Deformation and fracture behavior of high‐energy electron irradiated poly(vinylidene fluoride‐trifluorethylene) ferroelectric copolymer films under uniaxial tension

The deformation and fracture behavior under uniaxial tension were characterized for high‐energy irradiated poly(vinylidene fluoride‐trifluorethylene) (P(VDF‐TrFE)) 68/32 mol % copolymer films. The results show that the stress–strain behavior of the irradiated copolymer films exhibits ductile polymeric behavior, with its fracture strain being more than five times of that of the nonirradiated ones but of much lower maximum strength. X‐ray diffraction (XRD) analysis and scanning electron microscope (SEM) observation are carried out to examine the microstructure and morphology changes caused by the uniaxial tension. It is demonstrated that the tensile mechanical field reintroduces the polar β‐phase that was previously lost through irradiation. It is suggested that the conformational change from the nonpolar phase to the polar β‐phase during the uniaxial tension, as well as the low crystallinity and loosely packed molecular chain structure, mainly contribute to the observed stress–strain behavior for the irradiated copolymer films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2563–2567, 2007     

Partially miscible EVOH/copolyamide‐6/6.9 blends: The effect of stretching on the structure

Binary blends of random copolymers, ethylene‐vinyl‐alcohol (EVOH) consisting of 38 mol % ethylene and Copolyamide‐6/6.9 with an approximate 1 : 1 comonomer ratio, were prepared via blown‐film extrusion and uniaxial stretching. The anisotropy induced by the uniaxial deformation of the polymer blends was characterized by X‐ray diffraction and birefringence measurements. The stretched films also were investigated via oxygen permeability. The results showed a sharp decrease in the apparent crystallite size throughout the entire composition range in comparison to the blown films. However, the order perceived within the amorphous phase in the EVOH‐rich blends increased (decrease in oxygen permeability), whereas in the copolyamide‐rich blends, orientation resulted in a decrease in the amorphous phase order (increase in permeability). Apparently, orientation destroyed the amorphous interpolymer complex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 813–822, 2000     

Modification of the structure and properties of poly(vinylidene fluoride–trifluoroethylene) 56/44 mol % copolymer by a proton‐irradiation treatment

The effects of high‐energy proton irradiation on the structure and properties of 56/44 mol % poly(vinylidene fluoride–trifluoroethylene) copolymer were studied with differential scanning calorimetry (DSC), X‐ray diffraction (XRD), relative permittivity, and polarization hysteresis measurements. Copolymer films prepared by hot compression molding were irradiated with a broad range of proton dosages (10–107 Mrad) at room temperature. The DSC results showed that the ferroelectric transition was strongly affected by the proton dosages. The XRD data indicated the reduction of polar ordering in the copolymer by the proton‐irradiation treatment. From the relative permittivity and polarization behavior, the copolymer film was found to be converted from a normal ferroelectric material to a relaxor ferroelectric material as the proton dosage was increased to 50 Mrad. The electrostrictive coefficient of the 56/44 mol % copolymer was enhanced after irradiation, and the optimized proton dosage for attaining the highest electrostrictive strain response was determined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2334–2339, 2005     

Structure development in multistage stretching of PTFE films

The structure of expanded poly(tetrafluoroethylene) (ePTFE) films that were produced by uniaxial or biaxial stretching of a calendared sheet were studied by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering, differential scanning calorimetry (DSC), and scanning electron microscopy. The molecular orientation of the stretched films was analyzed by WAXD flat films and pole figures. Biaxial orientation factors were computed to interpret the level of orientation quantitatively. DSC scans showed that oriented samples exhibited two melting peaks, one at the commonly observed temperature in the range 340–345 °C and one around 380 °C. The possible causes of this high‐temperature melting peak and its relation to previously described processes is discussed. The microporous nature of the ePTFE films is also briefly discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Crystalline structure and morphology of biaxially oriented polyamide‐11 films

