| Nanocapsules with special structure and morphology can prepare polymer materials with controlled release by encapsuling function chemical compound. At present, most nanocapsule shell is polymer or hybrid polymer, inorganic materials or alternating inorganic materials and polymer. There is enormous potential application merit that shell combines advantages of organic and inorganic materials by chemical reaction to carry out microscopic hybrid.Combined in-situ polymerization by encapsulation non-solvent alkane and hybrid method between styrene and organic silicon monomer, 3-trimethoxysilyl propyl methacrylate (MPS) with functional group of vinyl and siloxane Si-OR, organic-inorganic hybrid nanocapsules were synthesized by miniemulsion polymerization without core removed. In this process, nanocapsules were formed by radical copolymerization between St and MPS and hydrolysis-condensation reaction of Si-OR on the surface of the well-dispersed isooctane/monomers mixture submicro-droplets. Comparing conventional emulsion polymerization, it's possible that miniemulsion polymerization can prepare nanocapsules. It's concluded that micelle nucleation is fewer advance in formation of nanocapsules, while droplet nucleation is favorable in the miniemulsion polymerization.The main location of miniemulsion polymerization lied on monomer submicro-droplets. The hollow nanocapsules were formed on the surface of droplets because generated polymer could not dissolve in the mixture droplets. Nanocapsules were proved by theoretical arithmetic with thermodynamic criterion developing coefficient Si and Gibbs free energy G and experiment results. Added MPS and [SDS] below CMC (4.5g/L) prefer to form nanocapsules.The effect of feed order and miniemulsion polymerization conditions on nanocapsules morphology was discussed. Few nanocapsles were formed by adding monomers after ultrasound dispersion and its particle size distribution was in disorder. Monodispersion nanocapsules were obtained and maintained the size of the initial droplets in the polymerization process carried out by TEM images when [SDS]=1.33g/L. Bidispersionand complex particles cayyied out by TEM images were appeared when [SDS]=6.77g/L.From particles size distribution and TEM images with CA as costabilizer, it was found that there were two peaks with about 50nm, which indicated homogeneous nucleation, and about 400nm, which indicated droplet nucleation, respectively. Particle morphology was similar to CA when using octadecyl alcohol as costabilizer. The nanocapsules were also formed if the water-soluble initiator was insteaded by oil-soluble one.FTIR spectras of monomers and copolymer verified hybrid structure by disappearance of vinyl C=C bond (1200cm-1, 1634cm-1) and Si-OR bond (821cm-1, 1087 cm-1) under pH=7.0 and MPS/St=0.3. It illustrates free radical copolymerization and hydrolysis-condensation are coupled in this system. Hydrolysis-condensation happened to cause the branching and crosslinking structure with the increasing of MPS/St ratio and pH=4.0 or pH=9.18.Kinetics of miniemulsion polymerization and hydrolysis-condensation of Si-OR were also researched. It was found that miniemulsion polymerization did not have constant-velocity stage. Polymerization rate increased and nucleation time decreased with HD/SDS mass ratio increasing. Effect of SDS and KPS on the polymerization rate represented dX/dt～[SDS]0.375[KPS]0.132. The apparent hydrolysis rate constants were kh= 2.22×10-3min-1, 7.01×10-3min-1 and 7.89×10-3min-1 with KPS, AIBN and BPO as inititors, and kh=2.22×10-3min-1, 2.32×10-3min-1 and 2.45×10-3min-1 when MPS/St mass ratio were 0.3, 0.6 and 1.0, respectively. Gel fraction and condensation degree enhanced with MPS amount increasing. The rate of free radical copolymerization was affected unobviously by pH = 4.0 and pH = 9.18, but most Si-OR of MPS had hydrolyzed after ultrasound dispersation and gel fraction was higher under pH=4.0. |
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