Study Of Dual Stimuli Responsive Hollow Polymer Microgels With Interprenetrating Polymer Network Structure

Dual stimuli responsive hollow microgels which are able to respond to two different external stimuli have more intelligence as compared to single stimulus responsive hollow microgels. Guest molecules can be loaded into or released from the intelligent hollow microgels by more approaches, so they have good application prospect in drug controlled release, smart microreactor, biosensor, bioseparation, catalyst carrier, etc. Two kinds of polymers with different properties and functions can be blended on molecular level by interpenetrating polymer network (IPN) technique, and their properties and functions can be combined effectively with keeping their independence. In this thesis, the pH/temperature or glucose/temperature dual stimuli responsive hollow microgels with interpenetrating polymer network (IPN) or semi-IPN structure were synthesized by colloidal template polymerization, in-situ polymerization, introduction of phenylboronic acid groups by condensation reaction and/or etching of the template. Their chemical composition and structure and morphological structure were characterized, and the main factors affecting their stimuli responsivenesses were investigated. The main research works and the obtained results are as follow:(1)The hollow microgels with IPN structure based on crosslinked poly(N-isopropylacrylamide) (PNIPAM) and crosslinked poly(acrylic acid) (PAA) were prepared by sequential colloidal template polymerization and in-situ polymerization using the surface modified silica nanoparticles as templates, followed by etching of the template with hydrofluoric acid. Their chemical composition was characterized by Fourier transformation infrared spectroscopy (FTIR) and the IPN structure of their shells and the hollow structure of their cores were evidenced by transmission electron microscopy (TEM). Their hydrodynamic diameters measured at different temperatures or pH by dynamic light scattering (DLLS) show that theyhave both temperature and pH stimuli responsive properties, and the temperature responsive and the pH responsive components inside theirshells have little interference with each other.(2) Based on the above work, the PAA component within their shells was transformed into poly(N-phenylboronic acid acrylamide) (PAPBA) one through the coupling reaction between the amino groups of 3-aminophenylboronic acids and the carboxylic acid groups of the PAA component. The results obtained by FTIR and boron nuclear magnetic resonance (11B NMR) spectroscopy indicate that the hollow microgels formed after the coupling reaction are composed of poly(N-isopropylacrylamide) and PAPBA. The TEM characterization results confirm that they have the morphological structure of inner cavity and IPN structure. Their hydrodynamic diameters measured at different temperatures or under various glucose concentrations by DLLS show that they have both temperature and glucose stimuli responsive properties.(3) The core/shell composite particles with semi-IPN structured shells were prepared by introducing linear PAA polymers into the crosslinked PNIPAM network by one-step colloidal template precipitation polymerization using the modified silica nanoparticles as templates. Then, a novel type of intelligent hollow microgels with semi-IPN structure were prepared by transforming the carboxylic acid groups of the PAA component in their shells into phenylboronic groups through the coupling reaction, followed by etching of their templates with hydrofluoric acid. The chemical composition and morphological structure of the semi-IPN hollow microgels were evidenced by FTIR, 11B NMR, TEM and scanning electron microscopy (SEM). Their hydrodynamic diameters measured at different temperatures or under various glucose concentrations by DLLS confirm they have both temperature and glucose stimuli responsive properties.