Preparation Of Porous Polymers By An Ice Template Method

In this study, a modified cryopolymerization method was proposed to synthesize aligned porous hydrogels. Moreover, cryopolymerization was applied to synthesize hydrophobic porous polymers for the first time.Aligned porous poly(ethylene glycol) (PEG) hydrogels were prepared by combining directionally freezing and cryopolymerization. The obtained hydrogels showed a microtubular aligned structure parallel to the freezing direction in both dry state and swollen state, which was the replica of the ice crystals formed in the directionally freezing process. The obtained hydrogels possessed anisotropic compressive strength according to the pore directions. When using a lower freezing temperature, aligned porous hydrogels with smaller pore diameters could be prepared. The diameter of microtubules could be controlled to satisfy various applications by adjusting the monomer poly(ethylene glycol) diacrylate (PEGDA) molecular weight and freezing temperature. The mass transfer process in the aligned porous hydrogel could be simplified as one-dimensional diffusion, and could be precisely controlled when applied.Enzyme-degradable hydrogels with aligned pores were prepared via directionally freezing of a mixed solution of oxidized dextran (oxDex) and chitosan (CHI) followed by cryo-gelation. At the frozen state, imine bonds as the crosslinking points of the hydrogels were formed as a result of the reaction between the aldehyde groups on the oxDex and the amino groups on the CHI. Microtubular pores aligned along the freezing direction were obtained in the swollen state of the hydrogels. The pore size was adjustable ranging from 20 to 100 μm by controlling the freezing temperature in the directionally freezing step. Upon exposure of the hydrogels to chitosanase solution, chitosan can be hydrolyzed into short oligosaccharide fragments leading to collapse and degradation of the gel network. The degradation rate can be tuned by adjusting the gel composition and enzyme concentration.A macroscopically anisotropic PEG-PNIPAAm (poly(N-isopropylacrylamide)) hydrogel with a novel aligned dual-network microstructure had been fabricated, which displayed a unique anisotropic two-dimensional shrinkage in response to a temperature increase. It consisted of an aligned porous PEG scaffold as the primary network and PNIPAAm polymer inside the pores as the second network. The aligned porous PEG scaffold played a critical role in achieving the anisotropic shrinkage by not only templating formation of the PNIPAAm network but also constraining the axial shrinkage of the cylindrical samples.Cryopolymerization was used to synthesize porous polyacrylate. DMSO was used as solvent and benzoyl peroxide + dimethylaniline (BPO+DMA) was used as the redox initiator system. The obtained porous polyacrylate possessed a macroporous structure with unique localized orientational domains because of the crystallization behavior of DMSO. Macroporous polyacrylate can be used as efficient oil adsorbent with a superfast adsorption rate and easy recycling.