Accelerated solvent extraction (ASE) is applied for the
extraction of monomers and oligomers from polymeric
samples. Two polymers, nylon-6 and
poly(1,4-butylene
terephthalate), are selected as the model samples.
The
kinetics of mass transfer in ASE of polymeric samples are
discussed. The effects of various experimental parameters, such as temperature, pressure, static time, flow
rate, etc., on the ASE extraction efficiency are
investigated
systematically. Furthermore, some general guidelines
for
the optimization in ASE extraction of polymeric samples
are given. The extraction temperature and the type of
solvent used are found to be the most important parameters affecting the ASE extraction efficiency of polymeric
samples.
Numerous self-assembling molecules have been synthesized aiming at mimicking both the structural and dynamic properties found in living systems. Here we show the application of hydrogen/deuterium exchange (HDX) mass spectrometry (MS) to unravel the nanoscale organization and the structural dynamics of synthetic supramolecular polymers in water. We select benzene-1,3,5-tricarboxamide (BTA) derivatives that self-assemble in H2O to illustrate the strength of this technique for supramolecular polymers. The BTA structure has six exchangeable hydrogen atoms and we follow their exchange as a function of time after diluting the H2O solution with a 100-fold excess of D2O. The kinetic H/D exchange profiles reveal that these supramolecular polymers in water are dynamically diverse; a notion that has previously not been observed using other techniques. In addition, we report that small changes in the molecular structure can be used to control the dynamics of synthetic supramolecular polymers in water.
In biology, polymorphism is a well-known
phenomenon by which a
discrete biomacromolecule can adopt multiple specific conformations
in response to its environment. The controlled incorporation of polymorphism
into noncovalent aqueous assemblies of synthetic small molecules is
an important step toward the development of bioinspired responsive
materials. Herein, we report on a family of carboxylic acid functionalized
water-soluble benzene-1,3,5-tricarboxamides (BTAs) that self-assemble
in water to form one-dimensional fibers, membranes, and hollow nanotubes.
Interestingly, one of the BTAs with the optimized position of the
carboxylic group in the hydrophobic domain yields nanotubes that undergo
reversible temperature-dependent dynamic reorganizations. SAXS and
Cryo-TEM data show the formation of elongated, well-ordered nanotubes
at elevated temperatures. At these temperatures, increased dynamics,
as measured by hydrogen–deuterium exchange, provide enough
flexibility to the system to form well-defined nanotube structures
with apparently defect-free tube walls. Without this flexibility,
the assemblies are frozen into a variety of structures that are very
similar at the supramolecular level, but less defined at the mesoscopic
level.
State-of-the-art techniques for the mass spectrometric characterization of synthetic polymers have been applied to functional poly(methyl methacrylate), synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. The polymers were first separated effectively according to functionality by liquid chromatography (LC) at the critical conditions (i.e., almost no influence of molecular weight on retention). The separated polymers were characterized off-line by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and both off-line and on-line by LC-electrospray-ionization-quadrupole-TOF-MS (LC-ESI-QTOF- MS). The on-line ESI experiments confirmed a clear baseline separation of the hydroxyl-functional prepolymers according to the number of hydroxyl groups. Labile end groups of PMMA, such as the dithioester group, were lost in the MALDI-TOF-MS experiments, while they were observed intact in the ESI-QTOF-MS spectra. This indicates that in the present case ESI is a much softer ionization technique than is MALDI. The ESI-MS experiments provided direct evidence that the RAFT polymers still exhibited living characteristics in the form of the dithio moiety.
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