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Jack bean urease, the first nickel metalloenzyme, and crystallized enzymes have historical significance due to their several applications in the biomedical and other fields. For the first time, cross-linker free pH-responsive hydrogel-urease bioconjugates have been reported. Without the use of divinyl benzene or divinyl acrylamide derivatives, urease was immobilized inside the hydrogel matrix and various grades of bioconjugates were synthesized. The hydrogel-urease bioconjugate exhibits excellent swelling-deswelling and pH-responsive characteristics without affecting the urease enzyme. The pH-responsive bioconjugates were characterized by FT-IR, powder XRD, SEM, TGA, and UV-vis spectroscopy. Urea hydrolysis and enzyme affinity have been investigated at pH 4, pH 7, and pH 11 using bioconjugates and free urease. At basic pH, BCs showed excellent enzyme activity. In summary, this technique is effective for stabilizing biomacromolecules at different pHs for a variety of real applications.

Although pyridine bridged oxypolybenzimidazole (PyOPBI) membranes are considered to be promising high-temperature proton exchange membrane (HT-PEM) materials that have the potential to overcome man...

Hollow polymer nanocapsules (HPN) consisting of a ferrocenyl shell have been developed by crosslinking the polymer chains grafted over silica nanoparticles (SiNP) which were synthesized via the one pot grafting from surface initiated reversible addition–fragmentation chain transfer (RAFT) approach followed by removal of the sacrificial silica template. Copolymer brushes composed of a ferrocene containing polymer, poly[2-(methacryloyloxy) ethyl ferrocenecarboxylate] (pFcMA) and an alkyne terminated polymer, poly(propargyl 4-vinylbenzyl ether) (pPVBE), were constructed in three different motifs on the SiNP surface as a shell. Two types of block copolymer grafted SiNP, p(FcMA-b-PVBE)-g-SiNP and p(PVBE-b-FcMA)-g-SiNP, and a random copolymer grafted SiNP, rp(FcMA-co-PVBE)-g-SiNP were chosen to investigate the influence of polymer architecture on the HPN morphology. Various structural characterization studies of all the copolymer grafted SiNP confirmed the brush morphology on the particle surface consisting of a core–shell structure. In order to bring robustness to the copolymer shell, crosslinking of the polymer chains was performed using a diazide crosslinker, 1,4-bis(azidomethyl)benzene and pPVBE via the copper-azide click reaction. Various microscopic studies showed that the incorporation of 30 wt% of cross-linker yielded sufficient structural stability leading to HPN formation with a ferrocenyl shell after etching away silica with HF treatment. A random copolymer skeleton was found to be the best choice for use as a polymer shell to engineer a successful HPN structure compared to a block copolymer shell. In addition, encapsulation of oxide free aluminum nanoparticles (Al-NP) inside the hollow cavity of both block and random copolymers was successfully carried out to make a composite material consisting of both Al and Fe.

Metal organic frameworks (MOFs) have received considerable importance as proton conducting materials in recent times. However, most of the MOFs lack the ability to form film, which limits their app...

Despite several unique advantages, high-temperature proton-exchange membrane fuel cells (HT-PEMFCs) based on polybenzimidazole (PBI) membranes suffer from various drawbacks like weak chemical resis...

Phosphoric acid (PA) leaching, low proton conductivity and weak mechanical strength of the polybenzimidazole (PBI) membrane need to be improved considerably for the development of proton exchange membrane (PEM). We have addressed these issues by preparing a mixed matrix composite (MMC) membrane comprising of oxy-polybenzimidazole (OPBI) and imidazole ionic liquid modified silica (ImILSi). Imidazolium based ionic liquid was synthesized and grafted to the surface of the silica nanoparticles (SiNP) to obtain ImILSi which further blended with OPBI to obtain OPBI@ImILSi. The uniform dispersion nature of the ImILSi in the OPBI matrix and the strong H-bonded interfacial interactions between nanofillers and polymers are found to be primary reason for significant improvement of various physical properties of the MMC. TGA, DMA and stress-strain studies exhibited significant enhancement in the thermal and mechanical properties of the MMC membranes. Most importantly, due to the loading of hydrophilic ImILSi, the MMC membranes resulted higher PA loading (∼3-fold increase) which enabled the formation of facial proton transport nanochannels for their superior proton conduction under anhydrous environment and elevated temperature. For example, the OPBI@ImILSi-3% membrane showed proton conductivity value of 0.219 S cm−1 at 160 °C which is a ∼4-fold increase compared to OPBI membrane.

