Search

We present an experimental approach to studying the kinetics of polymer nanoparticle formation using molecular rotor molecules as fluorescence probes. By combining fluorescence lifetime analysis and fluorescence correlation spectroscopy, it is possible to simultaneously monitor the evolution of the local environment in the nanoparticles and their size. To assess the generality of the method, we select two common but very different methods for nanoparticle preparation: emulsion-solvent evaporation and miniemulsion polymerization. In both cases, three stages of the nanoparticle formation process were identified on the basis of their polymer content. In the initial stage of the process, the polymer content is low. Then it increases rapidly because of solvent evaporation or polymerization during the second stage. Finally, it reaches a plateau value. Furthermore, significant heterogeneities in the final nanoparticles were found that can be attributed to remaining solvent or monomer and the spatial variation of the polymer-free volume.

The development of mulch films from wastes of vegetables represents a sustainable alternative to the traditionally used polyethylene ones that follow the principles of circular economy. In this work, we obtained films based on two different industrial vegetable wastes, orange peels (OP) and spinach stems (SS), using hydrolysis at different times (6, 16, and 24 h) and temperatures (30, 50, and 70 °C). Hydrolysis carried out at 30 °C and 24 h has led to films with the best mechanical properties, while high temperatures (70 °C) combined with prolonged treatment times (16 and 24 h) led to materials with lower mechanical resistance and darker coloration. The films' characterization by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and uniaxial tensile tests elucidated their chemical structure and physicochemical properties. Additionally, the materials' interaction with water was evaluated and significantly improved by adding a carnauba wax coating. Optical properties, micro and macronutrient content and biodegradation in the soil of selected bioplastics were also determined. Results showed that the proposed materials present fast in-soil biodegradation, good potentiality for weed prevention and improvement of plant growth via soil fertilization.

Membrane modification is becoming ever more relevant for mitigating fouling phenomena within wastewater treatment applications. Past research included a novel low-fouling coating using polymerizable bicontinuous microemulsion (PBM) induced by UV-LED polymerization. This additional cover layer deteriorated the filtration capacity significantly, potentially due to the observed high pore intrusion of the liquid PBM prior to the casting process. Therefore, this work addressed an innovative experimental protocol for controlling the viscosity of polymerizable bicontinuous microemulsions (PBM) before casting on commercial ultrafiltration (UF) membranes. Prior to the coating procedure, the PBM viscosity modulation was carried out by controlled radical polymerization (CRP). The regulation was conducted by introducing the radical inhibitor 2,2,6,6-tetramethylpiperidine 1-oxyl after a certain time (CRP time). The ensuing controlled radical polymerized PBM (CRP-PBM) showed a higher viscosity than the original unpolymerized PBM, as confirmed by rheological measurements. Nevertheless, the resulting CRP-PBM-cast membranes had a lower permeability in water filtration experiments despite a higher viscosity and potentially lower pore intrusion. This result is due to different polymeric structures of the differently polymerized PBM, as confirmed by solid-state nuclear magnetic resonance (NMR) investigations. The findings can be useful for future developments in the membrane science field for production of specific membrane-coating layers for diverse applications.

The possibility to use the macromolecules present in vegetable biomass, with minimal processing, as alternative materials to produce new green bioplastics for packaging is very appealing. This strategy can help to mitigate environmental issues due to broad usage of conventional plastics. Since a large variety of vegetable waste, in terms of chemical composition and supramolecular organization, is produced by the food industry, many different bioplastics can be produced with the same protocol. Bioplastics films from carrot pomace, cocoa shells, spinach stems and orange peels will be characterized in terms of thermomechanical properties and biodegradability. The mechanical properties will be correlated with the composition and morphology as determined by means of a combination of techniques (solid-state NMR, SEM and confocal microscopy). The biodegradability of the films will be characterized in terms of Biochemical Oxygen Demand as function of time during 30 days of incubation in seawater.

