Poly(Urethane-Acrylate) Aerogels via Radical Polymerization of Dendritic Urethane-Acrylate Monomers.
ABSTRACT: The purpose of this work was to investigate the effect of multifunctionality on material properties of synthetic polymer aerogels. For this purpose, we present the synthesis and characterization of monolithic dendritic-type urethane-acrylate monomers based on an aliphatic/flexible (Desmodur N3300), or an aromatic/rigid (Desmodur RE) triisocyanate core. The terminal acrylate groups (three at the tip of each of the three branches, nine in total) were polymerized with 2,2'-azobis(isobutyronitrile) (AIBN) via free radical chemistry. The resulting wet-gels were dried with supercritical fluid (SCF) CO?. Aerogels were characterized with ATR-FTIR and solid-state 13C NMR. The porous network was probed with N?-sorption and scanning electron microscopy (SEM). The thermal stability of aerogels was studied with thermogravimetric analysis (TGA). Most aerogels were macroporous materials (porosity > 80%), with high thermal stability (up to 300 °C). Aerogels were softer at low monomer concentrations and more rigid at higher concentrations. The material properties were compared with those of analogous aerogels bearing only one acrylate moiety at the tip of each branch and the same cores, and with those of analogous aerogels bearing norbornene instead of acrylate moieties. The nine-terminal acrylate-based monomers of this study caused rapid decrease of the solubility of the growing polymer and made possible aerogels with much smaller particles and much higher surface areas. For the first time, aliphatic/flexible triisocyanate-based materials could be made with similar properties in terms of particle size and surface areas to their aromatic/rigid analogues. Finally, it was found that with monomers with a high number of crosslinkable groups, material properties are determined by multifunctionality and thus aerogels based on 9-acrylate- and 9-norbornene-terminated monomers were similar. Materials with aromatic cores are carbonizable with satisfactory yields (20?30% w/w) to mostly microporous materials (BET surface areas: 640?740 m² g-1; micropore surface areas: 360?430 m² g-1).
Project description:We report the synthesis and characterization of synthetic polymer aerogels based on dendritic-type urethane-norbornene monomers. The core of those monomers is based either on an aromatic/rigid (TIPM/Desmodur RE), or an aliphatic/flexible (Desmodur N3300) triisocyanate. The terminal norbornene groups (three at the tip of each of the three branches) were polymerized via ROMP using the inexpensive 1st generation Grubbs catalyst. The polymerization/gelation conditions were optimized by varying the amount of the catalyst. The resulting wet-gels were dried either from pentane under ambient pressure at 50 °C, or from t-butanol via freeze-drying, or by using supercritical fluid (SCF) CO?. Monomers were characterized with high resolution mass spectrometry (HRMS), ¹H- and solid-state 13C-NMR. Aerogels were characterized with ATR-FTIR and solid-state 13C-NMR. The porous network was probed with N?-sorption and SEM. The thermal stability of monomers and aerogels was studied with TGA, which also provides evidence for the number of norbornene groups that reacted via ROMP. At low densities (<0.1 g cm?3) all aerogels were highly porous (porosity > 90%), mostly macroporous materials; aerogels based on the aliphatic/flexible core were fragile, whereas aerogels containing the aromatic/rigid core were plastic, and at even lower densities (0.03 g cm?3) foamy. At higher densities (0.2?0.7 g cm?3) all materials were stiff, strong, and hard. At low monomer concentrations all aerogels consisted of discrete primary particles that formed spherical secondary aggregates. At higher monomer concentrations the structure consisted of fused particles with the size of the previous secondary aggregates, due to the low solubility of the developing polymer, which phase-separated and formed a primary particle network. Same-size fused aggregates were observed for both aliphatic and aromatic triisocyanate-derived aerogels, leading to the conclusion that it is not the aliphatic or aromatic core that determines phase separation, but rather the solubility of the polymeric backbone (polynorbornene) that is in both cases the same. The material properties were compared to those of analogous aerogels bearing only one norbornene moiety at the tip of each branch deriving from the same cores.
Project description:Development of photocatalysts (PCs) with diverse properties has been essential in the advancement of organocatalyzed atom transfer radical polymerization (O-ATRP). Dimethyl dihydroacridines are presented here as a new family of organic PCs, for the first time enabling controlled polymerization of challenging acrylate monomers by O-ATRP. Structure-property relationships for seven PCs are established, demonstrating tunable photochemical and electrochemical properties, and accessing a strongly oxidizing <sup>2</sup> PC<sup>.+</sup> intermediate for efficient deactivation. In O-ATRP, the combination of PC, implementation of continuous-flow reactors, and promotion of deactivation through addition of LiBr are critical to producing well-defined acrylate polymers with dispersities as low as 1.12. The utility of this approach is established through demonstration of the oxygen-tolerance of the system and application to diverse acrylate monomers, including the synthesis of well-defined di- and triblock copolymers.
