Macromonomer Research Articles

Ring‐opening metathesis polymerization for synthesizing molecular bottlebrushes via the grafting‐through strategy

AbstractMolecular bottlebrush (MBB) has been considered as an important type of unimolecular nanomaterial for widespread applications ranging from energy to biomedicine, due to its typical one‐dimensional molecular conformation with tunable aspect ratio and chemical composition. In the recently decades, the ring‐opening metathesis polymerization (ROMP) combined with the grafting‐through strategy has emerged as a powerful tool for synthesizing MBBs with various architecture, including (multi)block MBBs, core‐shell MBBs, random MBBs and Janus MBBs et al. In this review, the recent advances on the synthesis of MBBs including the rational preparation of NB terminated macromonomers (MMs) and the grafting‐through ROMP are briefly summarized. Moreover, the emerging progress on the grafting‐through ROMP performed in the aqueous media is also highlighted.

Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Bottlebrush Polymers

Ring-opening metathesis polymerization (ROMP) mediated by Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh] is widely used to make bottlebrush polymers by polymerization of a macromonomer (MM), typically a low molecular weight polymer functionalized with a norbornene. Termed the grafting-through method, this strategy requires a high degree of living character (“livingness”) to form well-defined bottlebrush polymers. Here, we studied how various anchor groups, the series of atoms connecting the polymerizable norbornene unit to the polymer side-chain, affect livingness in ROMP in a series of exo-norbornene polystyrene MMs. First, we calculated the HOMO and HOMO/LUMO gap energies of MM structures containing five different anchor groups using density functional theory methods, finding that these energies spanned a range of 10 kcal/mol. We then performed kinetics experiments on each MM with target backbone degrees of polymerization (Nbb) of 100 to measure the propagation rate constant (kp,obs) under identical conditions. A positive correlation between the HOMO energy and measured kp,obs values emerged, revealing a 7-fold variation in kp,obs values across the five MMs, suggesting different degrees of livingness among the anchor groups. A series of studies targeting Nbb values ranging from 100 to 2000 further highlighted these differences: The MMs with high kp,obs values reached higher conversions at high target Nbb values with lower dispersities (D̵) than the MMs with lower kp,obs values. Finally, we evaluated the synthesis of bottlebrush pentablock copolymers using the MMs at the two extremes by injecting an MM aliquot into a catalyst solution five consecutive times, allowing for polymerization of each block before the next injection. MM conversion at each step was higher, and the D̵ values for each block were lower for the MM with the highest kp anchor group compared to the lowest kp anchor group. Taken together, these studies highlight how the anchor group dramatically affects both kp and livingness in ROMP, which is crucial for the synthesis of precise bottlebrush (co)polymers.

Preparation and profile control evaluation of core‐shell structure and surface‐hydrophobic modified polyacrylamide microsphere

AbstractPolyacrylamide (PAM) microsphere has been widely used in the field of profile control to reduce water cut in heterogeneous reservoirs. However, its mechanical strength and plugging ability are still needed to be improved. In this paper, a core‐shell structure and surface‐hydrophobic polyacrylamide M‐P(AM‐PEP) microsphere was prepared by using acrylamide (AM), block polyether macro monomer (PEP) and modified SiO2 with double bond on the surface as monomers through dispersion polymerization. After the optimization of synthesis conditions, the results of SEM and TEM confirmed that M‐P(AM‐PEP) microsphere had the nano‐scale spherical shape and the inorganic core/polymer shell structure, while the contact angle test results showed that M‐P(AM‐PEP) microsphere had the surface‐hydrophobicity. Swelling experiments presented that the size of M‐P(AM‐PEP) microsphere can be increased by 6 times and had obvious self‐gathering behavior. The inorganic core and self‐gathering behavior are helpful for improving mechanical strength and plugging ability of PAM microsphere, respectively. Profile control and oil recovery improvement experiment showed that injecting 0.1 PV M‐P(AM‐PEP) microsphere can decrease the water cut and increase the oil recovery of 17.95%. This new microsphere could be an efficient technology for the profile control in the heterogeneous reservoir.

