Preparation And Properties Of Multi Stimuli-Responsive AIE Polymers Based On Maleic Anhydride Copolymers

Multi stimuli-responsive aggregation-induced emission（AIE）active polymers have great application prospects as intelligent luminescent materials.In this thesis,a series of tetraphenylethylene（TPE）containing monomers and TPE derivatives were synthesized.TPE-appended maleic anhydride copolymers（MCPs）were obtained by copolymerization and post modification methods,respectively.The maleic anhydride groups in the copolymers were modified by hydrolysis,amidation,and imidization.The fluorescence changes of the TPE-appended MCPs and their derivatives in response to multi stimuli,including pH,ionic strength,Ca²⁺,and bovine serum albumin（BSA）were studied.The main results are as follows:1.Three AIE-active monomers,TPE-VE,TPE-PE,and TPE-ST,were synthesized by the Williamson etherification of TPE-OH with vinyl（2-chloroethyl）ether,5-chloropent-1-ene,and 4-vinylbenzyl chloride,respectively.Inthecopolymerizationmethod,reversible addition-fragmentation chain transfer polymerization（RAFT）of the above monomers with n-butyl vinyl ether,2-methyl-1-pentene,styrene,and maleic anhydride was carried out,respectively,to obtain terpolymers denoted as PTVM,PTPM,and PTSM with controllable molecular weight.In the post modification method,TPE derivative TPE-NH₂with amino group was synthesized,and grafted to commercially available methyl vinyl ether-maleic anhydride copolymer（PVM）and ethylene-maleic anhydride copolymer（PEM）to obtain PVM-g-TPE and PEM-g-TPE.The alternating structure of the terpolymers was confirmed by carbon-13 nuclear magnetic resonance spectroscopy(¹³C NMR)and potentiometric titration results.The proton nuclear magnetic resonance spectroscopy（¹H NMR）verified the chemical structure and copolymer composition of the TPE-appended MCPs.Fourier transform infrared spectrometer（FTIR）and other methods confirmed the change of functional groups in the modification process of TPE-appended MCPs.2.TPE-appended MCPs and their derivatives have multi stimuli-responsive（AIE）characteristics.Based on the hydrodynamic radius（D_h）andζpotential results,these terpolymer hydrolysates experienced the conformational transition from an extended random coil to compact state with decreasing pH.NMR transverse relaxation time（T₂）proved that this transition was accompanied by a significant decrease in the mobility of the aromatic protons of TPE,resulting in a significant increase in fluorescence.Potentiometric titration curve indicated good agreement between the copolymer conformational transition region and the pH-responsive fluorescence transition region.According to potentiometric titration,computational modeling,and differential scanning calorimeter（DSC）results,the terpolymer hydrolysates with different“primary”structures have different hydrophobicity of comonomer units,intramolecular interactions,and the chain rigidity,thus generating significant differences on both the signaling and the stimuli acceptor sides.hPTSM-39 exhibited the highest pH-responsiveness with a dynamic range of 50 and an excellent fluorescence efficiency ofΦ=44.93%at pH=3.Ca²⁺and BSA can also cause a conformational transition in copolymer chains and induce a significant increase in fluorescence.hPTVM-39 showed the unique combination of high affinity for Ca²⁺（apparent K_d=0.32 mM）and low affinity for BSA（apparent K_d=95.0 mg/L）.For the amidation products of terpolymers,the introduction of tertiary amino groups that can be protonated at low pH caused fluorescence intensity to increase first and then decrease with decreasing pH.3.The post-modified copolymer hydrolysates PVM-g-TPE and PEM-g-TPE also exhibited good pH-responsive fluorescence behavior.Due to the joint actions of tertiary amine and carboxylic acid groups,the fluorescence intensity of their amidation products first increased and then decreased with decreasing pH.In this study,based on MCPs and their derivatives,a method for preparing multiple stimuli-responsive AIE copolymers with highly adjustable structure and fluorescence behavior through copolymerization and post modification has been established.Fundamental understanding on the copolymer structure-multi stimuli-responsive fluorescence behavior and fluorescence response mechanism has been gained,which is of great significance for developing an intelligent luminescence platform for chemo-sensing,bioimaging,and so on.