IMPROVED METHOD FOR PRODUCTION OF POLY(TRIMETHYLENE CARBONATE)

Abstract: A process for the production of poly(trimethylene carbonate) which comprises: reacting trimethylene carbonate and one or more alcohols, individually, or in combination, under inert atmosphere, optionally in the presence of a catalyst; and a process for the production of high molecular weight poly(trimethylene carbonate) which comprises: reacting trimethylene carbonate, a catalyst, and optionally one or more alcohols, under inert atmosphere.

Description: IMPROVED METHOD FOR PRODUCTION OF POLY (TRIMETHYLENE CARBONATE) FIELD OF INVENTION The present invention relates to a method of producing poly (trimethylene carbonate) (PTMC) . More particularly, the present invention relates to an improved method of producing poly (trimethylene carbonate) in which no decarboxylation is observed. BACKGROUND OF THE INVENTION In methods currently known in the art for the production of poly (trimethylene carbonate), problems with decarboxylation during the reaction are common and the products typically have an undesirably large percentage of allyl end groups. Allyl end groups are undesirable, because they reduce the hydroxyl functionality, result in dead ends, and are less effective in chemistry which requires hydroxy terminated species, such as, for example, in urethane or melamine chemistry. In addition, the transparency of poly (trimethylene carbonate) currently available in the art is typically not as clear as would be desirable, thus presenting problems in obtaining the clarity sought after in clear urethane or melamine coatings formulations. It is known in the art that cyclic carbonates can be converted in the presence of polyhydric alcohols at higher temperatures and under increased pressures into liquid to viscous polycarbonates of relatively low molecular weight. It is also known that cyclic carbonates can be converted without the presence of alcohols . Various groups of catalysts are known in the art for ring-opening polymerization, however previously used catalysts generally have one or more undesirable effects, such as, for example, longer reaction times, poor conversion, colour formation, decarboxylation, and the formation of alluyl end groups. Decarboxylation is undesirable because it yields ether links which reduce UV and thermal stability of the material and allyl end groups reduce the hydroxyl functionality. Kricheldorf, et al , used methyl triflate or triethyloxonium fluorborate to polymerize 1 , 3 -dioxan-2 - one, as discussed in J. Macromol . Sci . , Chem . , A26 (4) , 631-44 (1989) , however this article describes many side chemistries. In Makromol . Chem. , 192 ( 10 ) , 2391-9 (1991), Kricheldorf, et al , describe numerous bulk polymerizations of trimethylene carbonate, at various temperatures, using catalysts containing butyl groups, tin, and bromide, inter alia; ether groups were not found, and all polycarbonates contain a CH2CH2CH2OH end- group. It does not appear these products were examined for clarity. In the present invention it was found that using catalysts of the type described by Kricheldorf, et al resulted in products with less clarity than those described herein. In Polymer, 36(26), 4997-503 (1995), Kricheldorf, et al, used tin halides for polymerization of cyclotrimethylene carbonate. Additional work, described in J " . Polym . Sci . , Part A : Polym . Chem . , 33(13), 2193- 201(1995), described the use of BuSnCl 3 - , Bu 2 SnCl 2 -, and Bu 3 SnCl initiators. In both studies using tin-containing compounds the chemistry results in dead ends and further chemistry would be required to convert the halide end groups to hydroxy groups. An article by Kricheldorf, et al, in Macro ol . Chem . Phys . , 197 ( 3 ) , 1043-54 (1996), discloses the spontaneous and hematin- initiated polymerizations of trimethylene carbonate and neopentylene carbonate. This method would also result in dead ends . In an article titled, "Homopolymerization of 1,3 - dioxan-2-one to high-molecular-weight poly (trimethylene carbonate)", in J. Macromol . Sci . - Chem . , 29 ( 1 ) , 43-54 (1991), Albertsson, et al , discuss the use of sodium ethoxide or stannous 2 -ethylhexanoate as a transesterification catalyst. It was found that the polymer contained 2.6% ether linkages formed by decarboxylation during polymerization at high temperature. At page 51, it is stated "Immediately after the polymerization, all the polymers were transparent, but on cooling the polymers with low molecular weight became opaque due to crystallization of unreacted monomer". In J. Macromol . Sci . - Chem . , 29 ( 1 ) , 43-54 (1991), Albertsson, et al, discuss the homopolymerization of 