Subtle alterations in the mid-block of polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) have a significant impact on the mechanical properties of the resulting microphase separated materials. In samples with high butylene content, the ethylene-co-butylene (EB) phase behaves as a rubber, as seen by differential scanning calorimetry (DSC), time domain (TD) and Magic Angle Spinning (MAS) NMR, X-ray scattering at small (SAXS), and wide (WAXS) angles. In samples where the butylene content is lower&mdash, but still sufficient to prevent crystallization in bulk EB&mdash, the DSC thermogram presents a broad endothermic transition upon heating from 221 to 300 K. TD NMR, supported by WAXS and dielectric spectroscopy measurements, probed the dynamic phenomena of EB during this transition. The results suggest the existence of a rotator phase for the EB block below room temperature, as a result of nanoconfinement.

Micro and mesoporous materials are often used in catalysis, purification, composite filler, and other applications. Almond shell is an important agricultural byproduct that can be transformed to microporous and mesoporous carbon. In this work, we produced biochar from almond shell using a thermal treatment procedure in an inert atmosphere and characterized the pores with nitrogen adsorption, environmental SEM, and 129Xe NMR. The latter technique differentiates adsorbed and nonadsorbed xenon and permits the correlation of different processing conditions with xenon adsorption and diffusivity. The relevance of removing the ash produced during the charring process has been included in the study. Moreover, the xenon exchange between meso- and micro-pores has been directly observed by 129Xe NMR, demonstrating that after ash removal by water the materials have high accessibility of the pores by external fluids, thus increasing the usefulness as filtration or adsorption material.

The valorization of vegetable waste can create opportunities to produce new valuable bioplastics.In thisstudy, a one-step process to fully convert a variety of vegetable waste materials into bioplasticfilms is reported. The process is carried out in a diluted aqueous HCl solution at room temperature,it is easily scalable, and with no environmental concerns associated with the use of organic ordangerous chemicals. The generated bioplastics arecompletely biodegradable and environmentallyfriendly. Freestanding, flexible bioplastic films were obtained from vegetable waste like carrot,parsley, radicchio and cauliflower. They have similar mechanical properties with other bioplastics, like thermoplastic starch, and showed to have little migration in a food simulant. The color andthe functional properties (i.e. antioxidant capability) of the starting vegetables are preserved inthe bioplastics, thanks to the mild conditions of the fabrication process. The new conversionprocess allows the blending of the bioplastics with other natural or synthetic polymers, in order to improve their mechanical and gas barrier properties, like the oxygen permability (OP), thusexpanding their field of applications. Poly vinyl alcohol (PVA)/carrot bioplastic film showed an OPof 31.2 cm3 μm m−2 day−1 kPa−1, which is lower than the OP for other synthetic films, like highdensity polyethylene films (HDPE), and similar to edible materials like chitosan. &nbsp

Carminic acid, a natural hydrophilic dye extensively used in the food and cosmetic industries, is converted in hydrophobic dyes by acetylation or pivaloylation. These derivatives are successfully used as biocolourants for rubber objects. In this paper, spectroscopic properties of the carminic acid derivatives in dimethyl sulfoxide and in polybutylacrylate are studied by means of photoluminescence and time-resolved photoluminescence decays, revealing a hypsochromic effect due to the presence of bulky substituents as the acetyl or pivaloyl groups. Molecular mechanics and density functional theory calculations confirm the disruption of planarity between the sugar ring and the anthraquinoid system determined by the esterification.

The chemical shift of xenon (at natural abundance) dissolved in a variety of 1-butyl-3-methylimidazolium-based ionic liquids (ILs) has been measured with (129)Xe NMR spectroscopy. The large chemical shift differences observed are mainly related to the type of anion; the strongest deshielding effect is observed ILs with I(-), Br(-), and Cl(-) anions, and the strongest shielding is found for the bis(trifluoromethanesulfonyl)imide ([Tf2N](-))-based IL. The measured (129)Xe chemical shift variations correlate well with the IL structure organization imposed by the anions and with the size of the empty voids due to charge alternation patterns. Descriptors taken from literature data on X-ray and neutron scattering, as well as single-crystal structures where available, support this interpretation. The proposed methodology adds a new investigating tool to the elucidation of the short-range order in ILs. The observed chemical shift trend provides information about how these solvents are organized.