Polybenzimidazole (PBI) random co-polymers containing alicyclic and aromatic backbones were synthesized using two different dicarboxylic acids (viz., cyclohexane dicarboxylic acid and terephthalic acid) by varying their molar ratios. The synthesized co-polymers were characterized by inherent viscosity (IV) measurements, Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1H NMR) spectroscopy, X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA). The co-polymer composition was determined by 1H NMR spectroscopy. The cyclohexyl based PBI possessed a lower proton conductivity (114 mS cm−1) than terephthalic acid based PBI (220 mS cm−1). The aromatic PBI had a high tensile modulus of 11 GPa, whereas the modulus of cyclohexyl PBI was only 2 GPa. By suitably selecting the monomer concentration, the co-polymer properties can be altered (both proton conductivity and mechanical properties). Among different co-polymers, one synthesized using 30 mol% cyclohexane dicarboxylic acid and 70 mol% terephthalic acid exhibited good elongation (8%) and modulus (10.5 GPa) values and improved proton conductivity (242 mS cm−1). In the doped condition, the co-polymer registered an elongation of 52% and a tensile modulus of 170 MPa. The high conductivity of this composition is attributed to the presence of ordered domains (shown by field emission scanning electron microscopy) present in the co-polymer in the doped condition. The co-polymers are thermally stable and the thermal stability increased with an increase in the aromatic content. Thus, alicyclic–aromatic co-polymerization is a viable technique to prepare high-temperature proton exchange membranes.

In this report, non-hydrogen bonded, segmented polyurethane (SPU) of ferrocene functionalized polybutadiene diol has been synthesized and studied in depth to understand the role of ferrocene moiety in the structure-property relationship of SPU. Interactions among hard segments of SPU through the ferrocene moiety played a vital role in the separation of hard and soft segments. Ferrocene attached hydroxyl terminated polybutadiene (HTPB) diol was polymerized with isophorone diisocyanate followed by curing at 70 °C to obtain polyurethane (PU). Dynamic mechanical analysis (DMA) and an in-depth small angle X-ray scattering (SAXS) studies revealed the presence of a strong microphase separation between hard and soft segments which resulted in the formation of nano hard segment domain (HSD) in PU and thus yielded SPU. Though spectroscopic studies of SPU could not identify any hydrogen bonding between the PU chains but due to the presence of ferrocene moiety on the adjacent carbon of urethane group, favorable electrostatic interaction between the hard segments has been identified. This interaction was found to be the driving force for the formation of micrometer scale assemblies of nano HSD, as clearly seen in scanning electron microscopy, and the size of nano HSD assembly increases with increasing ferrocene content in the HTPB. This dependency confirming that the presence ferrocene functional moiety is responsible for formation of assembly of nano HSD which in turn enhanced tensile strength and aggregation induced emission intensity of the resulting SPU.

In this work, montmorillonite clay was organically modified using two surfactants which are largely different in their chemical structure - one is dimethyldihydrogenated ammonium chloride tallow (DDACT), that contains two long alkyl chains and the other is tributyl phosphonium molecule (TPB), a molecule containing short alkyl chains. The objective of the work is to study the effect of these surfactants’ structure on the properties of OPBI for proton exchange membrane (PEM) fuel cell applications. The morphology study of the membranes using PXRD and TEM revealed intercalated nanostructures using both the clays. The increment in thermal stability and Tg was found to be higher in the case of TPB modified clay membranes than the tallow amine modified clay membranes. Acid doping and swelling studies were performed and the values again reflected the nature of the surfactant used with phosphonium cation containing membranes showing higher PA doping levels. Specific swelling volume of the membranes portrayed the controlled swelling behaviour of all the nanocomposite membranes. Proton conductivity of the membranes were found to be lower than the pristine OPBI owing to the tortuous conduction pathway created by the clay sheets.

In this work, iron containing hydroxyl terminated polybutadiene (Fe-HTPB) based binder cum burn rate catalyst has been developed without altering the crucial physical properties of HTPB. Ferrocene, the source of Fe in the Fe-HTPB, has been grafted at the terminal carbons of HTPB to ensure no alternation in microstructure of HTPB which in turn helped in retaining physical properties of pristine HTPB. The structure and the presence of ferrocene as the end cap groups of the Fe-HTPB were confirmed by solid-state NMR and MALDI-TOF-MS analysis. Control over the viscosity and Fe content of the Fe-HTPB was achieved by varying the grafting reaction recipes and conditions. The Fe content, as measured by inductively coupled plasma - atomic emission spectroscopy (ICP-AES) in the Fe-HTPB varied from 0.06% to 0.165% (by weight) and found to be responsible for increasing viscosity of Fe-HTPB from 5857 mPa S to 11,890 mPa S. Non aluminized composite solid propellants (CSPs) with 86% (wt%) ammonium perchlorate loading were prepared using Fe-HTPB as a binder for studying the burn rate efficiency. Burn rates of CSPs made from Fe-HTPB binders were found to be enhanced by ∼125% compared to CSPs of pristine HTPB. At 40 bar pressure, the burn rate of CSPs made from Fe-HTPB and pristine HTPB binders are 20.56 and 9.07 mm/s burn rate, respectively. In addition, all the CSPs made from Fe-HTPB were found to be very stable as their pressure index is less than 0.5.

Correction for ‘Rational design of microporous polybenzimidazole framework for efficient proton exchange membrane fuel cells’ by Harilal et al., J. Mater. Chem. A, 2022, https://doi.org/10.1039/d2ta00734g.

