The Preparation And Performance Of Research Of Thermoresponsive Spin-labeled Hydrogels As Separable DNP Polarizing Agents On Poly(N-substituted Acrylamides)

In the past few decad,as a result of polyacrylamide type of hydrogels in aqueous solution as the typical temperature sensitive response characteristics,and became the research focus in the scientific researchers.Poly（N-isopropyl acrylamide）is a kind of temperature sensitive response of the classic intelligent hydrogels,temperature sensitive response is mainly because of its distinctive molecular chain of hydrophilic groups and hydrophobic groups at the same time.For their linear chain,there is minimum critical temperature（LCST）.And for different polyacrylamide derivatives,as a result of different substituent on its side chain,for the phase change temperature usually there are differences.Generally,the hydrogel exists on the side chain of the higher the proportion of hydrophilic group,is the higher the LCST of the polymer hydrogel,on the contrary,if the water gel on the side chain is,the higher the proportion of hydrophobic groups is the polymer hydrogel LCST is lower.Poly（N,N-diethyl acrylamide）of the phase change temperature and PNIPAM are similar,is another common win min polymer.Because in the side chain of PDEA there isn’t–NH hydrophilic group,and PDEA could not like PNIPA as intramolecular hydrogen bond donor.Therefore,people usually take PDEA compared with PNIPAM,to explore-NH hydrophilic groups,and PDEA could not like PNIPA as intramolecular hydrogen bond donor.Therefore,people usually take PDEA compared with PNIPAM,to explore-NH for polyacrylamide hydrogel classes in the influence of the volume phase transition behavior in different environmental temperature.Dynamic nuclear polarization（DNP）is an electronic and nuclear double resonance technology,nuclear polarization degree enhancement can be several orders of magnitude,effectively improve the detection sentivity of nuclear,DNP in NMR and MRI has been widely used.While DNP allows a significant enhancement of NMR signals bu several orders of magnitude,major drawbacks of the method include enhanced nuclear relaxation times due to the presence of unpaired electrons and the toxicity of radicals,which is the limiting factor for in vivo applications in magnetic resonance imaging.Thus,an efficient separation of the polarization agent is a key of requirement for possible applications in medicine.Inorder to satisfy the research request for a variety of DNP applications,in this paper,taking advantage of thermo-sesitivety of Poly（N-substituted acrylamides）,spin-labeled hydrogels has been fabricated,which not only presents temperature sensitivity and polarization characteristics better,but also has better swelling and separation effect.First of all,this article on the application and development of intelligent hydrogels were reviewe and the enhancement of dynamic nuclear polarization mechanism and experimental platform were introduced simply.Secondly,thermoresponsive spin-labeled polymer hydrogels have beensynthesized by copolymerization of N-（acryloxy）succinimide（NASI）with N-isopropylacrylamide（NIPA）and N,N-diethylacrylamide（DEAAM）using N,N-methylene-bis-acrylamide（MBA）as the cross-linking agent,2,2-azobisisobutyronitrile（AIBN）as the initator and4-amino-2,2,6,6-tetrmethyl-1-piperidinoxy（4-NH₂-TEMPO）as the spin-label agent.The hydrogels were characterized by NMR and FT-IR repectively.Their volume phase transition temperatures also measured by DSC.Furthermore,the DNP enhancement times were studied by EPR and home build DNP.The results indicate that PNIPA-T and PDEA-T both has good temperature response and fast swelling rate,the lowest critical temperature of PNIPA-T spin labeled hydrogel（LCST）is about 32℃,the PDEA-T spin labeled hydrogel LCST is about 28℃;Compared with PNIPA-T and PDEA-T,PNIPA-T has better DNP polarization efficiency,PNIPA-T spin labeled hydrogel DNP maximum enhancement times is-142,while PDEA-T DNP maximum enhancement times is-101;PNIPA-T polarization retention time is about 0.7s,PDEA-T polarization retention time was about 1.2s.Finally,N-isopropylacrylamide（NIPA M）as main monomers,we have synthesized series of different proportion spin labeled PNIPAM hydrogel.In different temperature and microwave power,we have studied the effect of PNIPA-T hydrogel DNP polarization enhancement times and retention time for different dosage of4-NH₂-TEMPO.The results show that the PNIPA-T spin labeled hydrogel LCST decreases with the increase of the content of 4-NH₂-TEMPO;when the dosage of4-NH₂-TEMPO is 2%,PNIPA-T DNP polarization efficiency is best,0.8%PNIPA-T spin labeled hydrogel DNP maximum enhancement times is about-124,2%PNIPA-T spin labeled hydrogel DNP maximum enhancement times is about-151,5%PNIPA-T spin labeled hydrogel DNP maximum enhancement times is about-146;0.8%PNIPA-T polarized spin labeled hydrogel retention time is about 1.1s,2%PNIPA-T polarized spin labeled hydrogel retention time is about 0.7s,5%PNIPA-T polarized spin labeled hydrogel retention time was about 0.35s.