We studied the network structure of elastomers based on polyisoprene, polybutadiene, and their blends in the narrow range of formulations compatible with actual use in the automotive tyre industry. Cross-link density (CLD) was quantified comparatively by low-field 1H multiple quantum time domain nuclear magnetic resonance (MQ TD-NMR) and by equilibrium swelling technique. The robustness and agreement of the two methods was demonstrated in measuring minute alterations of unfilled vulcanizates beyond the optimum cure time. Comparison with samples where polysulfidic bonds were selectively cleaved also demonstrates that the length of the sulfur chain constituting the cross-link does not significantly affect residual dipolar coupling. Kraus, Lorenz, and Parks correction for filler restriction on swelling is validated by MQ TD-NMR, which also allows extracting information on cross-link distribution not provided by swelling measurement. Cross-link distributions in the blends were demonstrated to be significantly different from the weighted average of the pure samples, while average proton–proton residual dipolar coupling values correspond. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42700.

Controlled morphogenesis and shape replication are challenges for several rapidly developing fields of materials science. Indeed, although complex forms have been generated by the condensation of inorganic matter in organized media, the shaping of plastic matter on the micrometre scale is still limited to simple forms that are typically obtained as inverse replicas of channel-like cavities and colloidal crystals. Here we report the fabrication of individual plastic micro-objects that follow an elaborate design and are faithful copies of nanoporous inorganic morphotypes. The direct replica method produces an unprecedented library of curved geometrical solids made of plastics, such as cones, bicones, hollow cylinders, rings, test tubes, clubs and vases. The shape retention of the original structures on the microscale and the creation of a new nanostructure produced objects with homogeneous nanopores of 7 nm and cylindrical microcavities as large as 1 microm. This strategy of shape transcription from one material to another opens new perspectives in microfabrication, separation, anchorage and storage of chemical and biological species. Until now it has not been possible to realize such transformations.

The first molecular crystal showing permanent porosity, made by of tris-o-phenylenedioxycyclotriphosphazene TPP molecules, is presented. The empty-pore hexagonal structure was solved after isolation of diffraction-quality single crystals and showed no residual electron density in the large unoccupied volume, shaped as straight nanochannels with a minimum diameter of 4.6 Å. Weak intermolecular interactions consolidate molecular stacks along the c axis (repeat period of 10.16 Å) and layers on the a–b plane (a=11.45 Å), ensuring the stability of the assembly. We showed the remarkable sorption properties of the porous molecular crystal with respect to important gases that participate in a network of soft interactions. Methane and carbon dioxide could be incorporated with high efficiency in the novel adducts (60% and 100% occupation, respectively, of the available sites, guest–host molar fraction of up to 1.25) with high selectivity over other gases. Unprecedented observations of the gases in van der Waals crystals and their topology could be provided by fast MAS NMR spectroscopy. The impressive upfield shifts caused by the aromatic ring currents of the host on gas molecules at the van der Waals contacts provided an unconventional tool for measuring the intermolecular gas-host distances and ricognizing the specific interactions that contribute to the overall stabilization. The multiple receptors lining the channel walls and the tight fit with the guests recall the specificity of biological nanochannels.

Porous materials were prepd. using the novel polymorph of tris(o-phenylenedioxy)cyclophosphazene (TPP). The empty channellike structure was obtained from the hexagonal TPP/benzene inclusion compd. by mild evacuation of the volatile guest. Continuous flow laser-polarized 129Xe NMR spectroscopy is applied for the 1st time to study gas diffusion in the open-channel structure

A porous single-crystal collects xenon atoms from the gas phase and orients them macroscopically, as highlighted by hyperpolarized xenon NMR.

