Novel Methods For Preparing Polymeric Hollow Particles

In this dissertation, some novel methods for preparing polymeric hollow particles were explored. The influences of experimental conditions on the morphologies of the hollow particle were investigated. On the other hand, ultrafine hydrogel fibers were produced by electrospinning.Seeded emulsion polymerization is a common method to prepare core-shell particles. Novel microgel@hydrophobic-polymer core-shell particles with poly(methyl methacrylate) (PMMA) as the shell and poly(N-isopropylacrylamide) (PNIPAAm) hydrogel particles (microgels) as the core have been fabricated by a seeded emulsion polymerization of methyl methacrylate with the PNIPAAm microgel latex as the seed emulsion. The microgel leaves a void inside the core-shell particle upon dehydration. On the basis of PNIPAAm@PMMA core-shell particles, we introduced electrostatic interaction between the cationic core and anionic surfactant sodiumdodecyl sulfate (SDS), used polystyrene(PS) as the shell to improve the productivity of the well defined core-shell particles, and produced P(NIPAAm-DMC)@PS/SDS hollow particles. Furthermore, we replaced SDS with a polymerizable (reactive) anionic surfctant (HEC-18Na) and prepared P(NIPAAm-DMC)@PS/HEC-18Na hollow particles. The temperature dependence of microgel sizes before and after being coated by PS was investigated. The morphology and size of the hollow particles were observed by transmitted electronic microscopy and scanning electronic microscopy. The influences of surfactants and shell monomer concentrations on the morphologies were investigated preliminarily.Spontaneous vesicles formed when cationic and anionic surfactants together with some monomers and crosslinkers were mixed in aqueous solution. The vesicles were stabilized after the polymerization of the monomers and crosslinkers, which giving hollow particles with diameters of 100~200nm. The influences of molar ratios of anionic and cationic surfactants, solid contants, surfactants types and the initiator systems (KPS, AIBN, KPS/SSA and BPO/SSA) on the morphology and size of hollow spheres were investigated.Electrospinning is a facile and versatile method for the preparation of sub-microsized or nanosized ultrafine fibers from polymer melts or solutions. We prepared ultrafine hydrogel fibers that were responsive to both temperature and pH signals through electrospinning of the mixture of a copolymer of acrylic acid (AA) and hydroxyethyl mathacrylate (HEMA) and poly(N-isopropylacrylamide) (PNIPPAm) in the dimethylformamide (DMF) solution. The fibers were heat treated at 140 °C for crosslinking. The swelling behavior of hydrogel fibers was investigated preliminarily. It was found that the hydrogel fibers exhibited both pH-responsive and temperature-responsive swelling behavior.