Syntheses of PAM Microgel Surfacely Covered with Alkyl Quaternary Ammonium Surfactant/Keggin-Type Polyoxometalate Complexes

摘要

The composite microspheres of poly(lacrylamide) microgels (PAM) surfacely covered with [2-(methacryloyloxy)ethyl]dodecyldimethylammonium (MEDDAB)tungstophosphate (HPW) complexes (MEDDAB-HPW) were synthesized by using ion-exchange reaction between MEDDAB located within the porous PAM microgels and HPW in aqueous solution. The morphology and component of the composite microspheres were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, respectively. The results indicated that PAM/MEDDAB-HPW composite microsphere with different hierarchical surface structures could be obtained by controlling the weight ratio of MEDDAB to HPW in the microgels and cross-linking degree of PAM microgels. Although the surface morphologies of the composite microspheres prepared in different conditions were different, a general feature was that the composite microspheres have the core-shell structure and the wrinkly surface covered with the particles of MEDDAB-HPW complexes. The formation of the wrinkly surface is attributed to the difference in shrinkage between inside and outside of PAM microgel frameworks due to deposition of MEDDAB-HPW on the surface, and the formation of MEDDAB-HPW small particles originates from the reaction between MEDDAB aggregation and HPW. For this composite microsphere, PAM hydrogel core is suitable to store water-soluble substances, and the shell composed of the surfactant/Keggin-type polyoxometalate complexes is not only amphiphilic but also catalytic. Additionally, PAM/MEDDAB-HPW composite microspheres with big size and MEDDAB-HPW particles with small size make the composite microspheres not only easy for separation but also beneficial for catalysis. This material provides an example to construct microreactors with new structure used in diphase catalytic reaction.