Preparation And Characterization Of Multi-Stimuli Responsive Polymer And Microspheres

During the past decades,the development of stimuli-reponsive polymers has received intensive attention due to its potential applications in drug delivery, biological sensors,chemical separations,cell culture,enzyme immobilization,sensor, bioelectrical catalysis.Temperature is the most widely used stimulant in environmentally responsive polymer systems.The change of temperature is not only relatively easy to control,but also easily applicable both in vitro and in vivo.And besides the temperature,light stands as the most desirable external stimulant due to its chemical purity and controllability.Compared with the single-stimulus,the interest in multi-responsive copolymers has increased due to their promising potential as intelligent materials.In this context,a variety of synthetic methodologies comprising of free radical polymerization,soap-free emulsion polymerization and precipitation polymerization are approached to prepare different forms of multi-responsive polymers and microspheres based on DNQ moiety and NIPAM.The results of each part are listed as follows:(1) A series of poly(N-isopropylacrylamide-co-N-hydroxymethylacrylamide) P(NIPAM-co-NHMA) copolymers were firstly synthesized via free radical polymerization.Then,the hydrophobic,photosensitive 2-diazo-1,2-naphthoquinone (DNQ) molecules were partially and randomly grafted onto P(NIPAM-co-NHMA) backbone through esterification to attain a triple-stimuli(photo/pH/thermo) responsive copolymers of P(NIPAM-co-NHMA-co-DNQMA).UV-vis spectra showed that the lower critical solution temperature(LCST) of P(NIPAM-co-NHMA) ascended with increasing hydrophilic comonomer NHMA molar fraction and can be tailored by pH variation as well.The LCST of the P(NIPAM-co-NHMA) went down firstly after DNQ modification and then shifted to higher value after UV irradiation. Meanwhile,the phase transition profile of P(NIPAM-co-NHMA-co-DNQMA) could be triggered by pH and UV light as expectation.(2) The amino-containing crosslinked thermo-sensitive microgels PNIPAM-NH₂ prepared by surfactant-free emulsion polymerization(SFEP) with MBA as chemical cross-linker and AEMA and NIPAM as functional monomers.The synthesis process was influenced by the dose of initiator KPS and MBA and the results indicated that the microgels had monodispersity and colloidal stability when KPS was 4%.The microgels with lower cross-linking density had more rapid volume phase transition accompanied with bigger pore size,whereas their counterparts bore more regular spherical morphology.Via the reaction between sulphonyl chloride and amino groups, photo-/thermo-/pH responsive microgels were prepared with different ratios of DNQ to amino groups.Microgels with the higher DNQ modification density exhibited more obvious change of VPTT and swelling/deswelling ratio.The unreacted amino group endowed the pH-responsive property for the microgel and led to the different hydrodynamic diameter.The magnetic Fe₃O₄ paticles were adsorbed on the microgel by the electrostatic interaction.(3) Fe₃O₄@SiO₂ particles were prepared by a modified St6ber method followed by functionalized by 3-(trimethoxysily)propyl methacrylate(MPS).The magnetic and thermo-/pH-responsive microspheres were prepared by coating the Fe₃O₄@SiO₂ partieles with the cros-linked poly(NIPAM-coAEMA) shells via precipitation polymerization.The thickness of the cross-linked polymer shell can be controlled by varying the dosage of comonomors NIPAM and AEMA.The modifacation of DNQ and the unreaction amino groups endowed the composition microspheres Fe₃O₄@SiO₂@PNIPAM-NH₂ for the photo and pH-responsive property.The VPTT of the composition microspheres Fe₃O₄@SiO₂@PNIPAM-NH₂ went down firstly after DNQ modification and then shifted to higher value after UV irradiation.