders any recycling of the enzyme less efficient. The leaching of the enzyme is related to the hydrophobic/hydrophilic balance of the reaction medium, primarily influenced by the nature of the monomers as discussed further below. In one aspect the present invention relates to an improved enzymatic polyesterification process which is capable of reducing the cost and increasing the efficiency of production of a polyester by enzymatic methods particularly when carrying out such a process on a commercial scale. In another aspect the present invention relates to a polyester product which is resistant to degradation by hydrolysis particularly m the presence of water and heat and a process for its production. The present invention m one aspect provides a process for producing a polyester comprising as repeated units d) residues of at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof ; or (n) residues of (a) at least one aliphatic dicarboxylic acid or a carboxylic acid derivative thereof (b) at least one aliphatic diol or polyol, and optionally (c) at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; which process comprises reacting the components defined in (I) or components defined in (ii) m the presence of a lipase and optionally m the presence of water such that the molar ratio of acid groups to hydroxyl groups m the reactants is 1:1 to 1:1.1 and wherein bound enzyme is removed from the reaction mixture and is then used m a further polymerisation of components defined in (I) or (ii) . As used herein the term "polyester" is intended to encompass materials produced by the process of the invention from any suitable combination of the monomers defined herein. Aliphatic hydroxycarboxylic acids suitable for use m the process of the present invention include those of formula (1) ; HOCH 2 - R 1 - C0 2 H (1) wherein R 1 is a bond or divalent radical of a substituted or unsubstituted straight, branched or cyclic C x to C 12 alkyl group optionally having one or more carbon-carbon double bonds and optionally having one or more carbon-carbon triple bonds. Suitable aliphatic dicarboxylic acids include those of formula (2) : H0 2 C - R 2 - C0 2 H (2) wherein R 2 is a bond or a divalent radical defined as for R 1 . Suitable aliphatic diols include those of formula (3) : HOCH 2 - R J - CH 2 OH wherein R 3 is a bond or a divalent radical defined as for R 1 or a divalent radical comprising a straight or branched C 2 to C 12 alkyl group or a cyclic C 4 to C 12 alkyl group optionally comprising at least one hetero atom, such as nitrogen or oxygen, interrupting the carbon chain. Further suitable diols include higher molecular weight materials such as polytetramethylene glycol , polypropylene glycol , polyethylene glycol and polycaprolactone . Preferred such diols have hydroxyl values m the range from 10 to 450 mg KOH/g, more preferably 20 to 280 mg KOH/g . Suitable aliphatic polyols include those of formula HOCH 2 - R 4 - CH 2 0H (4) wherein R 4 is a divalent radical defined as for R 1 and bearing at least one hydroxyl substituent. Each of the C x to C 12 alkyl groups mentioned above may be substituted or unsubstituted and may be cyclic, branched or straight chain, optionally having at least one carbon-carbon double bond, either m the cis- or trans- conformation and optionally having at least one carbon-carbon triple bond. When the C j^ to C 12 alkyl group has more than one double or triple carbon-carbon bond, these bonds may be conjugated or non-conjugated. The C x to C 12 alkyl group is optionally substituted with one or more substituents (which, when there are two or more substituents, may be the same or different) each selected from halogen atoms, for example fluorine, chlorine or bromine; hydroxyl; -NHR S where R 5 is hydrogen or a C 1 to C 12 alkyl; carboxyl; and -C0 2 R 6 where R 6 is hydrogen or a C λ or C 12 alkyl . Preferably the hydroxycarboxylic acid has from 2 to 14 carbon atoms, for example glycolic acid, lactic acid, 2- hydroxybutyπc acid, 2-hydroxyιsobutyrιc acid, 2-hydroxy- caproic acid, 2-hydroxyιsocaproιc acid, citric acid or malic acid. The hydroxyacids must have a non-steπcally hindered primary or secondary hydroxyl . Preferred hydroxy acids are hydroxy- straight chain aliphatic carboxylic acids. Preferably the dicarboxylic acid has from 3 to 14 carbon atoms, for example, succinic acid, fumaric acid, citric acid, malic acid, malonic acid, maleic acid, adipic acid or sebacic acid. Most preferably it is adipic acid. As used herein m connection with aliphatic hydroxycarboxylic acids and aliphatic dicarboxylic acids the term "carboxylic acid derivative" refers to esters and acid anhydrides. An ester of a diacid may be a monoester or a diester, for example a mono or dialkyl ester. Preferably the alkyl groups are each of 1 to 4 carbon atoms, and more preferably the derivative is a methyl or ethyl ester or diester, most preferably methyl adipate or dimethyl adipate . Preferably the diol has from 2 to 14 carbon atoms and is an α,ω-dιol, for example 1 , 4-butanedιol , diethylene glycol, ethylene glycol, propylene glycol, 1 , 5-pentanedιol , 1,6- hexanediol or 1 , 12 -dodecane diol, most preferably 1,4- butanediol or 1 , 6-hexanedιol . In aspects of this invention m which a diol comprising a hetero atom is used, the diol is preferably diethanolamme or diethylene glycol . The polyol has at least three hydroxyl groups of which at least two must be non-sterically hindered primary or secondary hydroxyl groups. Preferably the polyol has 3 , 4 or 5 hydroxy groups. Tertiary hydroxyl and sterically hindered primary and secondary hydroxyls are unlikely to react under the conditions of the present invention but will nevertheless provide branch points when subsequently reacted with isocyanates. Suitable polyols include pentaerythritol and tπols, especially glycerol . Use of glycerol generally results m a linear polymer as the enzyme preferentially esterifies the primary hydroxyls, the secondary hydroxyl being sterically hindered, but branched products may be obtained using certain enzymes. Owing to the low temperatures used in the present process compared with those of conventional chemically catalysed polyesterifications , it is possible to polymerise hydroxyacids and diacids, such as lactic acid, glycolic acid and oxalic acid, which decompose at