SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Macromolecular rapid communications

29

The development of sustainable renewable polymers from natural resources has increasingly gained attention from scientists, engineers as well as the general public and government agencies. This review covers recent progress in the field of renewable bio-based monomers and polymers from natural resources: terpenes, terpenoids, and rosin, which are a class of hydrocarbon-rich biomass with abundance and low cost, holding much potential for utilization as organic feedstocks for green plastics and composites. This review details polymerization and copolymerization of terpenes such as pinene, limonene, and myrcene and their derivatives, terpenoids including carvone and menthol, and rosin-derived monomers. The future direction on the utilization of these natural resources is discussed.

Concepts: Ecology, Polymer, Polymer chemistry, Monomer, Natural resource, Isoprene, Terpenes and terpenoids, Limonene

28

Initiated chemical vapor deposition (iCVD) has been shown to be suitable for blanketing surfaces with thin polymer coatings of ≈1-2 nm and greater. In this work, iCVD coatings of polytetrafluoroethylene (PTFE) deposited on carbon nanotube (CNT)-based surfaces show CNT-templated PTFE single crystal growth. While the coating forms disoriented agglomerates when deposited on an amorphous carbon background, “shish-kebab” structures are observed when grown on single-walled carbon nanotubes (SWCNT) as well as CNT buckypaper. It is shown that the shish-kebab structure is composed of PTFE lamellae arranged with the chain backbones running parallel to the SWCNT axis. This result allows one to control not only the surface chemistry using PTFE but also the coating surface topology.

Concepts: Chemistry, Carbon, Solid, Carbon nanotube, Allotropes of carbon, Materials science, Chemical vapor deposition, Potential applications of carbon nanotubes

27

Catalytic natures of organometallic catalysts are modulated by coordinating organic ligands with proper steric and electronic properties to metal centers. Carbon-based nanomaterials such as graphene nanoplatelets are used with and without N-doping and multiwalled carbon nanotube as a ligand for ethylene polymerizations. Zirconocenes or titanocenes are immobilized on such nanomaterials. Polyethylenes (PEs) produced by such hybrids show a great increase in molecular weight relative to those produced by free catalysts. Specially, ultra-high-molecular-weight PEs are produced from the polymerizations at low temperature using the hybrid with N-doped graphene nanoplatelets. This result shows that such nanomaterials act a crucial role to tune the catalytic natures of metallocenes.

Concepts: Hydrogen, Carbon, Solid, Carbon nanotube, Graphene, Polyethylene, Polymerization, Ziegler-Natta catalyst

27

This paper describes a facile method for the preparation of porous gelatin beads with uniform pore sizes using a simple fluidic device and their application as supporting materials for cell culture. An aqueous gelatin droplet containing many uniform toluene droplets, produced in the fluidic device, is dropped into liquid nitrogen for instant freezing and the small toluene droplets evolve into pores in the gelatin beads after removal of toluene and then freeze-drying. The porous gelatin beads exhibit a uniform pore size and monodisperse diameter as well as large open pores at the surface. Fluorescence microscopy images of fibroblast-loaded gelatin beads confirm the attachment and proliferation of the cells throughout the porous gelatin beads.

Concepts: Protein, Cell biology, Microscope, Liquid, Surface tension, Drop, Liquids

27

A new approach is developed to fabricate highly oriented mono-domain LCE nano/microstructures through micro-molding in capillaries. Gratings and microwires as two typical examples are fabricated and characterized by polarizing optical microscopy, optical microscopy, and scanning electron microscopy. The gratings with precisely controlled sizes and smooth surface are obtained by filling the channels with a nematic monomer mixture followed by the photo-crosslinking. After peeling off the gratings from the substrate, the free-standing microwires are obtained. A uniform orientation of the mesogenic units is observed for the molds with channel width less than 20 μm. Reversible thermomechanical effect is demonstrated by using the microwires obtained through this approach.

