Role of boric acid in the formation of poly(vinyl alcohol)-iodine complexes in undrawn films

The role of boric acid in the formation of poly(vinyl alcohol) (PVA)-iodine complexes in undrawn films has been investigated by using wide-angle X-ray diffraction (WAXD) and high-resolution solid-state ¹³C NMR spectroscopy. From UV-vis absorption spectroscopy, it is confirmed that boric acid is necessary for the formation of the complexes in films that are treated with I₂/KI aqueous solutions at relatively low I₂ concentrations. The WAXD profiles indicate that, irrespective of the presence of iodine, crystallite sizes perpendicular to the chain axis become smaller by the addition of boric acid in the swelling media. Moreover, small crystallites and surficial parts of larger crystallites may be partially dissolved in the swelling process with water and boric acid suppresses the re-crystallization in the drying process with or without iodine. The ¹³C spin-lattice relaxation time analysis reveals that there exist two components called the mobile and the less mobile components in the films and the latter component, which contains the complexes and the crystalline component, is increased in the fraction by the presence of boric acid. The evaluation of the CH resonance line shows that some of the intermolecular hydrogen bonds are broken by boric acid, which increases the intramolecular hydrogen bonds. The CH₂ lineshape analysis also reveals that the gauche fraction is appreciably increased in the less mobile component by the addition of boric acid. These facts suggest that boric acid may promote the formation of PVA-iodine complexes particularly in the surficial areas of the crystallites probably by reducing the molecular mobility of the PVA chains by causing cross-linking among them.     

Elongation-induced phase separation of poly(vinyl alcohol)/poly(acrylic-acid) blends as studied by C CP/MAS NMR and wide-angle X-ray diffraction

The membrane samples of poly(vinyl alcohol)/poly(acrylic-acid) (PVA/PAA) blend with different draw ratios were studied by both ¹³C CP/MAS NMR and wide-angle X-ray diffraction (WAXD) measurements. Phase separation induced by elongation of the sample was observed and the change of the phase structure with draw ratio was found to be dependent on the composition of the blend samples.     

Structural and property changes during uniaxial drawing of ethylene-tetrafluoroethylene copolymer films as analyzed by in-situ X-ray measurements

The structure-property relationship during uniaxial drawing of high-molecular-weight ethylene-tetrafluoroethylene copolymer (ETFE) film was analyzed based on a combination of in-situ wide-angle X-ray diffraction (WAXD) and stress measurements. In-situ WAXD patterns indicated that the hexagonal (100) reflection transformed from the initial un-oriented ring into equatorial spots via split arcs at temperatures both below and above T_g, but that the critical strain when such transition occurred was delayed above T_g. Drawing above T_g produced an equatorial concentration of the spot reflections; thus, the extended chain crystal was enhanced as a result of elongation of the strain-hardening region. In contrast, the draw below T_g remained less oriented even just before breaking. However, the high orientation component also appeared beyond the critical strain; it could be assigned to the so-called “tie molecules” that bind the deformed lamellae. Changes in resultant tensile strength could be interpreted by these extended chain crystals and characteristic tie molecule components.     

CP/MAS C NMR analysis of the structure and hydrogen bonding of melt-crystallized poly(vinyl alcohol) films

The structure and hydrogen bonding of the melt-crystallized atactic poly(vinyl alcohol) (A-PVA) films, which were carefully prepared without significant thermal degradation, have been characterized by CP/MAS ¹³C NMR spectroscopy. The ¹³C spin-lattice relaxation analysis has revealed that there exist three components with different T_1C values, the crystalline, less mobile noncrystalline and mobile noncrystalline components, in good accord with the results for different PVA samples previously reported. It should be noted that the T_1C values of the crystalline and noncrystalline components are appreciably smaller for the melt-crystallized films than those for the un-annealed and annealed samples prepared by casting from the aqueous solution. The ¹³C NMR spectra of the crystalline and noncrystalline components are separately recorded by using the difference in T_1C and their CH lines are successfully resolved into three and seven constituent lines by the least-squares curve fitting, respectively. Moreover, the statistical analysis of the integrated intensities of the constituent lines thus obtained enables to determine the probability f_a for the formation of intramolecular hydrogen bonding in the successive two OH groups along each chain and another probability f_t of the trans conformation for the crystalline and noncrystalline components. It is found that the f_a value is relatively larger for the melt-crystallized films than those for the un-annealed and annealed samples. On the basis of these results, the features of the melt-crystallization and the resulting crystalline-noncrystalline structure are discussed by particularly considering effects of intra- and inter-molecular hydrogen bonding on the crystallization.     

