Novel fluorescent polyimides (PIs) were prepared from a new diamine, 4-(4-(4-amino-2-(4,5-diphenyl-1H-imidazol-2-yl) phenoxy)phenoxy)-3-(4,5-diphenyl-1H-imidazol-2-yl)benzenamine, and three tetracarboxylic dianhydrides. The new symmetrical diamine was successfully synthesized by the nucleophilic substitution reaction of hydroquinone with 2-(2-chloro-5-nitrophenyl)-4, 5-diphenyl-1H-imidazole (I). The PIs synthesized here are amorphous and soluble in polar aprotic solvents and demonstrate the ability to form films; their inherent viscosities ranged from 43 to 82 ml g À1 . The PIs had suitable thermal stability and relatively high T g values (245-274 1C), 10% weight loss temperatures in excess of 500 1C and char yields at 600 1C in air up to 62%. The PIs show emission in the solid state and in dilute (0.20 g per 100 ml) N,N-dimethyl acetamide solution at 431-464 nm with photoluminescence (PL) quantum yields in the range of 11-25%. The chemiluminescence activity of PIs in the presence of peroxyoxalate was also investigated. Polymer Journal (2010) 42, 648-656; doi:10.1038/pj.2010.57; published online 30 June 2010Keywords: fluorescent; polyimides; solubility; synthesis; thermal stability INTRODUCTION Aromatic polyimides (Pls) generally possess excellent thermal, mechanical, electrical and chemical properties. Therefore, they have been used in many applications such as electronics, coatings and adhesives, composite materials and membranes. 1-3 However, these polymers are difficult to process because of their high glass transition temperatures (T g ) or high melting temperatures (T m ) and their limited solubility in organic solvents. 4,5 Considerable efforts have been made to improve the solubility and melting processability of PIs while maintaining their desired properties. 6-8 Significant synthetic efforts in the area of high-performance polymers have been focused on improving the processability and solubility of PIs through the design and synthesis of new monomers. Various structural modifications can be made to the PI backbone to modify the polymer properties, such as insertion of flexible linkages on the main chain, 9-13 use of noncoplanar 14 or asymmetric monomers [15][16][17][18][19] and incorporation of pendant groups in the polymer backbone, 20-29 with results including lower interchain interactions or a reduced polymer chain stiffness. Depending on the type and amount of structural modifications, melting temperatures can be lowered and solubility improved, resulting in processable materials. Introducing bulky pendant substituents and heteroaromatic rings into PI chains has been considered to be an efficient method to provide not only enhanced solubility but also good thermal and thermo-oxidative stability. 22 The rigidity based on the
Epoxy-silica nanocomposites were obtained from directly blending diglycidylether of bisphenol-A (DGEBA)-based epoxy and nanoscale silica (NS) and then curing with 4,4 0 -diaminodiphenylamine (DDA). The effect of amount of nanosilica (NS) particles as catalyst on the mechanism and kinetic parameters of cure reaction of DGEBA/DDA system was studied. The kinetics parameters were obtained from nonisothermal differential scanning calorimeter (DSC) data using the Kissinger and Ozawa equations. The exothermic peak was shifted toward lower temperatures in DGEBA/DDA/NS system with increasing the amount of nanoslica particles. However, the existence of NS particles with hydroxyl groups in the structure in the mixture of DGEBA/DDA catalyzes the cure reaction and increases the rate constant. The activation energy of cure reaction of DGEBA/DDA system obtained from two methods were in good agreement, and showed a decrease when NS particles were present in the mixture. The mechanism of reaction of DGEBA with DDA was carried out by isothermal curing in the oven at 1308C and measuring the disappearance peak of epoxide group at 916 cm À1 using FTIR. The diffusive behavior of two systems was investigated during water sorption at 258C and the experimental results fitted well to Fick's law. Diffusion coefficient of cured sample from DGEBA/DDA/10% NS blend decreased in comparison with the sample without NS particles.
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