Well-Defined Ambipolar Block Copolymers Containing Monophosphorescent Dye

Well-defined ambipolar block copolymers containing carbazole, oxadiazole moieties, and only one homoleptic iridium­(III) complex between the carbazole and oxadiazole blocks were successfully synthesized by sequential living anionic polymerization with controlled molecular weights (Mw), a narrow molecular weight distribution (Mw/Mn < 1.15), and a high conversion yield (98–100%). The optimum conditions for the successful controlled synthesis of an oxadiazole-containing the homopolymer of poly­(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) have been established by controlling the nucleophilicity strength of the carbanion. In addition, the location and concentration of the homoleptic iridium­(III) complex were controlled by linking it to 1,1-diphenylethylene, which exhibits monoaddition characteristics in the main chain of the block copolymer

Effect of Biphenyl Spacers on the Anionic Polymerization of 2‑(4′-Vinylbiphenyl-4-yl)pyridine

The pyridine-containing monomer 2-(4′-vinylbiphenyl-4-yl)­pyridine (VBPPy), synthesized by the Suzuki coupling reaction, was successfully polymerized using diphenylmethylpotassium (DPM-K) as an initiator within 360 min at −78 °C, resulting in 100% yield and polydispersity <1.3, as with the living anionic polymerization of 2-vinylpyridine (2VP) and 2-(4-vinylphenyl)­pyridine (VPPy). By the block copolymerization of VBPPy with 2VP, VPPy, and methyl methacrylate (MMA), it was proven that the nucleophilicity of living poly­(2-(4′-vinylbiphenyl-4-yl)­pyridine) is between that of living poly­(2-(4-vinylphenyl)­pyridine) and that of living poly­(methyl methacrylate). Among the block copolymers, PVBPPy-b-PMMA was used to make nanocomposites in which gold (Au) nanoparticles (NPs) were present only in the PVBPPy zone of the phase-separated PVBPPy-b-PMMA) (fVBPPy = 0.23) film

Effect of Solvent Composition on Transformation of Micelles to Vesicles of Rod−Coil Poly(<i>n</i>-hexyl isocyanate-<i>block</i>-2-vinylpyridine) Diblock Copolymers

The self-aggregation behavior of an amphiphilic rod−coil block copolymer of poly(n-hexyl isocyanate-block-2-vinylpyridine) (PHIC189-b-P2VP228) (fP2VP = 0.78, Mn = 24.5K) in a tetrahydrofuran (THF)/water system was examined using dynamic light scattering (DLS), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The presence of a certain amount of water in the THF-based polymer solution induced a morphological transition from spherical solid micelles to open mouth platelike vesicles. The size of the aggregates increased with an increase in water content in the mixed solvent of THF/water. In the range of 30−40% water, the polymer formed vesicles with an interdigitated architecture of poly(n-hexyl isocyanate) (PHIC) at the center of the membrane and with the poly(2-vinylpyridine) (P2VP) block forming the outer layers and pointing toward the solvent. However, at higher water contents, the thickness of the bilayer increased due to the rearrangement of the vesicle membrane from a flip-flop to a lamellar architecture. After the degradation of the PHIC from the vesicles at basic pH, hollow spherical aggregates remained stable. After removing the THF from the mixed solvent using dialysis, large-sized compound vesicles were formed

2‑Isopropenyl-2-oxazoline: Well-Defined Homopolymers and Block Copolymers via Living Anionic Polymerization

Poly­(2-isopropenyl-2-oxazoline) (PIPOx) has drawn significant attention for numerous applications. However, the successful living anionic polymerization of 2-isopropenyl-2-oxazoline has not been reported previously. Herein, we describe how well-defined PIPOx with quantitative yields, controlled molecular weights from 6800 to over 100 000 g/mol and low polydispersity indices (PDI ≤ 1.17) were synthesized successfully via living anionic polymerization using diphenyl­methyl­potassium/diethyl­zinc (DPM-K/Et₂Zn) in tetrahydrofuran (THF) at 0 °C. In particular, we report the precise synthesis of well-defined PIPOx with the highest molecular weight ever reported (over 100 000 g/mol) and low PDI of 1.17. The resulting polymers were characterized by ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR) along with size exclusion chromatography (SEC). Additionally, the reactivity of living PIPOx was investigated by crossover block copolymerization with styrene (St), 2-vinylpyridine (2VP), and methyl methacrylate (MMA). It was found that the nucleophilicity of living PIPOx is of this order: living PS > living P2VP > living PMMA > living PIPOx. The self-assembly behavior in bulk of PIPOx-<i>b</i>-PS-<i>b</i>-PIPOx triblock copolymers having different block ratios of 10:80:10 and 25:50:25 was studied using transmission electron microscopy (TEM). The formation of spherical and lamellar nanostructures, respectively, was observed