The effect of the uniaxial and biaxial stretching and subsequent solution annealing of extrusion‐cast polyamide‐11 films on the crystalline structure and morphology was investigated with differential scanning calorimetry, wide‐angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy, and small‐angle X‐ray scattering (SAXS). The extrusion‐cast polyamide‐11 films exhibited elevations in the glass‐transition and cold‐crystallization temperatures with a constant crystallinity and a constant melting point during aging under room conditions (20–26 °C and 20–31% relative humidity). WAXD and SAXS suggested that chain‐folded lamellae of coexisting α‐ and β‐crystals existed in all the stretched polyamide‐11 films. WAXD pole figures indicated that hydrogen bonds in the hydrogen‐bonded sheets of these two crystalline forms apparently formed between antiparallel chain molecules. The unit cell parameters [a = 9.52 Å, b = 5.35 Å, c = 14.90 Å (chain axis), α = 48.5°, β = 90°, and γ = 74.7° for a triclinic α form and a = 9.52 Å, b = 14.90 Å (chain axis), c = 4.00 Å, α = 90°, β = 67.5°, and γ = 90° for a monoclinic β form] for polyamide‐11 crystals were proposed according to the results of this study and the results of previous investigators. The unit cell parameters of the stretched extrusion‐cast polyamide‐11 films varied, depending on the stretching conditions (the stretch temperature and stretch ratio). As the stretch temperature and stretch ratio were increased, the crystal became more similar to the form described previously and was accompanied by an increase in the long spacing of crystalline lamellae. Annealing the stretched films in a boiling 20% formic acid solution made slightly more perfected crystals. The hydrogen‐bonding α(010) + β(002) planes, which are nearly parallel to both amide group planes and zigzag methylene sequence planes of the biaxially stretched films were found to be parallel to the film surface. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2624–2640, 2002     

Characterization of PET films modified by tetraethylenepentamine (TTEPA)

Tetraethylenepentamine, a long‐chained multifunctional amine, was used to attach nitrogen (N) groups to the surface of a polyethylene terephthalate film. The N content of the modified films was determined by X‐ray photoelectron spectroscopic analysis as well as titration measurements. The physical properties of the modified films were studied using weight‐loss measurements, X‐ray diffraction, and environmental scanning electron microscopy. Contact‐angle measurements were used to establish the changes in wettability of the modified films. The applicability of the surface‐tension‐component theory and the equation‐of‐state approach to this system is briefly discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 623–633, 2001     

Alternating copolymer of thiophene andN‐(phenylethynyl)pyrrole. New π‐conjugated alternating five‐membered ring copolymer and its packing structure

An alternating copolymer, Copoly‐1 , of thiophene and N‐(phenylethynyl)pyrrole was prepared by palladium‐catalyzed polycondensation. Powder X‐ray diffraction (XRD) analysis indicated that Copoly‐1 formed a stacked packing structure with doubly‐running polymer main chains. Optical data support the molecular and packing structures of Copoly‐1 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2219–2224, 2005     

Ionic aggregates in Zn‐ and Na‐neutralized poly(ethylene‐ran‐methacrylic acid) blown films

The morphology of ionic aggregates in semicrystalline Zn‐ and Na‐neutralized poly(ethylene‐ran‐methacrylic acid) (EMAA) ionomer blown films has been explored with scanning transmission electron microscopy (STEM) and small angle X‐ray scattering. The ionic aggregates of Zn‐EMAA are spherical, monodisperse, and uniformly distributed in as‐extruded pellets and blown films prepared at low and high blow‐up ratio. Thus, although the biaxial stresses of film blowing are sufficient to alter the PE superstructure, the ionic aggregates in Zn‐EMAA are unaffected. In contrast, the morphology of Na‐EMAA as detected by STEM changes from featureless in the as‐extruded pellets to a heterogeneous distribution of Na‐rich aggregates in the blown films. This transformation in Na‐EMAA morphology is consistent with our earlier study of quiescent annealing, suggesting that the morphological change is the result of thermal processing rather than the biaxial stresses of film blowing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3549–3554, 2005     

Conformational variation and crystalline phase transformation of low syndiotactic polypropylene films in stretched and stress‐relaxed states

