Characterization of poly(D,L-lactic acid) synthesized by direct melt polymerization and its application in Chinese traditional medicine compound prescription microspheres

From D,L‐lactic acid and with 0.5 wt % stannous chloride (SnCl2) as a catalyst under an absolute pressure of 70 Pa and at 165–170°C, poly(D,L‐lactic acid) (PDLLA) with an intrinsic viscosity of 0.2302 dL/g was synthesized after 10 h of melt polycondensation. This directly produced PDLLA was systematically characterized with gel permeation chromatography, Fourier transform infrared, 1H‐NMR, differential scanning calorimetry, and X‐ray diffraction. The weight‐average molecular weight of PDLLA was 17,800 Da, and the weight‐average molecular weight/number‐average molecular weight ratio was 1.25. It was partly crystalline, and its crystallinity was 20.8%. When first applied to the Chinese traditional medicine compound prescription Osteitis no. 1 PDLLA microsphere (G‐PDLLA‐MS), the optimal conditions for the extraction of the effective components in three raw herbs (Herba epimedii, Fructus psorakae, and Angelicae) and for the preparation of G‐PDLLA‐MS were determined with orthogonal testing. After the extractant was obtained by ethanol reflux, G‐PDLLA‐MS was prepared with a gelatin concentration of 8%, an inner water phase/oil phase volume ratio of 1.5:1, a stirring rate of dispersion of 1000 rpm, and a PDLLA concentration of 20%. Differential scanning calorimetry and scanning electron microscopy proved that G‐PDLLA‐MS had a good spherical shape. The practical average particle size of G‐PDLLA‐MS was 8.59 μm, and the particle sum between 2 and 12 μm was greater than 92%; this meets the requirement for an arthritis cure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 195–200, 2005