The effects of molecular structures and mobility on the thermal properties of epoxy-bridged polyorganosiloxanes have been investigated by solid-state 29Si and 13C solid state NMR in this study. Epoxy-bridged alkoxysilanes precursors with mono-(APDES), di-(APMDS), tri-(APTES) functional ethoxysilane terminal groups have been synthesized and thermally cured with or without the addition of catalysts to obtain epoxy-bridged polyorganosiloxanes. Three kinds of catalysts including acidic, basic, and organometalllic compounds have been used as the curing catalyst for the direct thermal curing of epoxy-bridged polyorganosiloxane precursors. The structures of epoxy-bridged polyorganosiloxanes with respect to the catalysts are quantitatively investigated. Acidic BF3·MEA shows the best catalytic effects on the formation of T3 and D2 structures in the epoxy-bridged polyorganosiloxanes from tri-functional epoxy-APTES and di-functional epoxy-APMDS precursors, but basic NBu4·OH has better enhancement on the formation of M1 structure in the epoxy-bridged polyorganosiloxanes from mono-functional epoxy-APDES precursor. TEM spectra show that the epoxy-bridged polysilsesquioxanes of epoxy-APTES precursors exhibit polysilsesquioxanes nano domain around 45-55 nm under the catalysis of dibutyltindilaurate (DBTDL), but show bigger polysilsesquioxanes nano domain around 50-150 nm under the catalysis of basic tetrabutylammonium hydroxide (NBu4·OH) in epoxy matrix after direct thermal curing process.The coefficient of thermal expansion of the epoxy-bridged polyorganosiloxanes are affected by the functionality of terminated alkoxysilanes and the species of catalyst used during curing process. The epoxy-bridged polysilsesquioxanes of epoxy-APTES precursor possesses the lowest coefficient of thermal expansion compared with the other two epoxy-bridged polyorganosiloxanes from mono-, and di-functional epoxy-bridged polyorganosiloxanes precursors. There is no obvious Tg observed in the epoxy-bridged polysilsesquioxanes of epoxy-APTES precursor from the analysis of TMA and DMA. 13C solid state NMR has been used to investigate the molecular motion behaviors of epoxy-bridged polyorganosiloxanes structures with respect to the changes in Tg and CTE. The (the relaxation time of 13C after the spin lock process) of the epoxy-bridged polysilsesquioxanes of epoxy-APTES precursor is longer than that of epoxy-APMDS precursor, which indicates that the molecular mobility of epoxy-bridged polysilsesquioxanes of epoxy-APTES is highly restricted due to the strong intermolecular interaction of nano hybrid network. 相似文献
Summary: The epoxy copolymers containing sulfone groups, diglycidyl ether of bisphenol‐A – Bisphenol‐S (DGEBA‐S) were synthesized by a hot‐melt method. The thermal properties of the epoxy systems initiated by two cationic latent catalysts, i.e., N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH), were investigated by using a dynamic DSC, DMA, and TGA. The mechanical properties were measured by single‐edge‐notched (SEN) beam fracture toughness tests. As a result, the thermal stability and mechanical interfacial properties of the DGEBA‐S/catalyst system were found to be higher than those of the DGEBA/catalyst. This was probably due to the fact that the introduction of sulfone groups with a polar nature to the main chain of the epoxy resins led to an improvement of thermal stability and toughness of the cured epoxy copolymers.