Low syndiotactic polypropylene (sPP; rrrr = 80%) films were isothermally crystallized at 0 °C (sample S₀) and 90 °C (sample S₉₀) for 65 h, respectively. Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction were used to characterize the structure transformation and orientation behavior of samples S₀ and S₉₀ at both stretched and stress‐relaxed states. It was found that stretching (λ = 0–700%) induces the transformation of the chain conformation from helical to trans‐planar form for both S₀ and S₉₀ films. The stretched S₀ and S₉₀ samples show well oriented trans‐planar chains as well as partially retained helices. Simultaneously, crystalline phase transformation occurs during the stretching and relaxing processes of the investigated sPP samples, i.e., stable form I crystals can be transformed into metastable form III or mesophase by stretching samples, and vice versa. For stretched S₀ sample, form III with trans‐planar conformation, which generally exists in highly stretched sPP, cannot be observed, even at higher strains. For sample S₉₀, however, stretching might induce the formation of both the form III crystals and mesophase with trans‐planar chains; releasing the tension, form III again gets converted into trans‐planar mesophase and form I crystals. In the stretched and stress‐relaxed states of samples S₀ and S₉₀, the difference of the delicate orientation behavior and relative content of chain conformation and crystalline form can be attributed to the different heat‐treating methods of the low syndiotacticity sPP. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2924–2936, 2005     

Influence of the annealing conditions on the polarization and electromechanical response of high‐energy‐electron‐irradiated poly(vinylidene fluoride trifluoroethylene) copolymer

In this study, we investigated the influence of annealing conditions before irradiation on the ferroelectric and electromechanical properties of uniaxially stretched high‐energy‐electron‐irradiated poly(vinylidene fluoride trifluoroethylene) (HEEIP) copolymer (68/32 mol %) films. For films annealed at one fixed temperature before the irradiation (one‐step annealing), the highest crystallinity, which was highly desirable for enhancing the electromechanical response, was obtained only for films annealed between 132 and 136 °C. In addition, annealing over 10 h in this temperature window resulted in a large increase in the crystal lamellar thickness, which was required for reducing the polarization hysteresis to a minimum in the HEEIP samples. For improvements in the mechanical qualities of the uniaxially stretched films, a two‐step annealing procedure was investigated; that is, before the irradiation, the films were first annealed at a lower temperature to release the mechanical stress in the films due to the stretching and then were annealed in the high‐temperature window to raise the crystallinity and crystalline size. The experimental results indicated that this approach could produce uniaxially stretched HEEIP films with much improved mechanical qualities. Furthermore, the uniaxially stretched HEEIP films with this two‐step annealing exhibited the same electromechanical response as or an even higher one than that from the one‐step‐annealed HEEIP films. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 797–806, 2003     

Polypropylene/montmorillonite nanocomposites toughened with SEBS‐g‐MA: Structure–property relationship

Polypropylene (PP)/organo‐montmorillonite (Org‐MMT) nanocomposites toughened with maleated styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) were prepared via melt compounding. The structure, mechanical properties, and dynamic mechanical properties of PP/SEBS‐g‐MA blends and their nanocomposites were investigated by X‐ray diffraction (XRD), polarizing optical microscopy (POM), tensile, and impact tests. XRD traces showed that Org‐MMT promoted the formation of β‐phase PP. The degree of crystallinity of PP/SEBS‐g‐MA blends and their nanocomposites were determined from the wide angle X‐ray diffraction via profile fitting method. POM experiments revealed that Org‐MMT particles served as nucleating sites, resulting in a decrease of the spherulite size. The essential work of fracture approach was used to evaluate the tensile fracture toughness of the nanocomposites toughened with elastomer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3112–3126, 2005     

Electron spin resonance studies of anisotropy in semiconducting polymeric films

X‐band electron spin resonance was employed to study the structural anisotropy in several polythiophene derivatives. Because of the dominating homogeneous width, the obtained absorption spectra were Lorentzian‐shaped. Information about the structural anisotropy was obtained from the position and width of the absorption peak. Qualitatively, the anisotropy was in full agreement with earlier results from X‐ray diffraction, including a flip in molecular orientation with respect to the film substrate between solution‐cast and spin‐cast films. With the Monte Carlo technique, the spectra were fitted with a biaxial g tensor, an anisotropy parameter S, and an intrinsic width σ. The simulations showed that g could be treated as pseudo‐uniaxial, with the unique axis along the side chains rather than along the ring normal. Closed‐form analytical expressions relating g to the anisotropy were obtained and used for a quantitative assessment of the molecular anisotropy. Because the molecular g tensor for these materials was not known, a known value of S for one of the samples obtained by X‐ray diffraction was used for normalization. Fairly consistent values were obtained for both g and S. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3011–3025, 2003     

