Structural Studies on Syndiotactic 1,2‐Poly(1,3‐butadiene) by X‐Ray Measurements and Molecular Mechanics Calculations

Summary: Two samples of syndiotactic l,2‐poly(1,3‐butadiene) with different constitutional and configurational regularities were characterized by DSC analysis and X‐ray powder diffraction. Possible models of the crystal structure were obtained by molecular mechanics calculations performed with various sets of potential functions. X‐ray powder profiles calculated for these models were in good agreement with experiments. The agreement between simulated and experimental X‐ray powder profiles was improved by taking into account, in the calculated models, the presence of configurational defects. This indicates that configurational defects can be included in the crystal phase.

Projection along the b axis of a portion of the crystal structure of sPBD12 containing a [mm] triad in the energy minimum.     

Determination of the Crystal Structure of Isotactic cis‐1,4‐Poly(1,3‐hexadiene) by X‐Ray Diffraction and Molecular Mechanics

The crystal structure of isotactic cis‐1,4‐poly(1,3‐hexadiene) has been determined through a combination of X‐ray diffraction analysis and molecular mechanics. Two reasonable values for unit cell parameters were obtained from the fiber diffraction pattern of a well‐oriented sample. Energy maps performed on a molecular model of the polymer chain yielded an absolute minimum corresponding to a conformation having the internal parameters similar to those of an s(2/1) helical polymer chain. Packing energy minimizations performed for all the orthorhombic and monoclinic space groups having crystallographic s(2/1) chain symmetry indicate unequivocally that the best mode of packing is obtained for a crystal structure characterized by a unit cell with parameters a = 8.98 Å, b = 7.82 Å, and c = 8.10 Å in the P2₁2₁2₁ space group. The calculated powder and fiber diffraction patterns of this structural model are in very good agreement with the experimental diffraction patterns. Similarities and differences with the crystal structures of isotactic cis‐1,4‐poly(1,3‐pentadiene) and isotactic cis‐1,4‐poly(2‐methyl‐1,3‐pentadiene) are discussed.

     

Structural Analysis of Liquid Crystal Polymer Based Nanocomposites by X‐Ray Scattering

The main theme of this work is to support the unusual melt‐state rheological properties of the clay‐containing nanocomposites of thermotropic liquid crystal polymers by small‐ and wide‐angle X‐ray scattering. The changes of dispersion of silicate particles in the LCP matrix as well as change in crystal growth of LCP were extensively studied by X‐ray scattering in both small‐ and wide‐angle regions. The generalised indirect Fourier transformation technique developed by Glatter was used to study the structural changes in nanocomposites with temperature. This is a new approach recently proposed by us for the quantitative analysis of the nanoparticles dispersion in the polymer matrix.

     

Determination of Poly(4,4′‐diphenylsulfonyl terephthalamide) Crystalline Structure Via WAXD and Molecular Simulations

The crystal structure of poly(4,4′‐diphenylsulfonyl terephthalamide) (pt‐PSA) is studied by X‐ray diffraction and molecular simulation. Although the number of observed reflections is limited to warrant a precise determination of the unit cell structure and symmetry, a reasonable monoclinic unit cell is suggested with dimensions of a = 0.645 nm, b = 0.488 nm, c = 3.010 nm, and γ = 122.5°. A twofold molecule with two monomeric units forming a large zigzag conformation satisfies the X‐ray diffraction data. A layer structure is formed in the crystal phase, which is stabilized by the hydrogen bond between ? NH and ? C?O and the parallel‐displaced π–π stacking from the distortional coplanarity of the benzene rings and amide group.

