8 research outputs found
Ionically Cross-Linked Shape Memory Polypropylene
An ionically cross-linked
syndiotactic polypropylene (ix-sPP) was
synthesized by subsequent grafting of maleic anhydride (MA) to the
polymer followed by compounding with ZnO. The polymer network was
investigated by X-ray scattering, transmission electron microscopy,
and various thermal and mechanical analyses. The optimized polymer
network with 1 wt % MA grafting and 20 wt % ZnO exhibits a crystal
melting temperature of 125 °C and rubber elastic behavior up
to 203 °C and becomes a viscous polymer melt at higher temperatures.
This process is fully reversible. Further, ix-sPP is an exceptionally
stable ionic polymer network that matches the stability of the respective
covalently cross-linked polymer in terms of shape memory properties.
Additionally, the ionic cross-linking affords thermoplastic processability
and shape memory assisted self-healing
Solvent-Sensitive Reversible Stress-Response of Shape Memory Natural Rubber
We
found that constrained shape memory natural rubber (SMNR) generates
mechanical stress when exposed to solvent vapor. When the solvent
vapor is removed, the material reprograms itself. This process is
reversible and the stress answer is proportional to the solvent vapor
concentration. Further, the stress answer is specific to the solvent
Programming of Shape Memory Natural Rubber for Near-Discrete Shape Transitions
Typical
shape memory polymers are hot-programmed and show a shape
transition over a broad temperature range of 10 K and more. Cold-programmed
shape memory natural rubber (SMNR) recovers more than 80% of its original
shape within 1 K. The trigger point can be increased upon aging the
stretched SMNR over several weeks without losing the narrow trigger
range. This process can be accelerated by treatment of the stretched
SMNR with nonaffine solvent vapors. Affine solvent vapors of low concentrations
afford higher trigger points than that achieved by aging. This way,
even higher cross-linked natural rubber can be cold-programmed
Impact of Functional Satellite Groups on the Antimicrobial Activity and Hemocompatibility of Telechelic Poly(2-methyloxazoline)s
Polyoxazolines with a biocidal quarternary ammonium end-group
are
potent biocides. Interestingly, the antimicrobial activity of the
whole macromolecule is controlled by the nature of the group at the
distal end. These nonreactive groups are usually introduced via the
initiator. Here we present a study with a series of polymethyloxazolines
with varying satellite groups introduced upon termination of the polymerization
reaction. This allowed us to introduce a series of functional satellites,
including hydroxy, primary amino, and double-bond-containing groups.
The resulting telechelic polyoxazolines were explored regarding their
antimicrobial activity and toxicity. It was found that the functional
satellite groups greatly controlled the minimal inhibitory concentrations
against the bacteria <i>Staphylococcus aureus</i> and <i>Escherichia coli</i> in a range of 10 to 2500 ppm. Surprisingly,
the satellite groups also controlled the hemotoxicity but in a different
way than the antimicrobial efficiency
Cross-Linking of a Hydrophilic, Antimicrobial Polycation toward a Fast-Swelling, Antimicrobial Superabsorber and Interpenetrating Hydrogel Networks with Long Lasting Antimicrobial Properties
A hemocompatible,
antimicrobial 3,4en-ionene (PBI) derived by polyaddition of <i>trans</i>-1,4-dibromo-2-butene and <i>N</i>,<i>N</i>,<i>N</i>â˛,<i>N</i>â˛-tetramethyl-1,3-propanediamine
was cross-linked via its bromine end groups using trisÂ(2-aminoethyl)Âamine
(TREN) to form a fast-swelling, antimicrobial superabsorber. This
superabsorber is taking up the 30-fold of its weight in 60 s and the
granulated material is taking up 96-fold of its weight forming a hydrogel.