In this work, a pyridine based polybenzimidazole (PPBI) is synthesized (I.V. 3.3 dL/g) from pyridine dicarboxylic acid and hydrochloride salt of diaminobenzidine. The polymer is characterized by FTIR and 13C CP-MAS NMR. The resultant PPBI possesses high storage modulus of >10 GPa, tensile modulus of ∼1 GPa and tensile strength of ∼150 MPa. Amine functionalized silica nanoparticles in different degrees of amine grafting (LAC-low amine content/HAC-high amine content) are successfully incorporated into PPBI to result nanocomposite membranes. Both the neat PPBI and nanocomposites exhibit significant affinity towards phosphoric acid as indicated by the high acid uptake in short time (5 h). Proton conductivity of nanocomposites is increased by the addition of LAC/HAC nanoparticles (>250 mS/cm at 140 °C). The HAC nanoparticle enriched nanocomposite (HAC 7) reveals self-assembly of amino-silica nanoparticles due to base-base repulsion (imidazole-amine). Hydrophobicity of nanocomposite membranes is increased with increase in LAC/HAC content which is attributed to the strengthening of hydrogen bonding between PPBI and nanoparticles.

The present article reports the investigation on the effects of solvent and position of functionality on various physical properties of polyurethanes (PUs) based on hydroxyl-terminated polybutadiene (HTPB). The PU films (curative) were prepared by coupling HTPB (P0) with isophorone diisocyanate (IPDI) in various solvent media. The PUs obtained in different solvent media displayed similar thermal profile and glass transition temperature (Tg), but their tensile properties varied significantly. Optimized tensile properties were observed when tetrahydrofuran was used as the solvent media. In the course, the investigation of the functionality effect, tetrazole (M1, M2, and M3) were covalently attached at the terminal carbon of HTPB to obtain three modified HTPBs (P1, P2, and P3), thereby coupling with IPDI to obtain the corresponding tetrazole functional PUs films. Pristine (P0–PU) and functional PU (P1–PU, P2–PU, and P3–PU) films have similar thermal profile and Tg (−76 °C), but they have a notable enhancement in tensile properties; for example, tensile strength and elongation at break of P0–PU were found to be 3.21 MPa and 727%, respectively, whereas these values were 4.84 MPa and 958%, respectively, in the case of P3–PU. It was observed that on increasing the number of methylene group from 1 to 3 between HTPB and tetrazole moiety, the strength of hydrogen bonding increases, which facilitates better packing of urethane network in the PU and hence improves the tensile properties. Also, modification of pristine HTPB with tetrazole derivatives enhanced the calorific values of the resulting PUs.

We report successful synthesis of three types of pyridine bridged tetraamine (PyTAB) monomers namely PyTAB-COOH, PyTAB-OH and PyTAB-CF3 where additional functional groups –COOH, -OH, and –CF3, respectively have been tagged in the parent PyTAB for the synthesis of soluble polybenzimidazoles (PBI). These newly designed PyTAB monomers were polymerized with varieties of dicarboxylic acids to yield series of pyridine bridged PBIs (PyPBIs). Thermal stability, mechanical strength (storage modulus) and glass transition temperature of PyPBIs were found to be influenced by the presence of additional functionalities in the PyTAB monomer and attributed to the hydrogen bonding capability and hydrophobicity of the functional groups. Newly synthesized PyPBIs displayed greater stability in phosphoric acid (PA) when compared with the non-functionalized PyPBIs, former is stable up to 85% PA whereas later is only up to 60% PA. The increased intermolecular interactions and possibility of crosslinking between the polymer chains owing to the presence of functional groups in the functionalized PyPBIs caused the increased stability in PA. The significantly low swelling (

Surface functionalization of silica nanoparticles (SiNP) has gained attention as an efficient methodology in improving the properties of the proton exchange membrane (PEM). Here, we report the development of block copolymer grafted SiNP (BC-g-SiNP) as functional nanofiller which was further blended with oxypolybenzimidazole (OPBI) to prepare nanocomposite-based PEM. Block copolymer chains consisting of poly (N-Vinyl imidazole) (pNVI) and poly (N-Vinyl-1,2,4-triazole) (pNVT) were grown on the SiNP surface using grafting-from RAFT polymerization in one pot process. Two series of BC-g-SiNP namely pNVI-b-pNVT-g-SiNP and pNVT-b-pNVI-g-SiNP were synthesized by altering the polymer chain grafting sequence. A series of BC-g-SiNP was developed by varying chain length of each block to understand the effect of the chain sequence and length on the properties of nanofiller and their influence in altering the PEM properties. The block copolymer structure, chain sequence and chain length were confirmed by means of NMR and GPC analysis of the cleaved copolymer chains. The BC-g-SiNP exhibited core-shell morphology and thickness of the shell altered as the chain length and sequence of the grafted chains tuned. Phosphoric acid (PA) loaded OPBI/BC-g-SiNP nanocomposite PEM showed very high thermal, mechanical and chemical stabilities along with the proton conductivity as high as 0.278 S cm-1 at 180 °C in case of OPBI/P6(3%). A very clear-cut dependence of the PEM properties was observed on the architecture of the BC-g-SiNP such as chain length and sequence.

