The Preparation And Assembly Of DC-TMPTA Polymer Microspheres

Monodisperse polymer microspheres have been largely applied in many fields as a special morphological polymer material.Compared with the traditional methods for their preparation,precipitation polymerization does not need any additives and post-treatment.The microspheres thus prepared can self-assemble on a planar surface（2D）or in a three-dimensional template（3D）to form ordered suprastructures,such as colloidosomes.These ordered suprastructures endow materials with many special physical and chemical properties because of their highly ordered structure.Droplet template method developed in recent years has attracted wide attention because of its flexible experimental process,and easiness to adjust the size and shape of the assembled colloidosomes.Monodisperse P（TMPTA-DC）microspheres were first prepared through precipitation polymerization of dodecene（DC）with trihydroxymethyl propane triacrylate（TMPTA）as the crosslinker in water-ethanol（H₂O-EtOH）binary solvent with azobisisobutyronitrile（AIBN）as initiator.Microspheres and soluble oligomers were separated by centrifugation,and the yields of the polymer microspheres and the soluble oligomers were tested by gravimetry.The size and shape of the microspheres were observed by scanning electron microscopy（SEM）.Based on the results,the polymerization time,the amount of TMPTA used and the water amount in the polymerization were changed to study the effects on precipitation polymerization.The results showed that,with the prolongation of reaction time,the soluble oligomers yield decreased while that of the microspheres yield and the particle size gradually increased.However,at 8 h,the shape of the microspheres became irregular and the size distribution was broadened.Monodisperse polymer microspheres were prepared with TMPTA amount of 30 wt% relative to the total monomer.The monomer conversion increased with a further increase in TMPTA,and the microspheres aggregated at the same time.In addition,the soluble oligomers yield decreased while the microspheres yield increased with the increase in the amount of H₂ O in the binary solvent.Paraffin wax was added together with the monomers into the reaction system,which served as the third solvent to form wax droplets at melt state when temperature was adjusted above its melting point,the in-situ generated polymer microspheres were anticipated to organize themselves within the wax droplets as the template through one-step self-assembly.The effects of the surfactants,H₂ O amount in the solvent,shaking frequency,TMPTA amount and the polymerization time on the expected self-assembly of the polymer microspheres were studied.The results showed that,the wax was difficult to disperse as small sized and uniform droplets when there was no H₂ O in the reaction medium even under high shaking frequency.Supplying the system with a given amount of nonionic surfactants,uniform wax droplets of small size were obtained under high shaking frequency.In addition,similar uniform wax droplets were also obtained without the presence of any surfactant when a certain amount of H₂ O was added into EtOH under a certain shaking frequency.In a typical process,DC,TMPTA and AIBN were added into the reaction system together with wax,P（TMPTA-DC）microspheres generated through precipitation polymerization of DC and TMPTA,and adsorb on the surface of the wax droplets as stabilizer like in Pickering emulsion.Wax spheres with the primary polymer particles were obtained when the temperature was subject a deep dropping down by adding icing-water to the polymerization system with the presence of the wax droplets.Uniform wax spheres with the size（diameter）of 40 μm were formed when H₂O/EtOH mass ratio was 1:9,TMPTA was 30 wt% in the monomers and with shaking frequency at 300 osc/min.However,the soluble oligomers in the continuous phase and the polymer microspheres contained in the wax spheres greatly decreased when the amount of TMPTA was increased while all the other experimental conditions were kept unchanged.To obtain the portion of the soluble oligomers and the portion of the polymer microspheres in H₂O-EtOH phase and that in wax spheres at different polymerization stages,icing-water was added into the oscillator to drop down the temperature quickly,so that to half the polymerization.The results showed that,at the initial 0².5 h of the polymerization,both the microspheres and the soluble oligomers amounts in the wax phase were gradually increasing with time,with a more significant increase from 1.0 h to 1.5 h.At the same time,the amount of the polymer microspheres remained in H₂O-EtOH phase decreased with time.The portion of the soluble oligomers and that of the microspheres remained practically unchanged in both the wax droplets and the continuous phase afterwards.