Method Study for Constructing Anisotropic Functional Particles Based on PGMA Seed Emulsion Polymerization System

Author:Tian Lei

Supervisor:zhang qiu yu


Degree Year:2018





Up to now,science and technology has been in a period of multi-disciplinary cross-cutting,multi-field integration,mutual benefit and complementary advantages.Polymers and hybrid particles with controllable morphology and structure,including raspberry-like,acorn-like,Janus,bowl-like and hollow with open mouth,prepared by seed emulsion polymerization,have a vital part in the field of sensing,self-assembly,drug delivery and controlled release,solid surfactants,biological carriers,catalysts,surface enhanced Raman scattering(SERS),and superhydrophobic coatings.In particular,raspberry-shaped microparticles with hierarchical structure have been researched more deeply and have caught attention of researchers due to their unique morphology,high surface roughness,large specific surface and light scattering.There is a great deal of research work about theoretical research and methodology of cross-linked seed emulsion polymerization,in addition,cross-linked seed particles with various morphologies and compositions have been developed and used in seed emulsion polymerization,leading to a prosperous development of anisotropic particles.However,the mechanism of seed emulsion polymerization put forward by Sheu et al.based on the principle of thermodynamics is not applicable for the non-cross-linked seed particles since there is no cross-linked network inside the particles.Considering from the further development of seed emulsion polymerization in academic and industrial fields,novel seed emulsion polymerization techniques is urgently needed to fill the disadvantages in the non-crosslinked seed emulsion polymerization.In this paper,the seed swelling and emulsion polymerization system of PGMA was discovered and established.The fine-tuning,formation mechanism and application of the polymer particles with controllable structure and morphology of the solid-liquid monomer-swollen seed particles in PGMA seed emulsion polymerization were investigated deeply.What’s more,we proposed a general assembly strategy that micron-sized particles could connect together through crosslinked networks and hydrogen bonding interaction.Non-cross-linked PGMA was used as seed particles,dibutyl phthalate(DBP)as swelling agent,styrene(St)as agent,and seed emulsion polymerization of PGMA system was established.With the swelling time of PGMA seeds increasing,single-hole structure appeared on the surface of PGMA seeds and gradually grew.When PGMA seeds were only swelled by DBP,swollen PGMA particles still maintained complete spherical structure,while seeds were only swelled by St,small pores came out on the surface of the seeds and the size distribution of particles was broadened,which showed that DBP and St were necessary for forming monodispersed single-hole PGMA swollen particles.Therefore,we put forward the formation mechanism of the PGMA seed swelling system: St as polar solvent of DBP would promote the swelling effect of DBP,and then increased the swelling degree.A large amount of DBP diffused into the interior of the PGMA particles until the chemical potential achieved a balance.Due to the incompatibility of DBP in the aqueous phase,swollen DBP gradually separated from the seeds by phase separation,and accumulated on the side of the seed along with the monomer.With the further swelling of monomer,DBP(possibly dissolved some St)gradually separated from the seed particles,leaving holes on the surface of particles.By regulating Ss/Sp during the polymerization stage,protrusions with the size ranging from 1.0 to 2.0 μm were dispersed uniformly on the surface of raspberry-shaped PGMA/PSt particles,and the size of protrusion largened as the amount of monomer increased.With further developing PGMA seed emulsion polymerization,increasing the proportion of DBP/St in the swelling process,and Janus solid-liquid swelling particles were prepared.Separation degree of the protrusion and seed particles gradually augmented with the swelling time extending from 0 min to 12 min,and completely transformed into single-hole structure particles in the end.The size of liquid protrusions was controlled by the amount of St.The PGMA/PSt patchy particles with different protruding structures were prepared by adjusting DBP/St ratio and Sp content,and the formation mechanism of PGMA/PSt patchy particles was proposed.When the amount of Sp in the polymerization stage was low,the liquid protrusions on the surface of the swollen PGMA particles acted as a “monomer pool” due to the deficiency of the polymerization monomers,as the polymerization continued to proceed,leading to liquid protrusions gradually consuming and disappearing,and finally formed patchy particles with single-hole structure.When the amount of Sp was high,the liquid protrusions were not consumed and did not form large protrusions.At the same time,the swelling monomer formed protrusions on the surface of the particles and irregular patchy particles appeared.These protrusions were further swollen by monomers,polymerized and fused into large protrusions,and PGMA/PSt patchy particles were