9 research outputs found
Versatile Postmodification of Conjugated Microporous Polymers Using Thiol-yne Chemistry
Radical thiol-yne chemistry is used for the modification
of microporous
networks with aliphatic alcohols. The degree of functionalization
can be tuned by varying the reacted amount of thiol. Porosity analysis
indicates that the microporosity can be preserved within a certain
range, however, a decrease in pore size is observed
Phenolic Naphthoxazines as Curing Promoters for Benzoxazines
The
effect of phenolic hydroxyl bearing naphthoxazines as catalysts for
the ring-opening polymerization (ROP) of simple 1,3-benzoxazines was
investigated. The latent catalytic role of napthoxazines in the curing
process of the mixtures was demonstrated by DSC and FT-IR investigations.
It was found that phenolic naphthoxazines cause clear reduction in
ROP temperature, particularly when electron-withdrawing groups are
attached and an onset ROP temperature as low as 169 °C is attained.
Thermal properties of the final polymers were also analyzed, and no
significant effect of naphthoxazines on the thermal stability of the
cured polybenzoxazines was observed
Benzoxazine-Based Thermosets with Autonomous Self-Healing Ability
A self-healing
strategy for polyÂ(propylene oxide)Âs bearing benzoxazine units (PPO-Benz)
through supramolecular attractions is described. PolyÂ(propylene oxide)
bisamine (PPO) with a molecular wieght of 2000 Da was reacted with
formaldehyde and bisphenol A to yield desired PPO-Benz with 12 360
Da. The cross-linked polymer films were then prepared by solvent casting
of suitable compositions of PPO-Benz and carboxlic acid containing
benzoxazine monomer (Carb-Benz) in chloroform followed by thermal
ring-opening reaction of benzoxazine groups at 200 °C. Thermal
curing and thermal stability of the film and final products were investigated.
It was demonstrated that the self-healing capacity of the films was
improved by employing Carb-Benz in the formulation
Hydroxyl Functional Polybenzoxazine Precursor as a Versatile Platform for Post-Polymer Modifications
A new
postmodification approach for the benzoxazine based thermosets is
described. The approach involves attachment of hydroxyl functional
groups to the main-chain polybenzoxazine precursors through monomer
synthesis method. Hydroxyl functional polybenzoxazine precursor was
successfully synthesized by using appropriate combinations of hexamethylene
diamine with hydroxy functional diamine, namely 1,3-diaminopropan-2-ol
in conjunction with bisphenol A and paraformaldehyde, and characterized.
Modification reactions were performed by simple esterification reactions
of hydroxyl groups with 2-bromopropanoyl chloride and methacryloyl
chloride to yield ATRP macroinitiator and methacrylate containing
polybenzoxazine precursors, respectively. ATRP macroinitiator was
used to obtain polystyrene grafted polybenzoxazine precursors and
photopolymerization of methacrylate groups was carried out successfully.
The benzoxazine groups present in the all structures were shown to
readily undergo thermally activated ring-opening polymerization in
the absence of an added catalyst forming cross-linked networks. The
thermal stability of the cured polymers was investigated and compared
to that of a classical polybenzoxazine precursor
Teaching New Tricks to an Old Indicator: pH-Switchable, Photoactive Microporous Polymer Networks from Phenolphthalein with Tunable CO<sub>2</sub> Adsorption Power
Switchable, organic microporous networks were synthesized
by Sonogashira
coupling of tetrabromophenolphthalein with 1,4-diethynylenebenzene
using optimized reaction conditions. The resulting networks are microporous
and have specific surface areas exceeding 800 m<sup>2</sup> g<sup>–1</sup>. The microporosity and the pore polarity are sensitive
to the pH value as evidenced by nitrogen and carbon dioxide physisorption
experiments. The switching between the open and closed form of the
lactone ring is reversible, but some porosity is lost throughout the
process. The colored, alkaline salts of these networks are photochemically
active, as shown by the effective heterogeneous photosensitization
of the photopolymerization of methyl methacrylate with visible light
Post-Modification of Polybutadienes by Photoinduced Hydrogen Abstraction from Benzoxazines and Their Thermally Activated Curing
Side-chain benzoxazine functional
polybutadienes was synthesized by photoinduced hydrogen abstraction
process. First, photoactive benzoxazines having both chromophoric
carbonyl and hydrogen donating sites were synthesized using vanillin
or 4-hydroxybenzophenone by conventional benzoxazine synthesis methodology.
Irradiation of neat polybutadiene (PB) in the presence of the corresponding
benzoxazines, namely benzophenone benzoxazine (BPh-ptol) and vanillin
benzoxazine (Van-a) under 300–350 nm light, gave PBs with approximately
4–5 benzoxazine units per chain. Successful modification was
confirmed by the spectral and thermal investigations. It is demonstrated
that PBs attached with benzoxazines undergo thermally activated curing
without any catalyst to form polybutadiene thermoset with high char
yield
Combining Elemental Sulfur with Polybenzoxazines via Inverse Vulcanization
A novel strategy to obtain sulfur-rich
polybenzoxazine copolymers
by reacting allyl functional benzoxazine (BA-ala) and elemental sulfur
was described. Simultaneous inverse vulcanization and ring-opening
reactions of benzoxazine generated soluble copolymers in specific
feed ratios. Parameters such as monomer structure and feed ratios
on the polymerization were studied. The thermal stability of the copolymers
was investigated and compared to that of polybenzoxazines derived
from neat BA-ala by using thermogravimetric analysis and differential
scanning calorimetry. The surface properties of the materials as examined
by scanning electron microscopy confirmed that elemental sulfur and
benzoxazine copolymers can be produced without a phase separation
at the micrometer level. Moreover, a sponge-like insoluble macroporous
polybenzoxazine networks was obtained at the 20 wt % feed ratio of
sulfur
Preparation of microporous organic polymer through Schiff base chemistry and its potential application
<div><p>The uniform microporous organic polymer (MOP) was obtained in one-pot and one-step polymerization process through Schiff base chemistry under thermal conditions. The obtained anthraquinone–melamine based MOP (AM-MOP) displays high surface area (215 m<sup>2</sup>/g). AM-MOP was manually filled into a column with high pressure and used as packing material in the high-performance liquid chromatographic applications. The analysis of compounds such as polycyclic aromatic hydrocarbons, pesticides, flavonoids, and phenolic acids was performed to display a possible application by using AM-MOP packed column. Compared to the commercial columns, AM-MOP exhibits better selectivity factor and column efficiency arising from its strong <i>π</i>–<i>π</i> interaction activity. Furthermore, it has similar solvent uptake in both polar and nonpolar media, which explains good compatibility of the material with all mobile phases, from acetonitrile to methanol and water.</p></div
Mesoporous Graphitic Carbon Nitride as a Heterogeneous Visible Light Photoinitiator for Radical Polymerization
The use mesoporous graphitic carbon nitride (mpg-C<sub>3</sub>N<sub>4</sub>) in conjunction with tertiary amines as initiators
in visible-light-induced
free radical polymerization is described. The initiation mechanism
involves photoinduced free radical generation by scavenging holes
with amines and subsequent hydrogen abstraction. The efficiency of
the photoinitiation is controlled by the nature of the amines and
specific surface area of the carbon nitride powder. Apparently, amines
with higher basicity and available hydrogens provide more favorable
conditions for the photoinitiation process. Due to its heterogeneous
nature, the photoinitiator preserves its photoinitiation activity
after the polymerization and can easily be separated and used for
further polymerizations