elevated temperatures and it is thereby possible to produce polyesters not generally accessible by previous methods. In alternative embodiments the polyesters produced by the present process may comprise or consist of repeating units derived from the following components: a diacid and a diol; a diacid and a polyol; a diacid, a diol and a polyol; a diacid, a diol and a hydroxy acid; a diacid, a polyol and a hydroxy acid; a diacid, a diol, a polyol and a hydroxy acid, or any other suitable combination of repeating units of such monomers, for example combinations m which the diacid is used m the form of its methyl or ethyl ester or diester derivative. Preferred combinations of monomers are adipic acid/1 , 4-butanedιol , dιmethyladιpate/1 , 4-butanedιol , adipic acid/glycerol , adipic acid/1 , 4-butanedιol , adipic acid/diethylene glycol, adipic acid/diethylene glycol/tπmethylolpropane, diethylene glycol/adipic acid/dimethylolpropionic acid, adipic acid/1 , 6-hexanedιol . A further option is to incorporate into the polymer blocks of preformed polyester. Unlike the situation with conventional polyesterification where transesterification reactions will randomise any introduced pre-formed polyester blocks, the enzyme catalysed reaction will incorporate such blocks without any significant degradation thereof. It is thus a further aspect of the invention that the polymers optionally comprise two or more blocks of polyester wherein the composition of monomer residues in at least one of said blocks is different from the composition of monomer residues m at least one other of said blocks . Preformed polymer blocks may be included m the polymerisation reaction medium at any stage of the polymerization reaction. The preformed polymer blocks may themselves be produced by enzymatic polyesterification reactions or may be produced by conventional polymerization processes. Preferred preformed polyester blocks have acid numbers less than 40 mg KOH/g, more preferably less than 30 mg KOH/g . The reactive carboxylic acid groups and reactive hydroxy groups of the reactants are generally present m substantially equal numbers. The reaction may be carried out with a stoichiometric imbalance, but this generally results m a product having a lower weight average molecular weight than if the reactants are used m equimolar amounts. However, m particular aspects of the invention, the proportions may be adjusted slightly such that a polyester having terminal acid units or terminal hydroxy units is obtained. Polyesters having terminal acid units are useful in a variety of coating compositions whereas those with terminal hydroxy units may be - lo used as the soft segments in production of polyurethanes. In particular it is preferred that the molar ratio of acid groups to hydroxyl groups is from 1:1 to 1:1.1 such that a hydroxyl - terminated product is obtained. In the case where the resulting polymer has terminal hydroxyl groups the length of the polymer may be varied by varying the excess of hydroxyl groups present m the initial reaction mixture. For example, increasing the amount of hydroxyl groups relative to the number of acid groups m the reaction mixture will give rise to polymers of shorter chain length. In a preferred embodiment of the invention a tertiary amme is included m the reaction mixture. Tertiary amines suitable for use m the process of the present invention are any tertiary amines which are suitably volatile so as to be removed by the vacuum treatment at the polymerisation stage. Preferably the amme is a trialkyl amme and most preferably a tπ-Ci 4 -alkyl amme such as tπethylamme . Where an amme is used m the process of the present invention it is included an amount suitable to prevent coating of the enzyme bead with an impermeable layer of polymer, preferably in an amount of 0.05 to 5% by weight of the monomers, preferably 0.1 to 1% by weight of the monomers and most preferably 0.8% by weight of the monomers. The enzyme used in the process of the present invention may be bound on an inert carrier, for instance a polymer such as an anion exchange resin, an acrylic resin or a polypropylene, polyester or polyurethane resin or may be used m free form. When the enzyme is bound on an inert carrier it can easily be removed from the reaction mixture (e.g. by filtration) without the need for complicated purification steps. Preferably the bound enzyme is recovered from the reaction mixture and reused. At least some enzyme must be present in the reaction vessel until the reaction reaches completion. Where bound enzyme is used the bound enzyme may be removed from the reaction vessel after the initial oligomerisation step of the reaction has reached completion. Where the bound enzyme is removed at the end of the oligomerisation step the acid number of the resulting mixture of oligomers is preferably less than 200 mg KOH/g and more preferably between 170 and 20 mg KOH/g but may be lower, for instance, down to about 15 mg KOH/g. In the case where hydroxyl groups are present m excess, the oligomerisation step is complete when all the carboxylic acid bearing monomers have reacted to form an acid/base adduct . The bound enzyme may be removed after completion of the first step of the reaction for example by filtration. Removal of the bound enzyme after the initial oligomerisation step is advantageous to avoid damage to the bound enzyme during the conversion to polyester: As the reaction proceeds, the viscosity of the reactants increases and the increased shearing forces needed to stir the reaction mixture may cause damage to the bound enzyme. Where the bound enzyme is reused, it is preferably reused m a further polymerisation of components to make a polyester, preferably the bound enzyme is reused m a further implementation of a process of this invention. In order to improve the efficiency and cost effectiveness of the process it is advantageous to supplement the recovered bound enzyme with previously unused or "virgin" enzyme, which may be bound or free, for use m a further polymerisation reaction This is due to the loss by leaching of some of the bound enzyme into the oligomer mixture. When the re-used bound enzyme is supplemented with virgin enzyme it is preferred to include virgin enzyme in an amount of 1 to 25%, preferably 2 to 15%, more preferably 4 to 12% and