Abstract
In this study, a series of crosslinking agents, amino-polyorganosiloxane and epoxy- polyorganosiloxane were synthesized from 3-Amino- propyltrimethoxysilane (APTMS), γ-Glycidoxypropyl trimethoxy- silane (GPTMS) and 1,4-Bis(trimethoxysilyl) Benzene (BTB) via a sol-gel reaction. Boron trifluoride monoethylamine (BF3MEA) was used as catalyst. Furthermore, the amino-polyorganosilxane or epoxy- polyorganosiloxane was added to DGEBA type epoxy resin and 4, 4’- Methylene- dianiline (DDM) to prepare epoxy/polyorganosiloxane nanocomposites. The nanocomposites were anticipated to exhibit excellent thermal stability. FTIR and solid-state 29Si-NMR were used to investigate the reactivity of sol-gel reaction, curing reaction and the structure of the nanocomposites. XRD, SEM, Si Mapping and TEM were used to study the structure of polymer chains and morphology. DSC, TGA were used to analyze the thermal properties of the nanocomposites and calculate the kinetics of curing and thermal degradation. UV-Vis was used to analyze the transparency. DMA was used to analyze the dynamic mechanical properties. BF3MEA was proved to be an effective catalyst for sol-gel reaction of APTMS, but it can not promote the sol-gel reaction of GPTMS. The activation energy of curing reaction, Ea, slightly decreased from 56 to 54 kJ/mol by Ozawa’s method, and from 52 to 50 kJ/mol by Kissinger’s method with the increasing BTB contents in EP/APTMS/BTB system. The activation energy of curing reaction, Ea, significantly increased from 56 to 63 kJ/mol by Ozawa’s method and from 51 to 58 kJ/mol by Kissinger’s method with the increasing BTB contents in EP/GPTMS/BTB system. The EP/APTMS/BTB system possesses more T3 structures when the BTB content was lower than 10wt%. T1 structures appeared when BTB content was higher than 20wt%. The EP/GPTMS/BTB system possesses more T0 and T1 structures. The T structure of inorganic network will affect the Td5, Ea and dynamic mechanical properties of composite. From UV-Vis, XRD and SEM investigation, all nanocomposites were amorphous, possess excellent optical transparency and no phase separation. From TEM microphotographs, EP/APTMS/BTB (10wt%) possesses dense inorganic structure (particle size around 5-15nm), and EP/GPTMS/BTB (10wt%) possesses loose inorganic structure. EP/APTMS/BTB system with BTB content lower than 10wt% showed good dynamic mechanical property and thermal stability (Td5 increased from 336℃ to 371℃, char yield increased from 27.4 to 30.2%, Ea of thermal degradation in N2 increased from 139 to 176 kJ/mol, Ea of thermal degradation in air increased from 172 to 205 kJ/mol). EP/GPTMS/BTB system exhibited similar thermal stability and lower mechanical property. The Tgs of all nanocomposites decreased with the increasing BTB content.