Dynamic crystallization (DC) is a new characterization technique for measuring the chemical composition distribution (CCD) of semicrystalline copolymers. This technique fractionates polymers based on chain crystallizabilities under a constant cooling rate; a solvent is also fed through the column at a constant flow rate during the crystallization to enhance the physical separation of the polymer fractions. In this work, a DC model for ethylene/1‐olefin copolymers on the basis of population balance, crystallization kinetics, and axial dispersion is proposed. This model is found to describe the experimental DC profiles of an ethylene/1‐octene copolymer at various operation conditions very well.
Honeycomb hybrid films are formed using the particle‐assisted breath figure (BF) method. By adding silica particles into the casting polymer solution, regular arrays of micrometer‐sized pores with interior walls selectively decorated by the particles can be readily prepared. The modulation of the geometrical features of the obtained patterned surface is achieved by simply adjusting the casting conditions or the composition of the silica particle/polymer system. By tuning the amount and interfacial properties of the added particles, variable assembly morphologies of the particles within the pore array are obtained and thoroughly analyzed. The effect of the adsorption of the particles on the interfacial tension between water/solvent is also explored.
The preparation and study of a new poly(3‐alkyloxythiophene)—bearing a chiral center—is presented, with particular reference to the evolution of optical activity in passing from solution to solid state. The combination of optical analysis, electronic circular dichroism, and X‐ray diffraction of powders or films supplies strong indications of a possible use of this material as an inverse chiral probe.
This work investigates the synthesis of bio‐based pressure‐sensitive adhesives and their characterization in terms of mechanical properties relevant to processing and application. The synthesis of monomers based on various fatty acids derived from vegetable oils as renewable feedstock via a one‐step, a two‐step, and a three‐step route is described. The resulting monomers are polymerized via free radical polymerization resulting in high molecular weight polymers with adhesive properties. Adhesives are also obtained as aqueous dispersions by means of miniemulsion polymerization. In particular, the monomer acrylated methyl oleate ( 4ac ) and the thereof derived polymer are intensively studied. The synthesized homopolymers show characteristic mechanical and adhesive properties similar to conventional pressure sensitive adhesives.
A first‐principles map for the equilibrium morphologies of polymer–inorganic nanocomposites synthesized by miniemulsion polymerization is developed. The predictions are compared with literature results on the effect of the initiator type, surfactant concentration, monomer system, and surface characteristics of the inorganic nanoparticles on the morphology of the nanocomposites. The limitations of the morphology map are also discussed.
Whether manganese ion can induce DNA condensation at room temperature has not been clarified. In this study, direct evidence of Mn2+ ion‐induced DNA condensation is provided by single‐molecule measurements and atomic force microscopy characterization. It is shown that elevated temperature is not a requirement to induce DNA condensation, but helps to promote the process at the ensemble level. The finding suggests the failure of the Manning theory in explaining Mn2+‐DNA interactions and refreshes the view that divalent metal ions cannot cause DNA condensation. The localized binding of Mn2+ on DNA is believed to induce condensation.
Functional hybrid materials with optically active metal‐ligand moieties embedded within a polymer matrix have a great potential in (bio)materials science, including applications in light‐emitting diode devices. Here, a simple strategy is reported to incorporate terpyridine derivatives into the side chains of elastin‐like polymers (ELPs). The further binding of trivalent lanthanide ions with the terpyridine ligands generates an array of photoluminescence ranging from the visible to the near‐infrared regions. As thin films, these ELP‐based optical materials also exhibit distinct morphologies that depend upon the temperature of the aqueous solutions from which the hybrid polymers are spin coated or drop cast.