most preferably 5 to 10% by weight of the recovered bound enzyme. When the bound enzyme is removed immediately after completion of the initial oligomerisation, the further step of converting the resulting oligomers into a polyester must be carried out m the presence of enzyme and with removal of water, or other condensation products (e.g. methanol or ethanol when methyl or ethyl esters of carboxylic acids are used as monomers) which then drives the reaction to form high molecular weight products. The enzyme present may be an enzyme that has become detached from the support and that has leached into the polymerising mixture. This applies at least with one preferred enzyme, the Candida antarctica lipase mentioned below. However under some polymerization conditions, such as where more hydrophobic monomers, for example, polytetramethylene glycol, are used or polymerization is catalysed by an enzyme which is covalently bound to its support, the enzyme may not be leached from the support. The conversion of oligomer to polymer may be effected or accelerated by the addition at an appropriate stage of the reaction of further enzyme in free form (i.e. not bound to a support) . This non-bound enzyme can be added before, during or after removal of the bound enzyme, preferably non-bound enzyme is added after removal of the bound enzyme. In addition, the conversion of oligomer to polyester may be accelerated by raising the reaction temperature to at least 80°C, for example at least 85°C, 90°C, 95°C or 100°C. Suitable enzymes are commercially available lipases. Not all lipases function as polyesterification catalysts m the presence of substantial quantities of water (an example is the lipase from Mucor meihei ) so it may be necessary either to remove water during the reaction to retain the activity of the enzyme or to select enzymes which function when water is present . A preferred enzyme for use in the present process is the lipase derived from Candida antarcti ca , a non-specific triacylglycerol lipase [E.C. no. 3.1.1.3] for instance those available from Novo Industri AS, Novozyme 435 * , where the enzyme is immobilised (bound) on a macroporous acrylic resin or Novozyme 525 ** wherein the enzyme is not immobilised. This enzyme may be obtained commercially by recomb ant DNA techniques having the native sequence or genetically engineered modifications thereof although it may be extracted from the organism if desired. Other Examples of suitable commercially available enzyme are those available from 'Novozyme 435 is a registered Trade Mark " ovozyme 525 is a registered Trade Mark Boehrmger Mannheim GmbH, Chirazyme *** L-2, c-f, Lyo, where the enzyme is immobilised by covalent binding to its support and Chirazyme™ L-2, Lyo, BM, where the enzyme is not immobilised. Other suitable lipases can be identified by simple trial-and- error experimentation within the ability of those skilled m the art . The activity of the enzyme may be affected by materials present m the reaction mixture, for example the lipase from C. antarctica is inhibited by glycerol. At least with this enzyme it is preferable not to include polyfunctional monomers, particularly those with secondary alcohol groups, in the initial reaction mixture, but to delay their addition until after the reaction is started. Preferably polyfunctional monomers (which would be used to generate branch or graft points) are not added to the reaction mixture until after the initial oligomerisation step. The amount of enzyme used is not critical and is generally limited by economic considerations. Too little enzyme will result m a slow reaction whereas too much enzyme simply increases the cost unnecessarily. With the lipase from Candida antarctica (Novo Industri AS Catalogue Novozyme 435™ or Novozyme 525™) it has been found convenient to use from 0.1 to 1.5% by weight of supported enzyme based on the total weight of monomers, preferably 0.1 to 0.6% and most preferably 0.3 to 0.5% of enzyme. In the process of the invention where a mixture of used and unused "virgin" enzyme is used then these amounts refer to the amount of recovered enzyme. "'Chirazyme is a registered Trade Mark Surprisingly it has been found that many of the enzymes used in the reaction of the present invention are still active in the presence of water. The lipase from Candida an tarcti ca has been found to be such an enzyme. Processes using lipase from Candida antarc ti ca are preferably carried out in the presence of a small amount of water preferably an amount of 0.5 to 5%, more preferably 1 to 3% and most preferably 1.9% by weight of the monomers. The oligomerisation stage of the process is carried out at from 10 to 90°C preferably 20 to 70°C and more preferably 40 to 60 °C and at atmospheric or reduced pressure. Where the process is carried out at reduced pressure the preferred pressure is from 60-100 mbar. The polymerisation stage of the process is carried out at from 10 to 120°C preferably 40 to 110°C most preferably 60 to 100°C, at atmospheric or, preferably, reduced pressure. It is preferred to remove the water produced by the reaction both during the oligomerisation and polymerisation stages, particularly during the polymerisation stage. The water is conveniently removed by reducing the pressure under which the reaction is carried out and maintaining the pressure at, for example 5 to 10 kPa (50 to 100 mbar) at the start reducing to as low as 0.5 kPa (5 mbar) at the end. Alternatively the water may be removed with a wiped film evaporator under reduced pressure, for instance, 0.6666 kPa (5 mm Hg) or even 133.322 Pa (1 mm Hg) or less. In another alternative method a desiccant such as a molecular sieve is used, taking precautions to avoid physical damage to support enzymes due to abrasion between the desiccant and the enzyme support . In both stages or each stage individually of the process of the invention a bleed or sparge can be utilized to agitate the reaction mixture and help to evaporate water from the mixture. The gas used the bleed or sparge can be air or nitrogen which is preferably predπed, and is most preferably nitrogen. The total reaction time is generally from 6 to 48 hours, preferably from 12 to 24 hours. At the end of the polymerisation stage the reaction mixture preferably has an acid number of less than 1 mg