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Carfentrazone-ethyl is embedded in guar gum to prepare a polymer-herbicide conjugate gel formulation for a sustained release of the active ingredient (a.i.). The sprayable gel formulation was optimized at 0.5% (w/v) concentration. Strong interactions of the prepared composition of the polymer-herbicide conjugate system are shown through spectroscopic techniques, depicting the peak broadening of hydrophilic -OH bonds in the herbicide at 1743 cm

The conducting nanochannel is made up of poly(vinylidene fluoride) and its nanohybrid (NH) membrane through irradiation of high-energy (80 MeV) lithium ions followed by chemical etching. The NH is ...

A polymer gel electrolyte has been developed based on functionalized thermoplastic polyurethane for solar cell devices. Long-chain polyurethane is synthesized, and subsequently, a small pendant moi...

Acceleration of gelation in the biological environment and improvement of overall biological properties of a hydrogel is of enormous importance. Biopolymer stabilized gold (Au) nanoparticles (NPs) exhibit cytocompatibility and therapeutic activity. Hence, in situ gelation and subsequent improvement in the property of a hydrogel by employing Au NPs is an attractive approach. We report that stable Au NPs accelerate the conventional nucleophilic substitution reaction of activated halide-terminated poly(ethylene glycol) and tertiary amine functional macromolecules, leading to the rapid formation of injectable nanocomposite hydrogels in vivo and ex vivo with improved modulus, cell adhesion, cell proliferation, and cytocompatibility than that of a pristine hydrogel. NP surfaces with low chain grafting density and good colloidal stability are crucial requirements for the use of these NPs in the hydrogel formation. Influence of the structure of the amine functional prepolymer, the spacer connecting the halide leaving groups of the substrate, and the structure of the stabilizer on the rate promoting activity of the NPs have been evaluated with model low-molecular-weight substrates and macromolecules by 1H NMR spectroscopy, rheological experiments, and density functional theory. Results indicate a significant effect of the spacer connecting the halide leaving group with the macromolecule. The Au nanocomposite hydrogels show sustained co-release of methotrexate, an anti-rheumatic drug, and the Au NPs. This work provides insights for designing an injectable nanocomposite hydrogel system with multifunctional property. The strategy of the use of cytocompatible Au NPs as a promoter provides new opportunity to obtain an injectable hydrogel system for biological applications.

Electrochemical water oxidation requires highly active electrocatalyst system with improved catalytic activity, high mechanical stability and strong catalyst-support interaction. In this respect, a...

A green composite, derived from the biowaste pomegranate peel, is used for piezoelectric energy harvesting. A hybrid of poly(vinylidene fluoride) and pomegranate peel powder is prepared through a s...

A flexible, lead-free piezoelectric nanogenerator is demonstrated, which produces an electrical signal (voltage) under the application of stress. Barium titanate (BaTiO3) nanoparticles are embedded...

1,7Phenanthroline based bisboron dipyrromethenes (bisBODIPYs) B1 and B2 obtained via small substitutional changes (Cl/SCH3) have been described. The effect of RIR in emission enhancement in a viscous solvent (glycerol) has been studied besides vital role of intermolecular interactions scrutinized by Xray single crystal studies. The efficiency of intersystem crossing (ISC) in generation of singlet oxygen (ΦΔ∼ 19.2% and 56.7%) by photoirradiation using visible light along with distinct photostability has been investigated by 1,3-diphenylisobenzofuran (DPBF) titration studies. The 1O2 generation quantum yield and photosensitizing durability of the bisBODIPYs have been investigated by photooxidation of 1,5-dihydroxynaphthalene (DHN) in presence of B1 and B2 as photosensitizers. The pseudo-first-order rate constants for photooxidation reactions and consumption rates of DHN reflected appreciable 1O2 generation quantum yields (ΦΔ: B1, 29.0; B2, 57.8%). Density functional theory (DFT) studies showed distri...

Nanohybrid scaffolds of chitosan have been designed for controlled drug delivery and bone regeneration. Sulfonated graphene oxide has been used to develop the nanohybrids. Nanohybrid scaffolds show highly hydrophilic character and greater mechanical strength as compared to pure chitosan. Nanohybrid scaffolds show an interconnected uniform porous network structure exhibiting sustained release kinetics of the antibacterial drug, tetracycline hydrochloride. Nanohybrids are found to be highly biocompatible in nature and are able to support and proliferate MG63 osteoblast cells and thereby induce bone tissue regeneration. The in-vivo bone healing study shows that the developed nanohybrid scaffolds have the potential to regenerate the bone faster without any side effects as compared to pure scaffolds. Hence, the developed nanohybrid scaffold has good potential as a controlled drug delivery vehicle and in bone tissue engineering for faster healing.