We report a new colloidal synthesis of niobium-doped TiO2 anatase nanocrystals (NCs) that allows for the preparation of ∼10 nm NCs with control over the amount of Nb doping up to ∼14%. The incorporation of niobium ions leads to the appearance of a tunable, broad absorption peak that ranges from the visible range to the mid-infrared. This optical behavior is attributed to the substitution of Nb5+ on Ti4+ sites generating free carriers inside the conduction band of the TiO2 NCs as supported by optical and electron paramagnetic resonance spectroscopic investigations. At the same time, the incorporation of progressively more niobium ions drives an evolution of the shape of the NCs from tetragonal platelets to "peanutlike" rods. © 2013 American Chemical Society.

Polymer foams have significant potential as contact traces for reconstructing the dynamics of felonies or for proving the presence of individuals at crime scenes. Discrimination of such items may be carried out using techniques, such as infrared spectroscopy or microscopy, which are commonly employed in the forensic examination of trace evidence. However, in the case of foams made of polyether urethane, the discriminating power attained by this approach is not satisfying. Time domain NMR (TD-NMR) allows the investigation of these materials in terms of total proton content (H%), rigid phase fraction and mobility of the soft phase (solid echo T2). Proton content and rigid fraction are partially correlated, in agreement with the chemistry of the material. The H% and T2 values are instead practically independent, and their simultaneous measurement allows discrimination of a specimen with high precision, comparable to TGA, without damaging the sample and using less than 50 mg of the material.

A novel aldehyde-bearing trithiocarbonate has been synthesized and reacted with carbon nanostructures with different dimensionalities (nanotubes, fullerenes, graphite). The decoration of these carbon nanostructures with trithiocarbonate moieties should provide a powerful tool for the design of advanced carbon nanofillers.

We describe two synthesis approaches to colloidal Cu(3)P nanocrystals using trioctylphosphine (TOP) as phosphorus precursor. One approach is based on the homogeneous nucleation of small Cu(3)P nanocrystals with hexagonal plate-like morphology and with sizes that can be tuned from 5 to 50 nm depending on the reaction time. In the other approach, metallic Cu nanocrystals are nucleated first and then they are progressively phosphorized to Cu(3)P. In this case, intermediate Janus-like dimeric nanoparticles can be isolated, which are made of two domains of different materials, Cu and Cu(3)P, sharing a flat epitaxial interface. The Janus-like nanoparticles can be transformed back to single-crystalline copper particles if they are annealed at high temperature under high vacuum conditions, which makes them an interesting source of phosphorus. The features of the Cu-Cu(3)P Janus-like nanoparticles are compared with those of the striped microstructure discovered more than two decades ago in the rapidly quenched Cu-Cu(3)P eutectic of the Cu-P alloy, suggesting that other alloy/eutectic systems that display similar behavior might give origin to nanostructures with flat, epitaxial interface between domains of two diverse materials. Finally, the electrochemical properties of the copper phosphide plates are studied, and they are found to be capable of undergoing lithiation/delithiation through a displacement reaction, while the Janus-like Cu-Cu(3)P particles do not display an electrochemical behavior that would make them suitable for applications in batteries.

Blends of chlorinated polyethylene and nylon-6/-6,6/-12 terpolyamide were prepared. The ratio of the two components was systematically varied within the blends. The mechanical behavior of the samples was analyzed with tensile tests and dynamical mechanical analysis showing that, for several ratios, materials with improved mechanical properties typical of thermoplastic elastomers were obtained. In such a mechanical regime, a co-continuous phase-separated morphology was clearly evidenced at the microscopic scale by 3D laser scanning confocal fluorescent microscopy (LSCFM). At blend compositions where plastic tensile behavior is observed, LSCFM reveals dispersed spheres of one component in the other.