Synthesis and characterization of new interpenetrated hydrogels from N-isopropylacrylamide, 2-oxazoline macromonomer and acrylamide

New interpenetrated hydrogels (IPN), sensitive to pH and temperature, were synthesized by sequential free radical polymerizations in aqueous medium. In the first stage, a thermosensitive hydrogel of poly(N-isopropylacrylamide) (HG-PNiPAAm) was prepared, and in the second stage a hydrogel of acrylamide and 2-oxazoline macromonomer (MM) containing carboxylic acid ester groups was synthesized in the presence of the PNiPAAm hydrogel. In both stages, bisacrylamide was used as a crosslinker. The 2-oxazoline macromonomer was a random copolymer of methyl-3-(oxazol-2-yl)-propionate (EsterOxa) (23 % mol) and 2-methyl-2-oxazoline (MeOxa) (77 % mol) with a polymerization degree of 21 and contained a vinylbenzene end group for radical polymerization. Five different IPN-hydrogels were synthesized, the amount of the oxazoline was varied systematically, and the EsterOxa units were finally hydrolyzed to carboxylic acid groups. The structure of the IPNs was characterized by 1H HR-MAS NMR spectroscopy. All IPN hydrogels showed a conformational transition when varying the temperature or the pH value and these transitions were a function of the composition of the IPN hydrogel. While pure HG-PNiPAAm resulted in a transition temperature of 31 °C, this value rose to 50 °C and higher for MM-H containing IPNs. This property was shown macroscopically as a contraction or expansion of the hydrogel but also in the 1H HR-MAS NMR measurements. The sensitivity to pH in the IPN hydrogels was manifested as a contraction of the volume of the hydrogel at low pH. While introducing poly(acryl amide) PAAm increased the degree of water absorption, increasing the amount of hydrolyzed EsterOxa macromonomer within the hydrogel decreased this absorption at high pH values. These features were attributed to the formation of hydrogen bonds between the acid and amide or protonated amino groups. A lower initial swelling at elevated temperatures but constant switching pH value (pH = 6) supported this reasoning. Importantly, at 20 °C and pH = 5.7 all IPN had a similar degree of swelling Q of 34 to 39, strongly reduced due to the IPN structure compared to a PAAmMM hydrogel (Q > 200). The reported IPNs result from a straight forward synthesis and are thus an interesting material for future applications as potent actuator and sensor materials.

Solvent Effects in Grafting-through Ring-Opening Metathesis Polymerization

Ring-opening metathesis polymerization (ROMP) utilizing Grubbs’ third-generation catalyst ((H2IMes)(Cl)2(pyr)2RuCHPh) shows the characteristics of living polymerizations, including molecular weights increasing with monomer conversion and the ability to make (multi)block copolymers. However, irreversible termination reactions still occur due to catalyst decomposition, leading to terminated chains, especially in the context of sterically demanding monomers such as macromonomers (MMs). In this work, we performed identical ROMP reactions on three different MMs in six solvents commonly used in ROMP with varying levels of purity. The solvents included ethyl acetate (EtOAc), dichloromethane (CH2Cl2), chloroform (CHCl3), toluene, tetrahydrofuran (THF), and N,N-dimethylformamide (DMF). All polymerizations were conducted under air targeting a bottlebrush polymer backbone degree of polymerization (Nbb) of 100. All three MMs included a norbornene on the α chain end and had a molecular weight (Mn) of ∼4 kg/mol. They included one polystyrene MM with a bromine on the ω chain end and two poly(n-butyl acrylate) MMs with either a bromine or a trithiocarbonate group on the ω chain end. Solvent choice, and in some cases the level of purity, led to significant differences in the propagation rate in these ROMP grafting-through reactions. Of the solvents tested, the propagation rates in EtOAc and CH2Cl2 were approximately 4-fold and 2-fold faster, respectively, than that in CHCl3, toluene, and THF for all MMs. Propagation was much slower in DMF for the polystyrene MM than all the other solvents and on par with the slower solvents for the two poly(n-butyl acrylate) MMs tested. The purity of the solvent in some cases had a profound effect on the propagation rate: In the case of EtOAc, purification led to a 2-fold decrease in propagation rate; in contrast, purification of THF was required to observe full conversion of a MM to a bottlebrush polymer. The functional group on the ω chain end did not influence the rate of ROMP. Utilizing UV–vis spectroscopy to measure catalyst decomposition, the main polymer termination route in ROMP, we uncovered dramatic solvent effects, where the catalyst decomposed over 10 times faster in THF and DMF than in toluene. Finally, studies targeting Nbb = 500 or 1000 revealed that toluene, EtOAc, and CH2Cl2 demonstrated the highest degree of “livingness” in ROMP. These results will enable the synthesis of complex polymer architectures using ROMP with a high degree of living character.