1 , 3-dioxan-2-one to high molecular weight poly (trimethylene carbonate) using either EtONa or stannous 2 -ethylhexanoate as the transesterification catalyst. This chemistry generated significant amounts of decarboxylation. In an article by Albertsson, et al , J " . Macromol . Sci . , Pure Appl . Chem . , A29 ( l ) , 43-54 (1992), there is described the homopolymerization of 1,3-dioxan- 2 -one to high molecular weight poly (trimethylene carbonate) . This chemistry also generated significant amounts of decarboxylation. In J " . Polym . Sci . , Part A: Polym. Chem., 32(2), 265-79 (1994), Albertsson, et al , describe a new type of copolymer synthesized from 1,3- dioxan-2-one and oxepan-2-one using either tin octoate, zinc acetate, dibutyltin oxide, or tributyltinchloride as the catalyst . In European Patent Application EP-A-0778304 there is disclosed a method of rendering polyesters such as polylactides, lactide/glycolide copolymers, and poly (trimethylene carbonates) hydrophobic by reaction of terminal OH and/or C0 2 H groups with long-chain fatty acids and/or fatty alcohols or their derivatives. This reference primarily discloses a particular product and would result in dead ends in urethane and coatings applications . An alkyl halide-initiated cationic polymerization of cyclic carbonate is described in an article by Ariga, et al, J " . Polym . Sci . , Part A : Polym . Chem . , 31 ( 2 ) , 581-4 (1993) . It is believed this chemistry would produce one dead end for every initiator group. A rare earth halide was used in the ring-opening polymerization of trimethylene carbonate, as well as ε- caprolactone, in an article by Shen, et al , J " . Polym . Sci . , Part A : Polym . Chem . , 35 ( 8 ) , 1339-1352 (1997) . Rare earths are typically pro-oxidants and, therefore, would be expected to negatively impact ageing properties of poly (trimethylene carbonate). In an article by Ariga, et al , in Macromolecul es , 30(4), 737-744 (1997), there is disclosed the cationic ring-opening polymerization of cyclic carbonates with an alkyl halide as initiator. The methods discussed in this reference would produce dead ends, thus making the products unsuitable for urethanes and coatings. The use of an alcohol -acid catalyst for the ring- opening polymerization of cyclic carbonates is described in an article by Matsuo, et al , J " . Polym . Sci . , Part A : Polym . Chem. , 36 ( 14 ) , 2463-2471(1998). The product of this method would result in dead ends and would require hydrolysis to produce active end groups. In Polym . Prepr. (Am. Chem. Soc . , Div. Polym. Chem.) , 35(2), 144-145 (1998), an article by Deng, et al , describes the ring-opening polymerization of ε- caprolactone and trimethylene carbonate catalyzed by lipase Novozym 435. In this case, the removal of the lipase would be problematic. In an article by Bisht, et al, in Macromolecules, 30(25), 7735-7742 (1997), the use of lipase-catalyzed ring-opening polymerization was extended to cyclic carbonate monomers . An article by Matsuo, et al , in Macromol . Chem . Phys . , 199 ( 1 ) , 97-102 (1998), describes the ring-opening polymerization of a 7-membered cyclic carbonate in nitrobenzene; and of a 6-membered cyclic carbonate in dichloromethane, the latter generally accompanied by partial elimination of C0 2 . This paper supports the observation that decarboxylation occurs when polymerizing trimethylene carbonate . There is still a technical demand for the development of a process by which poly (trimethylene carbonate) of a quality that would exhibit optimum properties for use in urethane chemistry could be obtained, and which would also be economical and uncomplicated in operation. It would be particularly desirable in the art if poly (trimethylene carbonate) could be made in one simple step, while avoiding the typical decarboxylation and formation of allyl end groups. It would constitute a great advance in the art and would be extremely advantageous commercially if pol (trimethylene carbonate) could be made with essentially 100% hydroxypropyl end groups and as clear and colorless as water. SUMMARY OF THE INVENTION The present invention provides a process for the production of poly (trimethylene carbonate) which comprises: reacting trimethylene carbonate and one or more alcohols, individually or in combination, under inert atmosphere, optionally in the presence of a catalyst . DETAILED DESCRIPTION OF THE INVENTION In view of the many variables that would influence the polymerization, the fact that hydroxy end groups are easy to dehydrate, and that the carbonate unit is easily decarboxylated, it was by no means foreseeable that the process according to the present invention