Synthesis Of Monodisperse Functional Crosslinked Poly (Divinylbenzene) Microspheres Via Precipitation Polymerization In Acetic Acid

Monodisperse crosslinked polymeric microspheres are receiving significant attention because of their wide applications.Among numerous synthesis methods,precipitation polymerization can obtain micron-sized microspheres with clean surfaces via a single step without the use of any stabilizers or surfactants.The most commonly used solvent in precipitation polymerization is acetonitrile which is toxic and limits its industrial application.In this dissertation,for the first time,we reported a new precipitation polymerization system:precipitation polymerization in acetic acid.And the following are the main results.Monodisperse crosslinked poly(divinylbenzene)(PDVB-55) particles were prepared via precipitation polymerization in acetic acid for the first time.Pumpkin-like particles and microspheres were obtained. The PDVB-55 particles were highly crosslinked,uniform and well separated.The average diameter of the PDVB-55 particles was measured to 2.69μm and the CV was 4.66%.The yield of particles was 85%.On the surface of the particles there were a significant amount of residual double bonds.After nucleation(2h),the total amount of particles in the system was a constant.The CV displayed a decrease and the amount of spheres and the spherical evenness of the particle surfaces improved with the polymerization time.Compared with acetonitrile system,the acetic acid system had higher yields,smaller size,not spherical but pumpkin-like particles.A particle forming and growth mechanism including a prolonged nucleation was raised to explain the formation of pumpkin-like particles.As the temperature was increased,the shape of the particles became more spherical and the yields were increased.As the monomer loading was increased,more homo-coagulated particles were obtained, and the yields and CV were increased.For a DVB loading below 1 vol%, monodisperse microspheres with smooth surfaces and narrow diameters were successfully obtained.As the AIBN loading was increased,there were no differences with the particle morphology,but the yields and CV were increased.When adding good solvent methyl ethyl ketone(MEK) into acetic acid system,the shape of the particles became more spherical and CV were increased.Monodisperse PDVB-55 microspheres were obtained with MEK content 30 vol%.Microgels were obtained with 60%MEK, and space-filling macrogels were prepared with 90%MEK.When adding poor solvent n-heptane,more homo-coagulated particles were produced. For n-heptane concentrations up to 50 vol%,cauliflower-like particles could be observed.When adding MEK and heptane,the diameters and CV were increased,and the yields were decreased.Summarized from reported result,for the first time,the regularity of dispersive term(δ_d) of Hansen solubility parameters on particle morphology in PDVB-55 precipitation polymerization system was reported.Microspheres or particles are formed in the range of moderateδvalues for both parameters,δ=20.2～24.3 or=16 MPa^1/2,and what is very important,δ_d around 15.4 MPa^1/2,respectively.δ_h should below 13.5 MPa^1/2.Cyclohexane, cyclohexanone,n-Butyl acetate,and 1,4-Dioxane were used to verify this regularity and positive results were obtained.The regularity came from the non-polar monomer and particles.For the first time,UV irradiation precipitation polymerization in acetic acid was reported to prepare monodisperse crosslinked poly (divinylbenzene) microspheres with monomer loading 2 vol%,AIBN loading 3 wt%and UV irradiation intensity 8000μwcm^-2(wave length 365nm),24h.The average diameter of the monodisperse crosslinked PDV-55 microspheres was measured to 2.03μm,the CV was 2.5%and the yield was 52%.The irradiation system can avoid coagulation because of the rapid nucleation(20min) with spherical nuclei which was 10 times faster than thermo initiated system,and the photo initiated crosslink which made the particle surface polymer chains shrank towards the surfaces.The nucleation and particle forming mechanisms of irradiation system were similar with those in thermo system.As the monomer loading was increased,more homo-coagulated particles were obtained and the diameters were increased.The yields were firstly increased and then decreased.As the AIBN loading was increased,the diameter and yields were increase while the CV was decreased.And there were no differences with the particle morphology.Without any initiator,UV irradiation system could also get monodisperse microspheres.As the irradiation intensity was increased,the shape of the particles became more spherical.The diameters and yields were increased and CV was decreased.Monodisperse Poly(Styrene-co-DVB) microspheres were successfully obtained via precipitation polymerization in acetic acid.The recipe:Styrene contents from 60 vol%to 80 vol%,heptane and acetic acid mixture as solvent with heptane contents from 30 vol%to 70 vol%. Particle forming and growth mechanism was similar with those in PDVB-55 system and the total amount of particles was a constant after nucleation.Monodisperse Poly(MMA-co-DVB) microspheres were also successfully obtained.The recipe:acetic acid as solvent,MMA contents from 10 vol%to 30 vol%.Microsphere hydrophilic properties were increased.Particles were stable in NaOH saturating water solvent.Monomer loadings were successfully enhanced via multi-step precipitation polymerization.Narrow disperse particles were obtained with monomer loading up to 10 vol%.For the first time,stable system was obtained with monomer loading 7 vol%via precipitation polymerization in saturating oligomer solvents.In this way,solvents were recycled.