Synthesis and micellar property of amphiphilic brush-arm star copolymers via living ROMP

Norbornene macromonomers (MMs) with polystyrene (PS) or poly(tert-butyl acrylate) (PtBA) side chains were synthesized by a combination of atom-transfer radical polymerization (ATRP) and click reactions. A series of amphiphilic linear and star-shaped brush block copolymers were obtained through sequential ring opening metathesis polymerization (ROMP) of MMs by the use of the highly active olefin metathesis Blechert's catalyst and tri-functionalized Blechert's catalyst respectively, followed by hydrolysis reaction. These well-defined diblock molecular brushes can undergo further self-assembly to form spherical micelles in solution, which have been characterized using DLS, AF4-MALLS, AFM, TEM and fluorescence spectra. The dynamic diameter increases as the hydrophilic backbone content increases for the vast majority of the linear and star copolymers. Brush-arm star diblock amphiphilic copolymers have smaller hydrodynamic diameter and aggregation number than the corresponding linear analogues. Moreover, the critical micelle concentration (CMC) values of star diblock copolymers show less sensitive to the variety of composition.

Molecular Polymer Brushes Made via Ring‐Opening Metathesis Polymerization from Cleavable RAFT Macromonomers

AbstractThe use of labile covalent bonds such as oximes and acetals for their application in the synthesis, and controlled triggered deconstruction, of molecular polymer brushes (MPBs) is reported. Macromonomers (MMs) are produced via reversible addition‐fragmentation chain transfer (RAFT) polymerization using chain transfer agents (CTAs) featuring customized labile moieties. Ring‐opening metathesis polymerization (ROMP) of the MMs using the grafting‐through approach produced MPBs in which the cleavable CTA is incorporated along the backbone, between the brush mainchain and its side chains. Degradation (i.e., the detachment of side chains) of the brush is possible through exposure to an acid stimulus. Especially, ketoxime, solketal, and ethoxyethyl (EE) acetal‐based motifs demonstrate excellent orthogonality to the polymerization protocols. This study highlights how polymer architectures can be built from, and reverted to, single polymer chains by using well‐designed CTAs in a straight‐forward approach.

Removal of Methylene Blue by Hydrogels based on N, N-Dimethylacrylamide and 2-Oxazoline macromonomer