KOH/g. The process of the present invention can be operated efficiently and cost effectively on a commercial scale an industrial plant. This means producing batches of finished product of 100 kg or greater in a single implementation or "run" of the process. The process can be subjected to control by a suitable computerized laboratory or plant management system. The process may be, without prejudice, carried out a batch, continuous or single run fashion. Preferably, because of the need to supplement recovered bound enzyme to ameliorate losses through leaching, the process is run m a "fed batch" manner. In another aspect the invention provides a process for producing a catalyst free or substantially catalyst free polyester which process comprises (I) treating polyester made by an enzymatic polymerisation process a manner so as to denature the enzyme or (n) using monomers and/or reaction conditions which do not permit the catalyst to leach through into the final product. In a process of this invention which uses a polyester made by an enzymatic polymerisation process, said polyester can be any polyester which is made by polymerisation catalysed by a lipase, and is preferably a polyester made using the preferred lipase of this invention and most preferably is a polyester made by a process of this invention. In a process of this invention which comprises treating a polyester a manner so as to denature the enzyme, the treatment used can involve exposure to any conditions which cause the denaturing of the enzyme. The denaturing treatments used are preferably heat treatments, more preferably heat treatment to above 150 °C. Such heat treatments can be carried out by for example heating in a conventional flash heater or thin film heater. Where a process of this invention involves denaturing an enzyme, denaturing means rendering an active enzyme catalyst inactive by destruction of the native conformation and hence active state or configuration of the molecule . The invention also provides a polyester comprising as repeated units (l) residues of at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; or (n) residues of (a) at least one aliphatic dicarboxylic acid or a carboxylic acid derivative thereof, (b) at least one aliphatic diol or polyol, and optionally (c) at least on aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; which polyester is catalyst free or substantially catalyst free. Where polyesters of this invention are catalyst free this means that there is no or very little active enzyme catalyst contained m the polyester. Such polyesters can preferably withstand an extended period of exposure to water and heat without decomposition by hydrolysis. Preferred polyesters are able to retain their original acid number for an extended period of time when exposed to 0.2% water by weight of the polyester and heat treatment to 60 °C. The most preferred polyesters have an acid number of less than 1 mg KOH/g after being made up to 0.2% water by weight of the polyester and being incubated for 15 days at 60°C. Generally processes of the present invention enable the production of high weight average molecular weight polyesters, for instance up to or higher than 8 kDa, especially up to or higher than 10 kDa. The polyesters produced by the process of the present invention generally have a minimum weight average molecular weight of 200 Da, preferably 600 Da, more preferably 1000 Da and most preferably 4 kDa. The weight average molecular weight of the polyester is measured using gel permeation chromatography . The polyesters produced by the process of the present invention generally comprise from 6 to 50 monomer units, preferably from 10 to 40 monomer units and most preferably from 30 to 40 monomer units. Generally it has an acid number of from 0 to 50, preferably from 0 to 25 and more preferably from 0.5 to 10. Most preferably the polyester has an acid number of about 1. The polyesters produced by the process of the invention generally have a dispersity of 2.5 or less. Dispersities of 2.1 or 2.0 may be achieved and in one aspect of the invention the polyesters have a dispersity of 1.5 or less, preferably 1.3 or less, in particular when the process is carried out m solvent free conditions such as those described GB-A-2 286 401. Even m small amounts which are insufficient to act as a solvent for one or more of the reagents, certain organic liquids can have the effect of broadening the dispersity. For instance with Candida an tarcti ca enzyme, about 0.5% toluene in the reaction mixture can result m a dispersity similar to or perhaps even broader than that obtained by non-enzymatic methods. It is likely that other aromatic hydrocarbon liquids can have a similar effect and should be avoided if a polymer having narrow dispersity is desired. The dispersity is calculated as follows: Dispersity, d = Weight Average Molecular Weight Number Average Molecular Weight the number and weight average molecular weights may be obtained by methods well known to those skilled in the art such as gel permeation chromatography. Polyesters which contain cyclic diester impurities may, if required, have their cyclic diester content reduced by methods such as wiped film evaporation or high vacuum distillation. After application of such methods, contents of from as low as 0.3 to 0.7% by weight of the cyclic diester impurities can be achieved. The presence of cyclic diester impurities can be detected using gas chromatography, mass spectrometry or High Performance Liquid Chromatography (HPLC) According to a preferred embodiment of the present invention the polyesters having hydroxy terminal groups are further reacted with at least one lsocyanate to produce polyurethanes. Generally the bound enzyme is removed from the polyester before the reaction with isocyanate. This prevents the enzyme and its support from interfering with the polyester/isocyanate reaction. Preferably the enzyme remaining in the polyester is denatured before the reaction with isocyanate. Generally water produced during the polyesterification is also removed before reaction with isocyanate . The polyesters of the invention have sharp melting points (unlike conventionally produced polyesters) and impart to the polyurethanes excellent physical properties such as desirable combinations of hardness and flexural and tensile strength. Certain polyesters produced m accordance with the present invention are novel materials and form further aspects of the invention. Polyesters and polyurethanes and polymer compositions comprising polyesters and polyurethanes of the present invention find uses as shaped articles and foams, particularly for motor vehicles . Any polymer of the invention can be incorporated into a polymer composition. The invention will now be illustrated by the following Examples which are not intended to limit the scope of protection. EXAMPLE 1 Butylene adipate process - oligomeπzation stage only - 500ml scale Materials 1. 