Reseach Of Temperature Sensitive Nanogels With Tuned Temperature Sensitivity

Thermo-sensitive nanogels get more attention due to it's temperature-responsive properties. At present, N-isopropylacrylamide (NIPAAm) is the most studied monomer for the preparation of thermo-sensitive nanogels. Usually, the phase transition temperature of the nanogels is tailored by copolymerizing ionic monomers with NIPAAm. However, it has been not reported that the phase transition temperature of non-ionic nanogels is tuned by copolymerizing a high concentration (>15 wt%) of non-ionic monomer with NIPAAm. The reason is that the high content of strongly hydrophilic monomer easily induced quick aggregation of the resulting particles and didn't form nanogels. In this thesis, it has been found that a low iniator concentration can significantly increase the stability for the polymerization system of synthesizing thenno-sensitive nanogels with a high content of a strongly hydrophilic monomer. For the first time, NIPAAm/DMA (N.N-dimethylacrylamide) nanogels comprising strongly hydrophilic monomer 40 wt% DMA and NIPAAm/AAmM(acrylamide) with up to 25 wt% AAm have been sysnthesized.P(NIPAAm-co-AAM) nanogels with the high content of a strongly hydrophilic monomer AAM and P(NIPAAm-co-DMA) nanogels with the high content of a strongly hydrophilic monomer DMA have been sysnthesized via emulsion precipitation polymerization by using monomers NIPAAm, AAM, and DMA, crosslinker N,N-methylene diacrylamide (BIS), surfactant sodium dodecyl sulfate(SDS), initiator ammonium sulfate (APS). The volume phase transition temperature (VPTT) of NIPAAm nanogels is about 32℃, and the lower crtitical solution temperature (LCST) of the nanogels increased with an increasing content of AAM or DMA. The polymerizations of P(NIPAAm-co-AAM) nanogels and P(NIPAAm-co-DMA) nanogels have been investigated by varying AAM and DMA contents, and initiator APS concentration. The size and size distribution of the nanogels were characterized by dynamic laser light scattering (DLS). Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy(NMR) were utilized to study the composition of the resulting nanogels. And UV-visible (UV-vis) spectroscopy was used to investigate the phase transition temperatures of the resulting nanogels. The main achievements are as follows:(1) At the initiator APS concentration of 0.005 wt%, P(NIPAAm-co-AAM) nanogels with a high content of up to 25 wt% AAm have been successfully synthesized. With increasing AAM content, the size of the resulting nanogels increased. As initiator APS concentration is higher than 0.005 wt%, increasing APS concentration led to the unstable nanogels.(2) At the initiator APS concentration of 0.005 wt%, P(NlPAAm-co-DMA) nanogels with a high content of up to 40 wt% DMA have been successfully synthesized. With increasing DMA content, the size of the resulting nanogels increased. As initiator APS concentration is higher than 0.005 wt%, increasing APS concentration led to the unstable nanogels.(3) AFM images of the nanogels showed that the resulting nanogels looked spherical and that the nanogel size increased with increasing a strongly hydrophilic monomer AAM or DMA.(4) NMR and FTIR characterization of the nanogels showed that hydrophilic monomer prepared by the accession of the structure of the hydrogel increased hydrophilic groups to enhance hydrophilicity.(5) UV-visible spectroscopy showed that the phase transition temperature of the nanogels was increased from 32℃to 48℃with increasing strongly hydrophilic AAM or DMA.