New hydrogels (HG) were synthesized in aqueous medium by free radical polymerization of N,N-dimethylacrylamide (DMAA) and 2-oxazoline macromonomer (MM) initiated by potassium persulfate (KPS) and catalyzed by N,N,N,N′-tetramethylethylenediamine (TEMED). In this polymerization, the monomer DMAA was also used as a crosslinker because it has the ability of self-crosslinking in the presence of peroxodisulfate initiator type. The macromonomer (DP = 24) was a gradient copolymer of 2-methyl-2-oxazoline and methyl-3-(oxazol-2-yl)-propionate with a styryl end group. 1H high-resolution (HR)-MAS NMR spectroscopy allowed to confirm the structure of hydrogels and to determine the molar content of DMAA and MM in each of them. Hydrogels (HG-H) containing carboxylic groups were obtained by basic hydrolysis of HG. Hydrolyzed hydrogels (HG-H) were used for the adsorption of methylene blue (MB) in aqueous medium. It was found that the MB adsorption increased as the initial MB concentration increased, and maximum adsorption capacities were found. The influence of pH value on MB adsorption was evaluated, showing that the MB adsorption capacity of the hydrogels was higher at pH value ≥ 5.7. Adsorption isotherms were studied using Langmuir and Freundlich models. The latter model describes best the process suggesting a possible adsorption mechanism through electrostatic interactions between MB and HG-H hydrogels. The MB adsorbed inside the hydrogels, could be removed with an acidic solution and therefore the hydrogel could be applied to adsorb MB again.

On Particle Size Distributions in Catalytic Chain Transfer Emulsion Polymerization: Chain-Extension and the Use of Derived Macromonomers as Reactive Surfactants in Emulsion Polymerization.

Catalytic chain transfer emulsion polymerization (CCTP) and subsequent chain extension via reversible addition-fragmentation chain transfer (RAFT) were used to synthesize amphiphilic macromonomers (MM), in the form of polymer latexes. The macromonomers consisted of two blocks whose first was a random copolymer of methacrylic acid and methyl methacrylate, at 35:65 mol:mol, while the second block was n-butyl methacrylate P[(MAA-co-MMA)-block-PBMA]. The block copolymer colloids were disintegrated and micellized upon addition of ammonia. The resulting nanosized polymer dispersions were used as reactive surfactants in the emulsion polymerization of n-butyl methacrylate. For this, a dual stage slow-fast monomer feed profile was used. The final polymer latexes were in the sub-100 nm range for the particle diameter at 30% w/w total polymer content. The emphasis of the work is to discuss and find an explanation for the observed particle size distributions in the three consecutive emulsion polymerization steps. The particle size distribution of the ω-unsaturated macromonomer latex synthesized by CCTP emulsion polymerization was found to be much broader than expected. This discrepancy is attributed to an extended particle nucleation period. The chain extension step in the macromonomer latex preparation showed considerable secondary nucleation. The presence of water-soluble macromonomer species from the CCTP emulsion polymerization step assured that control of chain growth persisted. The use of the amphiphilic macromonomers as reactive surfactants in the form of a nanosized aggregate seed dispersion showed that the average particle diameter could be tuned and that the molecular weight distributions could be regulated, when monomer starved conditions were used in the emulsion polymerizations.

Synthesis and Characterization of Stiff, Self-Crosslinked Thermoresponsive DMAA Hydrogels.

Stiff thermosensitive hydrogels (HG) were synthesized by self-crosslinking free radical polymerization of N,N-dimethylacrylamide (DMAA) and N-isopropylacrylamide (NIPAAm), adjusting the degree of swelling by carboxylate-containing sodium acrylate (NaAc) or a 2-oxazoline macromonomer (MM). The formation of hydrogels was possible due to the self-crosslinking property of DMAA when polymerized with peroxodisulfate initiator type. The MM was synthetized by the ring-opening cationic polymerization of 2-methyl-2-oxazoline (MeOxa) and methyl-3-(oxazol-2-yl)-propionate (EsterOxa), and contained a polymerizable styryl endgroup. After ester hydrolysis of EsterOxa units, a carboxylate-containing MM was obtained. The structure of the hydrogels was confirmed by 1H high-resolution (HR)-MAS NMR spectroscopy. Suitable conditions and compositions of the comonomers have been found, which allowed efficient self-crosslinking as well as a thermoresponsive swelling in water. Incorporation of both the polar comonomer and the macromonomer, in small amounts furthermore allowed the adjustment of the degree of swelling. However, the macromonomer was better suited to retain the thermoresponsive behavior of the poly (NIPAAm) due to a phase separation of the tangling polyoxazoline side chains. Thermogravimetric analysis determined that the hydrogels were stable up to ~ 350 °C, and dynamic mechanical analysis characterized a viscoelastic behavior of the hydrogels, properties that are required, for example, for possible use as an actuator material.

