Poly(methyl methacrylate)‐block‐poly(4‐vinylpyridine), polystyrene‐block‐poly(4‐vinyl pyridine), and poly(ethylene glycol)‐block‐poly(4‐vinylpyridine) block copolymers are synthesized by successive atom transfer radical polymerization (ATRP), single‐electron‐transfer nitroxide‐radical‐coupling (SET‐NRC) and nitroxide‐mediated polymerization (NMP). This paper demonstrates that this new approach offers an efficient method for the preparation of 4‐vinylpyridine‐containing copolymers.
A novel spacer‐free liquid crystalline polyrotaxane (LCPR) is synthesized by directly grafting 4‐phenylazobenzoyl chloride onto the hydroxyl of threaded α‐cyclodextrin (α‐CD) as the side‐chain. It is found that LCPR can form nematic LC phase above 180 °C or under the concentration of 5–0.2 wt% in dimethyl sulfoxide (DMSO) solution. The mechanisms of formation of thermotropic and lyotropic LC phase are proposed, respectively, which show the mobility of both threaded α‐CDs and substituted azo‐mesogens is responsible for the formation of LC phase. This mechanism is further demonstrated by the formation of crystalline phase under UV radiation, which is characterized by polarizing optical microphotograph and UV measurements.
The preparation of novel nanoparticles is described, which consist of a poly(lactic acid) (PLA) core obtained by the nanoprecipitation method with a shell made of oppositely charged β‐cyclodextrin polymer (poly‐β‐CD) assembled using the layer‐by‐layer technique. Characterization of these nanoparticles is accomplished through dynamic light scattering, ζ‐potential measurements, X‐ray photoelectron spectroscopy and electron microscopy. The release of a loaded lipophilic molecule, benzophenone (BP), is mainly controlled by diffusion of BP and by its host–guest interaction with the β‐CD cavities of the adsorbed poly‐β‐CD. Increasing the number of poly‐β‐CD layers results in a better control of the release through the partition equilibrium between free BP and BP included in the cavities inside the multilayers.
The synthesis of high‐aspect‐ratio (AR) CdSe (NRs) nanorods and their ordered assembly over large areas are reported. Long‐range ordering of hexagonal arrays of high‐AR NRs is achieved by a combination of controlled solvent evaporation and the use of an applied electric field. Vertically oriented assemblies of CdSe NRs functionalized with oligo‐ and polythiophene are also obtained. Aligned and oriented polythiophene CdSe NRs have potential applications in organic–inorganic hybrid bulk‐heterojunction photovoltaic devices.
In the present paper, new photoinitiators based on the meta‐terphenyl scaffold in combination with an iodonium salt and 9H‐carbazole‐9‐ethanol (CARET) are proposed for the free radical promoted cationic polymerization of epoxides upon visible light exposure using light emitting diodes at 405, 455, and 470 nm. Remarkably, a new high performance additive (i.e., CARET) is proposed here for cationic polymerizations. CARET shows some important advantages compared to other reported additives such as N‐vinylcarbazole or benzyl alcohol used as references. Excellent polymerization initiating abilities are found and a full picture of the involved chemical mechanisms is provided.
Novel branched polyoxymethylene copolymers are synthesized by cationic copolymerization of 1,3,5‐trioxane (TOX) with 3‐(alkoxymethyl)‐3‐ethyloxetane (ROX) using BF3·Et2O as an initiator. Four oxetane derivatives with different side‐chain lengths (from 1 to 6 carbons) are tested for copolymerization. The copolymer composition is controlled by the feed ratio of ROX, and influenced by the chain length of alkyl group on ROX. The incorporation ratio and side‐chain length of the ROX unit have great influence on the thermomechanical properties and crystallinity of the copolymers.
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.
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.
Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.
Fully atomistic molecular dynamics (MD) simulations have been performed to examine the effect of PEGylation on the structure and drug loading properties of 25%–100% PEGylated poly(amidoamine) (PAMAM)‐G4 dendrimers in complex with 5‐fluorouracil (5‐FU) as a model anticancer compound. Theoretical estimates predict a complex stoichiometry of 23:1 for the 5‐FU:PAMAM‐G4 system in high agreement with isothermal titration calorimetry and nuclear magnetic resonance (NMR) experiments, thus supporting the validity of our computational approach. MD simulations reveal a progressive increase in the total drug loading capacity as the PEGylation degree becomes higher. In systems with PEGylation degrees ≥50%, drug complexation occurs almost exclusively within outermost polyethylene glycol (PEG) chains, due to their higher affinity toward complexation with 5‐FU compared to PAMAM‐G4 branches. On the other hand, the 25% PEG‐PAMAM‐G4 system retains the internal complexation capability of PAMAM‐G4 and provides additional assistance for drug retention through the cooperative interaction with back folded PEG chains, appearing as the most suitable option for drug delivery applications.