1 , 4-Butanedιol , Dupont , 136. lg, 1.51 moles, 1.12 equiv. 2. Water, BDH, 6.3g (1.9% by weight of monomers) . 3. Triethylam e, Aldπch, 2.72g, 0.027 moles, 0.027 equiv., (0.8% by weight of monomers) . 4. Adipic acid, ICI, 196.6g, 1.35 moles, 1.0 equiv. 5. Novozyme 435™, bx. ref. no. LC 0015-8, activity certified as 8200 propyl laurate units/g (LU/g) , Novo, lg. (0.3% by weight of monomers) Procedure The butanediol, water, triethylamme and adipic acid were charged sequentially to a 500ml flange flask and the flask heated m an oil bath at 40°C. The flange flask was fitted with a condenser m reflux mode, a vacuum purge tap and an overhead stirrer unit. The reagents were stirred using an overhead stirrer at a speed of 160 rpm for a period of 2 hours at 40°C. The stirrer speed was adjusted down to 120 rpm and the Novozyme 435™ added. Stirring was continued for a further 4 hour period at atmospheric pressure. The bath temperature was raised to 60 °C. The condenser was changed over to distillation mode and a receiver flask and a vacuum adaptor fitted. Vacuum of 10 kPa (100 mbar) level was applied to the rig by means of a diaphragm vacuum pump linked to the vessel via a digital controller, for an overnight period of 16 hours. By morning a clear mobile solution had formed with only the immobilized enzyme insoluble; the latter was filtered off using a nylon filter cloth of mesh size 74 μm. The crude enzyme was reserved and used without further purification m a subsequent fed-ba tch operation - see Example 2. The filtered oligomer was tested for acid number characteristic, shown to be 158mg KOH/g. EXAMPLE 2 Butylene adipate process fed-ba tch technique - no. 9 of series of 12 pl us the original benchmark run. Materials 1. 1 , 4 -Butanediol , Dupont, 136. lg, 1.51 moles, 1.12 equiv. 2. Water, BDH, 6.3g, (1.9% by weight of monomers) . 3. Triethylamme, Aldrich, 2.72g, 0.027 moles, 0.027 equiv. (0.8% by weight of monomers) . 4. Adipic acid, ICI, 196.6g, 1.35 moles, 1.0 equiv. 5. Novozyme 435™, crude recovered grade, bulk recovered from previous fed-ba tch run (no. 8 of the series) . 6. Novozyme 435™, bx. ref. no. LC 0015-8, activity certified as 8200 propyl laurate units/g, Novo, 0.2g (10% by weight of original benchmark run - see Example no. 1 above) . Procedure The procedure adopted was as described m example no. 1, the JbenciimarJc run of the recyclability series described above, with sole modification that crude enzyme recovered from the previous fed -ba tch run no. 8 of the series replaced the bulk of virgin Novozyme 435 m used; a small additional supplement of fresh Novozyme 435 IM was also added to compensate for deactivation . These two enzyme grades were dosed at practically similar time. Following the process the crude enzyme was reserved as before and used without further purification m a subsequent fed -ba tch operation. The filtered oligomer was tested for acid number characteristic, shown to be 150mg KOH/g; consistent with <10 % deactivation of the enzyme catalyst from run to run. REFERENCE EXAMPLE 1 Hexylene adipate - example of a computer controlled laboratory reactor run. Materials 1. 1, 6-Hexanediol, BASF, 179.7g, 1.52 moles, 1.06 equiv. 2. Water, BDH, 7.3g, (1.9% by weight of monomers) . 3. Adipic acid, 208.6g, 1.43 moles, 1.0 equiv. 4. Novozyme 435™, bx. ref. no. LC 20001, activity certified as 7600 propyl laurate units/g, Novo, 3. Og (0.77% by weight of monomers) . Procedure Hexanediol and water were dosed to the 1 litre pot of a Buchi™ laboratory reactor, fitted with Midilab™ computer control of both the temperature of the heating jacket and the vacuum applied to the vessel; continuous monitoring display was available by means of a PC linked to the Midilab units. The jacket temperature was raised to 60°C, and the mix melted out with slow stirring. The stirring speed was raised to 200 rpm and adipic acid charged slowly; the mix was then stirred for 2 hours. A fine needle valve was m place on one of the vessel ports venting to atmosphere through an air- flow monitor, to allow the application of an air-bleed to the vessel _ιn vacuo . The vessel was fitted with a condenser m vertical distillation mode connected to a take-off adaptor, with vent to the vacuum line, leading to a receiver flask. The vacuum line led from the adaptor through a Dreschel bottle and then to the necessary automated on-off control valve; subsequently to a second on-line needle valve selected m capacity to permit the balancing of vacuum and air-bleed such that a continuous controlled bl eed could be administered, further facilitating the removal of water vapour. The stirrer speed was adjusted down to 120 rpm and the Novozyme 435™ added. At this juncture the set computer programme was initiated, instructing a further 4 hour period at atmospheric pressure, followed by the slow application of a vacuum by means of a diaphragm vacuum pump to a level of 15.5 kPa (155 mbar) ; a tiny air bleed being set by opening the large needle valve directly attached to the vessel . Controlled conditions were achieved by opening the aperture of the on-line needle valve such that the system attained balance and PC monitoring showed a steady state. The process was run for an overnight period of 16 hours. By morning a clear mobile solution had formed with only the immobilized enzyme insoluble; the process was validated by monitoring of the PC programme. The enzyme was filtered off using a nylon filter cloth of mesh s ze 74 μm. The filtered oligomer was tested for acid number characteristic revealed as 48 mg KOH/g. EXAMPLE 3 Hexylene adipate - example of a recent pilot plant operation. Materials 1. 1, 6 -Hexanediol , BASF, 115.7 kg, 980 moles, 1.06 equiv. 