A facile method for the simultaneous delamination and the lateral size reduction of layered double hydroxides (LDH) is reported. This method directly resulted in the delaminated mesoporous LDH nanoplatelets (nanodot LDH) with the high specific surface area (lateral dimensions as low as 10–30 nm and featured a thickness of ∼1 nm). Such prepared LDH was used as fillers for isotactic polypropylene (iPP). For the purpose of comparison, LDH having different surface areas were also used as fillers for iPP. The incorporation of nanodot LDH showed a remarkable improvement in the polymer properties with only 1 wt % loading. The uniformly dispersed LDH particles have a significant effect on the nucleation ability, thermal stability, and mechanical properties of iPP. The nucleation ability of iPP in the presence of nanodot LDH is the best compared to other iPP nanocomposites reported using LDH as fillers in the literature. Furthermore, the microstructure of the iPP nanocomposites was systematically investigated at m...

The weak binding between carbohydrates and proteins is a major constraint toward the development of carbohydrate-based therapeutics. To address this, here we report the synthesis of glycopolymer (GP)-grafted silica nanoparticles (SiNP) by using reversible addition–fragmentation chain transfer (RAFT) polymerization through the grafting-from approach using a multistep process. GP chains of various lengths with controlled molecular weight and narrow polydispersities were grown on the RAFT agent anchored SiNP surface using mannosyloxyethyl methacrylate (MEMA) as a glycomonomer. Spectroscopic (FT-IR, NMR) and thermogravimetric studies confirmed the grafting of poly(MEMA) chains on the SiNP surface and also showed that the dry DMF is a better solvent as compared to water/ethanol mixture for carrying out the MEMA polymerization on SiNP surface. The mean diameter of the dry GP-grafted SiNPs (GP-g-SiNPs) obtained from microscopic studies was in the range 50–60 nm, whereas the hydrodynamic diameter as obtained usin...

Proton exchange membrane (PEM) has been developed from the polymer blend of polybenzimidazole (PBI) and poly(azomethine-ether) (PAME). The effects of the blend compositions on the properties such as thermo-mechanical stability, proton conductivity etc. of PEM were studied. The miscibility of the blend membranes was confirmed by characterizing the blend samples using varieties of spectroscopy and thermo dynamical techniques. FT-IR and SS-NMR studies revealed the presence of specific interactions between the two polymers. All blend membranes showed single glass transition temperature (Tg) attributing that the this blend system is a miscible blend. The thermogravimetric studies confirmed that the blend membranes were more stable than the pristine PBI below 300 °C temperatures and less stable above 300 °C. Morphology probed by transmission electron microscopy studies displayed morphological features which consisted of both thread like structure and particle like structures thus confirming the uniform mixing of polymers in the blends. Mechanical stabilities of the blend membranes were quite high compared to the pristine polymers as obtained from the dynamic mechanical analyzer (DMA) studies. The blend membranes showed higher proton conductivity compared to pristine PBI. The proton conductivity increased upon increasing the percentage of PAME in the blend membranes. All these results indicated that the blend membranes are promising candidates for the application in high temperature proton exchange membrane in fuel cell.

Here we report a simple and one-pot method for the synthesis of glycopolymer based colloidal particles with tunable core–shell morphology using reversible addition fragmentation chain transfer (RAFT) polymerization. A hydrophilic carbohydrate functionalized monomer (called glycomonomer) namely allyl-α-D-glucopyranoside (α-Glu) was polymerized with the RAFT agent to yield a macro-sugar chain, which acts as a macro-RAFT agent, and then this chain was further extended by copolymerizing the hydrophobic styrene monomer. The resulting polymer chains consist of polystyrene (PS) as a hydrophobic chain and glycopolymer (GP) as a hydrophilic chain. Several microscopic techniques which include FE-SEM, TEM, AFM and confocal Raman imaging proved the formation of core–shell colloidal particle morphology of the synthesized PS–GP in which PS was found in the core of the particle and the shell was made up of GP. The tunability in the particle size and in the core (PS)–shell (GP) dimension was achieved by altering the macro-sugar chain length and hydrophilic monomer (sugar) concentration in the polymerization feed. The formation of more number of macro-sugar chains with the increasing sugar content in the feed led to the production of a large number of smaller sized micelles in the polymerization medium which yielded smaller size particles. The colloidal stability and the molecular weight of the resulting PS–GP core–shell nanoparticles were found to be dependent upon both macro-RAFT and sugar content in the reaction feed.

Summary Understanding structure-property relationship between polymer-nanoparticle interface and the distribution of interfacial region and its properties is crucial in establishing the bulk properties of polymer like mechanical stability and conductivity. In this article we try to draw a comparison of the effect of silica nanoparticles modified with three different modifiers on the properties of oxy-polybenzimidazole (OPBI) to understand the role played by the chemical structure of the organic modifying molecule. We highlight how small changes in the structure of the chosen molecule can bring about substantial improvements in polymer nanocomposites owing to the self-assembly of nanofillers. We use aminopropyltriethoxysilane (AMS), N-(3-trimethoxysilylpropyl) diethylenetriamine (LAMS) and ionic liquid modified silica (ILMS) for the surface modification of silica nanoparticles. The extent of interfacial interaction between each of these silica nanoparticles with OPBI matrix was found to be in the order OPBI/AMS

