Ring-opening polymerization of lactones in the presence of hydroxyapatite

The ring-opening polymerization of epsilon -caprolactone, delta -valerolact one (VL) and D,L-lactide, respectively, in the presence of different propor tions of hydroxyapatite (HA) was catalyzed by stannous (II)octoate (SnOct(2 )) at 130 degreesC and resulted in composites. The lactones were almost com pletely converted to the polymers within a reaction time of 70 up to 240 mi n. The number-average molecular weights M-n as determined by size exclusion chromatography decreased with increasing content of HA. The initiating eff iciency of HA as calculated from the difference of the polymerization degre es P-n obtained with and without HA turned out to be relatively low with ca . I I to 0.5% for I to 80 wt% HA, respectively. For the polymerization of V L, the initiating efficiency of HA was on the average threefold higher. The quantitative proof of non-extractable polymer on HA by means of thermograv imetric analysis, fourier transform infrared spectroscopy with photoacousti c detection and differential scanning calorimetry confirmed the initiating efficiency of HA as mentioned above. This poly(lactone) can be debound from HA by treatment with aqueous HCl. Hence it is assumed to be ionically boun d. (C) 2001 Elsevier Science Ltd. All rights reserved.