The use of cationic polymer based gene delivery vectors has several limitations such as low transfection efficiency, high toxicity, and inactivation by serum. The present work provides an inorganic based nanocarrier for efficient gene delivery and a method for preparing the same through a facile coprecipitation technique. The vehicle showed high loading capacity of DNA and can release the loaded DNA in a controlled pH-responsive manner. The developed gene delivery vehicle offers remarkable protection against DNase I and also provides protection against thermal damage. This vehicle also demonstrated efficient cellular uptake performance. Transfection and expression of plasmid gene encoding GFP proteins is achieved successfully by this LDH based vehicle. More interestingly, the developed Li-Al LDH efficiently induces GFP-p53 mediated apoptosis in HeLa cells exclusively sparing the normal tissue cells like NIH-3T3. The study demonstrates the potential of the developed inorganic based nanocarrier as a promising nonviral gene vector for tumor treatment.

A hole conducting layer for quantum dot sensitized solar cell (QDSS) as a function of redox behavior has been reported. Polyurethanes, comprising hard and soft segments, have been functionalized fo...

Poly(vinylidene fluoride) (PVDF) is processed at high temperature to generate energy from waste mechanical energy. The piezoelectric β-phase has been induced through uniaxial elongation of polymer films at high temperature. The extent of β-phase has been confirmed from a deconvoluted XRD pattern, found to be ∼75% of the electroactive phase, and able to demonstrate high piezoelectric effect as evident from the measured piezoelectric coefficient of −30 pC/N after a suitably processed and poled specimen. Bulk morphology and spectroscopic studies support the structural alteration. Following the direct piezoelectric effect, energy harvesting devices have been fabricated which show very high power output of 55.2 μW/cm2 using the processed and poled specimen. Thus, robust and easily processable polymeric material having very high energy conversion efficiency is demonstrated which is sufficient to power miniaturized devices.

Different hard segment content (HSC) polyurethanes (PUs) have been synthesized using linear (hexamethylene diisocyanate; HMDI) and alicyclic (isophorone diisocyanate; IPDI) diisocyanates to understand the effect on structure–property relationship and how it affects the shape memory behavior of PUs. Structural details have been elucidated through NMR and other spectroscopic techniques including the quantification of HSC. The nature of interactions between the polymer chains and their extent has been revealed. Thermal and mechanical properties as a function of the chemical structure and HSC indicate faster degradation in higher HSC. Layer-by-layer self-assembly through extensive hydrogen bonding has been established through XRD, small-angle neutron scattering, AFM, and optical images by capturing nanometer scale to micron scale inhomogeneities. The greater interaction in the HMDI system as compared to IPDI PUs leads to the crystallization of the hard segment. The differential shape memory effect has been re...

Two major problems in chemotherapy, poor bioavailability of hydrophobic anticancer drug and its adverse side effects causing nausea, are taken into account by developing a sustained drug release vehicle along with enhanced bioavailability using two-dimensional layered double hydroxides (LDHs) with appropriate surface charge and its subsequent embedment in polymer matrix. A model hydrophobic anticancer drug, raloxifene hydrochloride (RH), is intercalated into a series of zinc iron LDHs with varying anion charge densities using an ion exchange technique. To achieve significant sustained delivery, drug-intercalated LDH is embedded in poly(ε-caprolactone) (PCL) matrix to develop intravenous administration and to improve the therapeutic index of the drug. The cause of sustained release is visualized from the strong interaction between LDH and drug, as measured through spectroscopic techniques, like X-ray photoelectron spectroscopy, infrared, UV-visible spectroscopy, and thermal measurement (depression of melting temperature and considerable reduction in heat of fusion), using differential scanning calorimeter, followed by delayed diffusion of drug from polymer matrix. Interestingly, polymer nanohybrid exhibits long-term and excellent in vitro antitumor efficacy as opposed to pure drug or drug-intercalated LDH or only drug embedded PCL (conventional drug delivery vehicle) as evident from cell viability and cell adhesion experiments prompting a model depicting greater killing efficiency (cellular uptake) of the delivery vehicle (polymer nanohybrid) controlled by its better cell adhesion as noticed through cellular uptake after tagging of fluorescence rhodamine B separately to drug and LDH. In vivo studies also confirm the sustained release of drug in the bloodstream of albino rats using polymer nanohybrid (novel drug delivery vehicle) along with a healthy liver vis-à-vis burst release using pure drug/drug-intercalated LDHs with considerable damaged liver.

