POROUS MATERIALS FROM CRYSTALLIZABLE POLYOLEFINS PRODUCED BY GEL TECHNOLOGY

A new method for obtaining porous and porous fiber polymers is present ed. This method is based on using gel-type technology (without previou sly preparing polymer solutions) for crystallizable polymers, preparin g polyethylenes, and including polyethylenes of Very high molecular ma ss and isotactic polypropylene. The method consists in swelling crysta lline polymer films at elevated temperatures in a proper solvent with subsequent precipitation with a non-solvent at different conditions. I n this case, simultaneous or consecutive processes of phase separation of amorphous or/and crystalline type occurs; stretching the sample ca n also accompany this process. Complete phase diagrams of two-and thre e-component systems (polymer-solvent and polymer-solvent-precipitator) were constructed. Temperature-concentration boundaries of amorphous s eparartion (binodal) and crystallization (liquidus) are reported for t he system polyethylene-o-xylene - dimethyl formamide. Phase transition s of both types influence characteristics of the resultant porous stru cture. They were prepared by simultaneous (precipitation of a gel by d imethyl formamide at 25 degrees C) or consecutive (precipitation with a hot non-solvent at 138 degrees C and following cooling) phase separa tion. Studied were the effect of experimental conditions (temperature, times for solvation and precipitation, polymer molecular mass, the th ermodynamic quality of solvents and parameters of film stretching) on peculiarities of the structure and quantitative characteristics of fin al porous and fiber-porous polyolefins. It has been demonstrated that the method proposed allows us to obtain a crystalline and highly porou s polymer with open poros, a bimodal size distribution and with a high ly developed inner surface. Further high strength and small shrinkage are characteristic of the fiber-porous materials. The method under dis cussion appears to be universal, it does not require a preliminary pre paration of polymer solutions and can be realized within a general tec hnology of polymer films and sheet processing. Highly porous polymers obtained by this technology, primarily based on polyethylenes of very high molecular mass, can be used as neutral supports for multi-functio nal membranes, polymeric covers, frame systems for implants and other applications.