Copolymerization of ethylene with 4‐penten‐1‐ol (4P1O) is conducted by using a half‐titanocene catalyst. The incorporation of 4P1O is high as approximately 10 mol%. The assignments of the 13C NMR spectrum and the analysis of the sequence distribution show the existence of not only the alternative structure but also the repeated 4P1O units. The product of the reactive ratios is calculated as ca. 2.
Sub‐micrometer spheres of poly(glycidyl methacrylate) (PGMA) with a layer of poly(allylamine hydrochloride) (PAH) film are prepared by an easily controlled assembly method. The gold nanoparticles (Au NPs) exhibit a discontinuous structure on the PGMA@PAH particle surface, exhibiting a surface interaction between the PGMA spheres and the Au NPs. PAH not only modifies the surface of the PGMA particles but also affirmatively affects the crystallite of the PGMA particles. The real permittivity of the nanocomposite spheres is much higher than that of pure PGMA spheres. An improved thermal stability is observed in the nanocomposite spheres. The calculated bandgap (0.91 eV) of the nanocomposite spheres is observed to be lower than that (4.92 eV) of pure PGMA spheres.
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 homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)3] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)3/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 105 g mol‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)3/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).
An oxacyclophane framework is modified to include π‐conjugated segments positioned so as to allow an optimized face‐to‐face π‐stacking interaction between them. This unique architecture is first employed for the preparation of model compounds with defined interaction between two small molecular organic chromophores. The interaction allows facile through‐space energy transfer between the chromophores when they are held in the appropriate geometry. The oxacyclophane is thus employed in a polymer with consecutive short stretches of phenylene ethynylene such that polymer chain conjugation requires through‐space interaction between segments rather than the through‐bond π‐conjugation that typifies traditional conjugated polymers. The extent of the through‐space interactions along the polymer backbone is explored through photophysical measurements, calculations, X‐ray diffraction, and comparison with a variety of model and control materials.
Four‐arm poly(l ‐2‐hydroxybutanoic acid) [P(L‐2HB)]/poly(d ‐lactic acid) (PDLA) blends are phase‐separated to form P(L‐2HB)‐rich and PDLA‐rich domains. Hetero‐stereocomplex (HTSC) crystallization should occur at the interface of two types of domains. The crystallization temperature ranges, wherein HTSC crystallites, P(L‐2HB), and PDLA homocrystallites are crystallizable in the star‐shaped 4‐arm P(L‐2HB)/PDLA blends, are much narrower than those reported for linear 1‐arm P(L‐2HB)/PDLA blends, indicating that the star‐shaped architecture disturbs the isothermal crystallization of the blends. Exclusive HTSC crystallization is not observed for the star‐shaped 4‐arm blends during isothermal crystallization in marked contrast with the result reported for the linear 1‐arm blends.
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.
The synthesis of polymers with various functional groups has always been the core of polymer chemistry. Traditionally, there are two approaches to prepare such polymers: i) preparing functional monomers first and then conducting polymerization to get target functional polymers; and ii) post‐modification of a precursor polymer. Both methods unavoidably involve separation and purification of intermediate products, which is laborious and time‐consuming. A one‐pot synthesis strategy, which combines monomer preparation and controlled polymerization in just one reactor to generate well‐defined polymers efficiently, is thus proposed. Recent advances in the one‐pot synthesis of multifunctional polymers through a multicomponent system are provided in this article.
Polymeric microstructures can be immersed in an organic solution containing a reactive linker to functionalize the surface for attachment of nanoparticles, fluorescent dyes, proteins, DNA, and other species. However, organic media can swell and distort polymeric microstructures. Swelling and distortion can be irreversible when the linkers are themselves low‐molecular‐weight organics like ethylenediamine, which can bind to unreacted monomer groups or other functionalities within the polymer matrix. This work introduces an alternative approach for surface functionalization based on aqueous processing using higher‐molecular‐weight amines, which causes less distortion, but is comparably effective. The processes are compared by aminating crosslinked SU‐8 thin films and 3D “woodpile” microstructures, electrolessly depositing copper onto these primed surfaces, and measuring the amount of copper deposited and the degree of distortion caused by amination. The method provides a new route to low‐distortion SU‐8 microstructures and identifies a path for improving related processing with other polymeric materials and structure types.
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.
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