Transparent macroporous polymer monoliths

Free-radical polymerization of trimethylolpropane trimethacrylate (TRIM) was carried out in the presence of a variety of porogens at room temperature, yielding transparent (macro)porous polymer monoliths. Nz BET and surface area and Hg intrusion porosimetry data from the resulting polymers showed a variety of different pore sizes and pore size distributions. In the latter, three distinct maxima at 13, 50-60, and similar to 500 nm were found for small pores (<500 nm) whereas the observed pore size maxima for large pores (>500 nm) did not exhibit any regularity. Variation of initiator concentration, ratio of monomer to porogen, polymerization temperature, and cross-linker had no influence in obtaining transparent monoliths. Correlation of the transparency of the monoliths with the refractive index and solubility parameter of the corresponding porogens led to threshold values for the refractive index (1.42) above which, and for the total solubility parameter (similar to 20 (MPa)(1/2)) below which, a transparent polymer monolith is generally obtained, if one allows for exceptions. A correlation between pore size distribution and transparency, however, could not be found.