2. Water, deionized, 4.5 kg, (1-9% by weight of monomers) . 3. Adipic acid, 134.3 kg, 920 moles, 1.0 equiv. 4. Novozyme 435™, bx. ref. no. LC 20003, activity certified as 11950 propyl laurate units/g, Novo, 1.3 kg (0.52% by weight of monomers) . Procedure The process was run on pilot plant scale using a 500 litre vessel, equipped with an oil jacket and heating coils; vacuum application was by means of a water-ring pump. A nitrogen sparge could be applied through a dip-tube. Hexanediol and water were charged to the reaction vessel and heated with stirring at 60°C until molten; adipic acid was added and the mix left to stir for an overnight period. Enzyme was dosed early the next morning and after a 2 hour period, vacuum was applied with an air bleed m operation, such that the vacuum was around 60 mbar. After overnight processing the pot contents had reached acid number 25 mg KOH/g. The vessel was emptied and the pot contents filtered through a nylon cloth (74 μm mesh size) . The immobilized enzyme was recovered and retained its activity such that a further batch operation was possible on this scale without further purification. The filtered oligomer was transferred back to the vessel; the temperature of the pot was set at 100°C, the vacuum level at 4 kPa (40 mbar) and a nitrogen sparge applied at a level of lOL/m . After overnight processing, the product reached acid number of 2.9 mg KOH/g. To attain material of the desired specification a further overnight process was operated; characteristics of the finished products are set out m Table 1 below, compared to the conventionally derived analogue, Dynacoll™ 7360. Table 1 - comparison of characteristics of enzymatic and conventional polyester analogues. REFERENCE EXAMPLE 2 Hexylene adipate - regimen for small scale conversion of oligomer to polymer. Materials Hexylene adipate, oligomer, ref. FB 395/1 - derived from midpoint sampling of pilot plant process given m Example 3 above, 30g aliquot. Procedure The oligomer was transferred to a small cylindrical cell reactor of 100ml capacity and placed m an oil bath set at 100°C on a magnetic stirrer unit; a rugby ball stirrer bar was added to the reactor and the oligomer melted out. Vacuum of 1 kPa (10 mbar) was applied using a rotary o l pump through a digital controller to the vessel via a take - off adaptor fitted with a vent valve. The mix was stirred overnight for a period of 17 hours. By morning the viscosity had increased and acid number monitoring gave characteristic of 1.5 mg KOH/g showing conversion to a polymer. EXAMPLE 4 End processing technique-denaturation of enzyme residues. Materials 1. Hexylene adipate - finished product from pilot plant batch described Example 3 above, ref. Trixene™ 1339, DP9B bx. no. 9/6/875 - 500g. 2. Dynacoll™ 7360 - commercial sample - 500g. Procedure The polyester under test was melted out at 100°C and transferred to an electrically heated bath, capable of rapid heating to >200°C; a contact thermometer was placed the molten liquid, stirring was commenced and a foil jacket fitted. The head-space was placed under a nitrogen blanket. The pot contents were rapidly heated to 200°C and the temperature held for 3 minutes before the heat setting was reduced to 60°C. The water content of the mix was measured to be 0.01% by weight, and the water content was further adjusted to 0.2%. Similarly the water content of a commercial sample of Dynacoll™ 7360 was checked and found to be 0.09% by weight. Both samples, the test and the con trol were made up to water content 0.2% to give parity Various samples of both were transferred to tins and left in an oven thermostatically held at 60°C; untreated enzymatic polyester was also studied as a separate control . Acid number monitoring study was conducted over a period of over a month to check stability to hydrolysis. Results, set out Table 2 below disclose that the heat-treated enzymatic polyester is now resistant to hydrolysis and is practically as stable as its conventional counterpart. Table 2 - acid number characteristics variation with time of conventional and enzymatic polyhexylene adipates to show the effect of heat treatment. EXAMPLE 5 End - processing technique - denaturation of enzymatic residues - pilot plant scale. Materials Hexylene adipate - finished product from pilot plant batch described Example 3 above, ref. Trixene™ DP9B 1339, bx. no. 9/6/875 - 250kg. Procedure A major advance in denaturing the residual enzyme in the polyester batches was achieved on the pilot plant, by heating 250Kg of DP9B 1339 Bx. No. 12/6/897 to 180°C, with a nitrogen blanket for 4 hours. The temperature was then reduced, and the product emptied into a drum. Acid numbers were sampled before and after the process, consequent stability trials are correlated m Table 3 below; gel permeation data showed fidelity of characteristics before and after heat treatment (Table 4) . All water contents were made up to 0.2%, and the samples kept in the oven at 60 °C. Table 3 - correlation of acid number characteristics The product is now completely catalyst free - the acid number being <1 mg KOH/g. The GPC results show that the molecular weight showed no significant deviation following heat treatment . Table 4 - correlation of GPC characteristics EXAMPLE 6 Catalyst free hexylene adipate - example of a recent pilot plant operation including integral end-processmg. Materials 1. 1, 6 -Hexanediol, BASF, 115.7kg, 980 moles, 1.06 equiv. 2. Water, deionized, 4.5 kg, (1.9% by weight of monomers) . 3. Adipic acid, 134.3 kg, 920 moles, 1.0 equiv. 