Bone cement has found extensive usage in joint arthroplasty over the last 50 years; still, the development of bone cement with essential properties such as high fatigue resistance, lower exothermic temperature, and bioactivity has been an unsolved problem. In our present work, we have addressed all of the mentioned shortcomings of bone cement by reinforcing it with graphene (GR), graphene oxide (GO), and surface-modified amino graphene (AG) fillers. These nanocomposites have shown hypsochromic shifts, suggesting strong interactions between the filler material and the polymer matrix. AG-based nanohybrids have shown greater osteointegration and lower cytotoxicity compared to other nanohybrids as well as pristine bone cement. They have also reduced oxidative stress on cells, resulting in calcification within 20 days of the implantation of nanohybrids into the rabbits. They have significantly reduced the exothermic curing temperature to body temperature and increased the setting time to facilitate practitioners, suggesting that reaction temperature and settling time can be dynamically controlled by varying the concentration of the filler. Thermal stability and enhanced mechanical properties have been achieved in nanohybrids vis-à-vis pure bone cement. Thus, this newly developed nanocomposite can create natural bonding with bone tissues for improved bioactivity, longer sustainability, and better strength in the prosthesis.

Biodegradable poly(lactic acid) (PLA) is widely used to fabricate 3D scaffolds for tissue regeneration. However, PLA lacks cell adhering functional moieties, which limit its successful application in tissue engineering. Herein, we have tailored the cell adhesive properties of star shaped poly(d,l-lactide) (ss-PDLLA) by grafting gelatin to their 4 arms. Grafting of gelatin on PDLLA backbone was confirmed by 1H NMR and FTIR. The synthesized star shaped poly(d,l-lactide)-b-gelatin (ss-pLG) exhibited enhanced wettability and protein adsorption. The modification also facilitated better cell adhesion and proliferation on their respective polymer coated 2D substrates, compared to their respective unmodified ss-PDLLA. Further, 3D scaffolds were fabricated from gelatin grafted and unmodified polymers. The fabricated scaffolds were shown to be cytocompatible to 3T3-L1 cells and hemocompatible to red blood cells (RBCs). Cell proliferation was increased up to 2.5-fold in ss-pLG scaffolds compared to ss-PDLLA scaffold...

Brominated graphene (GBR) with ∼3% bromine content has shown novel peroxidase mimetic activity toward 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Optimum activity has been observed at pH 4.48 and after a minimum ∼30 min of equilibration time. Among the different analytes studied using the sensor combining TMB, H2O2, and GBR in phosphate buffer of pH 4.48, the S2– ion has effectively shown a short duration of sensing (∼2 min) within the detection range of 0.04–1 mM. A calibration curve for S2– ion estimation has been constructed with the experimental linearity in 0.04–0.4 mM range and having the limit of detection (LOD) value of 25.3 μM. A standard addition experiment has validated the method. A paper strip sensor has been fabricated for successful detection of S2– ion.

Reversible bidirectional shape memory is developed in thermoplastic polyurethane by designing different components to enable molecular switching from actuator domain to self-assembled rigid hard domain and vice versa under a temperature cycle. Polycaprolactone based special polyurethanes have been synthesized which exhibit appropriate self-assembly behavior suitable for the shape memory effect. Reversible bidirectional shape memory has been reported through induced strain and giving shape at particular temperature, and the results are compared with conventional polyurethanes which do not show any shape memory effect. The correlation between chemical structures, self-assembly, structural evolution, and shape memory effect has been made. Self-gripping is demonstrated revealing the novel mechanism of molecular flipping and temperature-induced structural change along with molecular aggregation.