Analysis of crystallization behavior and crystal modifications of poly(butylene‐2,6‐naphthalene dicarboxylate)

Information on the crystalline structure and the properties of poly(butylene‐2,6‐naphthalene dicarboxylate) (PBN) has not been well reported until now, but it is known that there are two different crystal modifications in PBN, as follows: one is formed in isotropic samples by annealing (α form); another appears by annealing with tension (β form). The relation between the crystal modifications and the kinetics of isothermal crystallization for PBN was investigated using in‐situ Fourier transform infrared spectroscopy (FTIR) and wide‐angle X‐ray diffraction (WAXD). The melting behavior of each crystalline form was also studied by means of FTIR and differential scanning calorimetry (DSC) measurements. From the analysis of the melt‐crystallized PBN specimens, the two crystalline forms coexisted in the isotropic samples melt‐crystallized at 230°C, but only the α crystal modification was observed in the films annealed at lower temperatures. In addition, it was revealed that, at 230°C, the β modification was formed only in the primary crystallization process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 561–574, 1999     

Structure evolution of α′‐phase poly(lactic acid)

Poly(lactic acid) films consisting of α′‐forms were prepared and uniaxially drawn. The effects of the draw rate at temperatures above the glass transition temperature on chain conformation, degree of crystallinity, and crystalline phase transformation were investigated by a combination of vibrational spectroscopy (infrared and Raman), differential scanning calorimetry, and wide‐angle X‐ray diffraction (WAXD). It was established that the α′‐crystal's phase of poly(lactic acid) films does not transform into either an α or β crystals on uniaxial drawing at a fixed draw ratio of 4. However, the degree of crystallinity was significantly increased on deformation. The structural change as a function of deformation also promotes an increase in the strain‐induced enthalpic relaxation endothermic peak appearing near the glass transition region. While the overall changes in physical properties can be attributed to the changes in the degree of crystallinity as a function of strain rate, polarized Raman spectra, and WAXD clearly illustrated changes and the differences in the amorphous and crystalline orientation as a function of processing conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1446–1454, 2011     

Wide angle X‐ray diffraction and Fourier transform infrared dichroism studies of stretched‐recovery‐restretched process of polyurethane/clay nanocomposite

An intercalated polyurethane (PU) /clay nanocomposite was prepared by in situ intercalative polymerization. The PU/clay nanocomposite pellet or film samples were stretched‐recovery‐restretched, using selfmade microstretching tools. The changes of the basal spacings of clay and the orientation of polymer chain segments during the stretched‐recovery‐restretched process were studied by wide angle X‐ray diffraction (WAXD) and Fourier transform infrared (FTIR) dichoism techniques. The WAXD results show that the basal spacing of clay did not change obviously, indicating that no macromolecular chains entered or moved out of the interlayer space, and the orientations of both hard and soft segments inside the interlayer space did not change obviously, either. The FTIR dichroism tests suggest that outside the interlayer space, the orientation of the hard chain segment increased, decreased, and then increased again during the stretched‐recovery‐restretched process. However, no obvious changes of the degree of orientation of the soft segment were observed during the processes, the slightly orientation might be released during the relaxation process before the measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 654–660, 2007     

Tensile behavior of Nafion and sulfonated poly(arylene ether sulfone) copolymer membranes and its morphological correlations

The tensile stress–strain behavior of Nafion 117 and sulfonated poly(arylene ether sulfone) copolymer (BPSH35) membranes were explored with respect to the effects of the strain rate, counterion type, molecular weight, and presence of inorganic fillers. The yielding properties of the two films were most affected by the change in the strain rate. The stress–strain curves of Nafion films in acid and salt forms exhibited larger deviations at strains above the yield strain. As the molecular weight of the BPSH35 samples increased, the elongation at break improved significantly. Enhanced mechanical properties were observed for the composite membrane of BPSH35 and zirconium phenylphosphonate (2% w/w) in comparison with its matrix BPSH35 film. The stress‐relaxation behavior of Nafion and BPSH35 membranes was measured at different strain levels and different strain rates. Master curves were constructed in terms of plots of the stress‐relaxation modulus and time on a double‐logarithm scale. A three‐dimensional bundle‐cluster model was proposed to interpret these observations, combining the concepts of elongated polymer aggregates, proton‐conduction channels, and states of water. The rationale focused on the polymer bundle rotation/interphase chain readjustment before yielding and polymer aggregate disentanglements and reorientation after yielding. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1453–1465, 2006     

