Uniqueness of Porous Polystyrene Particles
Porous polymer particles, in contrast to their non-porous counterparts, exhibit a range of unique properties stemming from their interconnected pore network. These include:
- High surface area
- Excellent permeability
- Low mass density
- Chemical stability
- Strong adsorption capabilities.
For instance, porous polystyrene (PS) particles possess a significantly higher surface area compared to non-porous PS particles, facilitating greater interaction with their surroundings. This enhanced surface area makes them particularly advantageous in applications such as catalysis and adsorption.
Figure. Schematic illustration of the preparation of porous polymer microparticles.
Applications Porous Polystyrene Particles:
- Catalysis: The high surface area and porosity make porous PS microspheres suitable as supporting materials for catalytic microreactors, offering high catalytic efficiency.
- Separation and Chromatography: Porous PS particles are used in chromatographic columns due to their permeability and high surface area, which result in lower back pressure and higher resolutions compared to non-porous particles.
- Absorption: Hypercrosslinked porous PS exhibits high surface areas and is useful for absorption.
- Solid Phase Synthesis: Porous resins offer more room to accommodate large molecules and prevent ‘saturation of resin' in solid phase peptide (SPPS) and organic syntheses (SPOS), especially when a non-solvent is necessary for transformation. Nonporous gels, in contrast, are preferred when a good solvent is used due to their swelling capabilities.
Synthesis Processes
1. Dispersion Polymerization: Monodisperse PS microspheres are synthesized in a water-ethanol mixture with APS (initiator) and PVP (steric stabilizer) at 70°C.
2. Emulsion System Method:
- Disperse PS seed particles in an oil-in-water emulsion system composed of toluene droplets dispersed in a water-ethanol mixture.
- The PS particles swell by toluene and transform into highly porous PS microspheres due to the uptake of the continuous phase.
3. Seeded Suspension Polymerization:
- PS seeds are prepared by emulsifier-free emulsion polymerization.
- Seeds are swollen with dibutyl phthalate and monomers.
4. Activated Swelling Method:
- Linear PS seed particles undergo porogen swelling, monomer and crosslinker swelling, polymerization, and extraction.
- Dibutyl phthalate (DBP) and toluene are used as a seed swelling activator and porogen.
5. Hypercrosslinking:
- PS resins undergo Friedel-Crafts reactions using a bis-halide and a catalyst
6. Water-Expanded PS Beads:
- Water absorbed PS beads are heated above their glass transition temperature to create pores.
Technical Notes:
- Porogen Selection: Choice of porogen determines pore characteristics.Toluene is an excellent solvent for polystyrene
- Solvent System: Water, ethanol, and toluene are essential to produce highly porous PS microspheres using the emulsion system method.
- Emulsion Stability: Key for pore formation in emulsion systems. The stability of toluene droplets in the water-ethanol continuous phase enables the PS particles to uptake the continuous phase and generate pores.
- Interfacial Tension: Control is important for particle shape.
- "Skin" Formation: Nonsolvents as porogens may lead to a dense polymer layer on the particle surface.
- Crosslinking Agents: Crosslinkers impact the porosity of porous polymer particles. Divinylbenzene (DVB) and ethylene dimethacrylate (EDMA) can be used as crosslinking agents.
- Swelling Temperature: Affects the surface of porous P(S-DVB) microparticles.
- Initiators: APS can cause electrostatic repulsion between particles.
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