A versatile method for the preparation of rigid submicron hollow capsules containing a temperature responsive shell

This paper presents a novel method for the preparation of temperature responsive and hollow polymer microcapsules consisting of a rigid cross-linked primary layer on the hollow core and temperature responsive shell. Temperature responsive and perfect core-shell structured magnetic polymer particles were prepared first by a two step seed emulsion polymerization process. i) Divinylbenzene (DVB) crosslinked magnetic@P(DVB) particles were obtained by the emulsion polymerization of DVB using potassium persulfate (KPS) as an initiator in the presence of an oil-in-water magnetic emulsion. ii) The magnetic@P(DVB) composite particles were then functionalized by the precipitation polymerization of N-isopropylacrylamide (NIPAm) with functional co-monomer aminoethylmethacrylate hydrochloride (AEMH) and cross-linker N,N'-methylenebisacrylamide (MBA). 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50) was used as an initiator. Core-shell magnetic@P(DVB)@P(NIPAm-AEM) particles were then treated with concentrated HCl. The treatment with HCl dissolved the iron oxide nanoparticles from the magnetic core to form hollow P(DVB)@P(NIPAm-AEM) particles. The hollow structure of temperature responsive P(DVB)@P(NIPAm-AEM) particles prepared was confirmed by Transmission Electron Microscopy (TEM). Dynamic light scattering (DLS) results prove that the P (DVB)@P(NIPAm-AEM) hollow microcapsules are submicron in size with a narrow size distribution, cationic surface charge and most importantly, volume phase transition above its lower critical solution temperature (LCST) of P(NIPAm-AEM) shell. This volume phase transition behaviour of the P (NIPAm-AEM) shell can be utilised as an on/off switch in controlling the permeability of biomolecules or drugs into/from the hollow capsules.