Conversion of the epoxy/catalyst systems as a function of curing temperature. 相似文献
Amine terminated poly(ether sulfone imide) (PESI) with various imide and ethersulfone contents but similar polymer molecular weights were blended with diglycidyletherbisphenol-A (DGEBA) and cured with diaminodiphenylsulfone (DDS). The imide group, a tertiary amine, is a catalyst of the curing reaction of DGEBA with DDS, but it is poorly compatible with uncured epoxy resin. The ethersulfone group is not a catalyst of the curing reaction of DGEBA with DDS, but it has a similar chemical structure as DDS and is compatible with epoxy resin while it is at a low degree of curing. Since PESIs used in this study had similar molecular weights, increasing imide content of PESI would reduce ethersulfone content. The influence of imide and ethersulfone contents of PESI on the phase separation and curing reaction of DGEBA/DDS/PESI blend was investigated using differential scanning calorimetry (DSC), time-resolved light scattering (TRLS), and polarized optical microscopy (POM). Though the imide group has a catalysis effect on the curing reaction of DGEBA with DDS, however, its poor compatibility with epoxy resin retards the curing reaction. Our experimental results revealed the morphology of the cured blends and the curing behavior was a compromise result of catalysis and compatibility of PESI with epoxy resin. 相似文献
The curing exotherm pattern is affected by the equivalent ratio of curing agent, boron trifluoride monoethylamine complex (BF3 · MEA), to epoxy resin. The diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) cures more slowly than the diglycidyl ether of bisphenol A (Epon 828). The glass transition temperatures (Tg's) of BF3 · MEA cured Epon 828 are increased with inceasing concentration of curing agent (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF3 · MEA (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF3 · MEA (0.0450 eq./epoxy eq.) cured Epon 828 and DGEBF are almost equivalent 43 and 44 kcal/mol, respectively. DGEBF when added to DGEBA improves the Tg and char yield with the BF3 · MEA curing system. The Tg of both resin systems can be increased by longer post cure, whereas the char yield does not appear to change significantly. No ester group formation is found for the BF3 · MEA-cured DGEBF, although this has been previously reported for the DGEBA system. The BF3 · MEA cure at 120°C is better than at 140°C because of vaporization and degradation of the curing agent at the higher temperature. The rapid gelation of the epoxy resin may be another reason for the lower degree of cure at high temperature. 相似文献
A polymer having high aromaticity and/or cyclic ring structures in the chain backbone usually gives high heat resistance and flame resistance. Five glycidyl ether-type epoxy resins are prepared from bisphenol A (DGEBA), 9,9-bis(4-hydroxyphenyl)fluorene (DGEBF), 3,6-dihydroxyspiro-[fluorene-9,9′-xanthane] (DGEFX), 10,10-bis(4-hydroxyphenyl) anthrone (DGEA), and 9,9,10,10-tetrakis(4-hydroxyphenyl)anthracene (TGETA) in order to study structure–thermal stability–flame resistance property relationships. In this study, trimethoxyboroxine (TMB) and diaminodiphenylsulfone (DDS) are employed as the curing agents. The char yield at 700°C under a nitrogen atmosphere and the glass transition temperature (Tg) for the uncured resins decrease according to the sequence TGETA > DGEFX > DGEA > DGEBF > DGEBA. The Tg values for these cured epoxy resins are DGEBA < DGEBF < DGEFX < DGEA. A Tg for the TGETA is not obtainable but would be expected to be the highest. The char yields at 700°C of these cured epoxy resins have the same trend as the uncured resins. DGEBF, DGEFX, DGEA, and TGETA added to the DGEBA system show increases in the char yield, Tg, and oxygen index with increasing concentration of these novel epoxy resins. 相似文献
The influence of the end groups of two liquid rubbers on curing kinetics, morphology, and hardness behavior of diglycidyl ether of bisphenol-A based epoxy resin (DGEBA) has been studied. The rubbers are silyl-dihydroxy terminated (PDMS-co-DPS-OH) and silyl-diglycidyl ether terminated (PDMS-DGE). Crosslinking reactions, investigated by shear rheometry, ranged 90–110 °C, using a constant concentration (5 phr) of liquid rubbers and 1,2-Diamino cyclohexane (1,2-DCH) as hardener agent. The gel time, tgel, of the neat epoxy significantly decreased when adding the elastomers, more so for the silyl-dihydroxy terminated elastomer; at 110 °C the reaction was nearly complete before rheological test started. The results suggest that the elastomers induced a catalytic effect on the curing reaction. Scanning electron microscopy revealed phase separation of the elastomer during the curing reaction with rubber domains about 5 μm size. However, the DGEBA/dihydroxy terminated elastomer composite cured at 110 °C exhibited a homogenous morphology, that is, the rapid reaction time would not allow for phase separation. Water contact angle tests evidenced either more hydrophilic (silyl-diglycidyl ether terminated rubber) or more hydrophobic (silyl-dihydroxy terminated rubber) behavior than the neat epoxy. The latter effect is attributed to the presence of aromatic rings in the backbone structure of PDMS-co-DPS-OH. Microindentation measurements show that the elastomers significantly reduced the hardness of the epoxy resin, the DGEBA/ether terminated composite exhibiting the lowest hardness values. Moreover, hardness increased as reaction temperature did, correlating with a reduction of microdomains size thus enabling the tuning of mechanical properties with reaction temperature. 相似文献