Ring-opening polymerization of lactones in the presence of hydroxyapatite.

The ring-opening polymerization of epsilon-caprolactone, delta-valerolactone (VL) and D,L-lactide, respectively, in the presence of different proportions of hydroxyapatite (HA) was catalyzed by stannous (II)octoate (SnOct2) at 130 degrees C and resulted in composites. The lactones were almost completely converted to the polymers within a reaction time of 70 up to 240 min. The number-average molecular weights Mn as determined by size exclusion chromatography decreased with increasing content of HA. The initiating efficiency of HA as calculated from the difference of the polymerization degrees P. obtained with and without HA turned out to be relatively low with ca. 11 to 0.5% for 1 to 80 wt% HA, respectively. For the polymerization of VL, the initiating efficiency of HA was on the average threefold higher. The quantitative proof of non-extractable polymer on HA by means of thermogravimetric analysis, fourier transform infrared spectroscopy with photoacoustic 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 bound.