Preparation Of Poly(N-Isopropyl Acrylamide)/polyethyleneimine Temperature Sensitive Microgel

In recent years,the temperature-sensitive microgels are a hotspot in the field of environmental protection,biomedicine and drug-oriented release,and so on.However,there is less research on relevant aspects of core-shell structure microgels with the both properties of temperature-sensitive and PH-sensitive.And the core and shell can have different corresponding to the external stimulus,to meet the special needs.In this paper,the 1-(3-dimethyl aminopropyl)-3-ethylcarbamine hydrochloride(EDC)was used as activator to activate the carboxyl group of acrylic acid,then the carboxylamine reaction was carried out with the amine base of the polyethylamine(PEI).Then put the temperature-sensitive polymer monomer N-isopropyl acrylamide(NIPAM)and pH-sensitive polymer polyethylene imine(PEI)to synthesize poly(N-isopropyl acrylamide)/polyethylene imine micro gel by soap-free emulsion polymerization,and N,N '-methylene double acrylamide(BIS)was as crosslinking agent,2,2'-azo 2(2-methyl propyl amidine)2 hydrochloride(V-50)was as the initiator.The polymerization reaction was carried out at the temperature above the LCST which was the low critical dissolution temperature of PNIPAM.The microgels formed by this way had nucleo-shell structure,the particle diameter of the same,and had properties of both temperature ang pH sensitive.The microgels were characterized by Fourier transform infrared spectroscopy(FT-IR),Ultraviolet visible spectrophotometer(UV-vis),transmission electron microscopy(TEM),dynamic light scattering(DLS)and Nuclear magnetic resonance spectroscopy(1H NMR),High performance liquid chromatography(HPLC),and so on.The results showed that the micro gel was a homogeneous spherical shape with submicron size,and a typical core-shell structure,and the microgel size decreases with the increase of temperature,the volume phase transition temperature is about 36.9 ?.The results showed,when synthesizing the ethylated PEI,the ethylation rate would change according to the pH of the synthesized ethylated PEI,the ethylation rates at pH= 4,5,6 and 7 were 0%,0.18%,1.3% and 1.5% respective.It would increase with the increasing of pH.In the synthesis of PNIPAM/PEI microgel,the NIPAM monomers and BIS crosslinking agent had reacted completely in 1h,and the reaction rate of the latter was faster than that of the former.The synthesis conditions of PNIPAM/PEI microgel significantly affected the size of the microgel obtained.When the dosage of crosslinking agent was little,PNIPAM/PEI micro gel particle size changed little under 60 ?,but under 20 ?,it showed a significantly lower with an increase in the amount of crosslinking agent.However,when the dosage of the cross-linking agent was very big,its volume couldn't be ignored,so its particle size presented the tendency of increase under 20 and 60 ?;With the decreasing concentration of monomer,PNIPAM/PEI micro gel particle size were presented to reduce under 20 and 60 ?.With the increase of dosage of initiator,the particle size of remain unchanged at 60 ?,but the micro gel particle size presented a trend of decrease at 20 ?.It was confirmed that the presence of PNIPAM and PEI components in microgels though the test results of FT-IR and 1H NMR,and the microgels had a similar nuclear shell structure,which was mainly composed of PNIPAM and the shell was mainly composed of PEI.PNIPAM/PEI microgel was a smooth spherical surface with good dispersion stability through TEM test.The test results of DLS in different temperature and pH conditions showed that PNIPAM/PEI microgel had not only obvious temperature sensitivity,but also pH sensitivity.