     

Structural Aspects of Poly(thiodiethylene terephthalate) Investigated by X‐Ray Powder Diffraction

Summary: The full‐profile refinement of X‐ray diffraction patterns was used to investigate two poly(thiodiethylene terephthalate) (PSDET) samples with different thermal history in order to thoroughly analyze their polymorphic aspects. In each sample, a crystalline (α or β) and a microcrystalline (α′ or β′) phase were identified together with an amorphous component. The crystal structures of all the ordered phases were determined. The data indicated an appreciable difference between the two crystalline forms, while the microcrystalline were rather similar. The results reported in this paper agree with the hypothesis that the polymorphic and morphological aspects of PSDET have to be correlated with the order degree and reorganization of crystallites and microcrystallites.

Projection along the a axis and c axis of α‐phase chain arrangement.     

Synthesis,Phase Behaviour and Mechanical Properties of Poly(2‐methyl‐1,3‐propanediol‐4,4′‐bibenzoate)

The synthesis and phase behaviour of PB32 is reported. The results indicate that PB32 develops a low‐ordered smectic mesophase of the type SmC_alt. The slow formation of such a mesophase allows the quenching of the isotropic melt into an amorphous state so that both amorphous glass and smectic glass can be obtained, which exhibit different glass‐transition temperatures. Mechanical tests indicate that the macromolecular chains in the mesophase of PB32 can be oriented either parallel or perpendicularly in relation to the streching direction, depending on the deformation conditions. Solid‐state ¹³C NMR spectroscopy results show that the mobility of the chains is rather similar in both phases.

     

Structural Investigation of Poly(3‐hydroxybutyrate) Spherulites by Microfocus X‐Ray Diffraction

A banded spherulite of bacterial poly(3‐hydroxybutyrate) (band spacing 120 μm) was linearly scanned along the radial direction in 3 μm steps by means of microfocus X‐ray diffraction using a synchrotron source with a beam diameter of 3 μm. A large number of X‐ray patterns was collected inside each band. Those taken at the center of the bands represented the two limiting diffraction patterns from which the exact orientation of the unit cell was inferred. The intensity of the reflections (020) and (002), taken as indicators of parallelism to the X‐ray beam of the unit cell's c‐ or b‐axis, respectively, changed periodically along the spherulite radius, alternating maxima with zero‐intensity zones. When the reflection (020) showed a maximum, the reflection (002) was practically nil and vice versa. This behavior clearly shows that the unit cell's mean position smoothly rotates around the a‐axis with increasing distance from the spherulite center. The identity of the cell rotation period with the band spacing derived from optical microscopy observations provides structural evidence that the extinction bands originate from a regular twisting of the lamellar crystals during their growth.     

Syndiotactic Polystyrene Containing ortho‐Dichlorobenzene: Crystal Structure of the Clathrate Form

Summary: The crystal structure of the clathrate form of syndiotactic polystyrene containing ortho‐dichlorobenzene has been determined, and compared with those of the other crystalline clathrate structures of s‐PS already known. This guest molecule, characterized by a quite different shape and volume from the others already described, gives rise to the only example of clathrate form of s‐PS presenting a statistical orthorhombic symmetry (cell constants a = 17.5 Å, b = 22.9 Å, c = 7.8 Å and space group Ccmb). This symmetry is generated by the random coexistence in the crystals of domains, with the same monoclinic P2₁/a symmetry found for the other clathrate forms, that can be realized by two different but energetically equivalent packings of the chains. The unit cell constants are a = 17.5 Å, b = 14.4 Å, c = 7.8 Å and γ = 127.4°. The shape of the guest molecule produces a significant modification of the cavities (if compared to δ form) realized mainly through a shift of the ac layers of chains delimiting the cavities along the a axis direction that turns out in the highest γ value found for these kinds of structures.

Schematic representation of the arrangement of the chains according to the orthorhombic (solid line) and to the monoclinic (dotted line) unit cells proposed for the crystal structure of the clathrate form of s‐PS containing o‐DCB.     

