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| PATENT DESCRIPTION |
II. Melting Point and Solubility in Organic Solvents The polymers synthesized according to the method herein display low melting points, as indicated in Table 3, and are soluble in organic solvents, such as chloroform, and methylene chloride up to 40% w/v. These properties of the aliphatic-aromatic polymeric anhydrides allow for fabrication into microspheres or films from solution. III. Hydrolytic Degradation Hydrolytic degradation of these aliphatic-aromatic polymers display zero-order kinetic degradation profiles. A zero-order kinetic degradation profile results in a linear relationship between percentage degradation and time. At 37.degree. C. in phosphate buffer (0.1 M, pH 7.40), poly(CPA), poly(CPV) and poly (CPO) maintain a linear relationship up to 100% degradation. See FIG. 2. This demonstrates that surface erosion, as opposed to bulk erosion, is taking place. These compounds further display their integrity over time when degradation rates are measured in conjunction with drug release rates. Drug incorporated matrices were formulated by compression molding. The model drug p-nitro aniline (PNA), sieved to the same size range, was mixed with 200 mg polymer manually and the mixture was pressed onto circular discs of 15 mm diameter and 1 mm thick in a Carver Test Cylinder Outfit at 30 Kpsi. P-Nitroaniline is used as a model drug because it absorbs strongly in the near visible range and provides minimum interference with the UV analysis of the matrix degradation products. The polymer erosion and drug release kinetics were followed by measuring the UV absorbance of the periodically changed buffer solutions in the Perkin-Elmer UV spectrophotometer. The optical densities at 381 nm (absorption maximum for p-nitroaniline) and 250 nm for degradation products were measured to determine the respective results. FIGS. 3 and 4 demonstrate clearly that the release of p-nitroaniline follows the degradation of the polymer, indicative of an intact matrix with surface erosion. The obvious importance of this invention is that the polymer matrix does not remain to degrade slowly over time in vivo long after the drug has been delivered. This is the result of the fine uniform distribution of aliphatic and aromatic residues in the polymer. Another useful property of this invention is that a polymer with a required degradation profile may be obtained by choosing the appropriate length of the aliphatic moiety. For example, p(CPV) with an aliphatic chain of four methylene groups degraded completely after two weeks while p(CPO) with seven methylene groups degraded about 120 days. Copolymers of these aromatic-aliphatic monomeric diacids also display zero-order degradation, with a time frame indicative of the monomers selected. See FIG. 5. This invention has been described with reference to its preferred embodiments. Variations and modifications of the method of synthesizing polymers with uniform aliphatic and aromatic residues and which display zero-order degradation profiles, and the polymers, will be obvious to those skilled in the art. It is intended that all of these variations and modifications be included within the scope of the appended claim. |
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