Project description:A type of grafted acrylate copolymer resins, containing 3-oxo-N-allyl-1,2-benzisothiazole-2(3H)-carboxamide monomer and heterocyclic monomers, was synthesized through the copolymeri- zation of methyl methacrylate (MMA) and butyl acrylate (BA) with functional monomers. The structures of the monomers and copolymers were validated by infrared (IR) and <sup>1</sup> H nuclear magnetic resonance (NMR) spectroscopies. The inhibitory activities of the copolymers on algae, bacteria, and barnacle larvae were measured, and the antifouling potencies against marine macrofouling organisms were investigated. The results showed that the grafted resin had significant inhibitory effects on the growth of three marine algae (Isochrysis galbana, Nannochloropsisoculata, and Chlorella pyrenoidosa), and three bacteria (Vibrio coralliilyticus, Staphylococcus aureus,and Vibrio parahaemolyticus). The target copolymers also showed excellent inhibition of the survival of barnacle larvae. Additionally, the release rate of the antifoulant and the results of the marine field tests indicated that the grafted copolymers had outstanding antifouling potency against the attachment of marine macrofouling organisms.
Project description:Polyurea-crosslinked Ca-alginate (X-Ca-alginate) aerogel beads (diameter: 3.3 mm) were evaluated as adsorbents of metal ions, organic solvents, and oils. They were prepared via reaction of an aromatic triisocyanate (Desmodur RE) with pre-formed Ca-alginate wet gels and consisted of 54% polyurea and 2% calcium. X-Ca-alginate aerogels are hydrophobic nanoporous materials (90% v/v porosity), with a high BET surface area (459 m<sup>2</sup>/g<sup>-1</sup>), and adsorb Pb<sup>II</sup> not only from ultrapure water (29 mg/g<sup>-1</sup>) but also from seawater (13 mg/g<sup>-1</sup>) with high selectivity. The adsorption mechanism involves replacement of Ca<sup>II</sup> by Pb<sup>II</sup> ions coordinated to the carboxylate groups of the alginate backbone. After treatment with a Na<sub>2</sub>EDTA solution, the beads can be reused, without significant loss of activity for at least two times. X-Ca-alginate aerogels can also uptake organic solvents and oil from seawater; the volume of the adsorbate can be as high as the total pore volume of the aerogel (6.0 mL/g<sup>-1</sup>), and the absorption is complete within seconds. X-Ca alginate aerogels are suitable for the decontamination of aquatic environments from a broader range of inorganic and organic pollutants.
Project description:When designing hydrogels for tissue regeneration, differences in polymerization mechanism and network structure have the potential to impact cellular behavior. Poly(ethylene glycol) hydrogels were formed by free-radical photopolymerization of acrylates (chain-growth) or thiol-norbornenes (step-growth) to investigate the impact of hydrogel system (polymerization mechanism and network structure) on the development of engineered tissue. Bovine chondrocytes were encapsulated in hydrogels and cultured under free swelling or dynamic compressive loading. In the acrylate system immediately after encapsulation chondrocytes exhibited high levels of intracellular ROS concomitant with a reduction in hydrogel compressive modulus and higher variability in cell deformation upon compressive strain; findings that were not observed in the thiol-norbornene system. Long-term the quantity of sulfated glycosaminoglycans and total collagen was greater in the acrylate system, but the quality resembled that of hypertrophic cartilage with positive staining for aggrecan, collagens I, II, and X and collagen catabolism. The thiol-norbornene system led to hyaline-like cartilage production especially under mechanical loading with positive staining for aggrecan and collagen II and minimal staining for collagens I and X and collagen catabolism. Findings from this study confirm that the polymerization mechanism and network structure have long-term effects on the quality of engineered cartilage, especially under mechanical loading.
Project description:A new pair of plladium complexes (Pd4 and Pd5) ligated with constrained N-(5,6,7-trihydroquinolin-8-ylidene)arylamine ligands have been prepared and well characterized by ¹H-, 13C-NMR and FTIR spectroscopies as well as elemental analysis. The molecular structure of Pd4 and Pd5 in solid state have also been determined by X-ray diffraction, showing slightly distorted square planar geometry around the palladium metal center. All complexes Pd1-Pd5 are revealed highly efficient catalyst in methyl acrylate (MA) polymerization as well as methyl acrylate/norbornene (MA/NB) copolymerization. In the case of MA polymerization, as high as 98.4% conversion with high molecular weight up to 6282 kg·mol-1 was achieved. Likewise, Pd3 complex has good capability to incorporate about 18% NB content into MA polymer chains. Furthermore, low catalyst loadings (0.002 mol %) of Pd4 or Pd5 are able to efficiently mediate the coupling of haloarenes with styrene affording up to 98% conversion.
