Two new chemically stable functional crystalline covalent organic frameworkds (COFs) (Tp-Azo and Tp-Stb) were synthesized using the Schiff base reaction between triformylphloroglucinol (Tp) and 4,4'-azodianiline (Azo) or 4,4'-diaminostilbene (Stb), respectively. Both COFs show the expected keto-enamine form, and high stability toward boiling water, strong acidic, and basic media. H3PO4 doping in Tp-Azo leads to immobilization of the acid within the porous framework, which facilitates proton conduction in both the hydrous (σ = 9.9 × 10(-4) S cm(-1)) and anhydrous state (σ = 6.7 × 10(-5) S cm(-1)). This report constitutes the first emergence of COFs as proton conducting materials.
We have reported the use of carboxylate-alumoxanes as efficient nucleating agents for isotactic polypropylene (iPP) with a possible structural correlation to the nucleation efficiency. The unique, butterfly-like structure of carboxylate-alumoxanes correlates well with the nucleation characteristics of iPP and, for the first time, the impact of a thermally induced, crystalline transition of carboxylate-alumoxanes, which alters neither the structural conformation nor the nucleation efficiency of the transformed material, is demonstrated.
Carboxylate–alumoxane derived
from p-n-alkylbenzoic
acids, where n-alkyl group changes from 2 to 8 carbon
atoms, exhibits dual nucleating ability and nucleates isotactic polypropylene
(iPP) into predominantly in the β-phase under specific conditions.
The selectivity of the β-phase nucleation depends on the concentration
of the nucleating agent, end melting temperature and cooling rate.
The β-phase obtained from p-n-alkylbenzoate–alumoxanes
is compared with the β-phase obtained from calcium pimelate
(CaP), an efficient β-phase selective nucleating agent, using
the results from DSC, WAXS, and SAXS analysis. The lamellar morphology
of iPP nucleated with different nucleating agents crystallized at
different crystallization temperatures (T
C) under controlled nonisothermal conditions are evaluated using SAXS
analysis. The long period increases with increasing crystallization
temperature and the long period of the β-phase is always larger
than that of the α-phase for a given crystallization temperature.
Furthermore, the variation of long period with crystallization temperature
clearly brings out two crystallization temperature ranges; the low
temperature range and the high temperature range. However, the β-phase
shows a lower changeover temperature compared to that of the α-phase.
The one-dimensional correlation analysis of the β-phase shows
that the thickness of the crystal lamellae (lc) increases
with T
C and exhibits the low and high
crystallization temperature ranges, while the thickness of the amorphous
layer (la) more or less remains constant. In-situ high temperature WAXS studies capture the β-phase
to the α-phase transition and the transformed material correlates
well with the lamellar thickness of the β-phase. The morphological
difference between the α- and the β-phases are discussed
and attributed to the differences in the impact properties and the
melting temperature. This study clearly demonstrates that the lamellar
morphology mainly depends on the T
C and
not on the nature of the nucleating agents.
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