The Formation Of High-level Morphology By RAFT Dispersion Polymerization

Inverse phase bicontinuous particles have a wide range of applications in biochemical reactors,templates,adsorption and separation due to their porous structure and high specific surface area.Polymerization-induced self-assembly(PISA)using reversible addition-fragmentation chain transfer(RAFT)dispersion polymerization can prepare block copolymer(BCP)particles with rich morphology at high solids content.At present,it is very difficult to prepare inverse phase bicontinuous particles based on PISA,and its formation mechanism is not clear,which greatly limits its large-scale application.In this paper,we prepared inverse phase bicontinuous particles by PISA based on RAFT dispersion polymerization.The effect of monomer type,stablizing block length,solid content and dispersing solvent on the formation of inverse phase bicontinuous particles were considered in this research.The details are as follows:1.The effect of styrene derivatives on the transformation of morphology in the PISA process was studied.RAFT dispersion polymerization was performed by using4-(2-tetrahydropyranyloxy)styrene(OTHPSt)and 4-tert-butoxystyrene(t BOS).The PDMA macromolecular chain transfer agent was used as a stablizing block,and the ethanol/water was solvent.When POTHPSt was used as the core-forming block,it is difficult to undergo morphological transformation due to the better solvophilicity of the core-forming block.However,when Pt BOS was used as the core-forming block,particles with inverse phase bicontinuous structure were successfully prepared.We found that shorter stablizing block and higher solid content were conducive to collision and fusion between particles by adjusting the reaction conditions,so that the morphology of the assembly evolved into an inverse bicontinuous structure.The results show that the optimal solid content for the synthesis of inverse phase bicontinuous structure particles is 30% w/v,and the optimal solvent condition is 7:3(ethanol/water,v/v).2.The influence of copolymer as core-forming on the morphology transformation in PISA was studied.The 4-tert-butoxystyrene and pentafluorostyrene(molar ratio 5:5)were used for copolymerization.The Fineman-Ross equation indicated that the copolymerization of these two monomers is highly alternating.It was helpful to control the morphology of particles by combining two different solvophilicity monomers.A variety of morphological assemblies,including tubular and inverse phase bicontinuous structure,can be realized by adjusting the experimental conditions,such as the length of the macromolecular chain transfer agent,the solid content,the water content of the mixed solvent and the molar ratio of two monomers.The shorter macro-CTA and higher solid content,such as using PDMA30 as the stablizing block,the ratio of mixed solvent is 95/5(ethanol/water,v/v),and the solid content is 30% w /v,are helpful to form high-level morphology due to the high probability of collision and fusion.When the solid content was low,such as 20% w/v and mixed solvent was90/10(ethanol/water,v/v),the collision and fusion between the assemblies is reduced,which is usually beneficial to the formation of tube.The water content in the mixed solvent was also very important in the PISA process.The controlled evolution of the morphology can only be achieved under a certain proportion of water content,which neither freezes the assembly,but also provides sufficient driving force for self-assembly.3.The effect of cosolvent on the transformation of morphology in the PISA process was studied.Defferent from the conventional binary mixed solvent(usually ethanol/water,methanol/water),the third solvent(good solvent for the second block of polystyrene)was introduced to conduct the PISA by using PEG-PS block copolymer system.It can effectively promote the transformation of the morphology into inverse phase bicontinuous structure by reasonably adjusting the solvent ratio.Unfortunately,when 1,4-dioxane(DIOX)and N,N-dimethylformamide(DMF)were used,the reaction system exhibits instability and poor repeatability.When tetrahydrofuran(THF)was used,it cound usually promote the transformation of the morphology to a high level to form inverse phase bicontinuous particles due to the similar solubility parameter between THF and polystyrene.We have obtained the optimal conditions for the formation of a inverse phase bicontinuous structure by adjusting the ratio of the mixed solvent,the solid content,that is,the solid content is30% w/v,and the ratio of mixed solvent is 1.15/0.45/0.4(methanol/THF/water).