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| PATENT EXAMPLES |
EXAMPLE I 300 grams of p-hydroxybenzoic acid was dissolved in 900 ml of a warm 2 to 1 mixture of water and acetone and allowed to crystallize at room temperature overnight. In a one liter three neck flask equipped with a mechanical stirrer, a condenser, and a dropping funnel was placed a solution of 138 grams of p-hydroxybenzoic acid and 80 grams of sodium hydroxide in 400 ml of water. Through the funnel, 102 grams of 1,3-dibromopropane was added over a period of 1.5 hours, while the contents of the flask were stirred and kept at reflux temperature. The mixture was refluxed for 3.5 hours followed by the addition of 20 grams of sodium hydroxide which was then refluxed again for 2 hrs. The fine powdery, white precipitate of the disodium salt was isolated by filtration and washed with 200 ml of methanol. The precipitate was dissolved in 1 liter of distilled water and extracted with 200 ml of ether to remove traces of the dibromide using a paper filter. The solution was then acidified using 6N sulphuric acid to a pH less than 2. The diacid was isolated by filtration and after freezing for 2 hrs was dried for 3 days using a lyophilizer yielding 120 grams. The diacid, carboxyphenoxypropane (CPP) was purified by placing 50 grams in 200 ml of analytical acetone and allowing it to swirl in solution overnight to remove unreacted p-hydroxybenzoic acid. To prepare the CPP polymer 40 grams of CPP powder was added to 500 ml boiled acidic anhydride at approximately 130 degrees C. under dry nitrogen reflux. The reaction was stopped after 15 min. and the solution was filtered through a filter paper to another 1 liter round bottom flask. The solution was then concentrated to 150 ml by evaporation. The solution was allowed to crystallize which was then separated by filtration and transferred to 200 ml of anhydrous diethyl ether in an erlenmeyer flask and allowed to swirl for several hours at room temperature. The white crystals were separated by filtration and dried in a calcium chloride desicator under vacuum. It is essential that the degree of polymerization of the prepolymer not be greater than 4 by G.C.P. A sebacic acid prepolymer was prepared by refluxing 60 grams of sebacic acid with 250 ml of acidic anhydride under nitrogen for 90 minutes. The excess acetic anhydride was evaporated from the prepolymer which was then recrystallized from toluene. The crystals were then filtered and recrystallized in a mixture of petroleum ether and anhydrous diethyl ether. The white crystals were then separated by filtration and dried under vacuum. The high molecular weight polyanhydride copolymer was prepared by mixing 0.8 grams of the CPP prepolymer with the sebacic acid prepolymer in a glass tube with a side arm equipped with a capillary nitrogen inlet. After the prepolymers were melted by imersing the tube in an oil bath at 180 degrees C., a high vacuum (less than 10.sup.-2 mm Hg) was applied through the side arm. The acetic anhydride condensation product was collected in an acetone/dry ice trap. During the polymerization a strong nitrogen sweep with vigorous agitation of the melt was performed for 30 seconds every 15 minutes. After 90 minutes the tube was removed from the oil bath and the viscous polymer was allowed to cool to 60-80 degrees C. The crude high molecular weight polyanhydride copolymer was purified under nitrogen and precipitated in dry petroleum ether from dichloromethane solution. The solution was pressure filtered through a 0.2 micron filter and dripped into 600 ml of dry petroleum ether that was stirred using a mechanical stirrer. The resulting white fiber-like precipitate was then extracted with anhydrous ether for several hours at room temperature. Polymer analysis was done by melting point determination, molecular weight by GPC's and UV analysis which revealed a weight average molecular weight of 118,000 and an intrinsic viscosity of 0.92 dl/g. |
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