Finely Designed P3HT-Based Fully Conjugated Graft Polymer: Optical Measurements, Morphology, and the Faraday Effect.

In this work, our group synthesized and characterized a fully conjugated graft polymer comprising of a donor-acceptor molecular backbone and regioregular poly(3-hexylthiophene) (RRP3HT) side chains. Here, our macromonomer (MM) was synthesized via Kumada catalyst transfer polycondensation reaction based on ditin-benzodithiophene (BDT) initiator. The tin content of MM was then investigated by inductively coupled plasma-mass spectrometry (ICP-MS), which allowed for accurate control of donor/acceptor monomer ratio of 1:1 for the following Stille coupling polymerization toward our graft polymer (BP). The structures of the polymers were then characterized by gel permeation chromatography (GPC), NMR, and elemental analysis. This was followed by the characterization of optical, electrochemical, and physical properties. The magneto-optical activity of graft polymer BP was then measured. It was found that, despite the presence of the acceptor backbone, the characteristic large Faraday rotation of RRP3HT was maintained in polymer BP, which exhibited a Verdet constant of 2.39 ± 0.57 (104) °/T·m.

Optically active hybrid particles constructed by chiral helical substituted polyacetylene and POSS

AbstractOptically active hybrid particles consisting of chiral organic component and inorganic component integrate the individual advantages of the components in one entity. This article reports a new type of optically active hybrid particles constructed by helical substituted polyacetylene and octavinyl polyhedral oligomeric silsesquioxane (OvPOSS). The hybrid particles were prepared in a two‐step process. First, helical substituted polyacetylene with pendent vinyl groups was synthesized and named as macromonomer (MM). Then, hybrid particles were prepared from MM and OvPOSS by free radical suspension polymerization, in which OvPOSS acted simultaneously as comonomer and crosslinking agent. OvPOSS and MM together constituted a crosslinked network and formed spherical, porous hybrid particles. The resulting hybrid particles exhibited the desired optical activity, according to circular dichroism spectroscopy measurement. As an organic/inorganic hybrid molecule itself, OvPOSS moderately improved the thermostability of the organic component and meanwhile increased the porosity of the hybrid particles. It also helped to tune the surface morphology of the hybrid particles. The present study provides a novel class of optically active hybrid particles, and the preparation strategy may further work as a versatile platform for developing novel chiral hybrid materials.

One‐step synthesis of macromonomers catalyzed by phosphazene base

AbstractHerein, we report one‐step synthesis of polymethacrylates‐based macromonomers (MMs) in the presence of an organocatalyst phosphazene base (t‐BuP4) and a functional initiator N‐butyl‐4‐vinylbenzamide (N‐BVBA) containing a secondary amide and a styrenic double bond. A series of styrenic MMs with controlled molecular weight and relatively narrow polydispersity were synthesized under mild conditions. Detailed NMR analyses of the initiation process suggested that the anionic polymerization was initiated by nitrogen anion generated from abstraction of the proton from the secondary amide. NMR and MALDI‐TOF MS analyses confirmed: (1) the selective polymerization of methacrylate‐type double bonds, (2) controlled chain‐end functionality of MMs with an unreacted styrenic double bond, as well as (3) the absence of transesterification between N‐BVBA and methacrylate monomers. Furthermore, the homopolymerization and copolymerization of the MMs with comonomers were carried out for the preparation of graft copolymers. Through conventional radical polymerization, graft copolymers with different grafting densities were obtained at high MMs conversions, indicating the high reactivity of MMs. Thus, the one‐step approach demonstrates a simple metal‐free access to the controlled synthesis of MMs, and the prepared MMs can polymerize efficiently to convert into graft copolymers.

Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

AbstractCationic bottlebrush homopolymers are polymerized using a grafting‐through approach by ring‐opening metathesis polymerization (ROMP) to afford well‐defined polymers. Quaternary ammonium macromonomers (MMs) are prepared by quaternizing tertiary amine MMs synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The quaternary ammonium MMs undergo ROMP to target molecular weights (Mn = 30 000–100 000 g mol−1) and a low dispersity (Đ = 1.10–1.30). Halide‐ligand exchange between the third generation Grubbs catalyst (G3) and halide counter ions (bromide and iodide ions) of MMs changes the catalyst activity throughout ROMP, causing it to deviate from pseudo‐first order kinetic behavior; however, the polymerization still follows controlled behavior without significant catalyst termination. Increasing steric bulk of the MMs decreases the polymerization rate as well. Amphiphilic block copolymers are synthesized by sequential polymerization of quaternary ammonium MMs and polystyrene (PS) MMs. Using a PS macroinitiator affords block copolymers with lower Đ values as compared to the less active cationic macroinitiator.

Synthesis and characterization of pH- and thermo-responsive hydrogels based on poly(2-cyclopropyl-2-oxazoline) macromonomer, sodium acrylate, and acrylamide

New graft copolymer hydrogels based on sodium acrylate, acrylamide, and styryl-terminated poly(2-cyclopropyl-2-oxazoline) macromonomer (MM) were synthetized by free radical polymerization using N,N′-methylenebisacrylamide as cross-linker. The polymerization was carried out in water at 5 °C and was initiated by sodium peroxodisulfate/N,N,N′,N′-tetramethylethylenediamine. The MM and the hydrogels were characterized by NMR and FTIR spectroscopy. In the hydrogels, the sodium acrylate provided the sensitivity to changes in pH value while the MM provided sensitivity to temperature. In dependence of their composition, the bi-sensitive hydrogels showed conformational transitions with variation of temperature or pH value. This property was shown macroscopically as a hydrogel volume contraction or expansion as it was determined by swelling experiments in water at different pH values and temperatures. Due to phase separation within the hydrogels facilitated by the graft copolymer network structure, both sensitivities could be addressed individually by both triggers and defined swelling states could be addressed over a wide range by adjusting both temperature and pH.

Molecular Behavior of Different Polycarboxylate Superplasticizers

Four different types of polycarboxylic superplasticizers were synthesized by using different macromonomers, and then the molecular behavior of GPC, infrared, nuclear magnetic, cement hydration heat and micromorphology were characterized. The results showed that different types of PCEs have different molecular behaviors. The research showed that the molecular weight and molecular weight distribution of PCE1 were the smallest, and these four different types of PCEs have better molecular weight and molecular weight distribution. The infrared spectra of the four PCEs were not much different. However, by 1H NMR, the macromonomer used in PCE1 when synthesised was MPEG. The macromonomer used in PCE2 and PCE4 when synthesised were TPEG, and the macro monomer used in PCE3 was HPEG. Cement hydration heat and scanning electron microscope data showed that PCE4 has the better early strength.

Na Conductive Polymer/Inorganic Composite Electrolytefor High Performance All-Solid-State Na Battery