Role of adsorbed iodine into poly(vinyl alcohol) films drawn in KI/I2 solution

We have investigated the microstructure of the poly(vinyl alcohol) (PVA) films using small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) techniques. The samples were uniaxially drawn in water or KI/I₂ aqueous solution and then dried in an air-oven at 333 K for 1 h prior to SAXS and WAXS measurements. It was found that for the films drawn in KI/I₂ solution PVA chains in the microfibrillar structure are more extended upon the film drawing compared to the case of the films drawn in pure water, which is resulted from the correlation function analysis on the SAXS data. Adsorbed iodines into the film were anticipated to act as junction points between the microfibrils via the formation of the PVA-iodine complexes.     

Packing mode and conformational transition of alkyl side chains in N-alkylated poly(p-benzamide) comb-like polymer

A series of rigid-rod poly(p-benzamide) polymers (PBA) with different length of flexible alkyl side chains, denoted as PBA(n)Cs, have been prepared by N-alkylation method. The alkyl side chain lengths varied from decyl (n=10) to octadecyl (n=18), with an interval of two carbon atoms. The packing mode and conformational transition of the alkyl side chains of the prepared PBA derivatives were characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimertry (DSC), and Fourier transform infrared spectroscopy (FTIR). WAXD results revealed that the derivatives form layered structure in which the distance between the backbones depends on the length of alkyl side chains. DSC studies indicated that melting transition temperature of PBA(n)Cs increases accordingly with increasing the alkyl chain length of the substituents. Meanwhile, DSC results proved that as the carbon atom number of the side group exceeds 14, alkyl side chains in PBA(n)Cs tend to crystallize FTIR spectroscopic investigation showed that the all-trans zigzag conformation is the most stable state for the alkyl side chain in PBA18C comb-like polymer. Temperature variation caused the reversible transition between trans and gauche conformational states of the side octadecyl group, and in turn made the molecular chain packing mode of PBA18C comb-like polymer undergo an reversible transformation from ordered packing to disordered packing.     

Crystalline structure of polyethylene containing vinylene units in the main chain

Polyethylene containing trans- or cis-vinylene units in the main chain has been synthesized by means of partial hydrogenation of trans- or cis-polypentenamer (TP or CP), and trans-polyoctenamer (TO). Crystalline structure of the polymers has been investigated with wide-angle X-ray diffraction, FT-IR analyses, solid-state NMR measurements and quantum chemical calculations of the NMR chemical shifts. These results clear that the partially hydrogenated TP or CP samples having an average number of methylene units of 6.9-8.4 per vinylene unit forms not only orthorhombic crystal but hexagonal-like crystal.     

Solid-state C NMR investigation of the structure and hydrogen bonding for stereoregular poly(vinyl alcohol) films in the hydrated state

The structure and hydrogen bonding of the hydrated stereoregular poly(vinyl alcohol) (PVA) films have been investigated by high-resolution solid-state ¹³C NMR spectroscopy. It is found by the ¹³C spin-lattice relaxation analysis that there exist three components with different T_1C values assigned to the crystalline, less mobile and mobile components for the hydrated syndiotactic PVA (S-PVA) and highly isotactic PVA (HI-PVA) films. The line shape analysis indicates that the probability of intramolecular hydrogen bonding is appreciably increased in the crystalline region for the S-PVA films by the hydration but a slightly helical structure, which is probably allowed by the formation of the successive intramolecular hydrogen bondings along the chains in the crystalline region, seems not to undergo any significant change by the hydration for HI-PVA. This fact indicates that intramolecular hydrogen bonding is more stable in the hydrated state in the crystalline region. As for the less mobile component, the line shape of the CH resonance line for the hydrated S-PVA or HI-PVA films is found to be very similar to that of the corresponding crystalline component, probably being due to the successive formation of intermolecular or intramolecular hydrogen bonding in the interfacial region, which mainly contributes to the less mobile component, for the S-PVA or HI-PVA films even in the hydrated state. The mole fractions of the mm, mr and rr sequences are also estimated for the mobile component that is produced in each stereoregular PVA sample by swelling with water and it is concluded that no prominent preferential partitioning of the mm, mr and rr sequences occurs in the crystalline and noncrystalline regions for the PVA films with different tacticities.     

