Electrospinning And Drop Casting Film Of PS-b-PHEMA Amphiphilic Block Polymer

Amphiphilic block copolymers represent a class of polymers that have blocks in the molecular structure including hydrophilic and hydrophobic chain segments;Due to the different chemical properties of the two chain segments,these polymers can self-assemble in the native state or in selective solvents into various structures,such as spheres,cylinders,sheets,vesicles,etc.In this paper,Atom Transfer Radical Polymerization(ATRP)is used to prepare a series of Polystyrene-block-poly(2-hydroxyethyl methacrylate(PS-b-PHEMA)diblock copolymers with different hydrophobic-hydrophilic segments ratios.This paper will focus on the effects of the self-assembly behavior of amphiphilic block polymers on the electrospinning membrane preparation,the influencing factors of honeycomb porous membranes and pore size of the prepared porous membranes.The specific content includes the following three aspects:1.Polystyrenes with benzyl bromide end group(PS-Br)were prepared by ATRP as macroinitiator initiating the next 2-Hydroxyethyl methacrylate(HEMA)preparation,so that PS-b-PHEMA diblock polymer forms.The paper will investigate the effect of temperature,reaction time and reaction solvent system as well as factors of synthesis of Amphiphilic block copolymers such as solvent amount,monomer initiator ratio,etc.Furthermore,the best reaction conditions for PS-b-PHEMA block polymer also need to be determined.The characterization results of GPC,¹H-NMR,FITR,etc.proved the successful synthesis of the diblock polymer,in which PS-b-PHEMA amphiphilic polymer is synthesized with a molecular weight between 38K and 70K,the polymerization degree of PHEMA block accounts for 2.4%-39.9%and the PDIs were all less than 1.3 and had good monodispersity.2.Using DMF as the solvent,electrospun fibers are fabricated from the synthesized PS-Br,PS-b-PHEMA polymer,of which diameter decreases with the increase of the spinning voltage,addition of THF,isopropanol that have low dielectric constant as a mixed solvent for spinning will result in an increase in fiber diameter.When adding THF(PS block selective solvent)to the DMF solvent for electrospinning,the addition of THF will increase the hydrophobic C-C bond content on the surface of the fiber membrane and increase the hydrophobicity of the fiber membrane.When adding isopropanol(PHEMA block selective solvent)to the DMF solvent for electrospinning,with the increase of isopropanol addition ratio,the micelle structure of PS₄₈₀-b-PHEMA₁₂and PS₃₉₅-PHEMA₈₃is changing,leading to changes in the morphology of the spinning fiber.When the content of isopropanol is from0wt%to 40wt%,PS-b-PHEMA self-assembled micelles will change from longer PS shell and PHEMA core structure to shorter PHEMA shell and PS core structure.At this time,the viscosity of the solvent is greatly reduced due to the reduction of chain entanglement,resulting in the electric field force being much greater than the viscous force and surface tension,and the spinning morphology is bead-like.The shell structure of PHEMA provides hydroxyl groups on the surface of the fiber membrane,which causes the fiber membrane to changefromhydrophobic(DMF/isopropanol=100/0)tohydrophilic(DMF/isopropanol=60/40).3.The PS-Br and PS-b-PHEMA porous membranes were prepared by the water drop template method,and the influence of solvent type,solution concentration,and the percentage of hydrophilic groups of the block polymer,on the pore structure and pore size of the fabricated ordered porous films are discussed.The results show that the amphiphilic block polymer by PS-b-PHEMA can better aggregate water droplets and prepare porous films with uniform pore size due to the presence of hydrophilic blocks compared to the homopolymer PS-Br.The solvent CH₂Cl₂,which has a higher volatilization rate and good compatibility with water,can prepare honeycomb porous membranes with regular morphology and uniform pore size,and the pore size decreases with the increase of solvent concentration.The honeycomb structured film prepared by PS-b-PHEMA,the proportion of hydrophilic blocks is too high(17.4%)or too low(0%)to prepare porous membranes with regular morphology,the polymer PS₄₇₀-PHEMA₃₀with PHEMA proportion of 6%has uniform pore size and porosity.