4. Novozyme 435™, bx. ref. no. LC 20003, activity certified as 11950 propyl laurate units/g, Novo, 1.3 kg (0.52% by weight of monomers) . Procedure The process was run on pilot plant scale using a 500 litre vessel, equipped with an oil jacket and heating coils; vacuum application was by means of a water - ring pump. A nitrogen sparge could be applied through a dip-tube. Hexanediol and water were charged to the reaction vessel and heated with stirring at 60°C until molten; adipic acid was added and the mix left to stir for an overnight period. Enzyme was dosed early the next morning and after a 2 hour period, vacuum was applied with an air bleed operation, such that the vacuum was around 6 kPa (60 mbar) . After overnight processing the pot contents had reached acid number 25 mg KOH/g. The vessel was emptied and the pot contents filtered through a nylon cloth (74 μm mesh size) . The immobilized enzyme was recovered and retained its activity such that a further batch operation was possible on this scale without further purification. The filtered oligomer was transferred back to the vessel; the temperature of the pot was set at 100°C, the vacuum level at 4 kPa (40 mbar) and a nitrogen sparge applied at a level of lOL/min. After overnight processing, the product reached acid number of 2.9 mg KOH/g To attain material of the desired specification a further overnight process was operated. The temperature of the pot was then immediately raised to 180°C whilst maintaining the vacuum level. After 4 hours the mixture was cooled and discharged from the pot . Analysis of the finished product as detailed for Example 5 showed that the enzyme had been denatured. EXAMPLE 7 Hexylene adipate oligomer - a fed-batch process using non- lmmobilised Candida an tarcti ca as a supplement. Materials 1. 1, 6 -Hexanediol , BASF, 179.7g, 1.52 moles, 1.06 equiv. 2. Water, BDH, 7.3g + 0.5g, (1.9% by weight of monomers) . 3. Adipic acid, 208.6g, 1.43 moles, 1.0 equiv. 4. Novozyme 435™, Novo, bx. ref. no. LC 20004, recovered and purified from pilot plant batch detailed as Example 3, previous activity certified as 10820 LU/g, 2.2g (0.57% by weight of monomers) . 5. Novozyme 525™, Novo, bx. ref. no. LCN 01001 activity certified as 14100 LU/g, 0. lg (5% w/w of mam bulk enzyme used) . Procedure The hexanediol, water (7.3g) and adipic acid were charged sequentially to a 500ml flange flask and the flask heated m an oil bath at 40°C. The flange flask was fitted with a condenser reflux mode, a vacuum purge tap and an overhead stirrer unit. The reagents were stirred at a speed of 160 rpm for a period of 2 hours at 40°C. The stirrer speed was then adjusted down to 120 rpm and the recovered Novozyme 435™ was added. A solution of Novozyme 525™ (non-immobilised Candida an tarcti ca) in water (0.5g) was prepared advance and, having stood overnight, was added to the mixture immediately after the Novozyme 435™. Stirring was continued for a further 4 hour period at atmospheric pressure. The bath temperature was then raised to 60 °C and the condenser changed over to distillation mode, a receiver flask and vacuum adaptor being fitted. A vacuum of 10 kPa (100 mbar) was then applied to the apparatus by means of a diaphragm vacuum pump, linked to the vessel via a digital controller, for an overnight period of 16 hours. A clear mobile solution was formed which contained the insoluble immobilised enzyme. The mixture was filtered through a nylon filter cloth of mesh size 74 μm. The residual crude immobilized enzyme was reserved for use m a subsequent batch- fed operation. The filtered oligomer was tested for acid number characteristic which was shown to be 60 mg KOH/g. EXAMPLE 8 Hexylene adipate - non- immobilised Candida antarctica as a supplement in the conversion of oligomer to polymer. Materials 1. 1, 6 -Hexanediol, BASF, 179.7g, 1.52 moles, 1.06 equiv. 2. Water, BDH, 7.3g + 0.5g, (1.9% by weight of monomers) . 3. Adipic acid, 208.6g, 1.43 moles, 1.0 equiv. 4. Novozyme 435 A Novo, bx . ref. no. LC 20004, recovered from pilot plant batch detailed as Example 3, previous activity certified as 10820 LU/g, 2.2g (0.57% by weight of monomers) . 5. Novozyme 435™, Novo, bx. ref. no. LC 20001 activity certified as 7600 LU/g, 0. lg (5% w/w of mam bulk enzyme used) . 6. Novozyme 525™, Novo, bx. ref. no. LCN 01001 activity certified as 14100 LU/g, 220mg. 7. Water, Analar, 0.5g. Procedure Hexylene adipate oligomer (ref FB 417/1) was formed using the process of Example 7 except that virgin Novozyme 435™ was used as a supplement instead of Novozyme 525™ solution. After the insoluble immobilized enzyme had been removed a 30g aliquot was transformed to a small cylindrical cell reactor of 100ml capacity. A solution of Novozyme 525™ m water (0.5g) was prepared m advance and, having stood overnight, was added to the reactor. The reactor was then placed in an oil bath set at 100 °C on a magnetic stirrer unit; a rugby ball stirrer bar was added to the reactor and the oligomer and lipase melted out. A vacuum of 1 kPa (10 mbar) was applied using a rotary oil pump through a digital controller to the vessel via a take-off adaptor filtered with a vent valve. The mixture was stirred under vacuum for 17 hours (an overnight period) . The resulting hexylene adipate polymer had an acid number characteristic of 1.6 mg KOH/g. EXAMPLE 9 Hexylene adipate - non- immobilised Candida an tarcti ca as a supplement in the conversion of oligomer to polymer. Example 8 was repeated except that the amount of Novozyme 525™ pre-dissolved in 0.5g of water was 44 mg . The resulting hexylene adipate polymer had an acid characteristic of 4.4 mg KOH/g. EXAMPLE 10 Hexylene adipate - without enzyme supplement in the conversion of oligomer to polymer. Example 8 was repeated except that 0.5g of water containing no enzyme was added to the oligomer in place of the solution of Novozyme 525™. The resulting hexylene adipate polymer had an acid number characteristic of 9.8 mg KOH/g. EXAMPLE 11 Uniform block copolymer - enzymatic preparation of novel polyester . Materials 1. Butylene adipate, 1000 MW polymer, Formrez™ V160/19, Lot no. 1903, 15g. 2. Hexylene adipate oligomer, ref. bx. no. FB 395/1 derived from mid-point extraction from pilot plant batch described in Example 3 (preceding to give Trixene™ DP9B 1339, bx. ref. no. 12/6/897), 15g, Procedure The butylene adipate polyester, acid number <1 mg KOH/g, MW 1000 daltons and the hexylene adipate oligomer, acid number 25 mg KOH/g, Molecular weight 2000 daltons were transferred to a cell reactor as in the regimen described in Reference Example 2, and melted out together. The mix was then subjected to the overnight vacuum and heat treatment detailed in Reference Example 2. By morning measurement of acid number revealed that complete polymerization had been effected, the acid number reduced to <1 mg KOH/g. Gel permeation chromatography confirmed significant changes in the product ref. FB 520/0 from the original artificial starting mixture ref. FB 503/1 see Table 5 below. Table 5 - correlation of GPC characteristics of starter and product for block copolymerization.