Synthesis and Characterization of a Novel Diblock Copolymer with a Polyrotoxane Block

A novel diblock copolymer with a polyrotaxane block α-cyclodextrins-poly (ε-caprolactone)-b-poly{2,5-bis[(4-methoxypheny)oxycabony]-styrene} (α-CD-PCL-b-PMPCS) was successfully synthesized by combining ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The diblock copolymer was confirmed by ¹H NMR, GPC and solid-state ¹³C CP/MAS NMR spectroscopic analysis. Its phase structures and phase transitions were investigated by thermogravimetric analyses and wide-angle X-ray diffraction (WAXD). WAXD and solid-state ¹³C CP/MAS NMR spectroscopic study confirmed that inclusion complexes domains of the polyrotaxanes assumed a channel-type structure.     

Manipulating ordered structure of ionic liquid crystalline polymers through tuning the alkyl spacer length

The fabrication of ordered structure is very important for the applications of ionic liquid crystalline polymers (ILCPs) or polymerized (ionic liquid crystal) (PILC). In this paper, we reported a facile approach to manipulate the ordered structure of ILCPs through adjusting the length of alkyl spacer. We designed and synthesized a series of ILCPs contained imidazolium, poly(2,5-bis{[m-(4-butoxy-4′-imidazolium phenyl) m-alkyl] oxy carbonyl} styrene bis (fluoroborate) salts) (denoted as P_4-m−BF₄, m represents the number of carbon in the alkyl spacers and m = 2, 4, 6, 10) via radical polymerization. Combined differential scanning calorimetry (DSC), polarized light microscopy (PLM), X-ray scattering, and two-dimensional wide-angle X-ray diffraction (2D WAXD), we found that the ordered structure of this ILCPs can transfer from smectic A phase (SmA) to hexagonal columnar (Φ_H) phase with the increase of spacer. Furthermore, these results were confirmed by reconstructed relative electron density map using fast fourier transform algorithm (FFT). The result revealed that the increase of alkyl spacer would affect the interaction between ions and side chain, and induce the packing of the side chains. It was evident that the alkyl spacer played an important role in the constructing of ordered structure and offered a new method to fabricate different ordered structure of ILCPs.     

Crystallization behavior of poly(l-lactic acid) affected by the addition of a small amount of poly(3-hydroxybutyrate)

The miscibility, crystallization and subsequent melting behavior in binary biodegradable polymer blends of poly(l-lactic acid) (PLLA) and low molecular weight poly(3-hydroxybutyrate) (PHB) have been investigated by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD). DSC analysis results indicted that PLLA showed no miscibility with high molecular weight PHB (M_w = 650,000 g mol⁻¹) in the 80/20, 60/40, 40/60, 20/80 composition range of the PHB/PLLA blends. On the other hand, it showed some limited miscibility with low molecular weight PHB (M_w = 5000 g mol⁻¹) when the PHB content was below 25%, as evidenced by small changes in the glass transition temperature of PLLA. The partial miscibility was further supported by changes of cold-crystallization behavior of PLLA in the blends. During the nonisothermal crystallization, it was found that the addition of a small amount of PHB up to 30% made the cold-crystallization of PLLA occur in the lower temperature. Meanwhile, the crystallization of PHB and PLLA was observed in the heating process by monitoring characteristic IR bands of each component for the low molecular weight PHB/PLLA 20/80 and 30/70 blends. The temperature-dependent IR and WAXD results also revealed that for PLLA component crystallization, the disorder (α′) phase of PLLA was produced, and that the α′ phase changed to the order (α) phase just prior to the melting point.     

A water-soluble organic-inorganic hybrid material based on polyhedral oligomeric silsesquioxane and polyvinyl alcohol

A novel series of organic-inorganic hybrid materials involving cage-like octa(3-chloroammoniumpropyl)silsesquioxane and Polyvinyl alcohol (OCAPS/PVA) were prepared via solution blending method. The obtained hybrid films were optically transparent and soluble in water. OCAPS/PVA hybrids were characterized by FT-IR, wide-angle X-ray diffraction (WAXD) scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA) and tensile test. The results showed that the hydrogen bond interactions were formed between OCAPS and PVA. OCAPS could be dispersed well in PVA matrix till its content was 10 wt%, while the aggregation and crystallization of OCAPS were observed when the content was up to 15 wt%. The glass transition temperature (T _g ) of OCAPS/PVA was found to increase from 53 °C to 60 °C, and the melting temperature (T _m ) decreased from 180 °C to 171 °C with increasing OCAPS content from 0 wt% to 15 wt%. The thermal stability of PVA main chain was improved by the addition of OCAPS and the thermal residue ratio also increased. The tensile strength of OCAPS/PVA decreased from 28 MPa to 19 MPa, while the elongation at break of hybrid films increased from 121% to 175%.     