In the present work, proton exchange membrane (PEM) based on series of polybenzimidazole (PBI) composites are prepared with acidic surfactant like molecules (ASMs) with an objective to improve properties of PEM especially proton conductivity. Composites are obtained by homogenizing poly (4, 4′-diphenylether-5, 5′-bibenzimidazole) (OPBI) in three different ASMs namely camphorsulfonic acid (CSA), p-toluenesulfonic acid (PTSA) and mono-n-dodecyl phosphate (MDP). FT-IR and solid-state NMR studies indicate the presence of interactions between OPBI and ASMs which are necessary for obtaining homogeneous composite membranes. Mechanical reinforcement is observed in case of composite membranes and storage modulus increases with increasing ASM loading in the composite. The detailed thermal analysis shows that phosphoric acid loaded (PA) composite membranes have higher thermal stability than the PA loaded pristine OPBI, it increases with increasing loading of ASM and it largely depends upon the type of ASM in the composite. Though OPBI is an amorphous polymer but ASMs self-organizes themselves in the polymer matrix owing to the strong interaction between OPBI and ASMs. As a result composite membranes display the crystalline character which in turn significantly influences the morphological features of the composites. Fibrillar to porous morphology are observed in composites depending on the type and loading of ASM. This morphological features and the crystalline nature of the composites are found to be responsible for mechanical reinforcement and significant increase in PA loading. The PA doped pristine OPBI, OPBI/CSA-20%, OPBI/PTSA-20% and OPBI/MDP-20% composite membranes proton conductivities are 8.6 × 10−2 S/cm, 2.82 × 10−1 S/cm, 1.71 × 10−1 S/cm and 1.43 × 10−1 S/cm, respectively at 180 °C. OPBI/ASM composite membranes also display very low acid leaching in comparison to pristine OPBI owing to the formation of strong interaction between PA and polymer chains through ASMs.

In this article, we report preparation and studies of water dispersible polyurethane (WDPU) nanocomposite which has high hydrophobic characteristics with contact angle greater than 100° and strong thermo-mechanical properties. An in-situ method is developed for synthesizing the WDPU nanocomposites where hydroxyl terminated polybutadiene (HTPB) functionalized at the terminal carbon atoms with dinitrobenzene (DNB), named as HTPB-DNB, is the diol source for the polyurethane chain, two types of organically modified clays namely Cloisite-30B and dimethyl sulfoxide (DMSO) intercalated Kaolinite (OKao) are the nanofillers and an ionic diol co-monomer e.g. dimethylol propionic acid (DMPA) is used to incorporate the ionic characteristics in the polymer chain to ensure the water dispersibility of the resulting nanocomposites. Microscopy and light scattering studies prove the formation particles of 100–200 nm size, and the particles size and the polydispersity of WDPU nanocomposites vary as the loading and type of clay are altered. In depth analysis of 13C CP-MAS NMR spectra using full width half maxima (FWHM) of carbonyl carbon peak of PU chains reveals the interactions between the polyurethane and organoclay that helped in preparing stable WDPU nanocomposites. Structural analysis of nanocomposites reveal the formation of intercalated morphology till 3 wt% loading of Closite-30B and exfoliated structure for higher loading whereas aggregated structure in case of OKao nanocomposites. Thermo-mechanical and tensile behaviour of resulting nanocomposites are largely influenced by the clay type and loading which can be attributed as the consequence of the different morphology and structure of nanocomposites. The surface hydrophobicity of nanocomposite films is determined by measuring the contact angle which increases with increasing clay loading and all samples show contact angle greater than 100° attributing good hydrophobic surface of nanocomposites.

Despite the wide range of studies illustrating the influence of type and quantity of nanoclay on the macro properties of polymer nanocomposites, it has always remained a biggest challenge to study the chemistry of organic/inorganic interface on the final properties of polymer nanocomposites, a study that can indeed aid us in designing tailor-made materials e.g. proton exchange membranes (PEM). Hence in this study, we aimed to explore the influence of interface chemistry of nano-clay on the properties of poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI)/clay nanocomposite PEM for fuel cell. Cloisite clay modified organically with three surfactant molecules differing structurally in their cationic head group – cetyltrimethyl ammonium bromide (CTAB), cetylpyridinium bromide (CPyB) and cetylimidazolium bromide (CImiB) was utilized for making OPBI nanocomposite membranes by a simple solution blending route. 13 C CP MAS solid state NMR confirmed the hydrogen bonding interactions between the OPBI chains and clay particles. Formation of intercalated clay nanostructures in the OPBI matrix was revealed by WAXD and TEM analyses and this morphology was found to influence different properties in a favorable manner. TGA and DMA studies highlighted the influence of the different surfactants on the interfacial interactions in elevating/decreasing the thermal and glass transition temperatures of the nanocomposite membranes. The use of different surfactant modified clays induced sufficient hydrophobicity in the membranes that led to higher phosphoric acid (PA) loading and controlled dimensional swelling in both water and PA. The proton conductivity data particularly underscored the different degrees of interfacial interactions each of the three differently modified clays had in creating efficient proton transport pathways giving rise to higher proton conductivity while decreasing the activation energy barrier for the proton hopping. The results also revealed the critical role played by the clay particles especially by the organic modifier in preventing the leaching away of the doped acid from the nanocomposites membranes.

