Electrospun ionic nonwovens are obtained by green electrospinning of aqueous dispersions. The resulting nonwovens are termed as chameleon nonwovens since their surface properties can be tailored in a large variety by coating of different functionalities following the protocol of the layer-bylayer process (LBL). The dimensional stability of the electrospun fi bers in the chameleon nonwovens is achieved by photo-cross-linking after electrospinning and thereby overcoming the repulsive forces of the ionic moieties in the fi bers. Depending on the nature of the ionic moieties different materials are coated by LBL including dyes, antibacterial materials, silver, and gold nanoparticles. Enhanced coating effi ciency for coating of metal nanoparticles is observed when the chameleon nonwovens were precoated by a polyelectrolyte.
Bisphenol A diglycidyl ether (BADGE)
is cured thermally using phthalic
acid anhydride (PhA) or hexahydrophthalic anhydride (HHPA) as hardener
in the presence of different protected N-heterocyclic
carbenes (NHCs), from which the catalytically active NHCs are generated
in situ upon heating. It is found that the curing reactions proceed
in a well-defined manner, delivering highly cross-linked, high-T
g-thermosets using low catalyst loadings (0.1–1
mol % of NHC precursor). The polymerizations can be conducted under
air without loss of activity, employing mild curing temperatures (120–160
°C) and short reaction times. By contrast, at room temperature,
polymerizations proceed only very slowly and the mixtures remain processable
for weeks, enabling formation of a true single-component composition
suitable for applications where large processing windows or storage
are required. The curing process was followed in situ by DSC as well
as by rheological measurements. On the basis of these observations,
the structure of the NHC precursor is correlated with its polymerization
activity with regard to latency, temperature profile and polymerization
kinetics. The robust and fully homogeneous system consisting of the
protected NHC, BADGE, and HHPA was successfully tuned both in terms
of activity and pot life by choosing the appropriate protected NHC
out of 12 different precatalysts. The most rapid polymerization was
effected by N,N′-bis(2,4-dimethoxyphenyl-)tetrahydropyrimidinium-2-carboxylate
(6-OMe-CO
2
), while a dimeric
zinc-based NHC-complex (6-Mes-ZnCl
2
) displayed the longest pot times.
Given
their increasing importance in a variety of applications,
the preparation of carbon fibers with well-defined chemical structures
and innocuous byproducts has garnered a growing interest over the
past decade. We report the preparation of medium molecular weight
poly(methyl vinyl ketone) (PMVK) as a potential carbon fiber precursor
material which can easily undergo carbonization via the well-known,
acid-catalyzed aldol condensation with water as a sole byproduct.
Rheological studies further show that PMVK (MW ∼ 50 kg/mol)
exhibits excellent physical and thermal properties for the spinning
of single and multifilament fibers and easily produces carbon yields
of 25% at temperatures as low as 250 °C. Analysis of the carbonized
product also suggests a more defect-free structure than commercially
available carbon fibers.
Copolymers of MMA, BA, and MABP are prepared by radical emulsion polymerization in water. As a result aqueous dispersions of these copolymers are obtained with particle sizes around 60–120 nm. After addition of some PVA the dispersions are electrospun. The resulting fibers display different morphologies depending on the copolymer composition. Inter‐ and intra‐particle cross‐linking is achieved by photo‐cross‐linking induced by the MABP moieties yielding fibers with good thermomechanical properties depending on the content of MABP. With this approach, thermomechanically stable electrospun fibers with smooth surface structure can be obtained by electrospinning from water.
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