Study On Monomer And Morphological Regulation For RAFT Aqueous Dispersion Polymerization

Polymeric nanoparticles have extensive applications in biomedicine,templating,nanolithography and so forth.Polymerization-induced self-assembly?PISA?,especially via reversible addition-fragmentation chain transfer?RAFT?dispersion polymerization,provides a versatile and efficient method to prepare block copolymer nano-assemblies with diverse and controlled morphologies.Water is an abundant,economical,and green solvent with a high polarity as well as boiling point.Therefore,aqueous PISA syntheses are expected to bring ecological and economic benefits for industrial production of polymeric nano-objects.In this dissertation,focus on RAFT aqueous dispersion PISA,we conducted investigations as follows:1.Alkyl??hydroxymethyl acrylate monomers for aqueous PISA.A series of alkyl?-hydroxymethyl acrylates with tunable water solubility were systematically investigated.The water solubility decreased with larger alkyl groups for methyl?MHMA?,ethyl?EHMA?,isopropyl?i Pr HMA?,n-butyl?n BHMA??-hydroxymethyl acrylates.According to water solubility of monomers and corresponding homopolymers,MHMA and EHMA were identified as suitable candidates for aqueous dispersion PISA.Dispersion polymerizations of EHMA employing poly?ethylene glycol?macromolecular chain transfer agents(PEG₄₅-CTA,PEG₁₁₃-CTA)were systematically studied via either thermal or photoinitiation at40-70°C.Well-defined spheres,worms,lamellae and vesicles were obtained for EHMA-based dispersion PISA syntheses.The effect of temperature on molecular weight dispersity and morphologies are also discussed.Moreover,dispersion polymerization of MHMA with higher water solubility and dispersion-emulsion polymerization of i Pr HMA with moderate water solubility were further conducted to assess the effect of monomer solubility on morphologies.The monomers can be synthesized via Baylis-Hillman reaction,providing method for design and preparation of functional monomers.2.Polymer architecture promoting morphological evolution.Given current PISA syntheses limited to linear block copolymers,we develop an aqueous PISA formulation based on AB₂ star block copolymers via RAFT aqueous dispersion polymerization of diacetone acrylamide?DAAM?.2,4,6-Trichloro-1,3,5-triazine and activated esters were used to efficiently afford a difunctional macro-CTA bearing two chain transfer agents based on poly?ethylene glycol?methyl ether.Comparing to its linear counterpart,the star polymer architecture with higher packing parameter?p?can significantly promote morphological transition of self-assemblies to higher-order morphologies at lower solid contents and lower degrees of polymerization?DP?of the core-forming block.This demonstrates that polymer architecture is an important parameter to fabricate complex morphologies during PISA synthesis.3.Crosslinking density tuning the temperature-dependent morphological transition kinetics and rheological properties.In situ crosslinking of nano-objects was realized via statistical copolymerization of DAAM with an asymmetric crosslinker ALAM?allyl acrylamide?employing a PDMA₃₀ macro-CTA.The effect of in situ crosslinking on the morphologies of PDMA₃₀-PDAAM₁₀₀ lamellae were studied by TEM?transmission electron microscopy?,AFM?atomic force microscopy?and SEM?scanning electron microscopy?.Moreover,the reversible temperature-induced morphological transitions from PDMA₃₀-PDAAM₇₀lamellae to worms/spheres on cooling were investigated by TEM,variable-temperature ¹H NMR spectroscopy and rheology.The effect of crosslinking density?1-2 mol%?on the temperature-induced morphological transition kinetics as well as rheological properties were also investigated.