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EXAMPLE 1 Solution Polymerization of Sebacic Acid Using Phosgene or Diphosgene as the Coupling Agent A solution of 1 eq. diacid and 2.5 to 3 eq. base in an organic solvent was prepared. Either PVP or K.sub.2 CO.sub.3 was added as an insoluble acid acceptor. The resulting insoluble solid, PVP.HCl or KCl, respectively, was removed by filtration. The filtrate was added dropwise to a sufficient volume of petroleum ether to precipitate the polymer out of solution. The precipitated polymer was then isolated by filtration and dried in a vacuum oven for 24 hours at 40.degree. C. The results of the polymerization of sebacic acid, as a model, using either phosgene or diphosgene as coupling agents with various acid acceptors are shown in Table I. The poly(sebacic anhydride) has a weight average molecular weight up to 16,300. The results are similar for the (SA) using either phosgene or diphosgene. All of the p(SA) formed has the same melting point and IR absorbance characteristics of anhydride bonds. Insoluble polyamines, poly(4-vinylpyridine) (PVP), as well as soluble amines, TEA, pyridine, and TMEDA were used. The polymers formed with these reagents have similar molecular weights, indicating a similar role for the different amine bases as acid acceptors. Using a heterogeneous acid acceptor, PVP, does not affect the polymerization, as shown in Table I. A non-amine heterogeneous base, K.sub.2 CO.sub.3, yields a lower molecular weight polymer. This may be due to the formation of a soluble intermediate complex of acid-amine which increases the interaction with the coupling agent under homogeneous conditions. Although the PVP is insoluble in the reaction medium, it swells and forms a similar acid-PVP complex. K.sub.2 CO.sub.3, however, forms a heterogeneous mixture with the acid and thus reacts slower with the coupling agents to form the polymer. TABLE I ______________________________________ Polymerization of Sebacic Acid Using Phosgene and Diphosgene as Coupling Agents..sup.a Molecular Coupling Acid Weight IR MP Agent Acceptor Mw Mn (cm.sup.-1) (.degree.C.) ______________________________________ 1. Phosgene Sol. TEA.sup.b 14800 6250 1800 1740 75-77 2. Phosgene Sol. pyridine.sup.b 13700 5950 1800 1735 76-78 3. Phosgene Sol. TMEDA.sup.b 16300 6600 1805 1735 76-78 4. Phosgene Sol. PVP 13950 5350 1805 1735 80-81 5. Phosgene Gas Pyridine.sup.b 14100 6820 1805 1735 75-77 6. Phosgene Gas PVP 13200 6150 1800 1735 79-80 7. Diphosgene TEA.sup.b 12250 5780 1805 1735 76-78 8. Diphosgene Pyridine.sup.b 14300 6100 1805 1740 75-78 9. Diphosgene PVP 10900 5300 1800 1735 79-80 10. Phosgene Sol. K.sub.2 CO.sub.3 6200 2700 1800 1740 76-78 11. Diphosgene K.sub.2 CO.sub.3 6900 3500 1800 1740 77-78 ______________________________________ .sup.a Polymerization in chloroform, at 25.degree. C., for 3 hours. .sup.b Molecular weight and IR spectra were taken of the crude polymer. The IR spectra contained amineHCl absorbance peaks at 2900-2600 cm.sup.-1 GPC output contained an isolated peak attributed to the amineHCl salt. Mw was determined for the polymer peak only. The melting point was determine for the pure polymer. EXAMPLE 2 Comparison of Solution Polymerization Using Soluble and Insoluble amines A method similar to that of Example 1 was used to polymerize the dicarboxylic acids. However, when either triethylamine (TEA) or pyridine was used as the acid acceptor, the polymerization reaction was quenched in petroleum ether and the polyanhydride, not the acid acceptor, precipitated from solution. The precipitated polymer was redissolved in chloroform and washed rapidly with a cold solution of water at pH 6. The cloroform solution was dried over MgSO.sub.4 and the polymer re-precipitated by the dropwise addition of petroleum ether. Several solvents, toluene, DMF, DMSO, and dioxane, were tested using TEA as the acid acceptor. The precipitated solids were removed by filtration. The filtrate was evaporated to dryness in vacuo at 25.degree. C. The resulting solid was dissolved in chloroform, the polymer precipitated out by slow addition into petroleum ether, the precipitated polymer isolated by filtration and washed with diethyl ether to remove any traces of phosgene or diphogene. The composition, yield and melting points of the products formed with the various monomers and solvent mixtures are shown in Table II. TABLE II __________________________________________________________________________ Solution Polymerization of Diacids in Various Solvents. Analysis of Yield.sup.c mp.sup.b Monomer.sup.f Solvent Solution.sup.a Solid.sup.b (%) (.degree.C.) __________________________________________________________________________ 1. SA Chloroform.sup.e pSA/TEA.HCl -- .sup.d 2. Toluene.sup.e pSA pSA + TEA.HCl 20 78-79 3. N,N'-Dimethyl- pSA TEA.HCl 100 80-81 formamide 4. Dimethylsulfoxide -- -- -- 5. Pyridine pSA/TEA.HCl -- .sup.d 