Preparation And Properties Of Polyamide 6 Grafted By Nano-SiO₂ Through Surface-Initiated Anionic Polymerization

Recently, polymer based organic/inorganic hybrid materials, considered as innovative advanced materials, have gained considerable attention. Inorganic materials, such as montmorillonite and nano-SiO2 et al, present excellent thermal stability and hardness. The incorporation of nano-materials into polymer matrices is an extremely effective way to improve the thermal and mechanical properties of polymers. Nano-SiO2 which could enhance and toughen the polymer matrices was widely applied in filled modification of polymers. However, the high surface energy of nano-SiO2 could lead to generate clusters aggregation, so the advantage of it could not appear. These enhanced properties of nano-SiO2 can not be achieved due to the aggregation of the particles. Therefore, well-dispersed nano-SiO2 within the polymer matrices was the key factor when synthesizing of PA6 nanocomposites. Therefore, well-dispersed nano-SiO2 in PA6 matrices can increase the compatibility of them using the surface modification method, and this research was very important.A surface-grafting method to prepared PA6 nanocomposites was brought forward in this paper. First, the-OH of nano-SiO2 was reacted with p-NCO of toluene 2,4-diisocyanate, and the excess o-NCO was terminated by caprolactam monomer. The resulted nano-SiO2 grafted by caprolactam was used as activator and sodium caprolactam was used as initiator. The PA6/SiO2 nanocomposites were accomplished by surface-initiated anionic polymerization at 170℃. Due to the existence of acylated caprolactam beneficial to nucleophilic attack of caprolactam anion, the activation energy of the polymerization reaction was relatively low and and the polymerization reaction was accomplished in relatively short time. For comparision, pure PA6 and PA6/nano-SiO2 blend were prepared under the similar conditions using toluene 2,4-diisocyanate as activator.The synthesized activator was characterized with FT-IR and the grafting ratio of the organic compounds on the surface of nano-SiO2 was characterized by TGA. To optimize the preparation technology of activator, the effect of molar ratio of-NCO to-OH of nano-SiO2, reaction temperature and catalyst on the grafting ratio was researched in this paper. The crystallinity, thermal stability, dynamic mechanical property and dispersion of grafted polymer were characterized by DSC, TGA, SEM and DMA, respectively. Results showed that the addition of nano-SiO2 influenced crystallization of PA6 and the prepared PA6 grafted by nano-SiO2 showed better thermal stability and mechanical property than pure PA6 and PA6/nano-SiO2 blend. Furthermore, it showed better dispersion of nano-particles in PA6 than nano-SiO2/PA6 blend.