Synthesis And Properties Of TEMPO-containing Comb-shaped Polymers

Stable free radicals such as 2,2,6,6-tetramethylpiperidine nitroxyl radical?TEMPO?have unique stability and paramagnetic characteristics,and can be used as spin probes in biomedical applications.The paramagnetic property has much dependence on environmental information,such as the viscosity,polarity,temperature,configuration,and so on.Researchers usually need to immobilize TEMPO on a specific position of a polymer or matrix in order to analyze the environmental information of a specific system.Combshaped polymers are a class of macromolecules with densely grafted side chains on the polymer backbone.Compared to linear analogues with the same molecular weight,comb-shaped polymers have a smaller molecule size,more significant end effects,and stronger side chain exclusion effects,resulting in an extended chain conformation.In this work,a series of comb-shaped polymers containing TEMPO radicals were designed and synthesized by atom transfer radical polymerization?ATRP?,and the side chains with different softness were further grafted.The paramagnetic properties of comb-shaped polymers were also explored.The main results are as follows:?1?Synthesis and characterization of TEMPO-containing comb-shaped polymers with poly?methyl acrylate??PMA?side chainFirst,using ethyl 2-bromoisobutyrate?EBiB?as initiator,and hydroxyethyl methacrylate?HEMA?as monomer,linear poly?hydroxyethyl methacrylate??PHEMA?was prepared by ATRP.After further modification of hydroxyl groups on PHEMA,the macroinitiator PBiBEMA was obtained.Then,tert-butyl acrylate?t BA?monomer was polymerized to give comb-shaped polymer PHEMA-g-PtBA.The comb-shaped polymer PHEMA-g-?Pt BA-b-PMA?was further prepared by ATRP of methyl acrylate?MA?monomer.Subsequently,the tBA units in the comb-shaped polymer are hydrolyzed in the presence of trifluoroacetic acid?CF₃COOH?to give carboxyl groups.The TEMPO was finally introduced into the polymers by reaction between carboxyl group and4-glycidyl-2,2,6,6-tetramethylpiperidine nitroxyl radical?GTEMPO?,to gave comb-shaped polymerscontainingTEMPO,PHEMA-g-?PAA-g-TEMPO?and PHEMA-g-[?PAA-g-TEMPO?-b-PMA].The polymerswere comprehensively characterized by gel permeation chromatography?GPC?,nuclear magnetic resonance spectroscopy?NMR?,and differential scanning calorimetry?DSC?and elemental analysis.The electron paramagnetic resonance?EPR?technology was used to study the paramagnetic property of TEMPOcontainingcomb-shapedpolymersatdifferenttemperaturesand concentrations.The results show that the concentration of the polymers mainly affects the signal intensity of EPR spectra,while the temperature modulate the shape of EPR spectra.Obviously,the peripheral PMA segments shielded the internal TEMPO radicals,and greatly reduced the intermolecular spin-spin exchange effect,The EPR spectra were showed with superfine information of the structure.?2?Synthesis and characterization of TEMPO-containing comb-shaped polymers with polystyrene?PS?side chainsFirst,the comb-shaped polymer PHEMA-g-?PtBA-b-PS?was prepared by ATRP of styrene?St?using comb-shaped PHEMA-g-PtBA asmacroinitiator.Similarly,the tBA units in the polymer side chain were hydrolyzed by CF₃COOH to give carboxyl group,and the TEMPO groups were further introduced into by using the reaction between the carboxyl groupandGTEMPO,TheTEMPO-containingcomb-shapedpolymer PHEMA-g-[?PAA-g-TEMPO?-b-PS]with a peripheral side chain PS was obtained.The polymers weresystematically characterized by GPC,NMR,DSC and elemental analysis.The EPRtechnologywasusedtostudytheparamagneticpropertyof TEMPO-containingcomb-shaped polymers at different temperatures and concentrations.The results showed that,the signal intensity of the EPR spectrum becames stronger with the concentration increasing.With the temperature lowering,the EPR spectrum also underwent a series of change.Due to the shielding effect of the peripheral PS segments,the EPR spectra with superfine information can also be discriminated.In general,a series of novel comb-shaped polymers containing TEMPO,were synthesized in this work.The relationship between polymer structure and paramagnetic properties was systematically studied.The result is expected to provide a theoretical basis for the application of TEMPO-containing polymers in biomedical applications and the preparation of new functional materials.