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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.

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.

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.

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.

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 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.

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.

Thermoreversible gelation of polybenzimidazole (PBI) in phosphoric acid (PA) is investigated by studying the gel morphology, thermodynamics of the gelation, and gelation kinetics utilizing test tube tilting and UV–Vis spectroscopy techniques. Gelation kinetics studies reveal that both the gelation rate and critical gelation concentration (C∗t=∞) are function of gelation temperature (Tgel) and the molecular weight of PBI. Highly dense fibrillar network morphology with large number of longer and thinner fibrils is obtained for higher gel concentration and higher molecular weight PBI. Both the gel melting (Tgm) and gelation (Tgel) temperature depend upon the gelation concentration and molecular weight of PBI. The presence of self-assembled chains of PA molecules, which help to produce the PBI crystallites, is observed from the thermodynamical study. I.R. and Raman studies prove the presence of strong hydrogen bonding interaction between the PBI and the PA molecules, and the free PA molecules in the gel network. The gelation occurs in two-step processes which include a slow rate determining conformational transition from coil to rod and followed by aggregation of rod via crystallization. The PA loading of PBI membrane obtained from the PBI–PA gel is significantly high compared to the conventional imbibing process membrane. The PBI gel membrane displays very high thermal and mechanical stabilities. The high acid loading and superb thermo-mechanical stability are due to the gel network structure of the membrane. The proton conductivity of the membrane at 160 °C and 0% relative humidity (RH) is ∼0.1 S cm−1, which is higher than the reported values in the literature for the PBI. The activation energy of the proton conduction is 14–15 kJ/mol indicating faster proton transfer by hopping process inside the gel network.

Three different series of pyridine based polybenzimidazole (PyPBI) random copolymers consisting of meta-para pyridine linkages were synthesized from various stoichiometric mixtures of meta (2,4; 2,6 and 3,5) and para (2, 5) structure pyridine dicarboxylic acids (PDA) with 3, 3’, 4, 4’- tetra-aminobiphenyl (TAB) by solution polycondensation in polyphosphoric acid (PPA). The influences of the structural isomers of PDA on the PyPBI copolymerization and properties were elucidated by characterizing the resulting copolymers. The solubility of PDA monomers in PPA and the overall monomer concentration in the polymerization were found to be the deciding factors. The higher molecular weight PyPBI were obtained for higher para content copolymers due to the low solubility of para PDA in PPA. The introduction of para structure had enhanced the conjugation along the polymer chain. NMR study showed that the reactivity ratio of para PDA was not identical for all the three sets of PyPBI copolymers, it varied upon the positions of the dicarboxylic acids in the pyridine ring of meta PDAs (structural isomeric effect) with which 2,5 PDA is forming the copolymer. Introduction of para structure and meta PDAs structural isomers affected the thermal stability, flexibility and the photophysical properties of the PyPBI copolymers.