Although microbial fuel cells (MFCs) represent a promising bio-energy technology with a dual advantage (i.e., electricity production and waste-water treatment), their low power densities and high installation costs are major impediments. To address these bottlenecks and replace highly expensive Nafion, which is a proton exchange membrane (PEM), the current study focuses for the first time on membranes made from an easily synthesizable and more economical oxy-polybenzimidazole (OPBI) and its sulfonated analogue (S-OPBI) as alternate PEMs in single-chambered MFCs. The S-OPBI membrane exhibits better properties, with high water uptake, ion exchange capacity (IEC) and proton conductivity and a comparatively smaller degree of swelling compared to Nafion. The membrane morphology is characterized by atomic force microscopy, and the bright and dark regions of the S-OPBI membrane reveals the formation of ionic domains in the matrix, forming continuous water nanochannels when doped with water. These water-filled nanochannels are responsible for faster proton conduction in S-OPBI than in Nafion; therefore, the power output in the MFC with S-OPBI as the PEM is higher than in other MFCs. The open circuit voltage (460 mV), current generation (2.27 mA) and power density profile (110 mW/m2) as a function of time, as well as the polarization curves, exhibits higher current and power density (87.8 mW/m2) with S-OPBI compared to Nafion as the PEM.

In this work, we have carried out in-situ RAFT polymerization of poly (N-vinylimidazole) (PNVI) in the inter-galleries of Cloisite nanoclay. The polymerization was carried out in two sets of different solvent-initiator combinations: N, N-Dimethyl formamide (DMF) - azobisisobutyronitrile (AIBN) and water/ethanol mixture - 4,4′-azobis (4-cyanovaleric acid) (ACV), with varying monomer ratios in order to synthesize PNVI of three different molecular weights. The three PNVI modified Cloisite clays (named as CP-1, CP-2 and CP-3 corresponding to low, medium and high molecular weight PNVI, respectively) were characterized thoroughly. X-ray diffraction and field emission scanning electron microscope analysis revealed the extent of delamination of the clay layers after the polymerization. The CP-3 clay, containing high molecular weight PNVI, was completely exfoliated, whereas the CP-1 clay with low molecular weight PNVI formed intercalated structure and CP-2 showed partial exfoliation. Gel permeable chromatography was used to determine the molecular weights of PNVI and the thermogravimetric analysis revealed the quantities of PNVI polymerized in the clays galleries. Further, the PNVI modified clays were used to prepare nanocomposites with poly (4,4′-diphenylether-5,5′-benzimidazole) (OPBI). All the nanocomposite membranes exhibited higher storage modulus (up to ~170% increase at 400 °C), tensile properties, acid doping levels (~30 mol/OPBI repeat unit), proton conductivity (0.19 S/cm at 180 °C) and controlled acid leaching. The CP-3 clay, with exfoliated clay layers and freely dispersed PNVI chains in the OPBI matrix, resulted in effective interfacial interactions with the OPBI chains and consequently demonstrated higher property enhancement of the nanocomposite membranes than when the other two clays were incorporated.

This article addresses the effect of enhanced segmental mixing on various physical properties of ferrocenylsilane tethered polybutadiene based polyurethane (PU). To study this, 2-(ferrocenylpropyl) dimethylsilane (FPDS) has been grafted to the pendant vinyl double bond of hydroxyl terminated polybutadiene (HTPB) and 2, 4-dinitrobenzene attached HTPB (HTPB-DNB) through hydrosilylation reaction and then this resulting diols (FPDS-g-HTPB and FPDS-g-HTPB-DNB) were polymerized with isophorone diisocyanate (IPDI) to obtain FPDS-g-HTPB-PU and FPDS-g-HTPB-DNB-PU. Spectral (NMR, IR) analysis, molecular weight measurements and estimation of free hydroxyl contents were carried out to confirm the formation of these new diols. The careful variation of the grafting condition altered the extent of FPDS tethering on the diols which resulted varying amount of Si and Fe contents in these modified HTPBs. Density functional theory (DFT) calculation revealed the presence of various interactions of Si with various functionalities including ferrocene of the chain which resulted highly cross-linked polymer matrix. Cyclic voltammetry (CV) measurements of FPDS-g-HTPB-DNB displayed non-Nerstain reversible redox system with slow electron transfer process owing to the presence of DNB. Further, the PUs obtained from these HTPBs were prepared and characterized thoroughly in terms of thermal, mechanical, structural and tensile properties to study the segmental mixing between hard and soft segments of PUs owing to the presence of Si, Fe and DNB in the PU chain. Higher degree of segmental mixing was noticed when Si, Fe in the diol increased and also presence of DNB in the diol played a significant role in inducing the segmental mixing. The co-existence of segmental mixing and phase separation has been confirmed by small-angle x-ray scattering studies which further reaffirmed by FESEM analysis. Finally, composite solid propellants (CSPs) were prepared from these modified HTPBs and burn rate measurements were carried out. We found that CSPs obtained from FPDS-g-HTPB-DNB displayed ~10% higher burn rate than the CSP made from bare HTPB-DNB.