It fully prevents growth of the bacterium <i>Staphylococcus aureus</i>. The PBI network was swollen with 2-hydroxyethyl acrylate and glycerol
dimethacrylate followed by photopolymerization to form an interpenetrating
hydrogel (IPH) with varying PBI content in the range of 2.0 to 7.8
wt %. The nanophasic structure of the IPH was confirmed by atomic
force microscopy and transmission electron microscopy. The bacterial
cells of the nosocomial strains <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, and <i>Pseudomonas aeruginosa</i> are killed on the IPH even at the lowest PBI concentration. The
antimicrobial activity was retained after washing the hydrogels for
up to 4 weeks. The IPHs show minor leaching of PBI far below its antimicrobial
active concentration using a new quantitative test for PBI detection
in solution. This leaching was shown to be insufficient to form an
inhibition zone and killing bacterial cells in the surroundings of
the IPH
Conjugation of Ciprofloxacin with Poly(2-oxazoline)s and Polyethylene Glycol via End Groups
The
antibiotic ciprofloxacin (CIP) was covalently attached to the
chain end of polyÂ(2-methyloxazoline) (PMOx), polyÂ(2-ethyloxazoline)
(PEtOx), and polyethylene glycol (PEG), and the antimicrobial activity
of these conjugates was tested for <i>Staphylococcus aureus</i>, <i>Streptococcus mutans</i>, <i>Escherichia coli</i>, <i>Pseudomonas aeruginosa</i>, and <i>Kleisella
pneumoniae.</i> Chemical structures of the conjugates were proven
by <sup>1</sup>H NMR and electron spray ionization mass spectrometry.
The direct coupling of PMOx and CIP resulted in low antimicrobial
activity. The coupling via a spacer afforded molecular weight dependent
activity with a molar minimal inhibitory concentration that is even
higher than that of the pristine CIP. The antimicrobial activity of
the conjugates increases in the order of PMOx < PEtOx < PEG.
Conjugation of CIP and a quaternary ammonium compound via PMOx did
not result in higher activity, indicating no satellite group or synergistic
effect of the different biocidal end groups
Insights into the Kinetics of the Resistance Formation of Bacteria against Ciprofloxacin Poly(2-methyl-2-oxazoline) Conjugates
The
influence on the resistance formation of polymers attached
to antibiotics has rarely been investigated. In this study, ciprofloxacin
(CIP) was conjugated to polyÂ(2-methyl-2-oxazoline)Âs with an ethylene
diamine end group (Me-PMOx<sub>28</sub>-EDA) via two different spacers
(CIP modified with Îą,Îąâ˛-dichloro-<i>p</i>-xyleneî¸xCIP, CIP modified with chloroacetyl chlorideî¸eCIP).
The antibacterial activity of the conjugates against a number of bacterial
strains shows a great dependence on the nature of the spacer. The
Me-PMOx<sub>39</sub>-EDA-eCIP, containing a potentially cleavable
linker, does not exhibit a molecular weight dependence on antibacterial
activity in contrast to Me-PMOx<sub>27</sub>-EDA-xCIP. The resistance
formation of both conjugates against Staphylococcus
aureus and Escherichia coli was investigated. Both conjugates showed the potential to significantly
delay the formation of resistant bacteria compared to the unmodified
CIP. Closer inspection of a possible resistance mechanism by genome
sequencing of the topoisomerase IV region of resistant S. aureus revealed that this bacterium mutates at
the same position when building up resistance to CIP and to Me-PMOx<sub>27</sub>-EDA-xCIP. However, the S. aureus cells that became resistant against the polymer conjugate are fully
susceptible to CIP. Thus, conjugation of CIP with PMOx seems to alter
the resistance mechanism
Amphiphilic Polymer Conetworks Based on End-Linked âCore-Firstâ Star Block Copolymers: Structure Formation with Long-Range Order
Amphiphilic polymer conetworks are
cross-linked polymers that swell
both in water and in organic solvents and can phase separate on the
nanoscale in the bulk or in selective solvents. To date, however,
this phase separation has only been reported with short-range order,
characterized by disordered morphologies. We now report the first
example of amphiphilic polymer conetworks, based on end-linked âcore-firstâ
star block copolymers, that form a lamellar phase with long-range
order. These mesoscopically ordered systems can be produced in a simple
fashion and exhibit significantly improved mechanical properties