Ionic-crosslinked Functional Polymeric Hollow Microspheres Via "Self-templating" Approach

In recent years, the functional polymeric hollow microspheres have attracted wide attention in research and application due to their potential applications such as delivery and release for drugs, protection shield for proteins and DNA etc. Therefore, the hollow microspheres are expected to apply in the encapsulation and adsorption of the active substance because of their unique hollow structure.Many strategies have been developed for the fabrication of the functional polymeric hollow microspheres, such as emulsion polymerization, polymerization from template, and self-assembly of block copolymer. Among them, the template method has been widely used to prepare the functional polymeric hollow microspheres because of the good control over the size and dispersibility.In this work, the facile methods for the fabrication of functional polymeric hollow microspheres have been focused. The’self-templating’ approach was developed for preparation of the functional polymeric hollow microspheres via calcium ion crosslinking technique based on the common template method. It simplified the complicated process for the choice of templates, functionalization and grafted polymerization based on the templates. Compared with covalent crosslinking the grafted polymer brushes with the crosslinker, or grafting covalent crosslinking copolymer during the polymerization from templates, the ionic-crosslinked functional polymeric hollow microspheres was developed to prepare the disintegrable hollow microspheres in acidic media and temperature-sensitive hollow microspheres without the toxic cosslinkers. The main experiment sections were shown as follows:1. ionic-crosslinked polymeric hollow spheres via ’self-templating’ approachA novel ionic-crosslinked polymeric hollow sphere via ’self-templating’ approach have been designed and prepared after the cores of the PtBA had been etched. The poly(tert-butyl acrylate, PtBA) microspheres were synthesized by emulsion polymerization technique. The surface carboxylation of PtBA was carried out to complete the crosslinking with calcium ions by hydrolysis reaction. The hollow structure and stability in acidic media of the obtained hollow spheres were investigated by transmission electron microscope (TEM) and dynamic light scattering (DLS) analysis.2. Temperature-responsive poly(tBA-co-NIPAm-co-AA) hollow spheres via ’self-templating’ approachAccording to above ionic-crosslinked functional polymeric hollow microspheres and their disintegration in acidic media, the temperature-responsive monomers were introduced into polymerization system to fabricate the temperature-responsive and ionic-crosslinked polymeric hollow microspheres (TIPHMs) via the’self-templating’ approach from the poly(tert-butyl acrylate-co-N-isopropylacrylamide-co-acrylic acid) (poly(tBA-co-NIPAm-co-AA)) terpolymer nanoparticle templates. After the surface carboxyl groups of the terpolymer nanoparticles were crosslinked with calcium ions, the TIPHMs were achieved after the cores of the shell-crosslinked nanoparticles had been etched. Transmission electron microscope (TEM) and the dynamic light scattering (DLS) analysis were used to investigate the morphology of obtained hollow microsperes, the temperature-response and stability in acid media.3. Magnetic poly(tBA-co-NIPAm-co-AA) hollow microspheres via ’self-templating’ approachIn order to increase the magnetic targeted function of polymeric hollow microspheres to apply in the targeting drug delivery system, the magnetic poly(tBA-co-NIPAm-co-AA) hollow microspheres were obtained via the ’self-templating’approach based on above the temperature-responsive terpolymer templates. The terpolymer of poly(tBA-co-NIPAm-co-AA) were fabricated via emulsion polymerization, and the surface carboxyl groups were crosslinked with glycine modified ferroferric oxide (Fe3O4-Glycine), then the terpolymer templates were etched with acetone to obtain the magnetic temperature-responsive hollow microspheres. The temperature-response and magnetism of the magnetic temperature-responsive hollow microspheres were validated by DLS and VSM analysis.