Process and nanoparticle induced piezoelectric super toughened poly(vinylidene fluoride) (PVDF) nanohybrids have been demonstrated. The nanohybrids have been prepared by incorporating organically modified nanoclay through melt extrusion and solution route. The solution processed nanohybrid exhibit 1100% improvement in toughness as well as adequate stiffness as compared to pure PVDF without any trade-off. The structural and morphological origins of super toughening phenomena have been worked out. The unique crystallization behavior of PVDF on top of the silicate layers (β-phase, planar zigzag chain conformation, and subsequent polar γ-phase and α-phase as layered type) has been revealed to create an island type of structure, which in turn is responsible for greater toughness. The extent of piezoelectric β-phase has been enhanced by controlled stretching of the nanohybrid at moderately high temperature for better disentanglement, and 90% of the piezoelectric phase has been stabilized. The structural change ...

The effect of multi-walled carbon nanotube (MWCNT) on the crystal structure, unique crystallization, mechanical behavior, enzymatic degradation, and significant improvement in biocompatibility of p...

Novel polyurethanes have been synthesized using aliphatic diisocyanate and aromatic chain extenders with varying spacer length. Nanohybrids of those polyurethanes have been prepared using two-dimensional surface modified nanoclay by dispersing it in poly-ol followed by prepolymerization and subsequent extension with chain extenders of a range of length scales. Dramatic improvement in toughness and adequate enhancement in stiffness in presence of nanoclay have been observed for higher spacer length of chain extender exhibiting no trade-off for these new classes of nanohybrids. Step-by-step self-assembly starting from nanometer dimension molecular association to micrometer scale crystallite has been revealed through electronic structure calculation, X-ray diffraction, small angle neutron scattering, atomic force microscopy, and optical images. The role of hydrogen bonding has been uncovered for this type of supramolecular assembly which further aggravated in presence of organically modified nanoclay by maki...

Thermoreversible gelation of a copolymer, poly(vinylidene fluoride-co-chlorotrifluoroethylene), has been studied in a series of aromatic diesters (phthalates) with varying aliphatic chain length, n. The gelation rate gradually increases with increasing n, but no gelation occurs in dioctyl phthalate (n = 8), giving rise to a solvent dependency. Structures of gels and dried gels have been studied through X-ray diffraction and FTIR studies. Fibrillar morphology is evident for the series of solvents, but its dimension (both lateral and diameter) systematically changes with n. Solvent retention power of gels has gradually been increased with increasing n while the thermal degradation of copolymer occurs at same temperature, reflecting varying interactions between copolymer and various aliphatic chain length phthalates in gels. Phase diagrams of the gels exhibit the formation of two kinds of polymer−solvent complexes and have been predicted theoretically through electronic structure calculation. Both the small-...

Nanostructure, key to property alteration, has been widely diverse by using two-dimensional nanoparticle in different stages of polymerization. Molecular level self-assembly starting from nanoscale 2-D molecular sheet to optically observable microscale crystallite has been unraveled stepwise for thermoplastic elastomer for the first time. The nature of self-assembly can be tuned by judicious choice of polymerization procedure in the presence of organically modified nanoclay. The effect of modulated nanostructure and self-assembly has been explored for the unusual property enhancement including electronic, thermal, mechanical, barrier, and biological (genotoxicity). Both the stiffness and toughness increase in nano-biohybrid without any trade-off. The unique splintering phenomenon and its variation under a dynamic frequency have been investigated by changing the synthesizing route of nanohybrids using a fixed concentration of nanoparticle. For understanding the controlled cellular responses to the implant ...

We report the step by step self-assembly from nanostructure to microstructure (bottom-up approach through X-ray diffraction (1.6 nm), small angle neutron scattering (SANS) (11.6 nm), atomic force microscopy (70 nm smaller crystallite from enlarged image and 450 nm greater crystallites), and polarizing optical microscope (2 microm)) of aliphatic polyurethanes (PU) in contrast to aromatic polyurethanes depending on hard segment content (HSC). Polyurethanes of 10 to 80% HSC have been synthesized by using appropriate amount of polyol and chain extender. The effect of self-assembled patterns on mechanical properties both in solid and liquid state has been established exhibiting structure-property relationship of supramolecular polyurethanes. The crystallinity enhances but the degradation temperature decreases with increasing HSC. The characteristic length (measure of gap between lamellar crystallites), as revealed from SANS, gradually decreases with increasing HSC suggesting compactness of the crystallites through extensive hydrogen bonding. The Young's modulus increases with increasing HSC with a percolation threshold of hard segment (50%) while the toughness improves up to 30% HSC followed by gradual decrease in presence of bigger crystallites which promote brittle fracture. The origin of self-assembly in aliphatic PUs has been demonstrated through electronic structure calculations to form a loop structure with minimum intermolecular distance (2.2 A) while that distance is quite large in aromatic polyurethanes (4.6 A) that cannot form hydrogen bonds. The unique splintering of domain structure and its subsequent reformation under dynamic shear experiment has been established.