and copolymers obtained by the latest generation supported Ziegler-Natta catalysts. Hyperpolarized xenon gas rapidly flows into the open cavities and then penetrates the amorphous phases of polypropylene (PP) and ethylene-propylene copolymer (EPR) millimeter particles. Variable temp. HP 129Xe NMR demonstrated that xenon uptake is largely modulated by the motional state of the phases and is considerably reduced if glass transition is approached because the polymeric matrix becomes impermeable to the gas phase. This is an alternative method to detect the occurrence of the glass transition even in polymeric complex systems. The competitive absorption of xenon in PP and EPR microphases shows the morphol. of the particles and the phase architecture. The intermixing of the phases at micrometer level was established on the basis of the xenon diffusion rates. 2D 129Xe EXSY expts. disclose the freshly polarized xenon exchange pathways from the free gas to the EPR phase and, later on, between the polymeric phases.

Interlayer nanoporosity of hectorite pillared by tetraethylammonium ions is explored by hyperpolarized xenon NMR and relevant gases such as carbon dioxide revealing the adsorption capacity of the open galleries.

The mobility of a series of linear alkanes in their inclusion compound with tris(o-phenylenedioxy)-spirotriphosphazene is studied by high-resolution carbon-proton magic-angle spinning solid-state NMR spectroscopy. Two different carbon-proton dipolar recoupling experiments are compared with respect to their ability to yield precise site-specific, motion-averaged dipolar coupling constants. The most accurate results are obtained by analysis of extrema positions in Lee-Goldburg cross-polarization build-up curves. We present a comprehensive collection of coupling constants, which evidence a rotational motion of the all-trans chains around the channel axis, with some further averaging due to additional fluctuations, as previously found for alkanes in other host matrices such as urea. The order parameter increases toward the inner parts of the chains, and is largely independent of chain length. Notably, chains in a TPP host are not more ordered than in urea, even though the average TPP channel diameter is reported to be smaller. Significantly decreased order is found for highly filled short-alkane samples, which is interpreted in terms of an increased rate of mutual collisions. From residual dipolar couplings as well as carbon chemical shifts, we derive similar amounts of gauche conformers. Translational motions along the channels are further studied by proton double-quantum spectroscopy, which probes guest-host dipolar couplings. The extent of local-scale lateral motion is again correlated with the sample filling, and is a weak function of temperature, as expected from a case in which highly restricted single-file diffusion should dominate the mobility. Characteristic effects of sample aging are apparent in all our experiments.

Chain-dynamics of flexible synthetic macromolecules in the crystalline state has been clarifiedby multinuclear solid-state NMR observations. Massive motional phenomena are shown when chains arecrystallized in the hexagonal phase. Several examples have been surveyed, where motion is inducedby high temperature and pressure or favored by inclusion of moderate amounts of comonomer units inthe main chain and by the use of monomers containing mobile side chains. Also, motional phenomenaof fast spinning and large librations of the macromolecules are promoted when the isolated chainsare confined to nanochannels formed in hexagonal crystal structures of suitable matrices. The motionalbehavior can be modulated by the topology and the interactions in the unusual environments. Thisknowledge provides information about polymers in close contact with heterogeneous interfaces, suchas polymers in nanocomposites or at surfaces.

Self-organization of tris-o-phenylenedioxycyclotriphosphazene with a variety of linear π-conjugated molecules resulted in crystalline nanostructured adducts of exceptional stability. Linear conjugated molecules that contain various chains of building blocks (i.e., double bonds, phenyl and thiophene rings) could be included to form the adducts. The polyconjugated molecules were encapsulated in infinite nanochannels lined with aromatic groups, which offer tailored surroundings of weak interactions. The conjugated molecules are sustained by a diffuse network of CH•••π and π •• π interactions that, through cooperation, improve the robustness of the supramolecular adducts. The stabilizing interactions were recognized by using advanced high-resolution 2D hydrogen–carbon solid-state NMR techniques, which allowed to to localize, with rare accuracy, the hydrogen atoms involved in weak hydrogen-atom–π interactions and elucidate the dynamics of large supramolecular assemblies.

Advanced 2D solid state NMR techniques reveal weak intermolecular interactions that cooperatively sustain nanostructures of high molecular mass aliphatic polymers entrapped as guests in channels formed by an aromatic host.

