| solubility |
Practically insoluble in ethanol (95%), hexane, unbuffered
water, and xylene. On the addition of acetone, or a mixture
of ethanol (95%) and dichloromethane (1 : 1), a clear or turbid
viscous solution is produced. Hypromellose acetate succinate
also forms a clear or turbid solution in buffers of pH greater than
4.5 with the rank order of solubility for the various grades increasing with the ratio of acetyl over succinoyl
substitution. The exact pH value at which the polymer starts to
swell and dissolve depends on the buffer type and ionic strength,
although the rank order for the different grades is independent of
the buffer used. No solvent has been found to completely
dissolve hypromellose acetate succinate polymer; the resulting
clear or turbid solutions significantly scatter light in both static
and dynamic light scattering experiments, indicating that the
polymer may exist as colloids or aggregates. The data is collated
from the Shin-Etsu Chemical Co. Ltd and the research work of
the authors (R Chen, BC Hancock, and RM Shanker). |