Poly(1-adamantyl acrylate): Living Anionic Polymerization, Block Copolymerization, and Thermal Properties

Living anionic polymerization of acrylates is challenging due to intrinsic side reactions including backbiting reactions of propagating enolate anions and aggregation of active chain ends. In this study, the controlled synthesis of poly­(1-adamatyl acrylate) (PAdA) was performed successfully for the first time via living anionic polymerization through investigation of the initiation systems of <i>sec</i>-butyl­lithium/diphenyl­ethylene/lithium chloride (<i>sec</i>-BuLi/DPE/LiCl), diphenyl­methyl­potassium/diethyl­zinc (DPMK/Et₂Zn), and sodium naphthalenide/dipenyl­ethylene/diethylzinc (Na-Naph/DPE/Et₂Zn) in tetrahydrofuran at −78 °C using custom glass-blowing and high-vacuum techniques. PAdA synthesized via anionic polymerization using DPMK with a large excess (more than 40-fold to DPMK) of Et₂Zn as the ligand exhibited predicted molecular weights from 4.3 to 71.8 kg/mol and polydispersity indices of around 1.10. In addition, the produced PAdAs exhibit a low level of isotactic content (mm triads of 2.1%). The block copolymers of AdA and methyl methacrylate (MMA) were obtained by sequential anionic polymerization, and the distinct living property of PAdA over other acrylates was demonstrated based on the observation that the resulting PAdA-<i>b</i>-PMMA block copolymers were formed with no residual PAdA homopolymer. The PAdA homopolymers exhibit a very high glass transition temperature (133 °C) and outstanding thermal stability (<i>T</i>_d: 376 °C) as compared to other acrylic polymers such as poly­(<i>tert</i>-butyl acrylate) and poly­(methyl acrylate). These merits make PAdA a promising candidate for acrylic-based thermoplastic elastomers with high upper service temperature and enhanced mechanical strength

All-Acrylic Multigraft Copolymers: Effect of Side Chain Molecular Weight and Volume Fraction on Mechanical Behavior

We present the synthesis of poly­(<i>n</i>-butyl acrylate)-<i>g</i>-poly­(methyl methacrylate) (P<i>n</i>BA-<i>g</i>-PMMA) multigraft copolymers via a grafting-through (macromonomer) approach. The synthesis was performed using two controlled polymerization techniques. The PMMA macromonomer was obtained by high-vacuum anionic polymerization followed by the copolymerization of <i>n</i>-butyl acrylate and PMMA macromonomer using reversible addition–fragmentation chain transfer (RAFT) polymerization to yield the desired all-acrylic multigraft structures. The P<i>n</i>BA-<i>g</i>-PMMA multigraft structures exhibit randomly spaced branch points with various PMMA contents, ranging from 15 to 40 vol %, allowing an investigation into how physical properties vary with differences in the number of branch points and molecular weight of grafted side chains. The determination of molecular weight and polydispersity indices of both the PMMA macromonomer and the graft copolymers was carried out using size exclusion chromatography with triple detection, and the structural characteristics of both the macromonomer and P<i>n</i>BA-<i>g</i>-PMMA graft materials were characterized by ¹H and ¹³C NMR. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was employed for monitoring the macromonomer synthesis. Thermal characteristics of the materials were analyzed using differential scanning calorimetry and thermogravimetric analysis. The mechanical performance of the graft materials was characterized by rheology and dynamic mechanical analysis, revealing that samples with PMMA content of 25–40 vol % exhibit superior elastomeric properties as compared to materials containing short PMMA side chains or <25 vol % PMMA. Lastly, atomic force microscopy showed a varying degree of microphase separation between the glassy and rubbery components that is strongly dependent on PMMA side chain molecular weight

Synthesis and Characterization of Comb and Centipede Multigraft Copolymers P<i>n</i>BA‑<i>g</i>‑PS with High Molecular Weight Using Miniemulsion Polymerization