Two oligothiophenes, 4,4'-dipentoxy-2,2'-dithiophene and 4,4"-dipentoxy-2,2':5',2":5",2' ''-tetrathiophene, have been included in the nanochannels of the autoassembling host TPP (tris-o-phenylenedioxycyclotriphosphazene). The effect of the confinement on the structure and properties of the two dyes, as conformational arrangements, dynamics, and photophysical behavior, was addressed by the combination of high spinning speed solid-state NMR and time-resolved EPR spectroscopy. We compared the conformations of the dyes in their ground and photoexcited triplet states and described in detail the dynamics of the supramolecular adducts from 4 K to room temperature. Above 200 K surprisingly fast spinning rates of the dithiophene core were discovered, while the side chains show far slower reorientation motion, being in bulky gauche-rich conformations. These lateral plugs keep the planar core as appended in the space like a nanoscale gyroscope, allowing a reorientation in the motion regime of liquids and a long triplet lifetime at unusually high temperature. The nuclear magnetic properties of the guest dyes are also largely affected by the aromatic rings of the neighboring host, imparting an impressive magnetic susceptibility effect (2 ppm proton shift). The high mobility is due to the formation of a nanocage in a channel where aliphatic and aromatic functions isolate the thiophene moieties. Instead, two conformers of the tetrathiophene twisted on the central bond are stabilized by interaction with the host. They interconvert fast enough to be averaged in the NMR time scale.

A review presents examples of supramol. architectures and unusual states of aggregation as revealed by solid state NMR. In particular, polyphosphazenes and the formation of the mesophases are discussed, along with supramol. adducts of spirocyclophosphazenes and the formation of org. zeolites and gas diffusion into the nanoporous materials.

Ethanol associates easily with MgCl(2) to form adducts of complex architecture, but until now available characterization methods have failed to identify the pure stoichiometric compounds and their structures. To remedy this, we set about applying homonuclear and heteronuclear 2D correlated solid-state NMR spectroscopy to identify the pure compounds and the ethanol-to-magnesium coordination pattern. High spinning speed and Lee-Goldburg sequences were able to reduce the hydrogen spin-diffusion and homonuclear coupling in the crystalline solid, thus achieving high resolution also in the hydrogen domain. On this basis, the pure adducts, of interest as catalyst supports for Ziegler-Natta polymerization, were isolated for the first time. Magnesium coordination sites with given numbers of ligands and their multiplicity in the crystal cells were determined in the new-found stoichiometric complexes. Variable temperature and 2D carbon-carbon exchange NMR, as well as relaxation times in the fast motion regime, revealed the disordering phenomena generated by ethanol dynamics in the crystal. Decoding the intriguing polymorphism of the precursors permits to trace the genealogy of tailored MgCl(2) titanate granules, active as highly productive catalysts for the stereospecific polymerization of olefins.

Heteronuclear (1H-13C) correlation (HETCOR) expts. coupled with magic angle spinning (MAS) and phase modulated Lee-Goldburg (PMLG) decoupling were used to study nanocomposite materials. The nanostructured materials have high melting temp. and are based on poly(1,4-cis-butadiene) (Europrene NEOCIS BR 60) and poly(tetrahydrofuran) (PTHF, Mn 2900, Terathane DuPont) in a self-assembled arom. host, tris(o-phenylenedioxy)-spiro-cyclotriphosphazene (TPP) and perhydrotriphenylene (PHTP). The PMLG HETCOR expts. provide highly resolved spectra in the proton dimension and are particularly well suited for studying nanocomposite materials. When small amts. of host was mech. dispersed in poly(1,4-cis-butadiene) rubber, 2D-HETCOR data indicate formation of nanocrystals of inclusion compd. in bulk rubber. A neat upfield shift was obsd. for protons of polymer chains included in the unusual anisotropic environment of arom. rings of the host and lining the nanochannel walls.