The Na secondary batteries has been attracted attention by concerning depletion of elemental Li in the earth crust. However, as with conventional Li-ion batteries, Na batteries use flammable electrolytes including organic solvents such as ethylene carbonate, propylene carbonate. Therefore, battery systems are demanded to shift all-solid-state battery for the increasing safety. Although the β-Al2O3 is used as solid electrolyte of all-solid-state Na battery by using inexpensive material, ionic conductivities are low value due to having two-dimensional ion conduction path. In the contrast, the Na super ionic conductor (NASICON) were reported by Hong [1] as an inorganic electrolyte showing high ionic conductivity (10-4~10-3 Scm-1 at room temperature) by three-dimensional conduction path. However, in the case of pellet electrolytes fabricated by sintering method, capacity of all-solid-state battery exhibits low value due to low interfacial stability and high resistance between electrode and electrolyte. Therefore, we propose composite electrolyte of inorganic and polymer materials in order to fabricate new type solid electrolyte having high interfacial stability, ionic conductivity and flexibility. Herein, we report morphology, electrochemical properties and stability with Na metal anode on Na conductive polymer/inorganic composite electrolytes. Polymer/inorganic composite electrolytes were prepared by mixing of polyether-based macro monomer, NaN(SO2CF3)2 as an alkaline salt, 2, 2-dimethoxy-2-phenylacetophenone as a photoinitiator, acetonitrile as a solvent and Na3Zr2Si2PO12 (NZSP) powder as an inorganic electrolyte of NASICON type electrolyte. The composition percentage of NZSP were changed between 0 to 300wt%. After stirring, vacuum dried viscous liquid were casted to glass substrate and polymerized by UV irradiation to form composite electrolyte films. Thermal, transport and molecular properties of composite electrolytes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and AC impedance method, respectively. Fourier transform infrared spectroscopy (FR-IR) was applied in order to investigate interaction into composite electrolytes. Moreover, interfacial resistances were measured by AC impedance on Na symmetric cells which were maintained 60oC in order to evaluate interfacial stability. Fig. 1 show prepared polymer electrolyte (0 wt% NZSP) and composite electrolyte containing 30wt% NZSP powder (30wt% NZSP). In comparison with 0wt% sample, 30wt% sample exhibited high flexibility by improving stress distribution due to high ability of dispersion of NZSP particles, following Fig. 1(d). The composition dependence on glass transition temperature (T g), which is defined as the phase transition point glass state to rubber state, exhibited to decreasing tendency of T gs with addition NZSP under approximately 100wt% NZSP from Fig. 2. The decreasing T gs were considered to cause by interaction between polymer and inorganic electrolyte or ions (cation, anion) and inorganic electrolyte particles. Moreover, this phenomena could expect increasing ionic conductivity because of improving segmental motion of polymer and cationic mobility. In the over 100wt% NZSP samples, changing T g were not confirmed. In the comparison with 0wt% NZSP and 300wt% NZSP sample on Nyquist plots, although 0wt% NZSP sample showed symmetric semicircle spectrum, 300wt% sample showed asymmetric semicircle. In order to investigate detail of this phenomena, 300wt% sample was attempted to separate resistance components. As a result, two resistance components were contained, bulk resistance (R b) and grain boundary resistance (R gb) between NZSP particles. Fig. 3 show NZSP composition dependence on ionic conductivity. In the low composition range (<100wt% NZSP), relatively high value were confirmed in comparison with 0wt%. In the contrast, over 100wt% NZSP samples exhibited low value including Rb and Rgb by contribution of presence of high R gb. The composition dependence on interfacial resistance (R i) between Na metal and electrolyte is shown Fig. 4. The R i exhibited lowest value at 200wt% NZSP sample from Fig. 4. The 200wt% NZSP sample was considered to the change point for Na ion transport mechanism. Therefore, R i were suggested to could decrease by addition NZSP from above results. The polymer/inorganic electrolytes shifted difference transport mechanism from low to high composition range. Although ionic conductivity showed relatively high value in the low composition range, low value were confirmed over 100 wt% NZSP samples. The increasing ionic conductivity were considered to cause by improving segmental motion because of some interaction of composite electrolyte. The high composition range showed low value due to presence of high R gb. In the interfacial stability, R i exhibited lowest value at 200wt% NZSP sample. Therefore, the composite electrolytes of optimal composition are expected to realize high-rate operated all-solid-state Na battery. [1] H. Hong, et., al., Mat. Res. Bull., 11, 173-182 (1976). Figure 1

Synthesis of ultrahigh molecular weight bottlebrush block copolymers of ω-end-norbornyl polystyrene and polymethacrylate macromonomers