Claims: Claims 1. A process for producing a polyester comprising as repeated units (i) residues of at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; or (ii) residues of (a) at least one aliphatic dicarboxylic acid or a carboxylic acid derivative thereof (b) at least one aliphatic diol or polyol, and optionally (c) at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; which process comprises reacting the components defined in (i) or components defined in (ii) in the presence of a lipase and optionally in the presence of water such that the molar ratio of acid groups to hydroxyl groups in the reactants is 1:1 to 1:1.1 and wherein bound enzyme is removed from the reaction mixture and is then used in a further polymerisation of components defined in (i) or (ii) . 2. A process according to claim 1 wherein the lipase comprises lipase recovered from a previous implementation of the process according claim 1. 3. A process according to claim 2 wherein the recovered lipase is supplemented with previously unused lipase . 4. A process according to claim 3 wherein the unused lipase is employed in an amount of 10% by weight of the recovered lipase. 5. A process according to any one of the preceding claims wherein the bound enzyme is removed after the oligomerisation step as hereinbefore defined. 6. A process according to any one of the preceding claims wherein the reaction is carried out in the presence of a tertiary amine . 7. A process according to claim 6 wherein the amine is triethylamine . 8. A process according to any one of the preceding claims wherein the polyester comprises as repeating units residues of an aliphatic diol and an aliphatic dicarboxylic acid. 9. A process according to claim 8 wherein the aliphatic diol is 1 , 4-butanediol or 1 , 6-hexanediol and the aliphatic dicarboxylic acid is adipic acid. 10. A polyester obtainable by the process according to any one of the preceding claims. 11. A process for producing a catalyst free or substantially catalyst free polyester which process comprises treating polyester made by an enzymatic polymerisation process in a manner so as to denature the enzyme . 12. A process for producing a polyester according to claim 11 wherein the polyester comprises as repeated units (I) residues of at least one aliphatic hydroxycarboxylic acid or an ester or a carboxylic acid derivative thereof; or (ii) residues of (a) at least one aliphatic dicarboxylic acid or a carboxylic acid derivative thereof (b) at least one aliphatic diol or polyol, and optionally (c) at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof. 13. A process according to claims 11 or 12 wherein the treatment to denature the lipase is heat treatment. 14. A process according to claim 13 wherein the heat treatment involves heating the polyester to above 150 °C. 15. A process according to any one of claims 11 to 14 wherein the polyester is produced by the process of claims 1 to 9. 16. A polyester obtainable by the process of claims 11 to 15. 17. A polyester comprising as repeated units (i) residues of at least one aliphatic hydroxycarboxylic acid or an ester or an hydride thereof; or (ii) residues of (a) at least one aliphatic dicarboxylic acid or a carboxylic acid derivative thereof, (b) at least one aliphatic diol or polyol, and optionally (c) at least one aliphatic hydroxycarboxylic acid or a carboxylic acid derivative thereof; which polyester is catalyst free or substantially catalyst free. 18. A polyester according to claims 16 or 17 which has an acid number of less than 1 mg KOH/g after being made up to 0.2% by weight of water and being incubated for 15 days at 60°C. 19. A process according to any one of claims 1 to 9 or 11 to 15 wherein the lipase is from Candida antarctica . 20. A process according to any one of claims 1 to 9 , 11 to 15 or 19 wherein the process is carried out on a commercial scale/plant scale. 21. A process according to any one of claims 1 to 9, 11 to 15, 19 or 20 which further comprises reacting the polyester with isocyanate to form a urethane polymer. 22. A polymer composition comprising a polyester as claimed in any one of claims 10 or 16 to 18 or a polyurethane obtainable by the process of claim 21. 23. A shaped article comprising a polyester as claimed in any one of claims 10 or 16 to 18 or a polyurethane obtainable by the process of claim 21. 24. A process for producing a polyester as substantially hereinbefore defined with reference to any one of the Examples .

Inventors: BINNS FALMAI, TAYLOR ALAN, BINNS, FALMAI, TAYLOR, ALAN
Applicants: BAXENDEN CHEM LTD, BINNS FALMAI, TAYLOR ALAN, BAXENDEN CHEMICALS LIMITED, BINNS, FALMAI, TAYLOR, ALAN
Application year: 1998
Main classification: C12P7
IPC codes: C08G18, C08G63, C12P7