finally obtained.The prepared PGMA/PSt patchy particles had a wide range of applications.The morphology and size of particles played an important role in light reflection.The results showed that the construction of controllable protrusions on spherical particles could indeed greatly improve the light reflection performance of granular materials.It displayed that the prepared PGMA/PSt patchy particles had significant practical application value in the light reflection and thermal barrier coatings.Acidified PGMA/PSt patchy particles had good oil absorption characteristics.Once contacted with the oil droplets,the oil droplets were immediately absorbed and disappeared,which indicated that they could be used as an oil sorbent to treat oil spills.Non-cross-linked PGMA particles were used as seeds,DBP as swelling agent,St as swelling monomer,and the monomer was mixed with the hydrophilic monomer MAA to form a bowl-like hollow microcavity.The amount of MAA was adjusted to prepare PGMA/P(St-MAA)microcavity with different structures.By regulating the surface properties of the PGMA seeds and the polarity of the hydrophilic monomers,the prepared particles became irregular as the polarity of the surface groups increased.When the prepared PGMA-OH particles were used as seeds,the obtained particles presented unique red blood cell structure.As the polarity of the monomer increased,the surface roughness of the prepared polymer particles continuously raised.The PGMA/P(St-MAA)microcavity subjected to heat treatment with dioxane and water solute,as the ratio of dioxane increased,the opening of the particles diminished continuously,and some microcavity openings began to close when the dioxane/water volume ratio was 1/4.In addition,with RAFT agent DDMAT added into the GMA dispersion polymerization system,semi-transparent ellipsoidal particles could be formed.The formation mechanism of PGMA ellipsoid was proposed as follows.In the initial stage of polymerization,small PGMA spherical particles were mainly formed,as the polymerization time was prolonged,and the viscosity of the system was gradually increased.Under the influence of high viscosity and mechanical shear,low-molecular-weight PGMA particles were continuously stretched,and the aspect ratio of the particles continuously increased,which led to ellipsoidal particles finally.Different protrusion structure patchy particles were prepared by adjusting the monomer amount in the seed emulsion polymerization of PGMA ellipsoidal particles.In order to solve the time-consuming problem of the seed emulsion polymerization procedure,we proposed high-pressure swelling in the Teflon-lined stainless-steel autoclave and ultrasonic swelling in the ultrasonic generator.Different proportions of DBP/St were regulated to prepare Janus swollen seed particles with liquid protrusions.With the prolongation of swelling time,dimple-shaped single-hole structure particles were gradually formed and red-cell-shaped particles with a rough surface were obtained after polymerization.With the increase of the swelling temperature,the protrusions of the prepared patchy particles gradually decreased.When the swelling temperature increased to 80°C,the golf ball-shaped PGMA/PSt particles could be obtained.We regulated the swelling time and DBP/St ratio during the ultrasonic swelling and discovered the single-hole structure gradually increased with the prolongation of the ultrasound time when the DBP/St rate was fixed and that particle protrusion continued to increase but the amount decreased when the swelling time was fixed.With GMA as the swelling monomer,we controlled the polymerization ratio(Sp).With the increase of Sp,the protrusion structure of patchchy particles first increased and then decreased.When we increased the Sp to 5,a manageable number of 2.0-2.5 μm satellites were assembled and surrounded the core which was composed of the core-satellite superparticles.When St was used as the swelling monomer,the prepared particles changed from patchy to Janus-shaped particles composed of smooth hemispheres and raspberry-shaped hemispheres with the increase of the aomout of St.We added cross-linking agent to the seed swelling system and regulated the type and the amount of cross-linking agent to prepare crosslinked patchy particles with different structures.With EGDMA as cross-linking agent,open structure yolk-shell cross-linked patchy particles could be formed and the opening gradually decreased with the increase of Sp.The formation mechanism of microgels prepared by acid treatment of patchy particles is proposed.The epoxy group of PGMA undergoes a ring-opening reaction under the action of sulfuric acid.On the one hand,cross-linking between PGMAs occurs,on the other hand,hydroxyl groups are generated which can strengthen the hydrophilicity of particles and cross-linking between PGMA polymers forms a network between the microparticles to form a microgel.And the film-forming property and self-stripping performance of microgels are systematically studied.The double-layered microparticle gel/PET membranes prepared under the action of water occurs self-stripping phenomenon and the stripping rate decreases with the increase of the salt concentration in the water.