A Study On The Self-Assembly Behavior Of Ring-Opening Polymerization-Induced Self-Assembly(Ropisa)of Salicylic Acid O-Carboxyanhydride

Polymerization-induced self-assembly（PISA）is a promising route to the in situ formation of polymeric nanoscale morphologies via polymerization.In stark contrast to the classical two-step nanoprecipitation method comprising synthesis,PISA combines polymerization and self-assembly and shows the crucial advantages of high solid concentrations.Currently,most of the research is based on reversible addition-fragmentation chain-transfer polymerization（RAFT）polymerization.However,vinyl acetate and styrene monomers are often essential for reversible addition-fragmentation chain-transfer polymerization-induced self-assembly（RAFT-PISA）.To address the problem that the polymer formed by RAFT which normally produces nonbiodegradable structures,researchers have developed ring-opening polymerization of N-carboxylic anhydride-induced self-assembly,forming vesicles with hydrophobic chain segments in biodegradable structure.At present,few reports on self-assembly induced by ring-opening polymerization.Our research group reported for the first time that proposed a new OCA-PISA methodology for accessing bioactive nanoparticles,the development of synthesis technology for PSA-containing nanocarriers will provide a great opportunity to intensively broaden SA clinical application.However,how to accurately control the morphology and size of the obtained assembly for different applications remains a problem to be solved.Therefore,this paper systematically studied the effects of different factors on the self-assembly process and assembly morphology,and further explored the driving force in the SAOCA ring-opening polymerization-induced self-assembly process.The main research contents of this paper are as follows.（1）Using 1,5,7-triazidebicyclo[4.4.0]dec-5-ene（TBD）as a catalyst,polyethylene glycol monomethyl ether M_n5000(m PEG₅₀₀₀-OH),polyethylene glycol monomethyl ether M_n2000(m PEG₂₀₀₀-OH)as macromolecular initiators to achieve ring-opening polymerization-induced self-assembly of SAOCA at room temperature to form AB-type diblock copolymer nanoparticles.The effects of different factors on the control of nanoparticle morphology and size during SAOCA ring-opening polymerization-induced self-assembly were investigated in-depth.By prolonging the self-assembly time,the assemblies are transformed into nanoparticles of different morphologies or sizes after fusion and rearrangement from irregular gradual nucleation.The relative length of the hydrophobic chain segments affects the stretch of the chain segments and thus the shape and size of the assemblies.The size of the monomer solids affects the polymer concentration and thus the rate of chain motion and N_agg,leading to changes in the shape and size of the assemblies.（2）The study of PISA is mostly focused on AB-type block copolymers,and ABA-type block copolymers are less studied.Using polyethylene glycol M_n4000(HO-PEG₄₀₀₀-OH)as a macroinitiator,the ring-opening polymerization-induced self-assembly of SAOCA was achieved at room temperature to form ABA-type block copolymer nanoparticles.The polymerization-induced self-assembly behaviors of AB-type block copolymers and ABA triblock copolymers were compared.Due to the different distribution of poly（salicylic acid）on the block copolymer chain,the solvation degree of the overall polymer chain is different,which affects the self-assembly behavior to form nanoparticles with different morphologies.