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T. Philip Gnanarajan A. Sultan Nasar N. Padmanabha Iyer Ganga Radhakrishnan 《Journal of polymer science. Part A, Polymer chemistry》2000,38(22):4032-4037
A set of poly(urethane‐imide)s were prepared using blocked Polyurethane (PU) prepolymer and pyromellitic dianhydride (PMDA). The PU prepolymer was prepared by the reaction of polyether glycol and 2,4‐tolylene diisocyanate, and end capped with N‐methyl aniline. The PU prepolymer was reacted with PMDA until the evolution of carbon dioxide ceased. The effect of tertiary amine catalysts, organo tin catalysts, solvents, and reaction temperature were studied and compared with the poly(urethane‐imide) prepared using phenol‐blocked PU prepolymer. N‐methyl aniline blocked PU prepolymer gave a higher molecular weight poly(urethane‐imide) at a lower reaction temperature in a shorter time. Amine catalysts were found to be more efficient than organo tin catalysts. The reaction was favorable in particular with N‐ethylmorpholine and diazabicyclo(2.2.2)octane (DABCO) as catalysts, and dimethylpropylene urea as a reaction medium. The poly(urethane‐imide)s were characterized by FTIR, GPC, TGA, and DSC analyses. The molecular weight decreased with an increase in reaction temperature. The thermal stability of the PU was found to increase by the introduction of imide component. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4032–4037, 2000 相似文献
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Alaa S. Abd‐El‐Aziz Leslie J. May Andrea L. Edel 《Macromolecular rapid communications》2000,21(9):598-602
Synthesis and characterization of new thermally stable polynorbornenes functionalized with pendent flexible side‐chains are reported. The flexible side‐chains with terminal hydroxy groups were synthesized via SNAr reactions of cyclopentadienyliron‐complexed chlorobenzenes with aliphatic diols. Condensation of these side‐chains with exo,endo‐5‐norbornene‐2‐carboxylic acid led to the formation of substituted monomers which were characterized using one‐ and two‐dimensional NMR techniques. Ring‐opening metathesis polymerization of these monomers yielded polynorbornenes with pendent side‐chains. 相似文献
989.
Woojung Ji Leslie S. Hamachi Anusree Natraj Nathan C. Flanders Rebecca
L. Li Lin X. Chen William R. Dichtel 《Chemical science》2021,12(48):16014
Mechanistic understanding into the formation and growth of imine-linked two-dimensional (2D) covalent organic frameworks (COFs) is needed to improve their materials quality and access larger crystallite sizes, both of which limit the promise of 2D COFs and 2D polymerization techniques. Here we report a previously unknown temperature-dependent depolymerization of colloidal 2D imine-linked COFs, which offers a new means to improve their crystallinity. 2D COF colloids form at room temperature but then depolymerize when their reaction mixtures are heated to 90 °C. As the solutions are cooled back to room temperature, the 2D COFs repolymerize and crystallize with improved crystallinity and porosity, as characterized by X-ray diffraction, infrared spectroscopy and N2 porosimetry. The evolution of COF crystallinity during the solvothermal depolymerization and repolymerization processes was characterized by in situ wide angle X-ray scattering, and the concentrations of free COF monomers as a function of temperature were quantified by variable temperature 1H NMR spectroscopy. The ability of a 2D COF to depolymerize under these conditions depends on both the identity of the COF and its initial materials quality. For one network formed at room temperature (TAPB-PDA COF), a first depolymerization process is nearly complete, and the repolymerization yields materials with dramatically enhanced crystallinity and surface area. Already recrystallized materials partially depolymerize upon heating their reaction mixtures a second time. A related 2D COF (TAPB-DMTA COF) forms initially with improved crystallinity compared to TAPB-PDA COF and then partially depolymerizes upon heating. These results suggest that both high materials quality and network-dependent properties, such as interlayer interaction strength, influence the extent to which 2D COFs resist depolymerization. These findings offer a new means to recrystallize or solvent anneal 2D COFs and may ultimately inform crystallization conditions for obtaining large-area imine-linked two-dimensional polymers from solution.Conditions for which imine-linked 2D COF polymerizations are temperature-sensitive are identified that enable a dissolution/repolymerization process akin to molecular recrystallization. 相似文献
990.
Mark Niemeyer Philip P. Power 《Angewandte Chemie (International ed. in English)》1998,37(9):1277-1279
A “one-legged thallium” is observed in the arylthallium(I ) compound 2,6-Trip2C6H3Tl (Trip=2,4,6-iPr3C6H2), which was synthesized from the corresponding organolithium compound and thallium chloride. X-ray structure analysis reveals that 2,6-Trip2C6H3Tl is monomeric in the solid state and contains a singly coordinated thallium atom (see space-filling model on the right). 相似文献