Synthesis And Characterization Of N,N'-bis(acryloyl)cystamine Cross-linked Poly(N-isopropylacrylamide

Microgels have the advantages of small toxicity,small size effect and good biocompatibility,and are widely used in gene carriers,controlled release drugs,catalysis and biosensors.Intelligent microgels can respond to changes in environmental conditions,and poly(N-isopropyl acrylamide)(PNIPAM)microgels are a typical temperature-responsive microgel whose volumetric phase transition temperature(VPTT)is close to the human body temperature,so the synthesis and application of such microgels has been the attention of many researchers.On the other hand,with the popularization of resource recycling and environmental protection concepts,degradable polymer materials have gradually become research hotspots,and the introduction of degradable groups such as disulfide bonds under certain conditions into microgels has become an important means for preparing degradable microgels.This dissertation first adopts the method of soap-free emulsion polymerization,with N-isopropyl acrylamide(NIPAM)as a monomer,ammonium persulfate(APS)as an oxidant,tetramethylethylenediamine(TEMED)as a reducing agent,containing N of disulfide bonds degradable under reducing conditions,N’-Bis(acryloyl)cystamine(BAC)was used as a crosslinker,and dimethylformamide(DMF)was used as a solvent to dissolve BAC,and a series of PNIPAM microgels were successfully prepared by the redox initiation system of APS and TEMED.The composition,structure,temperature sensitivity,degradation properties,and rheological properties of the resulting PNIPAM microgels were discussed in detail using test instruments such as dynamic light scattering(DLS),ultraviolet-vis spectrometer(UV-vis),transmission electron microscopy(TEM),Fourier infrared spectroscopy(FT-IR),nuclear magnetic resonance hydrogen spectroscopy(~1H-NMR),and rotational rheometer.The product microgel is observed by TEM to appear as a regular spherical shape;the microgel is shown to contain disulfide bonds by FT-IR test;the microgel is observed by DLS to have obvious temperature sensitivity,and its particle size decreases significantly with the increase of temperature within a certain temperature range,and the VPTT is about 30°C.The earlier BAC is added during the soapless emulsion polymerization process,the larger the average particle size and better the monodispersity of the resulting PNIPAM microgel.Through the exploration of the degradation performance of PNIPAM microgels,we found that for the same microgel,the greater the concentration of reducing agent disthiothreitol(DTT),the faster the degradation rate and the degree of degradation of the microgel;the addition time of BAC also affects the degree of degradation,and the later the BAC is added,the greater the degree of degradation of the corresponding microgel.On the other hand,PNIPAM microgels prepared with methanol as a solvent to dissolve BAC,although temperature sensitive,did not observe significant degradable properties.In the rheological performance test of PNIPAM microgels,it was found that a certain concentration of microgel dispersion had in situ gelatinization performance,and the greater the mass concentration of PNIPAM microgels,the lower the gelation temperature;when the mass concentration is fixed,the higher the temperature,the shorter the gelization time.Finally,using the resulting PNIAPM microgel as the support,the strong affinity between the thiol group and gold generated after the disulfide bond break was used to explore the gold-carrying hybridization performance by in situ reduction method,and the PNIPAM-Au hybrid microgel with gold nanoparticles loaded inside the microgel was successfully prepared.This hybrid microgel has a regulatable optical property,that is,its plasma resonance(LSPR)absorption peak undergoes a significant redshift with increasing temperature.