The nanocomposite material formed by in situ polymn. of Me methacrylate in the periodic mesoporous silica MCM-41 was characterized by carbon and silicon CP MAS NMR spectroscopy. Cross polarization dynamics demonstrate the efficient magnetization transfer from the polymer hydrogens to the silicon atoms and the intimacy of the two nanophases. The results are implemented by (1H-29Si) 2D HETCOR expts.

Deuterium NMR data for tris(o-phenylendioxy)spirocyclotriphosphazene (TPP) and H-bonded inclusion compds. (ICs) with linear polyethylene (PE) and alkanes and PEO demonstrate that rapid motions including librations and torsion of the chain occur in the nanochannels. The PE and linear alkanes confined in restricted cylindrical spaces of TPP present motions in the liq. regime already at low temp., and the chain mobility is faster than that in the wider channels of PHTP (perhydrotriphenylene). The extra room in PHTP promotes defects, while tightness likely promotes smooth chain motions.

Low-temp. (220-290 K) ethylene-propylene copolymer crystn. was followed by DSC and solid-state NMR spectroscopy that can detect the formation of even small and short-living cryst. aggregates (min. lifetime of 3 ms). NMR at 282 K reveals a sharp and reversible melting-crystn. transition in the copolymer with 74% ethylene units. The trans conformation fraction identifying the aggregates is detected at all temps. independent of the thermal history, as at each temp. a quick gauche/trans equilibration is realized with no evidence of hysteresis. Transition occurs in both ethylene homosequences and heterosequences, indicating the inclusion of propylene units in the aggregates. The heterosequences do not aggregate in a sep. phase, proved by the fast equilibration of the hydrogen magnetization to the same relaxation times as for the homosequences (T1r(1H) value of »4 ms). Both chain mobility and fast carbon spin-lattice relaxation times (T1(13C) » 1 s) are promoted by the random distribution along the chain of the propylene units that push the vicinal chains apart. The copolymer chain segment behavior in the aggregates is dynamic, similar to that of polyethylene, as arranged in the hexagonal packing obtained at high temp. and pressure and to that of polyethylene mesophases confined to cryst. nanochannels.

The present chapter is aimed at presenting the characterization of nanocomposites formed by mesoporous silica and surfactants or polymers. The hybrid materials were prepared in the former case by condensation of silica about micellar aggregations of surfactants [1, 2]; in the latter case novel polymer nanocomposites were formed by direct polymerization or by absorption of polymers in the pores of the mesostructured silica. The materials provide intimate interactions between the nanophases, and thus a challenging field for NMR characterization of the extended interfaces. The steric limits imposed to the chains by the rigid siliceous structure permit the controlled reduction of the degrees of conformational and translational freedom as compared to the bulk phases. Concerning polymers, unusual states of aggregation can be observed massively in these nanocomposites and basic phenomena, like glass transition or crystallization, are to be re-explored in the confined state. Preliminary NMR characterization of nanophase properties like confined crystallization of alkyl chains, or monomer reactivity in the inclusion state are described hereafter.

Matrix polymerization can be viewed as an intriguing procedure for the preparation of homogeneous blends that are otherwise difficult or practically impossible to prepare. Poly(p-phenyleneterephthalamide) has been synthesized by direct polycondensation in the presence of poly(N-vinylpyrrolidone) or poly(4-vinylpyridine) as polymer matrices. The molecular weight effect of the latter polymers on the intrinsic viscosity of the aramid has been investigated. Poly(p-phenyleneterephthalamide), characterized by intrinsic viscosity as high as 14.2 dL/g, is obtained when high molecular weight poly(N-vinylpyrrolidone) is used. The intimate composites formed in situ have been characterized by solid-state NMR. The parent and daughter polymers in the composite present the same proton T1 relaxation times in the rotating frame, and this value differs from that of the neat polymers; this result demonstrates the intimacy of the blend at the level of a few nanometers.

