Preparation Of Porous Polymer Via Chemically Induced Phase Separation

Chemically induced phase separation is a method for preparing porous polymer. Before curing reaction, solvent or thermoplastic mixes with thermosets and arrives to a homogenous state. With the development of curing, the molecular weight of the thermosetting resin increases and makes the miscibility with solvent or thermoplastic bad, which induces phase separation. Phase structure evolves and coarses. The porous monolith is obtained by washing and drying the cured product or thermal degradation of thermoplastic. The method of preparation for porous materials compared with the traditional methods is simple and easy to operate; simultaneously can control the pore size and distribution. This paper follows the work:1. Macroporous monolith was prepared via chemically induced phase separation using diglycidyl ether of bisphenol A (DGEBA) as a monomer, 4,4'-diaminodiphenylmethane (DDM) as a curing agent, and epoxy soybean oil (ESO) as a solvent. The morphology of the cured systems after removal of ESO was examined using scanning electron microscopy, and the composition of epoxy precursors/solvent for phase inversion was determined. The phase separation mechanism was deduced from the optic microscopic images to be spinodal decomposition. The pore structure of the cured monolith was controlled by a competition between the rates of curing and phase separation. The ESO concentration, content of curing agent, and the curing temperature constituted the influencing factors on the porous morphology. The average pore size increased with increasing ESO concentration, increasing curing temperature, and decreasing content of curing agent.2. Porous monolith prepared with a thermoplastic polymer, polypropylene carbonate (PPC) via chemically induced phase separation was proposed. As DGEBA was cured with DDM, the system became phase separated having PPC particles dispersed in epoxy matrix. After PPC particles were removed by thermal degradation, a porous structure was obtained. The phase separation mechanism was determined by the initial composition and illustrated by a pseudo phase diagram. With low concentration of PPC, the system followed mechanism of nucleation growth; otherwise, spinodal decomposition. The intermediate and final morphologies of the system were studied using optical and scanning electron microscopy, respectively. With PPC concentration increase, the epoxy/PPC went though the change of the dispersed phase, co-continuous phase and phase separation. After 90 min of curing, the system became into solid and fixed. The pore size increased with increasing the concentration of PPC as well as raising the curing temperature.3. Hydroxy terminated polypropylene carbonate took part in epoxidation, and epoxied polypropylene carbonate was synthesized, which was characterized by Fourier transform infrared spectroscopy. The epoxy value of products was 6.8%.4. Porous structure of thermosetting monolith with large porosity was obtained by epoxied polypropylene carbonate via chemically induced phase separation. With low concentration of epoxied polypropylene carbonate, dispersed pore occurred. Increasing the concentration, pore diameter increased and distribution grew broader. Epoxy spheres appeared when epoxied polypropylene carbonate was in high concentration. Between the two critical concentrations, stratification occurred, which the upper and bottom layers were pore structure, and the middle layer was epoxy spheres.5. Chemically induced phase separation between epoxy resin and polypropylene carbonate under different curing temperatures was observed using opitial microscope. When the concentration of epoxied polypropylene carbonate was 35 wt%, the epoxy resin/epoxied polypropylene carbonate under curing temperatures all followed the mechanism of spinodal decomposition; simultaneously, epoxied polypropylene carbonate dispersed in epoxy resin. With increase of curing temperature, size of epoxied polypropylene carbonate increased.