Project description:Microfluidic gradient generators have been used to study cellular migration, growth, and drug response in numerous biological systems. One type of device combines a hydrogel and polydimethylsiloxane (PDMS) to generate "flow-free" gradients; however, their requirements for either negative flow or external clamps to maintain fluid-tight seals between the two layers have restricted their utility among broader applications. In this work, a two-layer, flow-free microfluidic gradient generator was developed using thiol-ene chemistry. Both rigid thiol-acrylate microfluidic resin (TAMR) and diffusive thiol-acrylate hydrogel (H) layers were synthesized from commercially available monomers at room temperature and pressure using a base-catalyzed Michael addition. The device consisted of three parallel microfluidic channels negatively imprinted in TAMR layered on top of the thiol-acrylate hydrogel to facilitate orthogonal diffusion of chemicals to the direction of flow. Upon contact, these two layers formed fluid-tight channels without any external pressure due to a strong adhesive interaction between the two layers. The diffusion of molecules through the TAMR/H system was confirmed both experimentally (using fluorescent microscopy) and computationally (using COMSOL). The performance of the TAMR/H system was compared to a conventional PDMS/agarose device with a similar geometry by studying the chemorepulsive response of a motile strain of GFP-expressing <i>Escherichia coli</i>. Population-based analysis confirmed a similar migratory response of both wild-type and mutant <i>E. coli</i> in both of the microfluidic devices. This confirmed that the TAMR/H hybrid system is a viable alternative to traditional PDMS-based microfluidic gradient generators and can be used for several different applications.
Project description:Photoinitiated silane-ene chemistry has the potential to pave the way toward spatially resolved organosilicon compounds, which might find application in biomedicine, microelectronics, and other advanced fields. Moreover, this approach could serve as a viable alternative to the popular photoinitiated thiol-ene chemistry, which gives access to defined and functional photopolymer networks. A difunctional bis(trimethylsilyl)silane with abstractable hydrogens (DSiH) was successfully synthesized in a simple one-pot procedure. The radical reactivity of DSiH with various homopolymerizable monomers (i.e., (meth)acrylate, vinyl ester, acrylamide) was assessed via 1H NMR spectroscopic studies. DSiH shows good reactivity with acrylates and vinyl esters. The most promising silane-acrylate system was further investigated in cross-linking formulations toward its reactivity (e.g., heat of polymerization, curing time, occurrence of gelation, double-bond conversion) and compared to state-of-the-art thiol-acrylate resins. The storage stability of prepared resin formulations is greatly improved for silane-acrylate systems vs thiol-ene resins. Double-bond conversion at the gel point (DBCgel) and overall DBC were increased, and polymerization-induced shrinkage stress has been significantly reduced with the introduction of silane-acrylate chemistry. Resulting photopolymer networks exhibit a homogeneous network architecture (indicated by a narrow glass transition) that can be tuned by varying silane concentration, and this confirms the postulated regulation of radical network formation. Similar to thiol-acrylate networks, this leads to more flexible photopolymer networks with increased elongation at break and improved impact resistance. Additionally, swelling tests indicate a high gel fraction for silane-acrylate photopolymers.
Project description:Interpenetrating polymer networks (IPNs) based on triisocyanate-terminated poly(urethane-imide)s (PUIs) were prepared by in situ interpenetrating reactions between modified polyurethane (PU) with different ratios of polyimide (PI). The effects of PU, which was made from hydroxyl-terminated polybutadiene modified with triisocyanate, and the amounts of PI on the mechanical properties, thermal properties, and crystalline character of the IPNs were discussed. Triisocyanate-terminated PUI showed that the highest tensile strength was 38 times that of the diisocyanate-terminated materials. Supramolecular cross-linking from an additional hydrogen-bonding network of modified PU and the degree of interpenetration with a regular imide structure of PI were introduced, which accounted for the remarkable improvement in mechanical properties of IPNs. Preferable thermal stability and glass transition temperature for the hard segment of IPNs were rewarded with increasing PI content. X-ray diffraction revealed vigorous segmental mixing between the soft and hard segments of modified PUI. Scanning electron micrographs showed the "fibrous assembly" morphology and short-range-ordered structure of modified PUI.
Project description:Atomic force microscopy has been applied to an acrylate polymer microarray to achieve a full topographic characterisation. This process discovered a small number of hydro-responsive materials created from monomers with disparate hydrophilicities that show reversibility between pitted and protruding nanoscale topographies.