Distribution of chain defects and microstructure of melt crystallized polyethylene

A combined study using wide-angle X-ray diffraction (WAXD) and small-angle X-ray diffraction (SAXD) of a series of mostly low density polyethylenes with a wide range of chain defect concentrations (0.1–7%) crystallized from the melt is reported. The data presented here complement the earlier results obtained by Swan⁷ and Holdsworth and Keller⁸ for copolymers. The concurrent unit cell expansion and long period decrease with increasing chain defect concentration leads to a picture of chain defects (branches, unsaturations) being distributed between the crystalline lamellae and the surface layer. Based on a model which assumes inclusion of defects within the lattice by means of a generation of 2gl kinks, (supported by the parallel increase of paracrystallinity) an estimation of the concentration of chain defects, ?_c, incorporated into the crystal lattice (<1%) is attempted. The density of defects in the non-crystalline regions, ?_a, turns out to be substantially larger than ?_c and supports the view of a clustering of defects, ?_c and ?_a are both increasing functions of ? with a tendency to level off for ? > 6. According to this model, the fraction of defects incorporated into the lattice does not exceed 20% of the total number of defects in any of the samples investigated. The fraction of defects excluded from the lattice (>80%), on the other hand, sets a higher permissable limit to the crystal thickness value achieved.     

Order-disorder transition in eicosylated polyethyleneimine comblike polymers

Order-disorder transition (ODT) behavior in eicosylated polyethyleneimine (PEI20C) comblike polymer obtained by grafting n-eicosyl group on polyethyleneimine backbone was systematically investigated by the combination of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy as well as solid-state high resolution nuclear magnetic resonance (NMR) spectroscopy. DSC investigations showed two obvious transitions, assigned to the transitions (1) from orthorhombic to hexagonal and (2) from hexagonal to amorphous phase, respectively. These transitions are induced by the variations of alkyl side chain conformation and packing structure with temperature changing, which consequently lead to the destruction of original phase equilibrium. The ODT behavior can also be confirmed by spectroscopic methods like WAXD, FTIR and NMR. The ordered structure and the transition behavior of the alkyl side chains confined by the PEI backbone are obviously different from those of pristine normal alkanes. The transition mechanism of ODT and the origin of the phase transition behavior in PEI20C comblike polymer were discussed in detail in this paper.     

Crystal structure and morphology influenced by shear effect of poly(l-lactide) and its melting behavior revealed by WAXD, DSC and in-situ POM

Shear effect on crystal structure, morphology and melting behavior of poly(l-lactide) (PLLA) were investigated by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and in-situ polarized optical microscope (POM). Influences of steady shear on PLLA melt was investigated during annealing. The impacts of crystallization temperature (T_c) and shear rate (SR) on crystal structure, crystal growth rate, nucleation, and melting behavior were studied. It could be clarified into the low (<20 s⁻¹) and high shear rate ranges in terms of the crystal structure, growth rate, nucleation and melting behavior. It was found that phase transition and recrystallization during heating completely changed the stack structure. A new stable structure was established after a temperature jump in the melting range. Cylindric morphology arranged with spherulite was also observed in the polymer films at high T_c influenced by shear effect.     

Synthesis of a New Lead(II) Coordination Polymers with N-donor Ligand as Precursor for Preparation of PbO Nano-structure; Spectroscopic, Thermal, Fluorescence and Structural Studies

A new coordination polymer of lead(II) nitrate complexes with bridging trans-1,2-bis(4-pyridyl)ethene (bpe) ligand, [Pb(µ-NO₃)₂(bpe)(MeOH)]_n (1), has been synthesized and characterized by elemental analysis, FT-IR, ¹H, ¹³C-NMR, thermal analysis and single crystal X-ray diffraction. In compound 1, lead(II) ions are bridged by nitrate ligands forming linear chains, which are also further coordinated by neutral bpe and methanol ligands into a two-dimensional polymeric chain. This polymeric precursor has been used to prepare PbO nano-particles using two different method. The prepared lead(II) oxide nano-structure was characterized by scanning electron microscopy and X-ray powder diffraction.     