Poly(epsilon-caprolactone) (PCL)/layered silicate nanocomposites have been prepared via solution route. Two different organically modified nanoclays were used to compare the variation in properties based on organic modifications. The nanostructures, as observed from wide-angle X-ray diffraction and transmission electron microscopy, indicate intercalated and partially exfoliated hybrids depending on the nature of organic modification in nanoclay. The nanohybrids exhibit significant improvement in thermal and mechanical properties of the matrix as compared to neat polymer. The nanoclays act as nucleating agent for the crystallization of PCL. The biodegradability of pure PCL and its nanocomposites have been studied under controlled conditions in enzyme, pure microorganism (fungi), compost, Ganges water, and alkaline buffer solution. The rate of biodegradation of PCL has enhanced dramatically in nanohybrids and depends strongly on the media used. Scanning confocal, electron, and atomic force microscopes have used to demarcate the nature of biodegradation of pristine PCL and its nanocomposites. The change in biodegradation is rationalized in terms of the crystallization behavior and organic modification in nanoclays of the nanohybrids vis-a-vis the neat polymer. The extent of compatibility was measured quantitatively through the interaction parameter for two different nanoclays to compare and establish the reason for variation in their properties in nanohybrids. A biodegradation mechanism has been revealed for PCL and its nanocomposites through enzyme activity in varying pH environment.

The thermoreversible gelation of poly(vinylidene fluoride-co-hexafluoro propylene) copolymer have been studied in a series of phthalates, Ph-(COO C(n)H(2n+1))(2) with n = 1-8. The gelation rate increases with increasing aliphatic chain length up to n = 6, and the gelation phenomena does not occur for higher n > 6. The fibrillar morphology is evident for dried gels whose dimension (both lateral and thickness) becomes shorter and thinner with increasing n. The structures of the gels formed in various phthalates have been investigated by small-angle neutron scattering and small-angle X-ray scattering techniques, suggesting sheet-like structure, where the interplanner distance increases with increasing aliphatic chain length. The scattering intensity I(q) decreases with q according to the Ornstein-Zernike model, where q = (4pi/lambda) sin theta (2theta and lambda are scattering angle and wavelength of neutron) and the correlation length, xi, assigned to the average distance between the neighboring crystallites, also increases with increasing aliphatic chain length of diesters. The detailed thermal analyses and phase diagrams of the copolymer gels have been studied in a wide range of phthalates. Further, polymer-solvent complexes leading to the formation of two distinct compounds have been reported. A systematic change of compound composition has also been observed in the whole range of phthalates studied here. On the basis of electronic structure calculation, a model has been proposed to elucidate the conformation of copolymer chain in presence of various phthalates and their complexes, which offer the cause of higher gelation rate for longer aliphatic chain length up to n = 6, no gelation phenomena occurs for n > 6, and formation of two copolymer-solvent compounds. The mechanical properties (storage modulus and viscosity) decrease with increasing aliphatic chain length of phthalates and realignment of fibrils occurs at particular frequency depending on the strength of fibrillar gels.

Poly(vinylidene fluoride-co-hexafluoropropylene) (HFP) nanocomposites with layered silicate have been synthesized via the melt extrusion route. The intriguing nanostructure, crystalline structure, morphology, and thermal and mechanical properties of the nanocomposites have been studied and compared critically with pristine polymer. HFP forms intercalated or partially exfoliated nanostructure (or both) in the presence of nanoclay, depending on its concentration. The bombardment of high-energy swift, heavy ions (SHI) on HFP and its nanocomposites has been explored in a wide range of fluence. The nanoclay induces the piezoelectric beta-phase in bulk HFP, and the structure remains intact upon SHI irradiation. SHI irradiation degrades pure polymer, but the degradation is suppressed radically in nanocomposites. The heat of fusion of pristine HFP has drastically been reduced upon SHI irradiation, whereas there are relatively minute changes in nanocomposites. The coarsening on the surface and bulk of HFP and its nanocomposite films upon SHI irradiation has been measured quantitatively by using atomic force microscopy. The degradation has been considerably suppressed in nanocomposites through cross-linking of polymer chains, providing a suitable high-energy, radiation-resistant polymeric material. A mechanism for this behavior originating from the swelling test and gel fraction (chemical cross-linking) as a result of SHI irradiation has been illustrated.