6. Dioxane pSA/TEA.HCl TEA.HCl .sup.d -- 7. CPP Chloroform TEA.HCl pCPP 100 265 8. TPA Chloroform TEA.HCl pTPA 100 >300 __________________________________________________________________________ .sup.a The solvent was evaporated and the residue was analyzed. .sup.b Analysis of the precipitated solid. .sup.c Pure polymer. .sup.d Yield cannot be determined due to the presence of TEA.HCl. .sup.e Polymerized using either diphosgene or sebacoyl chloride as coupling agents. .sup.f SA is sebacic acid, CPP is 1,3bis(p-carboxyphenoxy)propane, TPA is Terephthalic acid. The use of a solvent system wherein the polymer is in one reaction phase (either as a precipitate or in solution), and the acid acceptor-hydrochloride acid complex is in a second phase, complementary to the polymer, is an alternative to the use of an insoluble acid acceptor. Table II describes polymerization of SA in several solvents with TEA as an acid acceptor. Polyanhydrides were obtained in good yield in toluene and in DMF. TEA in toluene or DMF is complementary to the use of PVP in chloroform. In both approaches, the p(SA) is soluble in the reaction media. The insoluble hydrochloric acid-acid acceptor complex, whether an insoluble amine, PVP.HCl, or TEA.HCl salt, is removed by filtration, leaving a polymer of greater than 99.7% purity with no need for further purification. EXAMPLE 3 Solution Polymerization comparing an Acid Chloride as the Coupling Agent with Phosgene and Diphosgene as the Coupling Agent Solution polymerization was performed as before, using either phosgene, diphosgene or an acid chloride as the coupling agent and an acid acceptor. Reactions between sebacic acid (1 eq.) and sebacoyl chloride (1 eq.) were performed in chloroform and toluene in the presence of either PVP (insoluble) or TEA (soluble). In a typical polymerization, 0.5 g (0.5 eq.) disphosgene was added dropwise into a stirring mixture of 2.02 g (1.0 eq.) sebacic acid and 3 g (2.5 eq.) poly(4-vinylpyridine) in 20 ml chloroform. After 3 hours at 25.degree. C., the insoluble PVP.HCl was removed by filtration. The filtrate was quenched in 100 ml petroleum ether. The precipitated polymer was isolated by filtration, washed with anhydrous diethyl ether and dried for 24 hours at 40.degree. C. in a vacuum oven. A comparison of the purity of p(SA) synthesized using soluble and insoluble amines, TEA and PVP, respectively, with diphosgene or sebacoyl chloride as coupling agents, as shown in Table III, demonstrates that when soluble base, TEA, was used as an acid acceptor, the polymer contains a significant amount of TEA.HCl salt. The ratio of the salt to the polymer was 4:1 and 2:1 for the coupling agents diphosgene and sebacoyl chloride, respectively. When PVP, an insoluble acid acceptor, was used p(SA) of greater than 99.7% purity was obtained for both coupling agents. PVP has another advantage besides high purity of the end product. It can be regenerated by neutralization with a sodium bicarbonate solution. Recycled PVP has a similar activity to that of the original PVP as an acid acceptor and forms a polyanhydride identical to the original polyanhydrides. TABLE III __________________________________________________________________________ Presence of Amine hydrochloride in Solution Polymerized pSA as a Function of the Acid Acceptor. Polymerization Yield TEA:PSA mp Elemental Method.sup.a (%).sup.e IR.sup.b 'H NMR.sup.c /Elemental GPC.sup.d (.degree.C.) (% N, % Cl) __________________________________________________________________________ 1. A .sup.f + 4.3:1/3.5:1 + 70-185.sup.g 7.21, 19.63 2. B 62 - -- - 81-82 0.18, <0.10 3. C .sup.f + 1.9:1/2.4:1 + 68-185.sup.g 5.26, 13.14 4. D 65 - -- - 81-83 0.11, 0.027 5. E 60 - -- - 81-83 0.11, 0.015 __________________________________________________________________________ .sup.a A is TEA/diphosgene; B is PVP/diphosgene; C is TEA/sebacoyl chloride; D is PVP/sebacoyl chloride, E is regenerated PVP/diphosgene. .sup.b Typical absorbance of TEAHCL follows (film cast); 2740 (w), 2600 (s, broad), 2530 (w, sharp), 2500 (s, sharp) cm.sup.-1. .sup.c 'H NMR of TEAHCl (CDCl.sub.3): 3.11 (q,2,J = 7.3 Hz), 1.42 (t, 3, = 7.3 Hz); 'HNMR of PSA (CDCl.sub.3): 2.45 (t, 4, J = 7.3 Hz), 1.66 (br t 4, J = 7.3 Hz), 1.33 (br s, 8). .sup.d Sharp peak at Rt = 12.3 min. .sup.e Pure poly(sebacic anhydride) .sup.f Yield cannot be determined due to the presence of TEA.HCl. .sup.g m.p. of TEA.HCl is 261.degree. C. Attempted purification of polymers synthesized with TEA as the acid acceptor using rapid water extraction results in a decrease in molecular weight and hydrolysis, as evidenced by GPC and IR spectra. The IR spectra of the polymer before and after purification reveals the disappearance of the amine salt (2740-2500 cm.sup.-1). The IR spectra of polyanhydrides prepared with PVP as an acid acceptor reveals pure unhydrolyzed polymer. |
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