Crystallization behavior and morphology of double crystalline poly(butylene succinate)-poly(ethylene glycol) multiblock copolymers

The crystallization kinetics, morphology and crystal structure of biodegradable double crystalline poly(butylene succinate)-poly(ethylene glycol) (PBS-PEG) multiblock copolymers (PBSEGs) were studied with different composition and segment chain length by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). The isothermal crystallization kinetics results show that the overall crystallization rate and the equilibrium melting point of PBS increase with the increasing PBS fraction and the segment chain length (L_PBS); on the other hand, the higher content or longer PEG segment within PBSEGs possesses larger crystallization rate of PEG chains. The nucleation mechanisms are demonstrated to be instantaneous 3D and 2D aggregates for PBS and PEG segments within PBSEGs, respectively (except for PBSEG_2K?50, 2D and 3D aggregates for PBS and PEG segments, respectively). POM observations indicate that the PBS within PBSEG multiblock copolymers presents banded spherulites in the investigated temperature range. After quenched to lower temperature, PBS templates the morphology for PEG crystallization, and PEG crystallization just changes the magnitude of birefringence (lighting the spherulites) but not influences the superstructure. Finally, WAXD measurements determine that the crystal structure is not changed with the compositions.     

Solid-state characterization of polyethylene reactor powders and their structural changes upon annealing

Polyethylene reactor powders prepared under different conditions were characterized using transmission electron microscopy, ¹H nuclear magnetic resonance and X-ray diffraction techniques. The molecular weight of the polyethylene reactor powders was around 1 × 10⁵. A unique domain morphology, quite different from the usual melt- or solution-crystallized lamellar structure, was observed, independent of polymerization temperature (T_poly). Annealing of reactor powders caused the aggregation of these crystalline domains, due to the significant molecular motion of the amorphous chains, before melting. The critical temperature was 20 °C higher than each T_poly, and corresponded to the temperature at the active catalyst site producing the chain growth. The morphologies of powders prepared at the lower T_poly contained smaller crystals that exhibited a constrained monoclinic form. In contrast, only usual orthorhombic crystals of larger size were found within the powder prepared at the higher T_poly. These results suggest that the competitive processes of chain propagation and crystal growth upon polymerization may lead to unique variations of the crystalline and amorphous phases, but with similar intermediate components in the phase that connects them.     

Solid-state C NMR investigation of the structure and dynamics of highly drawn polyethylene—detection of the oriented non-crystalline component

The structure and dynamics of highly drawn polyethylene samples were studied by solid-state ¹³C NMR spectroscopy. The analyses of the ¹³C spin-lattice relaxation time (T_1C) and the ¹³C spin-spin relaxation time (T_2C) have revealed that at least three components with different T_1C and T_2C values, which correspond to the crystalline, less mobile non-crystalline, and rubbery amorphous components, exist for these materials, as in the case of isothermally crystallized samples. However, another component with a mass fraction of 0.13-0.18 exists which has a ¹³C chemical shift very close to that of the orthorhombic crystalline phase but has an extremely small T_1C. Since this component is believed to have the all-trans conformation, it is termed fast all-trans. The chemical shift anisotropy (CSA) spectra for various samples that have small T_1C values have been recorded and resolved into those of the non-crystalline and fast all-trans components. As expected, the CSA spectra of the less mobile non-crystalline and rubbery amorphous components that have the smallest T_1C values display only a slight asymmetry. In contrast, the CSA spectrum of the fast all-trans component displays higher asymmetry. However, the spectrum is still much narrower than that of the normal orthorhombic crystalline phase, indicating a high degree of motional averaging. It is proposed that this component should be a highly oriented non-crystalline component, which may exist as taut tie-molecules traversing the non-crystalline region. To account for the narrow CSA, this component must undergo rapid fluctuation with large amplitudes at the torsional potential minimum in each C-C bond and possibly an additional random jump or diffusional rotation around the chain axis. Additional measurements obtained by aligning the draw axis of the sample parallel or perpendicular to the static magnetic field indicate that the fast all-trans component is oriented along the drawing direction and subjected to rapid motion around the chain axis.     

Enhanced photoluminescence property of Dy co-doped BaAl2O4:Eu green phosphors

Eu²⁺-doped BaAl₂O₄ green phosphors were prepared by a conventional solid-state reaction and the effects of Dy³⁺ co-doping on the photoluminescence property were investigated. The phosphors were characterized by X-ray powder diffraction (XRD), fluorescence spectroscopy, field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD showed that all prepared samples exhibited a hexagonal BaAl₂O₄ phase. Fluorescence spectroscopy showed that the photoluminescence efficiency increased with increasing Eu²⁺ concentration until 3 mol% then decreased at higher concentrations due to concentration quenching effect. Moreover, Dy³⁺ co-doping increased the photoluminescence efficiency of the Eu²⁺-doped BaAl₂O₄ phosphor.