would be able to fulfill such varied improvements as producing a water white product with virtually all end groups being hydroxypropyl groups, with no measurable allyl groups, using no solvent, moderate temperatures, and atmospheric pressure . Preferred products of the present invention generally have one or more of the following features : - they are the colour of (i.e. as clear as) water, have virtually all end groups being hydroxypropyl groups and/or have no measurable allyl groups. In addition, preferably no decarboxylation is observed during the polymerization and no other groups are detected. The nature of the end groups and the degree of decarboxylation may be conveniently measured by Nuclear Magnetic Resonance spectroscopy (NMR) . The present invention is especially useful for producing low molecular weight poly (trimethylene carbonate) . The reaction generally proceeds rapidly, typically 30 to 120 minutes. In the alternative embodiment for producing higher molecular weight products without an initiator, the reaction typically proceeds in from 5 to 30 hours. Whilst the product of Example 3 herein was produced in about 20 hours, the reaction could take place in a much shorter period. Alcohols that may be suitably employed in the process of the present invention include mono- or polyhydric alcohols . In a preferred embodiment of the process of the present invention, poly (trimethylene carbonate) characterized by the excellent properties described above is produced by reacting, trimethylene carbonate (TMC) with a polyhydric alcohol in the presence of a catalyst. The polyhydric alcohol may conveniently be a diol, triol or higher polyhydric alcohol . Among the diols illustrative of those that are useful in forming PTMC in the present invention are ethylene glycol , propanediol, butanediol , neopentyl glycol, pentanediol, hexanediol, and mixtures thereof. Triols considered useful include, for example, glycerin, trimethylolethane, trimethylolpropane, and higher functionality alcohols such as, for example, pentaerythritol . Preferred alcohols are propanediol and trimethylolpropane. The process can take place without a catalyst, however the catalyst provides the advantage of faster reaction times and greater transparency of the product. Suitable catalysts for the present invention include those selected from salts of Group IA or Group IIA elements of the Periodic Table. The catalyst is preferably a salt of lithium, potassium, sodium, calcium individually or combinations thereof. Good results may be obtained where the catalyst is an acetate. Examples include, but are not limited to, acetates of potassium, sodium, lithium, and calcium. By comparison, Group IVA compounds tend to be slower and result in a product with lower transparency. Particularly good results may be obtained using sodium acetate. The catalysts just described are effective in small amounts. The total weight of the alkali or alkaline- earth metal charged may be calculated to result in the desired total metal weight based on reactants. Whilst it is possible employ an amount of metal in the catalyst ranging from less than 1 ppm to greater than 10,000, typical expect amounts are in the range of from 5 to 1000 ppm, preferably from 10 to 100 ppm, more preferably from 10 to 50 ppm and most preferably 10 to 40 ppm. In the production of higher molecular weight polymers good results may be obtained using somewhat higher ppms, for example, from 40 to 150 ppm. In Example 3 the amount of sodium metal was 100 ppm. The catalyst is preferably in anhydrous form. Although a solvent need not be typically not used in the process of the present invention, it will be appreciated that the process may also be performed in the presence of a solvent . Suitable solvents include those solvents not containing hydroxyl groups. The poly (trimethylene carbonate) in the present invention was produced without a solvent . Suitable reaction temperatures that may be used in the process of the present invention include those in the range of from 50 to 160°C. A preferred range is from 100 to 150°C, more preferably from 110 to 140°, even more preferably from 110 to 135°C, and most preferably from 120 to 135°C. The process is generally performed in a kettle or reactor with a means of stirring under inert atmosphere. Said inert atmosphere may conveniently be nitrogen. The trimethylene carbonate, alcohol, and an anhydrous metal salt catalyst are typically placed in a polymerization kettle containing a stirring mechanism. The quantity of polyhydric alcohol, typically propanediol or trimethylolpropane, charged is typically a stoichiometric amount calculated to give the desired molecular