Dithiobenzoates are among the most popular agents for reversible addition‐fragmentation chain transfer (RAFT) polymerization. This is attributed to the better control over molecular weight and end‐group fidelity found in RAFT polymerization of methacrylates and methacrylamides. However, in polymerization of styrenes, acrylates, and acrylamides, their use has diminished, mainly in favour of trithiocarbonates, because of issues with retardation, as well as hydrolytic and thermal instability. This paper critically assesses developments in understanding the mechanism and kinetics of dithiobenzoate‐mediated RAFT polymerization from 2006 to 2013, with specific reference to the choice of reagents, polymerization conditions, side reactions, and factors leading to retardation.
Using linear side chains for conjugated polymers is hindered by their limited solubility in common organic solvents, creating problems during purification and processing, whereas branched alkyl chains generally preclude interchain interdigitation because their bulkiness usually hinders interchain interactions. To compensate the adverse effects from each side chain, it is shown that replacing commonly employed 2‐ethylhexyl (2EH) solubilizing groups with branched 5‐ethylnonyl (5EN) chains not only improves solution processability to PCDT‐BT polymer, but also induces an advantageous change in polymer self‐assembly and backbone orientation in thin films that correlates with an increase in transistor performance.
Synthesis of a novel multifunctional block based on asymmetrically substituted pentaerythritol, succinic acid, and tetraethylene glycol is reported. The proposed reaction conditions allow selective preparation of the product in high overall yield. The block can be used in the assembly of biocompatible polyester‐co‐polyether (PEPE) hyperbranched macromolecules, which allows the product to be considered as a promising intermediate for the development of new biomedical dendrimers. As an example, the use of the “block by block” strategy is employed to obtain a second‐generation dendron. It is shown that the approach is much more efficient than the pathway of step‐by‐step grafting of separate molecular fragments.
Size matters: the interface of nanodroplets in an inverse miniemulsion is used to produce polyphosphate nanocapsules by interfacial polycondensation. Phosphorus acts as a probe for 31P NMR spectroscopy to compare the polycondensation at the nanoscopic droplet with macroscopic interfaces proving less unwanted hydrolysis in miniemulsion by 1H–31P 2D‐heteronuclear multiple bond correlation spectra.
The effect of incorporating 2.85 nm red luminescent silicon nanoparticles as photoluminescence down‐shifters on the efficiency of organic solar cells based on regioregular poly(3‐hexylthiophene‐2,5‐diyl) and [6,6]‐phenyl‐C71‐butyric acid methyl ester is investigated. The silicon nanoparticles are deposited by spin coating and inkjet printing on different layers of the devices. The presence of the silicon nanoparticles in the organic solar cells does not result in any performance improvement and causes a significant degradation of the power conversion efficiency.
The synthesis of metal‐containing polymers and block copolymers has led to a rapidly expanding field of research interest for manifold potential applications. Within this contribution, some recent advances in the field of side‐chain ferrocene‐containing polymers focusing on poly(vinylferrocene) and poly(ferrocenyl methacrylates) are presented. The synthetic developments shown focus on living and controlled polymerizations, as well as surface‐initiated polymerization strategies. First attempts and recent developments for these novel redox‐responsive materials toward feasible applications are addressed.
Double‐network (DN) hydrogel has intrinsic tough mechanical properties due to its unique two contrasting network structures. The research on DN hydrogel is a fast growing field, mainly focusing on network structures, formation, and interactions at the molecular level. In this trend article, we take a critical review at the important and latest research findings, current research challenges, and future research directions in the DN hydrogel field. We discuss some issues on the discovery of fundamentally new phenomena versus performance benchmarking for different types of the DN hydrogels. Finally we offer our personal opinions to several unique aspects for future DN gel research.
Functional nanowires with photochromic spiropyran (SP) species are prepared by reversible addition–fragmentation transfer (RAFT) dispersion polymerization of styrene using poly(4‐vinylpyridine‐co‐spiropyranyl methacrylate) as a macro‐RAFT agent, and then electrospinning technology is used to fabricate fibers from the functional nanowires. The photoisomerization of SP in the nanowires and fibers is studied, and reversible photochromism for both nanowires and fibers is observed. Since the merocyanine (ME form) of the SP emits fluorescence and the SP form is non‐fluorescent, the fluorescence of the nanowires and the fibers can be switched on and off upon alternating UV and visible‐light irradiation.