Well-controlled polystyrene-polymethacrylate bottlebrush block copolymers (BBCPs) of ultrahigh molecular weight using ω-end-norbornyl polystyrene as the macromonomer for the first block were synthesized by combining living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). The ω-end-norbornyl polystyrene (NB-PSt), poly(tert-butyl methacrylate) (NB-PtBMA), poly(methyl methacrylate) (NB-PMMA), and poly(benzyl methacrylate) (NB-PBzMA) macromonomers (MMs) were synthesized by the LAP. The ROMP of the MMs led to poly(NB-g-St) (molecular weight, Mn = 1515 kDa, and dispersity, Ð = 1.12), poly(NB-g-tBMA) (Mn = 1470 kDa, Ð = 1.49), poly(NB-g-MMA) (Mn = 1128 kDa, Ð = 1.42), and poly(NB-g-BzMA) (Mn = 941 kDa, Ð = 1.16) bottlebrush homopolymers at degree of polymerization (DP) of 500. Synthesis of the BBCP, P(NB-g-St)-b-P(NB-g-tBMA) was well-controlled with high molecular weight and a low dispersity (Mn = 3002 kDa, Ð = 1.17) with a total DP of 976. The self-assembly of the resulting BBCP films revealed periodic lamellar morphologies with characteristic photonic crystal properties.

New strategy of improving the dispersibility of acrylamide-functionalized graphene oxide in aqueous solution by RAFT copolymerization of acrylamide and acrylic acid

Graphene Oxide (GO) is a very unique material with a broad potential. However, modifying GO effectively to achieve maximum dispersion stability in a medium is very critical for various applications. In this paper, GO/poly(acrylamide-co-acrylic acid) (PAM-co-PAA) composites (GMAs) were readily prepared by a two-step method. Firstly, acrylamide (AM) monomer was immobilized onto GO sheets through an amidation reaction, followed by copolymerization of acrylamide (AM) and acrylic acid (AA) on the surface of GO sheets in a second step via reversible addition-fragmentation chain transfer (RAFT) polymerization, GO-AM (GM) acting as a macro monomer to participate in the copolymerization. Characterization by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) provided evidence for the successful polymerization of AM/AA on the surface of GM. Thermogravimetric analysis (TGA) revealed greater than 50 wt% grafting of PAM-co-PAA. X-ray diffraction (XRD) analysis showed that the d-spacing of the GO sheets increased with the introduction of the polymer. The morphological studies were performed by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscope (TEM), showing that a polymeric layer covered the surface of GO sheets. Compared to the original morphologies of GO sheets, the more disordered structures were attributed to the intercalation of polymer molecules into the spacing of the GO sheets and the reaction of functional groups on the surface of GO sheets. The dispersion stability test demonstrated that the reported facile method could generate GO-polymer hybrid nanomaterials stably dispersed in aqueous solution for more than 15 days, showing a great potential and practical applications for composite coatings.

Polyoxazoline-Based Bottlebrush and Brush-Arm Star Polymers via ROMP: Syntheses and Applications as Organic Radical Contrast Agents.

The synthesis of functional poly(2-alkyl-2-oxazoline) (PAOx) copolymers with complex nanoarchitectures using a graft-through ring-opening metathesis polymerization (ROMP) approach is described. First, well-defined norbornene-terminated poly(2-ethyl-2-oxazoline) (PEtOx) macromonomers (MM) were prepared by cationic ringopening polymerization. ROMP of these MMs produced bottlebrush copolymers with PEtOx side chains. In addition, PEtOx-based branched MMs bearing a terminal alkyne group were prepared and conjugated to an azide-containing bis-spirocyclohexyl nitroxide via Cu-catalyzed azide-alkyne cycloaddition (CuAAC). ROMP of this branched MM, followed by in situ cross-linking, provided PEtOx-based brush-arm star polymers (BASPs) with nitroxide radicals localized at the core-shell interface. These PEtOx-based nitroxide-containing BASPs displayed relaxivity values on par with state-of-the-art polyethylene glycol (PEG)-based nitroxide materials, making them promising as organic radical contrast agents for metal-free magnetic resonance imaging (MRI).