ABSTARCT RAFT is a unique technique for the surface functionalization of nanoparticles as it enables us to tailor-make the properties of the final brush polymers by altering the parameters like graft density, chain length etc. of the grafted polymers and also to have the preferred choice of end functional groups with narrow size distribution of the nanoparticles. In this study, we successfully grafted poly(vinylimidazolium)bromide (PVImBr) polyionic liquid (PIL) brush polymers on the surface of silica nanoparticles (SiNPs) using metal-catalyst-free and a simplified RAFT technique compared to reported methods. Two sets of nanoparticles, one with low grafting and molecular weight [PVImBr(L)-g-SiNP] and the other with high grafting and molecular weight [PVImBr(H)-g-SiNP] were prepared using the versatile 4-cyanopentanoic acid dithiobenzoate (CPDB) as RAFT agent. 1H NMR, FTIR, DLS, TGA and FESEM confirmed the grafting of the polymer, amount of grafted polymer and their sizes. These two sets of PIL grafted nanoparticles were used to make two sets of nanocomposites with poly(4,4′-diphenylether-5,5′- bibenzimidazole) (OPBI) at three different filler concentrations. The aim was to study the effect of PIL grafting and their molecular weights on the morphology and macro-scale properties of OPBI nanocomposites. It was found that PVImBr(H)-g-SiNP incorporated nanocomposite membranes resulted in better interfacial properties owing to the greater miscibility and interfacial interactions with imidazolium functional groups of OPBI chains. These membranes displayed greater tensile strength, storage modulus, acid loading, proton conductivity and more importantly significantly lowered acid leaching.

In this article, we report a new amorphous-crystalline polymer blend system consisting of poly (4, 4′-diphenylether-5, 5′-bibenzimidazole) (OPBI) and poly (aminophosphonate ester) (PAPE) polymers, the membranes of which were fabricated using the solution blending route. A series of blend membranes at different ratios were prepared and systematically analysed for chemical interactions, morphological changes and their physico-chemical properties studied for use as proton exchange membrane. While FT-IR spectroscopy established the hydrogen bonding interactions between N–H of OPBI and phosphonate ester group of PAPE, X-ray diffraction studies revealed the development of crystallinity in the membrane matrix. Interestingly, the gradual induction of crystallinity in an amorphous OPBI matrix was found to influence the properties of the blend membranes favourably. For instance, the blend membrane containing 25 wt% PAPE in OPBI matrix displayed the maximum property enhancement in terms of storage modulus, glass transition temperature (Tg), phosphoric acid (PA) doping level (37 mol/OPBI repeat unit) and most importantly proton conductivity (0.135 S/cm at 180 °C) which is almost twice the value for pristine OPBI (0.05 S/cm at 180 °C) under identical conditions. Although improved properties were observed at other blend ratios as well, the studies ascertain that the membrane with 25 wt% PAPE was found to be the threshold ratio up to which properties increase and beyond which i.e. at >25 wt% PAPE, there is a decrement in properties like mechanical stability and proton conductivity. An important reason for this was attributed to the creation of a right balance of amorphous and crystalline domains and appropriate intra and inter-polymer hydrogen bonding interactions in the matrix of 75/25 (OPBI/PAPE) blend membrane.

Polysaccharides are natural biological molecules with various properties including biodegradation and low toxicity which are advantageous features for the therapeutics development. Chemical modification of polysaccharides can be an effective tool to develop nanoparticle-enabled conjugates, therapeutics, photosensitizers, imaging agents, and sensors. Glyconanoparticles are nanoparticles which are surface-decorated with polymer chains consisting of carbohydrates. These particles play a vital role in the development of personalized medicines to meet various clinically unmet needs of the patients. In recent times, these particles are also found to be useful in drug delivery and imaging. This chapter mainly focuses on the controlled synthesis of nanoparticles based on polysaccharides by various living polymerization techniques. The living polymerization of polysaccharides is essential for preparing the multivalent glycoclusters and to conjugate various biologically important molecules, which helps in the development of polysaccharide-based therapeutic nanomedicine. In this chapter, we also highlight the recent literature based on polysaccharide nanoparticulate systems and our own work, and their potential uses in the biomedical areas.

Here, we report the successful synthesis of series of stimuli responsive amphiphilic diblock copolymers (SRABCs) poly(N-isopropylacrylamide-b-N-vinylcarbazole) [poly(NIPAAm-b-NVK)] through reversible addition fragmentation chain transfer (RAFT) polymerization. Copolymers with fixed hydrophilic [poly(NIPAAm)] block length and variable (with three different) hydrophobic [poly(NVK)] block lengths were synthesized and the block length ratio was confirmed from their molecular weight data. The self-assembly nature of synthesized block copolymers was confirmed by determining critical micelle concentration (CMC). Self-assembled block copolymers showed rice-grain like morphology for copolymers having equivalent hydrophobic/hydrophilic chain length but in case of block copolymers having smaller and bigger hydrophobic chain length with respect to hydrophilic chain length displayed vesicular morphology. The thermo and pH responsiveness of the block copolymers was found to be influenced by variation in length and chemical composition of the blocks. Due to their thermo and pH responsiveness resulted self-assembled structures underwent morphology transitions from vesicular and rice grain like to micellar structure in aqueous medium. The probable applications of the studied stimuli responsive amphiphilic diblock copolymers can be found in the nanotechnology and biotechnology are indicated.