A synthesis route to siloxane‐based thermoplastic elastomers (TPE) with functional hard blocks is described. The photophysical functionality is provided by oligothiophenes, namely terthiophene and bithiophene. Polyaddition of isocyanate‐bearing thiophenes and amine‐terminated siloxanes yields polymers incorporating a bisurea structure motive. Phase separation and strong hydrogen bonds provide ordering of the thiophenes, which is shown by wide‐angle X‐ray scattering (WAXS) and X‐ray powder diffraction (XRD). Fluorescence measurements reveal a strong red shift of emission of polymer films compared with polymer solutions, thus confirming the existence of hard block segments with an enhanced π system and higher charge–carrier mobility. Tuning of the optical band gap by different polymer compositions and various post polymerization treatments is demonstrated.
The effects of polymerization kinetics and chemical miscibility on the crosslinking structure and mechanical properties of polymers cured by visible‐light initiated free‐radical/cationic ring‐opening hybrid photopolymerization are determined. A three‐component initiator system is used and the monomer system contains methacrylates and epoxides. The photopolymerization kinetics is monitored in situ by Fourier transform infrared‐attenuated total reflectance. The crosslinking structure is studied by modulated differential scanning calorimetry and dynamic mechanical analysis. X‐ray microcomputed tomography is used to evaluate microphase separation. The mechanical properties of polymers formed by hybrid polymerization are comparable to the control formed by free‐radical polymerization. These investigations mark the first time that the benefits of the chain transfer reaction between epoxy and hydroxyl groups of methacrylate, on the crosslinking network and microphase separation during hybrid visible‐light initiated photopolymerization, have been determined.
Functionalization of carbon nanotubes (CNTs) is essential for the dispersion of CNTs in polymer matrices due to their inherence. However, conventional functional groups are insulating in nature, thereby destroying the basic structure of the CNTs and their electrical conductivity due to the harsh and long‐period acid treatments. Hence, a new method of functionalization is essential. In this article, a poly(vinyliedene fluoride) (PVDF) composite comprising graphene wrapped CNTs as a conducting filler is described. A strain‐gauge factor of ≈20 at low strain levels (0.1%) is with a 3 wt% graphene wrapped CNT hybrid in PVDF, which overwhelms conventional metal foil strain gauges as well as functionalized CNT or functionalized graphene based polymer composites for strain sensing.
Polystyrenes (PS) end‐functionalized with perfluorotridecyl (PFTD), perfluorodecyl (PFD), and perfluoroheptyl (PFH) groups are synthesized using the corresponding perfluoroalkyl initiators by atom transfer radical polymerization. Polymer thin films deposited on silicon wafers are studied by dynamic nanoindentation (NI). NI measurements of the 15k PFTD‐PS sample showed increases of about 80 and 300% in the storage and loss moduli, respectively, compared to the 15k PS homopolymer. Measurements made on different regions of the PFTD‐functionalized PS show a fivefold greater standard deviation compared to the 15k PS homopolymer. The effects for the PFD and PFH groups are smaller in all respects consistent with expectations.
A facile surface modification procedure for electrospun poly(butylene terephthalate) (PBT) fibers by surface‐initiated atom transfer radical polymerization (SI‐ATRP) is reported. Initiators are introduced through aminolysis and chemical vapor adsorption. SI‐ATRP is subsequently carried out to prepare a polymer‐grafted layer at the PBT fiber surface without altering the fiber geometry. After modification with a zwitterionic poly(sulfobetaine), poly(3‐(N‐2‐methacryloyloxyethyl‐N,N‐dimethyl) ammonatopropanesulfonate), the surface is superhydrophilic. The surface properties are thermally stable due to the high melting temperature of the PBT crystallites and are maintained for a prolonged period.
下载免费PDF全文