Pure silica of high surface area was prepared by the slow evaporation of colloidal solutions of silicic acid in organic solvents. The porous silica materials were characterized by nitrogen adsorption, adsorption of volatile organic molecules, and 29Si magic angle spinning (MAS) NMR. The absorption properties and the high concentration of silanols, detected by 29Si NMR resonances, are consistent with a surface area of 600−700 m2/g. The high surface area and the virtual lack of long-range order suggest the model of a “sponge” containing open and interconnected pores. The size of the pores or channels is relatively homogeneous and is affected quite markedly by the organic preparation medium. The pores of the structure obtained using tetrahydrofurane are on the subnanometer scale, an indication that the diffusive phenomena must be influenced by intimate organic−inorganic interactions during the slow evaporation of the solvent.

Polypropylene samples contg. 45% isotactic and 20% syndiotactic pentads were characterized by calorimetry and solid-state NMR. Iso- and syndio-sequences are able to crystallize in the same sample to form a complex mixt. of several allomorphs: monoclinic a2 phase together with disordered a phases for isotactic and extended chain together with helix forms for syndiotactic stereosequences. The fraction of each phase was established quant., due to the limited overlapping of the signals at room and high temp. The partition of stereosequences between the amorphous and cryst. phases was detd. at room and high temp. The distribution of the stereosequences in the amorphous phase was established at high temp. at the pentad level; thus, it was possible to det. the stereosequences already crystd. at that temp. Hydrogen spin-lattice relaxation times in the rotating frame, measured under spin diffusion conditions, demonstrate the segregation of iso- and syndiotactic crystallites and the intimacy of the phases of the same tacticity.

Mesoporous silica materials (MCM-41) were characterized by 13C and 29Si magic angle spinning (MAS) NMR. 13C chem. shifts reveal a high content of gauche conformations in the chain of cationic surfactant mols. within the nanopores. The 13C T1's and proton to carbon cross-polarization times (TCH) demonstrate that the surfactant inside the pores exhibits anisotropic motions progressively reduced from the chain end toward the polar head. Variable-temp. 13C MAS NMR spectra show a strong thermal dependence of the motions and highlight a gel-like aggregation of the surfactant. However, the transfer of magnetization from the surfactant protons to the silicons on the pore surface is efficient and obsd. by cross-polarization dynamics following the nonprotonated silicon atoms. Silicons and carbons receive magnetization from the same proton system, because a unique T1r(1H) is measured from the point of view of silicon and carbon nuclei. The authors' results demonstrate that there is such an interaction between the ammonium group of the surfactant and the silica surface which represents a strong limit to the motion of the aliph. chains.

Single-file diffusion behavior is expected for atoms and mols. in 1-dimensional gas phases of nanochannels with transverse dimensions that do not allow for the particles to bypass each other. Although single-file diffusion may play an important role in a wide range of industrial catalytic, geol., and biol. processes, exptl. evidence is scarce despite the fact that the dynamics differ substantially from ordinary diffusion. The authors demonstrate the application of continuous-flow laser-polarized 129Xe NMR spectroscopy for the study of gas transport into the effectively 1-dimensional channels of a microporous material. The novel methodol. makes it possible to monitor diffusion over a time scale of tens of seconds, often inaccessible by conventional NMR expts. The technique can also be applied to systems with very small mobility factors or diffusion consts. that are difficult to det. by currently available methods for diffusion measurement. Expts. using xenon in nanochannel systems can distinguish between unidirectional diffusion and single-file diffusion. The exptl. observations indicate that single-file behavior for xenon in an org. nanochannel is persistent even at long diffusion times of over tens of seconds. Finally, using continuous-flow laser-polarized 129Xe NMR spectroscopy, the authors describe an intriguing correlation between the obsd. NMR line shape of xenon within the nanochannels and the gas transport into these channels

Poly(ethylene oxide) (PEO)included in tris(o-phenylenedioxy)cyclotriphosphazine (TPP) and polyethylene included in the same matrix are characterized by 13C MAS NMR. TPP mols. provide a unique environment where the arom. rings face the included polymer chains.