Heikki Tenhu

Non-ionic Thermoresponsive Polymers in Water

Numerous non-ionic thermally responsive homopolymers phase separate from their aqueous solutions upon heating. Far fewer neutral homopolymers are known to phase separate upon cooling. A systematic compilation of the polymers reported to exhibit thermoresponsive behaviour is presented in this review, includ- ing N-substituted poly((meth)acrylamide)s, poly(N-vinylamide)s, poly(oxazoline)s, protein-related polymers, poly(ether)s, polymers based on amphiphilic balance, and elastin-like synthetic polymers. Basic properties of aqueous solutions of these poly- mers are briefly described.

Binding and release of drugs into and from thermosensitive poly(N-vinyl caprolactam) nanoparticles

Three model drug substances, the beta-blocking agents nadolol and propranolol and a choline-esterase inhibitor tacrine, were used in order to determine how different drug molecules affect the behavior of thermally responsive polymer nanoparticles composed of poly(N-vinylcaprolactam) (PVCL). Pure PVCL particles in water exist in a swollen state at room temperature, but the size of the particles decreases discontinuously when the temperature is raised above the volume phase transition temperature. At temperatures above this transition temperature, water is expelled out from the nanoscopic hydrogel particles. Light scattering studies revealed that the more hydrophobic drug substances, propranolol and tacrine, considerably swell the PVCL-microgel. The more hydrophilic drug, nadolol, decreased the transition temperature of PVCL particles, whereas the transition temperature values of pure PVCL particles and that of the added propranolol and tacrine were quite similar. Attenuated drug release results showed that the beta-blocking agents were tightly bound to the microgel, and this was more evident at higher temperatures. On the contrary, the release of tacrine across the cellulose membrane was increased when PVCL particles were present. Thus, both physical and chemical properties of the drugs clearly affected their binding to PVCL particles and the release of drugs was affected by the temperature.

Inkjet-printed gold electrodes on paper: characterization and functionalization.

Gold nanoparticles were synthesized and inkjet-printed on a paper substrate and IR-sintered to produce conductive electrodes. The electrodes were further functionalised by using self-assembled octadecanethiol monolayers (SAMs). The effect of sintering, print quality, and SAM formation were examined by topographical, chemical and electrical methods. With optimised printing parameters, a volume resistivity of ~1.6 × 10(-7) Ω m was attained by a single print layer.

Drug release characteristics of physically cross‐linked thermosensitive poly(N‐vinylcaprolactam) hydrogel particles

The effect of physical cross-linking was studied on the formation and properties of thermosensitive polymer particles of poly(N-vinylcaprolactam), PVCL, and PVCL grafted with poly(ethylene oxide) macromonomer, PVCL-graft-C(11)EO(42). Loading and release of model drugs into/from the hydrogel particles were evaluated. Thermosensitive particles were stabilized by cross-linkers, the most feasible of which was salicylic acid (SA). At 23 degrees C, below the lower critical solution temperature (LCST) of the thermosensitive polymers, stability of the hydrogels was poor, whereas at 37 degrees C stable hydrogel particles were formed. All the drugs and also the cross-linker (SA) were released more efficiently from the PVCL particles compared to the PVCL-graft-C(11)EO(42) particles. Drug concentration and pH affected clearly the rate and extent of drug release in physiological buffer. The higher drug release from the PVCL was based on the more open gel-like structure as opposed to PVCL-graft-C(11)EO(42) particles. Complex formation between the cross-linker and the polymers was due to the hydrogen bonding between the hydroxyl groups of SA and H-bond acceptors of the PVCL. In the case of PVCL-graft-C(11)EO(42), the ethylene oxide chain provided more opportunities for H-bonding in comparison to the pure PVCL, creating more stable complexes (more tightly packed particles) leading to sustained drug release.

Miktoarm stars of poly(ethylene oxide) and poly(dimethylaminoethyl methacrylate): manipulation of micellization by temperature and light

A novel method for preparation of miktoarm stars is presented, first employing Williamson ether synthesis with protected dipentaerythritol and preformed poly(ethylene oxide) (PEO) as reactants. This arm-first reaction gave, after modification, PEO macroinitiators with 4 or 6 initiation sites, which are located in the center of the main chain. The initiators were used for atom transfer radical polymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA; core-first method). Heteroarm stars were obtained with two hydrophilic PEO chains and 4 or 3 stimuli responsive PDMAEMA chains respectively. Both polymers had almost the same molecular weights. The star-shaped polymers were analyzed by NMR, size exclusion chromatography SEC, osmometry and mass spectrometry. The micellization of the polymers was investigated by light scattering, fluorescence spectroscopy and cryogenic transmission electron microscopy. At the conditions used (0.1 g/L in pH 8 buffer), PDMAEMA turns hydrophobic around 55 °C, forming micelles at higher temperatures. At low temperature, trivalent counterions like hexacyanocobaltate(III) allow additional micellization of the weak polyelectrolyte PDMAEMA, with PEO as the solubilizing agent. For this unique behavior the notion “confused micellization” is introduced, which is in analogy to schizophrenic micelles. The morphology of the aggregates depends strongly on the macromolecular architecture, giving spherical micelles for the star with 4 shorter PDMAEMA arms and vesicles for the star with 3 longer arms. The diameter of the vesicles, varying between 200 nm and 4000 nm at 10 °C, can be tuned by the cooling rate. This ionically induced micellization can then be reversed by UV-illumination, leading to disaggregation upon a photoinduced valency change of the counterion.