Comb and centipede multigraft copolymers, poly­(<i>n</i>-butyl acrylate)-<i>g</i>-polystyrene (P<i>n</i>BA-<i>g</i>-PS) with P<i>n</i>BA backbones and PS side chains, were synthesized via high-vacuum anionic polymerization and miniemulsion polymerization. Single-tailed and double-tailed PS macromonomers were synthesized by anionic polymerization and Steglich esterification. Subsequently, the copolymerization of each macromonomer and <i>n</i>BA was carried out in miniemulsion, and multigraft copolymers were obtained. The latex particles of multigraft copolymers were characterized using dynamic light scattering. The molecular weights of macromonomers and multigraft copolymers were analyzed by size exclusion chromatography. Moreover, the molecular weights and structures of macromonomers were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and ¹H nuclear magnetic resonance spectroscopy. The weight contents of PS in comb and centipede multigraft copolymers were calculated by ¹H nuclear magnetic resonance spectroscopy. The thermal properties of multigraft copolymers were characterized by thermogravimetric analysis and differential scanning calorimetry. The microphase separation of multigraft copolymers was observed by atomic force microscopy and transmission electronic microscopy. Rheological measurements showed that comb and centipede multigraft copolymers have elastic properties when the weight content of PS side chains is 26–32 wt %. Centipede multigraft copolymers possess better elastic properties than comb multigraft copolymers with the similar weight content of PS. These findings are similar to previous results on poly­(isoprene-<i>g</i>-polystyrene) comb and centipede copolymers made by anionic polymerization

Synthesis and Characterization of Graft Copolymers Poly(isoprene‑<i>g</i>‑styrene) of High Molecular Weight by a Combination of Anionic Polymerization and Emulsion Polymerization

In this work, high molecular weight “comb-shaped” graft copolymers, poly­(isoprene-<i>g</i>-styrene), with polyisoprene as the backbone and polystyrene as side chains, were synthesized via free radical emulsion polymerization by copolymerization of isoprene with a polystyrene macromonomer synthesized using anionic polymerization. A small amount of toluene was used in order to successfully disperse the macromonomer. Both a redox and thermal initiation system were used in the emulsion polymerization, and the latex particle size and distribution were investigated by dynamic light scattering. The structural characteristics of the macromonomer and comb graft copolymers were investigated through use of size exclusion chromatography, spectroscopy, microscopy, thermal analysis, and rheology. While the macromonomer was successfully copolymerized to obtain the desired multigraft copolymers, small amounts of unreacted macromonomer remained in the products, reflecting its reduced reactivity due to steric effects. Nevertheless, the multigraft copolymers obtained were very high in molecular weight (5–12 × 10⁵ g/mol) and up to 10 branches per chain, on average, could be incorporated. A material incorporating 29 wt % polystyrene exhibits a disordered microphase separated morphology and elastomeric properties. These materials show promise as new, highly tunable, and potentially low cost thermoplastic elastomers

Effect of Electron Beam and Gamma Rays on Carbon Nanotube Yarn Structure

<div><p>Individual carbon nanotubes (CNTs) exhibit excellent mechanical, electrical and thermal properties, leading to development of a new generation of advanced lightweight materials and spacecraft electronics substituting the electronics based on silicon. The direct assembly of CNTs into macroscopic fibers or sheets has been a way to overcome their dispersion and processing challenges. Because of a wide range of applications of this material, we investigate effectively the defects on CNT yarns structures created by electron beam and gamma sources and their impact on the morphology and mechanical properties. The irradiated samples with electron beam at doses of 400, 600 and 800 kGy had a decrease in the strength from 219.60 ± 18.90 MPa for pristine yarn to 108.86 ± 23.77, 153.15 ± 21.63, 170.50 ± 25.78 MPa, respectively. The sample irradiated with gamma in air at dose of 100 kGy had the strength increased slightly as compared with the pristine sample and an increase in the elasticity modulus from 8.79 ± 1.19 to 19.63 ± 2.02 GPa as compared to CNT pristine yarn. The quality of the CNT yarns that was gamma irradiated in air with absorbed dose of 100 kGy was not affected by the radiation process with improvement of 123% of the Young’s modulus.</p></div

Effect of Molecular Weight on the Ion Transport Mechanism in Polymerized Ionic Liquids

The unique properties of ionic liquids (ILs) have made them promising candidates for electrochemical applications. Polymerization of the corresponding ILs results in a new class of materials called polymerized ionic liquids (PolyILs). Though PolyILs offer the possibility to combine the high conductivity of ILs and the high mechanical strength of polymers, their conductivities are typically much lower than that of the corresponding small molecule ILs. In the present work, seven PolyILs were synthesized having degrees of polymerization ranging from 1 to 333, corresponding to molecular weights (MW) from 482 to 160 400 g/mol. Depolarized dynamic light scattering, broadband dielectric spectroscopy, rheology, and differential scanning calorimetry were employed to systematically study the influence of MW on the mechanism of ionic transport and segmental dynamics in these materials. The modified Walden plot analysis reveals that the ion conductivity transforms from being closely coupled with structural relaxation to being strongly decoupled from it as MW increases