Preparation And Morphology Control Of Anisotropic Non-spherical Polymer Particles

Anisotropic polymer particles have unique morphologies whose physicochemical properties are varied to traditional spherical particles.It has been widely used in catalytic carriers,biomedicine and functional coatings.In this paper,bowl-shaped polymer particles(BPMs)were prepared by dispersion polymerization,in which the monomer and the crosslinking agent were St(Styrene)and DVB(Divinylbenzene),respectively.Then,raspberry-like polymer particles were obtained via surface phase separation of BPMs.The contact details are as follows.(1)Dispersion polymerization method was introduced in preparation of BPMs.In order to prepare bowl-shaped particles with smooth surface and uniform particle size,relevant parameter had been investigated,such as DVB dosage,initial time of the feeding monomer,the dropping speed and St mass ratio.The depression size of the BPMs was affected by DVB dosage and St mass ratio.The optimum range of DVB dosage and St mass ratio were 1 wt%-6 wt% and 14:6-10:10,respectively.Initial feeding time and the dropping speed could make great influences on the smoothness of particles.The best initial feeding time was between 2h and 4h,the promoting dropping speed should be controlled from 0.167 g/min to 0.5 g/min.The cross-linked shells of BPMs would hinder the swelling process of monomer,which formed the bowl shape of particles.(2)With the phase separation of the BPMs cross-lined shells,small homogeneous protrusions generated on the particle surface.By accurately controlling the St mass ratio,the DVB dosage and the initial feeding time as well as the solvent polarity,the swelling growth process of the protrusions could be adjusted and therefore the morphology of anisotropic raspberry-like polymer particles could be controlled.The SEM result shows that anisotropic raspberry-like polymer particles with a distinct hierarchical structure could be obtained while the St mass ratio was 16:4.Furthermore,higher DVB concentration in the system would elevate the cross-linking degree of protrusions in phase-separated process and inhibit swelling on the protrusions induced by monomer and oligomer in the continuous phase.Particularly,the anisotropic raspberry-like polymer particles with a distinct hierarchical structure could be obtained while the DVB dose was 2 wt%.As the monomer feeding time was later,the monomer concentration in the system was smaller as well as the phase separation degree.The anisotropic raspberry-like polymer particles with obvious hierarchical structure could be obtained while the monomer feeding time was between 1.5 and 2 h.It is worth noting that the polarity of the dispersion medium not only affects the critical chain length during the oligomers nucleation process,but also determines the intensity of the surface tension between polymer and continuous phase,i.e.smaller surface tension favors the independent growth of protrusions caused by the swelling on particle surface.Specifically,the ideal raspberry-like polymer particles could be obtained while the percentage of isobutanol in the ethanol compound solvent was 50 wt%-75 wt%.(3)In view of the results from the AFM characterization analysis carried out on the surface adhesive forces of BPMs and raspberry-like polymer particles,it was found that the surface adhesive forces of both BPMs and raspberry-like polymer particles were uniformly distributed.The surface adhesive force of raspberry-like polymer particles were significantly smaller than BPMs.