Poly(ethylene imine) and tetraethylenepentamine as protecting agents for metallic copper nanoparticles.

The aim of this research was to explore the use of amine-containing polymeric and low-molar-mass organic protecting agents in the preparation of copper nanoparticles. Particles were synthesized using poly(ethylene imine) (PEI) or tetraethylenepentamine (TEPA) as protecting agents. The resulting particles were studied with UV-vis spectrometry, thermogravimetry, scanning electron microscopy, and transmission electron microscopy, wide-angle X-ray scattering with heating, X-ray photoelectron spectroscopy, and Auger electron spectroscopy. The average crystal sizes for the particles were at room temperature 8.5 and 19.4 nm for PEI and TEPA, respectively, and some surface oxidation was observed. The particles were sintered on paper, and the resistance and resistivity were measured. For Cu/PEI samples, the protecting agent was removed upon sintering at relatively low temperatures (between 150 and 200 degrees C). At this temperature range, particles exhibited a rapid increase in the crystal size. Sintered particles exhibited high conductivity, indicating that these kinds of materials might find use in paper-based printing.

Diblock copolymers consisting of a polymerized ionic liquid and poly(N-isopropylacrylamide). Effects of PNIPAM block length and counter ion on self-assembling and thermal properties

Amphiphilic diblock copolymers composed of a polymeric ionic liquid, PIL, and poly(N-isopropylacrylamide), PNIPAM, have been synthesized using RAFT reactions. The length of the PIL block was kept constant while the molecular mass of the PNIPAM block was varied. The PIL was poly(2-(1-butylimidazolium-3-yl)ethyl methacrylate tetrafluoroborate) which is insoluble in water owing to the bulky hydrophobic counterion. When the PNIPAM block was long enough, the polymers formed spherical micelles in water, which showed thermally responsive behaviour. Colloidally stable particles could be prepared also from the homopolymeric PIL. PNIPAM affects noticeably the properties of the PIL, and also the polycation has a strong effect on the thermal properties of PNIPAM in aqueous dispersions. As a reference, a polymer where bromide was the counter ion instead of the tetrafluoroborate ion was synthesized, providing a water soluble PIL block. The core–shell micelles formed by amphiphilic block copolymers in pure water and those by double-hydrophilic polymers in aqueous NaBF4 undergo partial structural inversion upon the thermal collapse of PNIPAM.

Synthesis and characterization of copper sulfide nanocrystallites with low sintering temperatures

To study nano-inks with relatively low sintering temperatures for fabrication of functional electronics on paper by inkjet printing technology, we have successfully prepared copper sulfide nanocrystallites protected by self-assembled monolayers. Systematic characterization was performed on as-prepared nanoparticles by FTIR, NMR, thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and wide-angle X-ray scattering (WAXS) with heating. The copper sulfide nanocrystallites with crystal sizes <1.5 nm show a hexagonal Cu2S phase at low temperatures but undergo significant consolidation/crystallization from 100 to 240 °C, accompanying a transformation from the hexagonal Cu2S phase to the cubic Cu1.8S phase when heated up to ca. 150 °C. The protective ligand burnout during heating is closely associated with the nanocrystallite consolidation. Further, the copper sulfide nanoparticles were deposited on paper and sintered at 240 °C in air. The sintered particles are composed of large crystals of cubic Cu1.8S with no serious degradation due to oxidation. The resistivity of the sintered particles was of the order of 1 × 10−5 (Ω m).

Cationic Amphiphilic Star and Linear Block Copolymers: Synthesis, Self-Assembly, and in Vitro Gene Transfection

A series of amphiphilic star and linear block copolymers were synthesized using ATRP. The core consisted of either polystyrene (PS) or poly(n-butyl acrylate) (PBuA), having different glass-transition (T(g)) values. These polymers were used as macroinitiators in the polymerization of the cationic 2-(dimethylamino)ethyl methacrylate (DMAEMA). The polymers were used to study the effects of polymer architecture and flexibility on the self-assembling properties, DNA complexation, and transfection. All polymers formed core-shell micelles in aqueous solutions and condensed plasmid DNA. Linear PDMAEMA-PBuA-PDMAEMA has transfection efficiency comparable to PEI25K in ARPE19 cell line. Glassy state of the micellar core and star-shaped architecture decreased the DNA transfection compared with the rubbery and linear polymer structures. The polymers showed low cellular toxicity at low nitrogen/phosphate (n/p) ratios.

Imidazolium‐Based Poly(ionic liquid)s as New Alternatives for CO2 Capture

Solid imidazolium-based poly(ionic liquid)s with variable molecular weights that contain the poly[2-(1-butylimidazolium-3-yl)ethyl methacrylate] (BIEMA) cation and different counter anions were evaluated in terms of CO2 capture and compared with classical ionic liquids with similar counter anions. In addition to poly(ionic liquid)s with often-applied ions such as BF4 (-) , PF6 (-) , NTf2 (-) , trifluoromethanesulfonate (OTf(-) ) and Br(-) , for the first time [BIEMA][acetate] was synthesised, which revealed a remarkably high CO2 sorption performance that exceeded the poly(ionic liquid)s studied previously on average by a factor of four (12.46 mg gPIL (-1) ). This study provides an understanding of the factors that affect CO2 sorption and a comparison of the CO2 capture efficiency with the frequently used sorbents. Moreover, all the studied sorbents were reusable if regenerated under carefully selected conditions and can be considered as suitable candidates for CO2 sorption.