Poly(vinylidene fluoride) (PVDF) has been made radiation-resistant through a nanocomposite (NC) route. The bombardment of high-energy swift heavy ions (SHI) on PVDF and its NCs with layered silicate has been studied in a range of fluences. The degradation of PVDF after SHI irradiation is suppressed radically in NCs. PVDF forms an intercalated nanostructure in the presence of nanoclay and, further, the ion fluence raises the extent of intercalation. The crystallinity and the heat of fusion of pristine PVDF have drastically been reduced after SHI irradiation, while there are relatively small changes in NCs even at higher fluences. The metastable piezoelectric beta form of PVDF gets stabilized by the presence of layered silicate, and the structure is retained upon SHI irradiation. The clay platelets act as nucleating agents, and SHI irradiation causes two crystallization temperatures for the samples exposed to high fluences. The damages created on the surface and bulk of PVDF and its NC films upon SHI irradiation have been measured quantitatively by using atomic force microscopy. The pitting dimensions and degradation are enhanced significantly beyond 10(11) ions/cm(2) fluence for pristine PVDF, which limits the use of PVDF for any ion irradiation application. The degradation is considerably suppressed in NCs, providing a suitable high-energy radiation-resistant thermoplastic polymer.

Nanocomposites of oligo-poly(caprolactone) (o-PCL) with layered silicates having a variety of organic modifiers have been prepared by simple mechanical mixing. The effect of organic modifier type o...

In the preparation of polymer/clay nanocomposites, organoclay plays an important role in lipophilizing and dispersing the clay into less polar polymer matrixes. Organic modifiers of various chain lengths were examined in different types of clays, smectite, montmorillonite (MMT), and mica, to prepare their corresponding organoclays. The layered structure and gallery spacing of organoclays and polylactide (PLA) nanocomposites shows that, with a modifier of the same chain length, the gallery spacing of the organoclay was largest for mica and smallest for smectite because of the higher ion-exchange capacity of mica and physical jamming of the modifier due to a restricted conformation at the core part of the clay of larger size. The increment of the modulus in a smectite nanocomposite, compared to that of PLA, is higher than MMT or mica nanocomposite due to better dispersion in a smectite system for the same clay loading. Being a well-dispersed system, smectite nanocomposites have better gas barrier properties...

New polylactide (PLA)/layered silicate nanocomposites have been prepared successfully by simple melt extrusion of PLA and organically modified montmorillonite. The d spacings of both the organically modified montmorillonite and intercalated nanocomposites were investigated by wide-angle X-ray diffraction (WAXD) analysis, and the morphology of these nanocomposites was examined by transmission electron microscopy (TEM). Using oligo(e-caprolactone) (o-PCL) as a compatibilizer, the effect of compatibilizer in nanocomposites was investigated by focusing on two major aspects: morphological analysis and mechanical property measurements. The intercalated nanocomposites exhibited remarkable improvement of materials properties in both solid and melt states as compared to that of PLA matrices without clay.

Intercalated nanocomposites of polypropylene (PP)/clay (PPCNs) were prepared by a melt extrusion process using maleic anhydride modified PP (PP-MA) and organophilic clay. The extent of intercalation of PP-MA chains in the space between silicate galleries increased with crystallization temperature Tc and decreased as clay content increased. As compared to matrix PP-MA, the dispersed clay particles in the PP-MA matrix acted as a nucleating agent and lowered the spherulite dimension with increasing clay content as revealed by light scattering experiments and polarizing optical microscopy. The PPCN crystallized at high Tc showed that a certain extent of segregation of the dispersed clay particles takes place around the boundary of the spherulites (interspherulite). Extensive intercalation occurred during crystallization, especially at high Tc due to the long time for full solidification of the melt. The degree of intercalation of PP-MA chains in the silicate galleries strongly depends on the time in the molte...