X‐Ray Diffraction Studies on the Phase‐Transformational Behavior of a Smectic Liquid‐Crystalline Elastomer Composed of Chiral Mesogens

Structural changes through successive phase transformations of a chiral smectic liquid‐crystalline elastomer are investigated by X‐ray scattering technique. In uniaxially deformed elastomers, the smectic layer seemingly tilts even in the SmA phase, in which an in‐plane chevron structure formed in the tilted smectic phase. On the basis of an analysis of the layer reflection peaks, the layer correlation length in the tilted smectic phases is shorter than that in the non‐tilted SmA phase, though smectic layers in the tilted smectic phases are better ordered than those in SmA.

Experimental arrangement for X‐ray measurements of the uniaxially deformed elastomer in the tilted smectic phase at room temperature.     

Columnar Assemblies of Aliphatic Poly(acetylene ester)s Prepared with a [Rh(norbornadiene)Cl]2 Catalyst. 1H and 13C NMR,X‐Ray Diffraction and AFM Studies

Alkyl propiolates: HC≡CCOOn‐C_mH_2m+1(m = 2˜4), acetylene esters were polymerized with a [Rh(norbornadiene)Cl]₂ catalyst in methanol as the polymerization solvent to produce poly(n‐alkyl propiolate)s, PAPAs, called polyacetylene esters, in relatively high yields. The resulting PAPAs were characterized in detail using ¹H and ¹³C NMR spectroscopy, X‐ray diffraction, and atomic force microscope methods. The data showed that the resulting polymers selectively have cis‐transoid form. The cis‐transoid isomer is not amorphous but holds a pseudohexagonal structure called a columnar assembly the diameter of which agrees with those estimated by the semiempirical calculation method (AM1). The crystalline ratios of the columnar assemblies were also estimated to be ca. 60 ˜ 70%. In the case of poly(ethyl propiolate), PEPA, the crystalline size was found to approximately agree with that estimated from the AFM images of the cast film of PEPA.     

Effect of Tacticity on the Structure of Poly(1‐octadecene)

Summary: A sample of poly(1‐octadecene), synthesized with a highly active heterogeneous Ziegler‐Natta catalyst, has been fractioned with heptane, giving soluble and insoluble fractions. Both fractions and the original polymer have been characterized by size exclusion chromatography, solution and solid‐state ¹³C NMR, DSC and X‐ray diffraction. The results show that the fractionation occurs on the basis of both molecular mass and tacticity differences, with the atactic content concentrated in the lower molecular mass chains. Thus, the soluble fraction, having a lower average molecular mass than the original sample, consists predominantly of atactic chains, whereas the insoluble fraction is mainly isotactic. The analysis of the solid‐state structure reveals that both atactic and isotactic fractions are able to crystallize, although their crystalline structures are different. The NMR and X‐ray data together support the “most probable” structure for the isotactic polymer advanced by Turner‐Jones. That structure is characterized by an orthorhombic crystal form, where a) the backbone crystallizes in a quaternary helical conformation, b) the sidechains are packed in a way analogous to orthorhombic polyethylene, and c) successive sidechains are conformationally inequivalent. Support for points b) and c) are respectively found in the chemical shift of the sidechains and in the splittings observed for backbone carbons and for some sidechain carbons located near the points of attachment. In addition, there is evidence that the mobility of sidechain sites at points near both the bonded and free ends are not uniform from chain to chain. On the other hand, the crystal form for the atactic polymer shows only sidechain order with some support for the notion that this order approximates the disordered hexagonal rotator phase of the alkanes.

X‐ray diffractograms of the three poly(1‐octadecene) samples.     