Concepts: Electron, Electron microscope, Microscope, Transmission electron microscopy, Scanning electron microscope, Surface, Liquid crystal, Diffraction grating

26

Biocompatible lipo-histidine hybrid materials conjugated with IR820 dye show pH-sensitivity, efficient intracellular delivery of doxorubicin (Dox), and intrinsic targetability to cancer cells. These new materials form highly uniform Dox-loaded nanosized vesicles via a self-assembly process showing good stability under physiological conditions. The Dox-loaded micelles are effective for suppressing MCF-7 tumors, as demonstrated in vitro and in vivo. The combined mechanisms of the EPR effect, active internalization, endosomal-triggered release, and drug escape from endosomes, and a long blood circulation time, clearly prove that the IR820 lipopeptide DDS is a safe theranostic agent for imaging-guided cancer therapy.

Concepts: Immune system, Cancer, Breast cancer, Heart, The Canon of Medicine, Chemotherapy, In vivo, In vitro

25

Well-defined ABC triblock copolymers based on two hydrophilic blocks, A and C, and a hydrophobic block B are synthesized and their self-assembly behavior is investigated. Interestingly, at the same solvent, concentration, pH, and temperature, different shape micelles are observed, spherical and worm-like micelles, depending on the preparation method. Specifically, spherical micelles are observed with bulk rehydration while both spherical and worm-like micelles are observed with film rehydration.

Concepts: Chemical properties, Hydrophobic effect, Copolymer, Solubility, Block, Blocking

24

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as transparent electrodes for organic light-emitting diodes (OLEDs) are doped with a new solvent 1,3-dimethyl-2-imidazolidinone (DMI) and are optimized using solvent post-treatment. The DMI doped PEDOT:PSS films show significantly enhanced conductivities up to 812.1 S cm(-1) . The sheet resistance of the PEDOT:PSS films doped with DMI is further reduced by various solvent post-treatment. The effect of solvent post-treatment on DMI doped PEDOT:PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated PEDOT:PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped PEDOT:PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized PEDOT:PSS films with the new solvent of DMI can be a promising transparent electrode for low-cost, efficient ITO-free white OLEDs.

Concepts: Cathode, Electrochemistry, Electrolyte, Electrode, Electrochemical cell, Diode, Ethylene glycol, Conductive polymers

24

The photochemical and electrochemical investigations of commercially available, safe, and cheap fluorescent brighteners, namely, triazinylstilbene (commercial name: fluorescent brightener 28) and 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene, as well as their original use as photoinitiators of polymerization upon light emitting diode (LED) irradiation are reported. Remarkably, their excellent near-UV-visible absorption properties combined with outstanding fluorescent properties allow them to act as high-performance photoinitiators when used in combination with diaryliodonium salt. These two-component photoinitiating systems can be employed for free radical polymerizations of acrylate. In addition, this brightener-initiated photopolymerization is able to overcome oxygen inhibition even upon irradiation with low LED light intensity. The underlying photochemical mechanisms are investigated by electron-spin resonance-spin trapping, fluorescence, cyclic voltammetry, and steady-state photolysis techniques.

Concepts: Light, Light-emitting diode, Lighting, Diode, LEd, Radical polymerization, Living polymerization, Black light

24

Thermal field-flow fractionation (ThFFF) is an interesting alternative to column-based fractionation being able to address different molecular parameters including size and composition. Until today it has not been shown to be able to fractionate polymers of similar molar masses and chemical compositions by molecular topology. The present study demonstrates that poly(butyl methacrylates) with identical molar masses can be fractionated by ThFFF according to the topology of the butyl group. The influence of the solvent polarity on the thermal diffusion behavior of these polymers is presented and it is shown to have a significant influence on the fractionation of poly(n-butyl methacrylate) and poly(t-butyl methacrylate). Fractionation improves with increasing solvent polarity and solvent polarity may have a greater influence on fractionation than solvent viscosity. It is found that the thermal diffusion coefficient, DT , as well as the hydrodynamic diameter, Dh , exhibit increasing trends with increasing solvent polarity. The solvent quality has a significant influence on the fractionation. It is found that cyclohexane, being a theta solvent for poly(t-butyl methacrylate) but not for poly(n-butyl methacrylate), significantly improves the fractionation of the samples by decreasing the diffusion rate of the former but not the latter.

Concepts: Function, Molecular diffusion, Diffusion, Transport phenomena, Convection, Solvent, Atomic diffusion, Mole