weight of poly (trimethylene carbonate) . In a preferred embodiment, the ratio of trimethylene carbonate to alcohol, preferably polyhydric alcohol, is from 1:1 to 100:1, respectively. The quantity of the catalyst charged may be calculated to result in the desired total metal weight, typically 40 ppm of metal based on reactants. For example, under nitrogen at atmospheric pressure, the kettle may be heated to typically 110 to 150°C, while the contents are stirred. The reaction generally takes up to 4 hours, preferably from 0.25 to 3 hours. However, the reaction typically proceeds fairly rapidly, taking from 30 to 120 minutes. The resulting polyols of the process of the present invention are generally produced faster and exhibit greater clarity than those produced using catalysts such as tin(II), aluminum (III), or titanium (IV), or without a catalyst, in all of which cases the reaction proceeds more slowly. In the reaction of trimethylene carbonate and an alcohol in the presence of a catalyst, pressure is not critical, and actually almost any pressure could be used, but the Examples herein demonstrate that good results were obtained using ambient pressures, conveniently at or near atmospheric pressure . The product of the process of the present invention will have properties that are determined by several factors, the most important factors being the amount and identity of any initiating alcohol (s), catalysts and catalyst amounts, and the process conditions. A manufacturer may vary the determining factors to predictably produce the molecular weight, polydispersity, and other characteristics needed for the intended application. In an alternative embodiment of the present invention, high molecular weight poly (trimethylene carbonate) is produced without the use of an initiator, using the catalyst described herein and longer reaction times. Said reaction comprises reacting trimethylene- carbonate, a catalyst, and optionally one or more alcohols, under an inert atmosphere. Monofunctional oligomers and polymers can be produced by the process of the present invention. The process is more efficient for producing materials of the same molecular weight with a higher functionality. For many applications a functionality of two or higher is required of the product. For convenience, the product can be referred to as a polyol if the molecular weight is from 134 to 20,000, with a hydroxyl functionality of 1 or higher, or as a high polymer if the molecular weight exceeds 20,000. Polyols have utility as a reactive component in urethane chemistry, melamine chemistry, esterification, epoxidation, and other processes, producing coatings, elastomers, adhesives, fibers, shaped articles, and a variety of other products. Preferred polyol molecular weight would be from 250 to 10,000, with a preferred functionality of 2 to 4. Poly (trimethylene carbonate) as high polymer with functionality of 2 or less can be readily thermoformed, deposited from solution, machined, or extruded into films, fibers, or shaped articles, while high polymer with high functionality can be predicted by those skilled in chemistry to have value especially as an adhesive or in the role of a reactive polyol. Poly (trimethylene carbonate) -as either a polyol or a high polymer is not readily degraded by heat, ultraviolet light, moisture, or heat, at temperatures up to at least 160°C. Preferred molecular weight for high polymer would be greater than 30,000, and preferred functionality would be greater than or equal to depending on the application and the economics . The present in invention will now be illustrated by the following Examples, which are not intended to limit the scope of the invention in any way. Example 1 Example 1 demonstrates the procedure used in the runs for which data is provided in Table 1. In a drybox, trimethylene carbonate monomer, propanediol, and an anhydrous alkali or alkaline earth metal acetate catalyst were placed in multiple open glass vials held upright in a reaction kettle containing a layer of sand for improved heat distribution. While a nitrogen atmosphere was maintained, the kettle was immersed in preheated oil . At designated intervals, the kettle was opened and vials with different catalysts but held the same distance from the kettle wall were removed for comparative analysis. Referring to Example 1(b) in Table 1, and the third run, 2.02 grams TMC and 0.10 grams PDO were placed in a polymerization kettle with a sodium acetate catalyst in an amount of 40 ppm sodium. Under nitrogen at atmospheric pressure, the kettle was heated to 130 °C. In the product 99.8% oligomer was measured. Results are shown in Table 1 : Table 1 (cont'd * Possible