Thermotropic Phase Behavior of a Liquid‐Crystalline Poly(ether ester) Derived from Hydroxydibenzoic Acid, 2‐Methyl‐1,3‐propanediol and R‐1,3‐Butanediol

The thermotropic phase behavior of a liquid‐crystalline poly(ether ester) derived from 4′‐hydroxybiphenyl‐4‐carboxylic acid and two different spacer diols (2‐methyl‐1,3‐propanediol and R‐1,3‐butanediol) has been analyzed by differential scanning calorimetry, real time synchrotron X‐ray diffraction and solid‐state ¹³C NMR. It has been found that the polymer develops a smectic mesophase that presents order inside the layers. This mesophase has a slow rate of formation, in such a way that it is possible to obtain either an amorphous glass or a liquid‐crystalline glass. These two phases exhibit different and independent glass transition temperatures: 95 °C for the amorphous one and 85 °C for the mesophase. The diffractogram of this mesophase shows two clear diffractions in the wide‐angle region and a long spacing (of low intensity) in the small‐angle region. All those features are characteristic of a mesophase of intermediate order, presumably of the type SmI, in contrast to the low‐ordered SmC_alt mesophase reported for the racemic polymer. Thus, the chirality of the spacer, which provides structural regularity, makes easier the packing of the chains, so that a more ordered mesophase is obtained. In addition, both the solid‐state ¹³C NMR line shapes and the value of are practically the same for the quenched and the annealed samples, indicating that the “ordered” phase obtained by annealing is not a three‐dimensional crystal, thus confirming its assignment as mesophase, with a considerable degree of conformational disorder.

     

In situ Structural Characterization of Semi‐Crystalline Polymer Latex Particles by Small‐Angle X‐Ray Scattering

Summary: The inner structure of polyurethane latex particles has been studied in situ using small‐angle X‐ray scattering (SAXS). From contrast variation SAXS measurements evidence could be given that the dispersed particles are semi‐crystalline. The semi‐crystalline structure gives a strong contribution to the measured intensities in an intermediate range of scattering vectors. This contribution, which is independent of the adjusted contrast, could be separated and the long period of the lamellar structure could thus be determined quantitatively to 11 nm. In addition, it was found that the particles exhibit a core‐shell structure which arises from electron‐rich acid groups that are preferentially located at the particle surface.

Transmission electron microscopy (TEM) picture of the PUR particles.     

Scanning Microbeam X‐Ray Scattering of Fibers Analyzed by One‐Dimensional Tomography

The investigation of structure gradients in polymer fibers or pipes by the X‐ray microbeam scanning technique is put on its theoretical fundament. The inverse Abel transform desmears measured data in X‐ray scattering fiber computer‐tomography (XSF‐CT). Fast, low noise algorithms from one‐dimensional tomography are available. They are applicable to scan data in which the X‐ray absorption, the small‐angle X‐ray scattering (SAXS), or the wide‐angle X‐ray diffraction (WAXD) is measured. The method is demonstrated by application to SAXS scan data from a polymer fiber. The resulting sequence of image‐space SAXS patterns is reflecting the nanostructure variation along the fiber radius.

     

Effect of Blend Composition on Scratch Behavior of Polystyrene/Poly(2,6‐dimethyl‐1,4‐phenyleneoxide) Blends

The relationship between the scratch behavior and molecular aggregation states of polystyrene (PS), poly(2,6‐dimethyl‐1,4‐phenyleneoxide) (PPO), and their blends, is investigated based on differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), polarized optical microscopy (POM), and indentation and scratch tests. DSC reveals that all the PS/PPO blends show the single glass transition temperature (T_g) and the T_g monotonically increase and T_g breadth exhibits a maximum, with an increase in PPO content. Furthermore, density and intermolecular chain distance obtained by WAXD exhibits maximum and minimum values at near 50 wt% of PPO, respectively. It is evident that densification occurs by blending PS and PPO. The scratch coefficient of friction (SCOF) value of PS is the largest and PS exhibits a fish‐scale pattern after scratch testing, while the SCOF value of PPO is much smaller than PS and PPO exhibits smooth groove formation. The PS50/PPO50 and PS20/PPO80 blends exhibit superior scratch and indentation resistance than PS and PPO. Damage morphology observation by POM and indentation tests reveals that molecular orientation is more restricted, and resistance against indentation increases for blends. This is due mainly to densification of the blend system.     

