Preparation And Properties Of Newly Hollow Polystyrene Nanospheres

Hollow polymer nanospheres (HPNSs) has wide application in many fields，like catalysis, absorption, nanoreactor etc., because of its unique nanostructurewhere polymer is used as block build the nanoshells, surrounding the hollowcavities. HPNS basically could be synthesized by self-assembly, template-assistedmethod,(mini-) emulsion polymerization and others. However the products whichare prepared by such methods mentioned above generally carried some inevitableshortcomings. For example, the nanospheres with bad monodispersity are easy toaggregate; the hollow nanospherical structure is hard to be maintained unbrokenlywith being dried in normal condition because of the low mechanical intensity ofthe polymer shell. These drawbacks seriously limit the application of HPNS,which has always being a challenge in the development of HPNS.Herein, we firstly synthesized SiO2/PS core/shell nanospheres whosepolymeric shell was prepared by emulsion polymerization of styrene withpre-crosslinking by divinylbenzene and core prepared by SiO2, basing ontemplate-assisting method. Subsequently SiO2/PS cross-linked nanospheres areprepared by introducing crosslinking bridges with hypercrosslinking, where AlCl3used as catalyst and CCl4or any other agent as crosslinking agent. Finally theHPNS was synthesized by etching SiO2template and drying in condition ofordinary pressure. The HPNS acquired enhanced mechanical intensity andmaintained well monodispersity because of the polymeric shell with densercross-linked structure, by means of hypercrosslinking. Moreover, most gelmicropores can be maintained through drying operation in ordinary pressurecondition. Thus a novel mono-disperse hollow PS nanospheres (HPNS) withmicroporous shell was successfully obtained. The structure of as-prepared novelmaterial was characterized by means of FTIR, DLS, Zeta potentiostat, SEM, TEM,Particle size analysis, TGA, N2absorption-desorption etc. The colloid stability, theability of control releasing and adsorption capacity of organic vapors were alsolearned. The research results were showed as follows: (1) The monodisperse HPNS with micropores was successfully prepared bymeans of hypercrosslinking, basing on template-assisting method. Subsequently,the controlling fabrication of HPNS with various cavity size, various degree ofpre-crosslinking and different cross-linked bridge, was successful to be achievedby manipulating the template size, DVB content and crosslinking agent. Theresults show that HPNS of115nm with hollow cavity of50nm possessed greatmono-dispersity with a PDI of0.005and high BET surface area and pore volume,calculated to be476m2g-1and0.61cm3g-1, respectively. HPNS could beintroduced other cross-linking bridge, such as-CH2C6H4CH2-,-CH2C6H4C6H4CH2-, by hypercrosslinking with different crosslinking agents.Above all, the BET surface area of HPNS with-CH2C6H4CH2-cross-linkingbridge could be achieved as high as445m2g-1.(2) Furthermore we prepared HPNSs in various crosslinking reactiontemperature and reaction time, to find out the best reaction condition ofpreparation. The results showed that reaction temperature had significant impacton the nano-structure of HPNS. HPNS obtained great mono-dispersity with a PDIof0.005and the most volume of micropores which come from the highest degreeof crosslinking of the polymeric shell with hypercrosslinking in75oC. The BETsurface area and micropore surface area were calculated to be as high as332m2g-1and183m2g-1respective. HPNS can maintain the perfect spherical morphologyand great mono-dispersity while the reaction time ranged from12h to24h.However, the formation of micropores came to saturation and the BET surfacearea kept evenly while the reaction time was extanded above4h.(3) In our study, this novel HPNS can keep great colloid stability in buffersolution with pH of2~13. HPNS also showed a good performance of adsorptionbecause of high surface area and abundant existing of micropores. As the volatilesolvent be absorbed by HPNS, the volatilizing of solvent molecule could becontrolled to a much longer time. Especially the volatilizing time of1,2-dichloroethane with the help of HPNS can be extended to longer as10timesas absolute1,2-dichloroethane’s. The absorption capacity of HPNS towardsorganic vapors such as toluene and THF can be as high as285mgg-1and234 mgg-1, tested by static saturated vapor absorption. SiO2/PS cross-linked core-shellnanospheres as the precursor of HPNS, also can be used to fabricate SiO2/PSyolk-shell nanospheres. Compared to preparation of HPNS, a2M NaOH solutioninstead HF to etch template12h on the normal condition in preparation ofyolk-shell nanospheres. Such a novel material with unique nano-structure hasgreat potential in applications of catalysis and electrochemistry.