excess Sn ++ ** Sn(II)Oct - Tin (II) acetoate *** Time ZERO is 11 minutes after immersing multireactor into hot oil, which dropped to 75°C before climbing to 125 C C at time ZERO then to 135 °C (within 2 minutes) . Ex. l(k)-l(s) also had varying periods of catalyst in the TMC (1-18 hours, Sn the longest), but similar periods with presence of PDO in vials. Example 2 In Example 2, in a drybox, trimethylene carbonate monomer (TMC), trimethylolpropane, and an anhydrous alkali or alkaline earth metal acetate catalyst were placed in a polymerization kettle containing a stirring mechanism. The quantity of trimethylolpropane (TMP) charged was the stoichiometric amount calculated to give the desired molecular weight of polytrimethylene carbonate. After holding at 24 °C under nitrogen for 0.5 - 20 hours, the kettle was immersed in oil heated to typically 130 °C. Samples were taken for analysis at appropriate times. In Example 2b, a second catalyst was added after the first sample was taken. The amount of trimethylene carbonate reacted, and other characteristics, were determined by nuclear magnetic resonance spectroscopy (NMR) . Some samples were titrated for hydroxyl content to determine the equivalent weight. Results are shown in Table 2: Table 2 (cont'd) 3 KOH, >14% Water 4 Gray Products Table 2 (cont'd) 5 Run 4 cooled in heating oil G Poor heating control especially 1 st & 3 rd hours PJ tr to o o 0 rt α 12 - εrεzo/ioda/iDd t..'9/lO OM Table 2 (cont'd) "Scratch" means product made from the starting materials in the Example description. Alternatively, the starting material may be product from a previous run in the same example. This is indicated by the run no. from which said starting material originates. Example 3 In Example 3, higher molecular weight poly (trimethylene carbonate) was produced. In a drybox, trimethylene carbonate monomer and an anhydrous sodium acetate catalyst were placed in a polymerization kettle containing a stirring mechanism. The quantity of the catalyst charged was calculated to result in the desired total metal weight, and was about 100 ppm of sodium based on reactants. The kettle was sealed with Schlenk connectors, then taken to the site of a stirring motor and a nitrogen source . Under nitrogen at atmospheric pressure, the kettle was heated to 135°C, while the contents were stirred. The compounds produced were measured by NMR to determine the % polymer present and the % unreacted starting material, TMC. The % oligomer and MW, were measured by GPC . Data are shown in Table 3: Table 3 *Oligomer not included in MW calculations From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various uses and conditions. Such changes and modifications would be considered within the scope of the invention.

Claims: C A I M S 1. A process for the production of poly (trimethylene carbonate) which comprises: Reacting trimethylene carbonate and one or more alcohols, individually, or in combination, under inert atmosphere, optionally in the presence of a catalyst . 2. A process for the production of high molecular weight poly (trimethylene carbonate) which comprises: Reacting trimethylene carbonate, a catalyst, and optionally one or more alcohols, under inert atmosphere. 3. The process according to Claim 1 or 2 , wherein said alcohols are selected from one or more monohydric or polyhydric alcohols, individually, or in combination. 4. The process according to any one of Claims 1 to 3 , wherein the reaction takes place at an elevated temperature . 5. The process according to any one of Claims 1 to 4, wherein the catalyst is selected from the group consisting of salts of elements from Group IA or IIA of the Periodic Table. 6. The process according to any one of Claims 1 to 5, wherein said alcohol is selected from diols, triols, and higher functionality polyhydric alcohols. 7. The process according to any one of Claims 1 to 6, wherein the alcohol is selected from the group consisting of propanediol, trimethylolpropane, individually, or mixtures thereof . 8. The process according to any one of Claims 1 to 7, wherein the catalyst is selected from a salt of lithium, potassium, sodium, calcium, individually or combinations thereof . 9. The process according to any one of Claims 1 to 8, wherein the catalyst is an acetate salt . 10. The process according to any one of Claims 1 to 9, wherein the temperature is from 100 to 160°C.

Inventors: BOON WYNDHAM HENRY, FORSCHNER THOMAS CLAYTON, GWYN DAVID ERIC, SMITH ROY FRANK, BOON, WYNDHAM, HENRY, FORSCHNER, THOMAS, CLAYTON, GWYN, DAVID, ERIC, SMITH, ROY, FRANK
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 2001
Main classification: C08G63
IPC codes: C08G18, C08G64