A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (Mn = 7.0 × 104 to 10.2× 104 g mol–1, PDI = 1.23–1.35) having different isotacticity [meso diad (m) =...

This Letter describes the first real space observation for the formation of a house of cards structure in polypropylene/clay nanocomposite melt under elongational flow by TEM analysis. Both strong strain-induced hardening and rheopexy features are originated from the perpendicular alignment of the silicate layers to the stretching direction.

Crystallization behavior of isotactic polypropylene (iPP) with extremely high isotacticity has been studied over a very wide range of crystallization temperature Tc (145 °C ≤ Tc ≤ 166 °C). Optical polarized microscopy observation reveals that morphologies obtained before and after Tc = 157.0 °C are different in nature. Differential scanning calorimetric measurement shows that the melting temperature (Tm) increases significantly with increase of both Tc and crystallization time t. A sudden jump in the slope of Tm versus log t plot is observed at Tc = 157.0 °C, which suggests a kind of order−disorder transition taking place at high Tc (≥157.0 °C) to allow better chain sliding diffusion. Such a disordering has been confirmed by means of X-ray measurements and will be reported in another paper of this series. It was also convinced that annealing at high temperature subsequent to lower temperature crystallization promotes much more rapid lamellar thickening than crystallization alone does at the same high temp...

The blending ability of poly(vinylidene fluoride) (PVF 2 ) depends on the head-to-head (H-H) defect structure present in the chain. With increasing H-H defect content, the lower critical solution temperatures (LCST) of PVF 2 /PMA blends decrease. This has been explained from the polymer-polymer interaction parameter (χ 12 ) values measured from the equilibrium melting point (T o m ) depression of the α phase of PVF 2 . A critical analysis on the method of measuring the equilibrium melting point from the Hoffman-Weeks plot has been done. For Hoffman-Weeks plots the T m (melting point) should be determined for the same and low level of crystallinity at each T c (crystallization temperature) to obtain correct results. If T m is counted for the same time of crystallization at each T c , erroneous results are obtained. Extrapolation of the T m -T a (T a = annealing temperature) plot to the T m = T a line also yields the correct T 0 m . χ 12 values are determined with all these T 0 m s, and it has been observed that the annealing method and the same crystallinity method yield almost same value of χ 12 , which can explain the LCST phase diagram of PVF 2 blends. Annealing results yield that PVF 2 up to 24 mol % H-H defect concentration would be miscible with PMA. χ 12 measured from T m s of the same time of crystallization and from the apparent melting points of PVF 2 blends yield incorrect results.

The gelation rates of poly(vinylidene fluoride) (PVF 2 ) gels have been measured for three commercial samples each in two different solvents at different polymer concentrations and also at different temperatures. The rate has been expressed as a combination of temperature-dependent function f(T) and concentration-dependent function (φ) n ; φ is the reduced overlapping concentration of the polymer chains. φ has a resemblance with the P - P c term of percolation theory, P being the conversion factor and P c its critical value. Exponent n has been measured from double logarithmic plots of t gel -1 and φ, and it lies between 0.45 and 0.6 which is closer to percolation exponent β (0.45) of a three-dimensional lattice. This indicates that three-dimensional percolation is a suitable model for this thermoreversible gelation process. The temperature-dependent function of the gelation rate has been found to be analogous to the temperature-dependent function of the nucleation rate of crystalline polymers in dilute solutions. There is some dependency of the gelation rate on the amount of H-H defect (-CF 2 CF 2 -) structures present in the polymers and also on the molecular weight of the samples. Solvents also have a significant influence on the gelation rate of the polymer : the poorer the solvent, the faster is the gelation rate. The critical gelation concentration (C t=α ∗ ) measured from gelation kinetics by an extrapolation procedure increases with temperature in each case. Thermodynamic analysis of the variation of C t=α ∗ with temperature reveals that about three to six crystallites (depending on the solvent and sample) are involved to produce a single crosslink in the gel.

Via batch process in an autoclave, we conducted foam processing on polypropylene (PP)/clay nanocomposite (PPCN) by using supercritical CO2 as foaming agent under 10 MPa at 134.7 °C. Through transmission electron microscopy observation, the biaxial flow-induced alignment of clay particles along the cell boundary was identified. Such aligning behavior of clay particles helps cells to withstand the stretching force from breaking the so thin cell wall and to improve the modulus of the foam.