Polymer, inorganic nanocomposites using hyperbranched polyalkoxysiloxanes

摘要

The present dissertation mainly about the preparation, modification and application of a premium precursor of silica--hyperbranched Polyethoxysiloxane (PEOS), which was firstly developed by DWI and has very good high temperature stability, good miscibility with most of the solvents and possibility to be modified easily. PEOS, which was used as a basic-material in all the synthesis of modified PEOS, and isobutyl modified PEOS (iBPEOS) and n-octyl modified PEOS (OPEOS), were synthesized via a one-pot catalytic condensation reaction of tetraethoxysilane (TEOS), with or without isobutyltriethoxysilane or n-octyltriethoxysilane as comonomers, with acetic anhydride. The low fraction of volatile compounds in the product was removed completely by passing through a vacuum thin-film evaporator. Amino groups modified PEOS (NH2-PEOS) and other amino modified silica precursors with different amino contents (2~10% and >20%, relative to ethoxy groups) were prepared via four different methods. An amphiphilic PEOS modified by both 10% amino groups and 10% n-octyl groups was synthesized. By means of in situ sol-gel technology using iPP with PEOS, iPP/silica composites were prepared on a 15 ml co-rotating twin-screw microcompounder via melt-blending. By varying the PEOS fed content, the dimension of the resulting silica particles, which are homogeneously distributed in the iPP matrix, varied from 100 nm to several micrometers. iPP/silica composites showed improved thermal stability under nitrogen and higher crystallinity degree. The compatibility between PEOS and molten iPP matrix was significantly improved with the modification of n-octyl groups on PEOS. Benefited from the better compatibility, the resulting composites have a much better transparency. Precondensed 3-aminopropyl triethoxysilane (PAPTES) was applied in iPP and significant positive effect to the thermal stability under air was detected. Pure PEOS was also used as an assistant to the exfoliation of layered silicate in iPP matrix. NH2-PEOS and other amino modified silica precursors were applied in the flexible polyurethane (PU) foams preparation. Three different methods were conducted: Polyol with dissolved-in NH2-PEOS or other amino modified silica precursors; isocyanate with dissolved-in PEOS or NH2-PEOS; Polyol with build-in NH2-PEOS or other amino modified silica precursors. When NH2-PEOS was dissolved in polyol, the transesterification between ethoxy groups and OH groups under the catalysis of NH2 groups cannot be prevented. For the second route, unmodified PEOS can hardly be dissolved in MDI / PMDI because of its low reactivity with isocyanate groups and the very different polarity. Concerning the complexity of the chemical structures of these mixtures, moving to next method of Polyol with build-in NH2-PEOS or other amino modified silica precursors would be needed to produce a series of product with predictable structures. NH2-PEOS and other amino modified silica precursors were firstly built in PolyIsocyanate PolyAddition (PIPA) polyol which is very commonly used in PU foam industry. PEOS with 3~10% amino groups were applied in IP585 and CP4702 with TDI as crosslink agent. With IP585, the weight content of NH2-PEOS varied from 8 wt% to 12 wt%. With CP4702 as the base resin polyol for PIPA preparation, weight content of NH2-PEOS varied from 4 wt% to 16 wt% and different final PIPA particles can be achieved. Since amino groups can catalyze the reaction between ethoxy groups in PEOS and OH groups in polyol, NH2-PEOS themselves may act as the crosslinking agent with polyol as base resin. Weight content of NH2-PEOS varied from 2 to 10 wt% and homogeneous liquids were obtained when the NH2[3~10]-PEOS hydrolyzed in acidic environment. Two blends were selected for foam preparation and the foams were too sticky and weak. Shown by TGA measurements, polyol with build-in NH2-PEOS has a better thermal stability both in air and nitrogen. Moreover, higher amino content may influence the thermal stability positively. Different procedures were applied to increase the stability of the polyol/PAPTES blends and three best samples with 20 wt% PAPTES or 20 % fully hydrolyzed APTES were chosen for the foam preparation. However, only two blends with 20 wt% PAPTES were successfully applied in the flexible PU foams and all the foams containing PAPTES failed the Cal 117 and Crib 5 tests. On the other hand, the adding of PAPTES may bring positive influence on the compression set resistance, the hysteresis and comfort index. Using a method similar to PEOS synthesis, polyalkoxytitanate (PAOT) as a precursor of TiO2 was prepared. PAOT has a much higher stability comparing with the monomer Ti(O-iPr)4 and can easily be stored in a solvent such as chloroform without use of any additional protections. With this precursor, a smooth TiO2 film can be prepared by spin-cast followed with H2 plasma-curing.