Preparation Of Phenolic Microspheres Via Water/’Water’ System

Phenolic resin microspheres are expected to have a wide application board because of its network structure and thermal insulation properties. For example, they have been utilized as lightweight adhesive in the field of building materials and chemical, precursor reinforcement of carbon foam, thermal ablation on aircraft materials since the phenolic resin powder was successfully obtained via bulk polymerization system. To date, few data has been reported and the most polymerization process method involving phenolic resin microspheres is traditional heterogeneous polymerization by using oil-soluble medium. A novel type of water/ ’water’ heterogeneous polymerization system hasn’t been reported yet, in which water-soluble monomers were dispersed in electrolyte solutions to prepare phenolic microspheres. In this paper, phenolic microspheres were obtained by condensation of phenol and formaldehyde as monomers in electrolyte solution via heterogeneous polymerization. A novel water/’water’ heterogeneous polymerization system was proposed and constructed, which was expected to enrich the polymerization method of step polymerization. On the other hand, organic silicone group was led into the phenolic resin structure to prepare low dielectric silicon modified phenolic microspheres due to the low dielectric of organic silicone. Main works are as follows.Ammonium sulfate solution was employed as’water’phase to prepare resorcinol/formaldehyde resin microspheres. The homogeneous and stable microspheres with rather smooth surface were prepared. Particle sizes of resulting microspheres vary from 0.4μm to 2.0μm while the polydispersity index (PDI) value is quite narrow ranging from 1.01 to 1.30, which meant the morphology of phenolic microspheres was unique. The reactions were conducted at different conditions and the effects of these reaction parameters on particle sizes, particle size distribution and morphology of microsphere were investigated. The results showed that particle size increased the increase of concentration of ammonium sulfate in’water’phase, the ratio of resorcinol to formaldehyde and the concentration of the monomers. On the contrary, the particle size decreased with the increase of amount of HEC, amount of catalyst and the agitation rate. What’s more, when the reaction temperature and reaction time increased, the particle size decreased to a minimum and then presented a rising trend.The effect of different inorganic salt dispersion medium on the polymerization system was investigated. The results showed that when the ions played catalytic role in the formation and maintenance of water structure were added into the system, stable and perfect phenolic microspheres were prepared while the destructive effect ions existed in the system would produce negative effect on the formation of microspheres.Trimethylchlorosilane was used to prepare the modified Phenolic resin. The results showed that hydroxyl on the phenolic resin could be completely replaced when dioxane was used as solvent as well as the pyridine was added as acid absorbent. The reactions were conducted at various concentrations of pyridine, proportions and feeding method of raw materials, reaction time and reaction temperature. The modified resin was experienced some treatment and added into above ’water’ phase, the phenolic microspheres were obtained under the action of the emulsifier, which owned the dielectric constant under 3.5(The frequency was greater than 1 MHz)The study results are expected to enrich the polymerization method of step polymerization. This system provides ideas and methods for the synthesis of special pre-polymer with high molecular weight or slightly spherical shape. What’s more, the polymerization method own the features of safety, environmentally friendly, low carbon, low cost, simple to achieve, which will provide a wide range of potential applications.