Synthesis Of High Performance Polymeric Hollow Nanocapsules And Design Of The Nanoporous Materials

Physical properties, such as the dielectric constant, thermal conductivity, refractive index could be tuned by the nano pore in the nanoporous materials. Therefore the nanoporous materials could be used as super thermal insulation material, ultralow-dielectric-constant material, anti-refraction material and so on.So far, the research for the nanoporous material had mainly focused on inorganic materials. Compared to inorganic nanoporous materials, the framework of polymeric nanoporous material has some advantages such as a large variety of monomers available for polymerization, easy processing and functionalization. However, the polymeric nanoporous materials are much more difficult to prepare due to their weaker mechanical properties compared to inorganic matrix. This thesis explored a novel method to prepare well-defined polymeric nanoporous material. Firstly, the non-collapsed hollow polymeric nanocapsules of high porosity were synthesized by interfacially confined RAFT minimeulsion polymerization. Then, these hollow nanocapsuless was used as building blocks to construct polymeric nanoporous material by chemical and physical methods. Thus, a novel super thermal insulation material was developed. The following conclusions were drawn:(1) The non-collapsed hollow polymeric nanocapsules were successfully synthesized by the interfacial RAFT miniemulsion polymerization. The volume average particle diameter could be tuned from 70 nm to 199 nm by decreasing the levels of the amphiphilic RAFT agent.The void fraction could be precisely tuned by changing the ratios of monomer to paraffin in oil droplet. With the void fraction increasing, the hollow nanocapsules were more likely to collapse. This collapse could be suppressed by simply increasing the amount of crosslinker. The fraction of the collapsed hollow capsules decreased nearly linearly with the increasing level of crosslinker. The hollow nanocapsules with a void fraction about 0.6 and shell thickness of 11.5nm could be fabricated without collapse.In such a case, the polymer shell of the hollow nanocapsules is mesoporous, which has high surface area 514m/g, extremely large pore volume 2.74 ml/g and a most probable pore diameter of 9 nm. The structures of the hollow nanocapsules are very stable not only in the solvent but also under harsh conditions like high temperature (200℃) and strong shear. The hollow nanocapsules are also able to fully re-dispersed in the solvent.(2) The powder of polymeric nanocapusles showed low thermal conductivity(as low as 0.016 W/(m·K)) which decreased with the increase of void fraction in polymeric nanocapsules. Polymeric nanoporous material was constructed by connecting the hollow polymeric nanocapsuls into bulk, using partially etherified melamine-formaldehyde resin solution as crosslinker. The porosity and pore size could be tuned by changing the solid content of emulsion, the amount of partially etherified melamine-formaldehyde resin solution and the void fraction of hollow nanocapsules. The thermal conductivity for the as-prepared polymeric nanoporous materials was related to the types of hollow nanocapsules with different void fractioan, the porosity of polymeric nanoporous materials and the amount of partially etherified melamine-formaldehyde resin:it could not be obtained polymeric nanoporous material with low thermal conductivity which was prepared by solid nanoparticles. However, compared to the other particles, the polymeric nanocapsules with shell/core=1:1 were the best type for constructing super thermal insulation material. In such a case, the thermal conductivity of the polymeric nanoporous material was 0.020 W/(m·K) with high performance of compress mechanical property,8.48Mpa; The thermal conductivity of polymeric nanoporous material decreased with the increase of the porosity of hollow polymeric nanocapsules used. The thermal conductivity decreased to 0.018 W/(m·K) when the porosity of the polymeric nanoporous material reached to 77.2% and the average pore size of 173nm; The thermal conductivity also decreased with the decrease of the partially etherified melamine-formaldehyde resin solution in the porous materials. However, if the partially etherified melamine-formaldehyde resin solution was not enough (the ratio of shell polymer to PMF more than 1.25),the prepared polymeric nanoporous material would crack.(3) The low porosity polymeric nanoporous material could be prepared by mixing polymer matrix with hollow polymeric nanocapsules through melt mixing. The hollow polymeric nanocapsules were almost full dispersed in the polymer matrix. Furthermore, increasing the fraction of hollow polymeric nanocapusles to 0.4 would not worsen the disperse condition. The fraction of collapsed nanocapsules in the polymeric nanoporous material would increase when using polymeric hollow nanocapsules with higher void fraction.(4) Blending the emulsion of nanocapsules with the latex of low Tg polymer could lead to the film formation. The emulsion of polymeric nanocapsules could form the continuous film when the mass ratio of nanocapsules to PBA was 5:3.The hollow nanocapsules with shell/core=1:1 would deform when the film made from them was under high temperature. The polymeric nanoporous material could be obtained by the formation of film made from the emulsion of nanocapsules with shell/core=4:1, which could keep its structure stable under high temperature.To increase the porosity of polymeric nanoporous material, we used epoxy to crosslink the carboxyl groups in polymer chain and amphiphilic macro-RAFT agent, then removed the non-crosslinked polymer chain and paraffin, with voids left in the film.