Structure of Poly(amino‐s‐triazine)s with Long Methylene Segments

Linear poly(amino‐s‐triazine)s with segments of ten and twelve methylene groups have been synthesized and characterized. Their structure has been studied by means of X‐ray and electron diffraction, and molecular simulation. The polymers are found to crystallize in a unit cell very similar in chain axis projection to that of polyethylene. Furthermore, molecular simulation indicates that the polymethylene segments of the polymer chains are placed with a setting angle very close to that found in the polyethylene structure. The packing of the new polymers appears to be further stabilized by intermolecular hydrogen bonds that involve all nitrogen atoms of the amino‐triazine units.     

Multiple Melting Behavior of Poly(thiodiethylene terephthalate): Further Investigations by Means of X‐ray and Thermal Techniques

Summary: The complex multiple melting behavior of poly(thiodiethylene terephthalate) (PSDET) was investigated by means of differential scanning calorimetry, X‐ray diffraction and hot‐stage optical microscopy. The phenomenon was ascribed to the existence of two different crystal structures (α and β), each of them being able to melt and recrystallize under the experimental conditions adopted. Linear and nonlinear treatments were applied in order to estimate the equilibrium melting temperature for α PSDET, by using the corrected values of T_m. The nonlinear estimation led to a higher value by about 25 °C. Isothermal crystallization kinetics of each crystalline form were analyzed according to Avrami's treatment. In both cases, values of Avrami's exponent, n, close to 3 were obtained, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three dimensional spherulitic growth. The rate of crystallization of each crystalline structure was found to become lower as the crystallization temperature is increased, as usual at low undercooling, where the crystallization process is controlled by nucleation.

XRD patterns of PSDET samples isothermally crystallized at the indicated T_cs.     

The Static Structure and Dynamics of Cadmium Sulfide Nanoparticles within Poly(styrene‐block‐isoprene) Diblock Copolymer Melts

The static structure and dynamic behavior of cadmium sulfide nanoparticles suspended in block copolymer matrix are investigated using transmission electron microscopy, small‐angle X‐ray scattering, and X‐ray photon correlation spectroscopy. The transmission electron microscopy study shows that cadmium sulfide nanoparticles are preferentially segregated within the polyisoprene domain of a poly(styrene‐block‐isoprene) diblock copolymer. For the dynamics study, X‐ray photon correlation spectroscopy captures the relaxation process of cadmium sulfide nanoparticles. The measured characteristic relaxation time reveals that the observed dynamics are hyperdiffusive. The characteristic velocity and corresponding activation energy, which are hallmarks of a hyperdiffusive system, are determined from the relationship between the characteristic relaxation time and the wavevector.

     

Click‐Chemistry: An Alternative Way to Functionalize Poly(2‐methyl‐2‐oxazoline)

CROP has been used to synthesize well‐defined POXZ with a monofunctional (iodomethane) or a bifunctional (1,3‐diiodopropane) initiator. POXZ has been functionalized with an azido group at one (α‐azido‐POXZ, = 3.58 × 10³ g · mol^?1) or both ends (α,ω‐azido‐POXZ, = 6.21 × 10³ g · mol^?1) of the macromolecular chain. The Huisgen 1,3‐dipolar cycloaddition has been investigated between azido‐POXZ and a terminal alkyne on a small or larger molecule (PEG). In each case, the click reaction has been successful and quantitative. In this way, different telechelic polymers (polymers bearing different functions such as acrylate, epoxide, or carboxylic acid) and block copolymers of POXZ and PEG have been prepared. The polymers have been characterized by means of FTIR, ¹H NMR, and SEC.

     

Synchrotron X‐ray and DSC Studies of the Phase Behaviour of Poly(diethylene glycol p,p′‐bibenzoate)

Time‐resolved synchrotron X‐ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p′‐bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110 °C. Moreover, the annealing of PDEB at temperatures above T_g for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained.

Scattering profiles corresponding to sample PDEB85 in a melting experiment.