In the present work, we have examined the role of triazine based functional moieties namely cyanuric chloride (CYC), 2-chloro-4, 6-bis (dimethylamino)-1, 3, 5-triazine (CBDT) and 1-chloro-3, 5-diazido-2, 4, 6-triazine (CDT), which are attached to the terminal carbons of hydroxyl terminated polybutadiene (HTPB), on the structure-property of polyurethanes (PUs). Triazine attached HTPB, called as modified HTPB, was polymerized with varieties of diisocyanates and the resulting PUs were further cured at 70 °C for 5 days to prepare the free-standing elastic PU films. Thorough spectroscopic studies (FT-IR and 13 C CP-MAS solid state NMR) of PU films could not identify any hydrogen bonding interactions between urethane bonds and triazine rings present in the soft segment (HTPB segment) of PU but revealed the presence of favorable electrostatic interaction between them because of the electron rich nature of triazine and the presence of polar substituents on the triazine ring. An in-depth small angle X-ray scattering study along with morphological study carried out by scanning electron microscopy confirmed that the interaction between urethane and triazine is the driving force for the formation of nanometer size mass fractals of hard segment domains (HSD) in the triazine attached HTPB-PU. Tensile strength and mechanical stability of modified HTPB-PU was found to be better than the native HTPB-PU owing to the formation of HSD. The current study also revealed the influence of nature and position of substituents in the triazine ring on the properties of modified PUs. The electron donating dimethyl amine groups of CBDT and segregation of PU chain were responsible for the strong photoluminescence of HTPB-CBDT-PU film compared to all other modified HTPB-PUs.

Preparation of stable, free-standing elastic film with hydrophobic surface from water-dispersible polyurethanes (WDPUs) is a challenging task. Here, we have prepared WDPUs from polybutadiene-based diols and the resulting PU films are satisfying the requisites. Two types of diols, namely, hydroxyl-terminated polybutadiene (HTPB) and terminal-functionalized HTPB with dinitrobenzene (DNB) [HTPB-DNB], were used to make WDPUs and the effects of diol structures were investigated. The synthesized WDPUs displayed particle morphology with size in the range of ∼130–270 nm and more than 1 year storage stability. WDPUs yielded stable and free-standing films upon curing and the resulting films showed high thermal and mechanical stabilities. The contact angle of the films is in the range of ∼80–100°, attributing the hydrophobic nature of the surface. Hard segment content of the PU varied from 30 to 40% (by weight) to tune the properties of WDPUs and the resulting films.

Despite the remarkable advances in recent times on polybenzimidazole (PBI) based proton exchange membranes (PEM), there are two most important limitations that restrict their uses: (1) declining of the mechanical strength at high acid doping level and (2) leaching of doped acid when membrane is in contact with water. In continuation with our earlier success (J. Mater. Chem. 2011, 21, 14897; ACS Appl. Mater. Interfaces 2014, 6, 21286) on the former concern, in this article we also addressed the latter problem associated with ‘Acid leaching’ along with the issue of mechanical strength at high PA loading. We have made an attempt to study how the surface modifier molecule plays a role in altering the morphology and structure of poly (4, 4′-diphenylether-5, 5′-bibenzimidazole) (OPBI) nanocomposite membranes thereby enhancing the PEM properties especially acid retention capability. Silica nanoparticles of 25 nm size were prepared and successfully modified with phosphate anion containing imidazolium ionic liquid (IL) and were incorporated in OPBI by solution blending method. The chemical interactions between the polymer and ionic liquid modified silica (ILMS) were confirmed by FTIR, NMR and WAXD studies. TEM images disclosed how these interactions led to the formation of self-assembled clusters in the OPBI matrix. All the ILMS nanocomposite membranes displayed high thermal, mechanical and oxidative stabilities. The IL-decorated silica nanoparticles prevented the leaching of phosphoric acid (PA), by hydrogen bonding interactions, from the PA doped membranes. This resulted in higher PA doping levels of the nanocomposites. The ability to retain more PA was also reflected in the high proton conductivity data of the ILMS nanocomposites – 15% ILMS loaded membrane which showed almost two fold increment in proton conductivity compared to the neat OPBI. This was attributed to the self – assembled clusters of ILMS nanoparticles in the matrix.

Here we report simple and robust one-pot method for the preparation of polystyrene (PS)/graphene oxide (GO) nanocomposite using reversible addition fragmentation chain transfer (RAFT) modified GO in surfactant free emulsion polymerization (SFEP). The results suggested that ionic comonomer, styrene sulfonate sodium salt (SS-Na), concentration plays vital role in forming PS/GO nanocomposite. X-ray and electron diffraction studies suggest that there is no recombination of GO sheets when moderate SS-Na concentration is used, resulting complete exfoliation of GO sheets in the PS/GO nanocomposite. The formation of core–shell particles in which PS is the core and polystyrene sulfonate sodium salt (PSS–Na) is the shell, and the specific interactions between functional groups of GO and PSS–Na are attributed as the driving forces for the PS/GO nanocomposite formation.