5 research outputs found
Synthesis and Thermal Curing of Benzoxazine Functionalized Polyurethanes
Benzoxazine
(BOX) functionalized polyurethanes (PU) are introduced
to provide a conceptually new thermal curing mechanism for polyurethanes.
3,4-Dihydro-3-methyl-2<i>H</i>-1,3-benzoxazine (P-m) was
carefully oligomerized through thermal treatment. In a straightforward
synthesis the newly formed hydroxyl groups are used for end-capping
reactions with isocyanate-terminated polyurethane prepolymers. The
isocyanate reactive hydroxyl content (IRH) of the benzoxazine oligomer
was investigated in detail via <sup>1</sup>H NMR spectroscopy, HPLC-MS,
indirect potentiometric titration in various solvents, and comparison
with model substances and found to be strongly influenced by hydrogen
bonding. The corresponding polyurethane/benzoxazine hybrid materials
(PU/BOX) can cross-link at elevated temperatures and do not suffer
from shelf-life issues or outgassing of blocked isocyanates. The thermally
activated curing reaction was investigated via rheology and DSC. Significant
improvements over state-of-the-art systems based on phenol-capped
PU prepolymers are shorter curing times, increased moduli, and drastically
increased glass transition temperatures
pH-Sensitive Nanocapsules with Barrier Properties: Fragrance Encapsulation and Controlled Release
A facile synthesis method for polymer
nanocapsules with high diffusion
barrier and stimuli-responsive release properties is presented. The
highly volatile fragrance α-pinene was used as hydrophobic model
compound for the encapsulation process, which is based on a miniemulsion-analogous
free radical polymerization process. The copolymer composition was
systematically varied, and increasing contents of methacrylic acid
as functional monomer in combination with high glass transition temperatures
enabled unusually high encapsulation efficiencies of ≥90% for
capsules with <i>z</i>-average diameters of <200 nm.
Temperature and pH change can be used as trigger to open the capsules,
and the release kinetics can be tailored depending on the polymer
shell composition. In contrast to more frequently applied barrier
microcapsules the nanocapsules provide drastically improved colloidal
stabilities. Furthermore, the barrier nanocapsule approach is principally
not restricted to fragrances and is expected to be compatible with
other hydrophobic actives