Synthesis Of Novel N-phenylaminomethyl Silsesquioxanes And Their Cooperation With PU

Polyhedral Oligomeric Silsesquioxane (POSS) is a kind of unique organic/inorganic hybrid molecular, with a size of ca.1-3nm. The silicon-oxygen frameworks provide the stiffness of the material and the organic groups provide the good compatibility with polymers. Reactive POSS could chemically cooperated into polymers and bring reinforcement in mechanical and thermal properties, but with low yields. It is significant to investigate the synthesis of reactive POSS with high yield and its application in polymers.A new functional N-phenylaminomethyl POSS was synthesized by controlled hydrolytic condensation from ND42in one step reaction, with the yield of64%. The POSS structure was ascribed to a T10and T12derivative mixture as main component by varied characterization methods such as NMR, Gel permeation chromatography (GPC) and Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS). It is calculated that the products tended to form T10with D5h symmetry and T12structures with D2d symmetry under the condition of hydrochloric acid and methanol.This novel POSS which acted as a nano-crosslinker was then reacted with polyether diisocyanate,a series of POSS-PU composites with different POSS concentration was prepared and characterized. The POSS/PU composites showed no macrophase separation up to52wt%POSS concentration. The high resolution transmission electron microscopy (HRTEM) images of POSS-PU composites showed a well separated nanostructure of POSS with a typical phase size of5-10nm. ATR-IR and solid state13C-NMR indicated that POSS was reacted with PU with high efficiency. Tg and storage modulus of POSS/PU composites increased with increasing POSS concentration characterized by DMA. A critical POSS concentration of26wt%was found, beyond which the POSS/PU showed a permanent network at high temperature. Young’s modulus largely enhanced with increasing POSS concentration at constant Ttest-Tg. All the enhanced mechanical properties could be ascribed to synergetic effect of POSS and PU, where POSS played a role as the nanoscale crosslinker in the PU system and formed network, thus hindered the motion of PU chain.The gelation of N-phenylaminomethyl-POSS/PU nanocomposites during curing and the viscoelastic properties at equilibrium state after curing were investigated by rheology. The gelation time of the composites decreased with the rise of curing temperature, and relaxation exponent at the critical gel was around0.7. The critical gel point of the POSS/PU composites at equilibrium state was found around2.5wt%at60℃. The chemical and physical gelations in the composites were investigated by exploring the rheological behaviors at different temperatures. The modulus of the equilibriated materials could be scaled by POSS concentration-frequency superposition only when chemical cross-links were retained, which implied the similarity of network that formed at different POSS concentrations.A novel N-phenylaminomethyl silica (NPAM-silica) which was similar with POSS was firstly synthesized by one-step emulsion polymerization. The NPAM-silica was mainly composed of fully condensed silsesquioxanes and a small quantity of partially condensed silsesquioxanes which was confirmed by29Si-NMR and MALDI-TOF MS. It was introduced into polyurethane (PU) as a chemical crosslinker. The high reactivity of NPAM-silica was investigated by means of ATR-IR and solid state Nuclear Magnified Resonance (SSNMR). TEM and AFM showed that the NPAM-silica had perfect compatibility with PU. The mechanical properties of NPAM-silica/PU nanocomposites were greatly enhanced, which was reflected in DMA and tensile tests at constant Ttest-Tg. What’s more interested was that the NPAM-silica/PU possessed higher storage modulus at the rubber plateau than that of N-phenylaminomethyl POSS/PU. The homogeneity of NPAM-silica/PU was better than that of POSS/PU which was characterized by TEM and small angle x-ray scattering (SAXS). The low cost and environmentally friendly functionalized NPAM-silica would have greater advantage of application in practice compared with N-phenylaminomethyl POSS.