Synthesis and characterization of polystyrene-blockpoly(vinylbenzoic acid): a promising compound for manipulating photoresponsive properties at the nanoscale

"Published online: 27 January 2015"Using reversible addition-fragmentation chain transfer (RAFT) polymerization, the effect of PSt macroRAFT and 4VBA ratio on the synthesis of a carboxylic acid functional block copolymer (PSt-b-P4VBA) was studied. PSt macroRAFT polymer was initially prepared followed by the insertion of 4-vinylbenzoic acid (4VBA) monomer. The chemical structure of the diblock copolymer was confirmed by NMR and FTIR. The effect of PSt macroRAFT and 4VBA ratio on copolymerization yield and on molecular weight distribution was assessed by gel permeation chromatography. The rate of polymerization did not change as the 4VBA/PSt macroRAFT ratio increased, indicating an ideal amount of 4VBA insertion. An optimal ratio of [PSt macroRAFT]:[AIBN]:[4VBA] was 1.2:1:180. DSC and XRD confirmed the amorphous structure of homo and copolymer. Thermal stability was higher for PSt-b-P4VBA forming activated porous carbon char by dehydration, carbonization and oxidation. SEM and STEM observations showed a morphological evolution between PSt macroRAFT and the correspondent copolymer.The authors acknowledge the n-STeP-Nanostructured systems for Tailored Performance, with reference NORTE-07-0124-FEDER-000039, supported by the Programa Operacional Regional do Norte (ON.2), PEst-C/CTM/LA0025/2013 (Strategic Project-LA 25-2013-2014)

Anterior cruciate ligament reconstruction: MR imaging findings

: More than two million people tear their anterior cruciate ligament (ACL) each year, and ACL reconstruction occupies a significant proportion of everyday orthopedic practice, being one of the most commonly performed sports medicine surgical procedures. Patients with postoperative symptoms are frequently imaged to monitor ligament grafts and to identify complications. Given the number of patients undergoing ACL reconstruction, knowledge of the potential complications of this surgery is essential for radiologists. This article provides a review of imaging of ACL reconstruction procedures and the potential complications specific to this surgery

Impact of Fuel Production Technologies on Energy Consumption and GHG Emissions from Diesel and Electric–Hydrogen Hybrid Buses in Rio de Janeiro, Brazil

In view of the GHG reduction targets to be met, Brazilian researchers are looking for cleaner alternatives to energy sources. These alternatives are primarily to be applied in the transport sector, which presents high energy consumption, as well as high CO2 emissions. In this sense, this research developed an LCI study considering two bus alternatives for the city of Rio de Janeiro: diesel-powered internal combustion buses (ICEB) and a hydrogen-powered polymer fuel cell hybrid bus (FCHB). For the FCHB, three hydrogen production methods were also included: water electrolysis (WE), ethanol steam reforming (ESR) and natural gas steam reforming (NGSR). The research was aimed at estimating energy consumption, including the percentage of energy that is renewable, as well as CO2 emissions. The results show diesel as the energy source with the highest emissions as well as the highest fossil energy consumption. Regarding the alternatives for hydrogen production, water electrolysis stood out with the lowest emissions

pH-Switchable Stratification of Colloidal Coatings: Surfaces “On Demand”

Stratified coatings are used to provide properties at a surface, such as hardness or refractive index, which are different from underlying layers. Although time-savings are offered by self-assembly approaches, there have been no methods yet reported to offer stratification on demand. Here, we demonstrate a strategy to create self-assembled stratified coatings, which can be switched to homogenous structures when required. We use blends of large and small colloidal polymer particle dispersions in water that self-assemble during drying because of an osmotic pressure gradient that leads to a downward velocity of larger particles. Our confocal fluorescent microscopy images reveal a distinct surface layer created by the small particles. When the pH of the initial dispersion is raised, the hydrophilic shells of the small particles swell substantially, and the stratification is switched off. Brownian dynamics simulations explain the suppression of stratifi-cation when the small particles are swollen as a result of reduced particle mobility, a drop in the pressure gradient, and less time available before particle jamming. Our strategy paves the way for applications in antireflection films and pro-tective coatings in which the required surface composition can be achieved on demand, simply by adjusting the pH prior to deposition

Investigating the Reactivity of a Novel Methacrylic Transmer in Solution RAFT-SCVP and Its Impact on the Structure of the Resulting Hyperbranched Polymers

A novel methacrylic-based R-transmer, named 2-(methacryloyloxy)ethyl 4-cyano-4-(((propylthio)carbonothioyl)thio)pentanoate, was synthesized, and its reactivity (propagation versus reversible chain transfer) in reversible addition–fragmentation chain transfer self-condensing vinyl polymerization (RAFT-SCVP) with methyl methacrylate (MMA) was studied to apprehend its impact on hyperbranched polymers (HBP) structure. The resulting HBP were characterized by nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC) and differential scanning calorimetry (DSC) to determine, respectively, their composition and degree of branching (DB), number average molecular weight (Mn) and dispersity (Đ), and glass transition temperature (Tg). Homopolymers of methacrylic-based R-transmer and copolymers with MMA were considered to study the reactivity of the methacrylic-based R-transmer with different initial molar ratios [MMA]0/[R-transmer]0 through kinetic studies and its consequences on HBP macromolecular characteristics and thermal properties. By varying the [MMA]0/[R-transmer]0 ratio from 1:1 to 100:1, HBP with increasing Mn (from 6,400 to 14,900 g mol–1) and Tg values (from 36.1 to 87.9 °C), decreasing Đ values (from 4.07 to 1.71) and DB values (from 0.30 to 0.03) were obtained