Properties of well‐defined alternating and random copolymers of methacrylates and styrene prepared by controlled/living radical polymerization

The physical properties of well‐defined alternating copolymers poly(methyl methacrylate‐alt‐styrene) and poly(n‐butyl methacrylate‐alt‐styrene), prepared by reversible addition–fragmentation chain transfer polymerization in the presence of Lewis acids, were investigated with differential scanning calorimetry, wide‐angle X‐ray scattering, and dynamic mechanical measurements. The properties were compared with those of random copolymers of the same overall composition and the corresponding homopolymers. Wide‐angle X‐ray scattering data showed that the alternating copolymers possessed a more regular comonomer sequence than the random copolymers. The thermomechanical properties of alternating copolymers and random copolymers were quite similar and typical for amorphous polymers, but in one of the cases studied the glass‐transition temperature for alternating copolymer was remarkably higher than for the random copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3440–3446, 2005     

Molecular orientation behavior of poly(vinyl chloride) as influenced by the nanoparticles and plasticizer during uniaxial film stretching in the rubbery stage

The structural evolution during uniaxial stretching of poly(vinyl chloride) films was studied using our real time spectral birefringence stretching machine. The effect of clay loading and the amount of plasticizer as well as the rate effects on the birefringence development and true mechanical response are presented with a final model summarizing the molecular phenomena during stretching. Mechano‐optical studies revealed that birefringence correlated with mechanical response (stress, strain, work) nonlinearly. This was primarily attributed to the preexisting strong network of largely amorphous chains connected via small crystallites that act as physical crosslinking points. These crystallites are not easily destroyed during the high‐speed stretching process as evidenced from the birefringence–true strain curves along with the X‐ray crystallinity measurements. At high speeds, the amorphous chains do not have enough time to relax and hence attain higher orientation levels. The crystallites, however, orient more efficiently when stretched at slow speeds. Apparently, some relaxation of the surrounding amorphous chains helps rotate the crystallites in the stretching direction. Overall birefringence is higher at high stretching speeds for a given true strain value. When the nanoparticles are incorporated, the orientation levels are increased significantly for both the crystalline and amorphous phases. Nanoplatelets increase the continuity of the network because they have strong interaction with the amorphous chains and/or crystallites. This in turn helps transfer the local stresses to the attached chains and increase the orientation levels of the chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 724–742, 2005     

Mechanical properties of oriented low‐density polyethylene with an oriented lamellar‐stack morphology

A quantitative study was undertaken of the anisotropy of low‐strain mechanical behavior for specially oriented polyethylene with controlled crystalline and lamellar orientation. The samples were prepared by the die drawing of injection‐molded rods of polyethylene and annealing. This produced a parallel lamellar structure for which a simple, three‐dimensional composite laminate model could be used to calculate the expected anisotropy. Experimental data, including X‐ray strain measurements of the lateral crystalline elastic constants, showed good quantitative agreement with the model prediction. The X‐ray strain measurements confirmed that the amorphous regions exert large constraints on the crystalline phase in the lateral directions, where an order of magnitude difference was found between the measured apparent lateral crystalline compliances in the lamellar‐stack sample and the expected values for a perfect crystal. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 755–764, 2000     

Nonvolatile write‐once read‐many‐times memory behaviors of polyimides containing tetraphenyl fluorene core and the pendant triphenylamine or carbazole moieties

To better understand the structure–property relationships, two novel aromatic diamines containing tetraphenyl fluorene (TPF) moiety through triphenylamine (TPA) unit and carbazole (Cz) unit modification are designed and synthesized, respectively. Four thermally stable and excellent solubility polyimides are prepared and characterized. The excellent film‐formation ability and thin film stability are investigated by X‐ray diffraction (XRD) and atom force microscopy (AFM) measurements, respectively. The memory devices are fabricated, PIs films with low water uptakes sandwiched between indium‐tin oxide (ITO) ground electrode and Al top electrode, and exhibit nonvolatile write‐once read‐many‐times (WORM) memory behaviors with low threshold voltages, due to increasing the retention time through regulating the energy level. The current conduction mechanisms of all devices are linearly fitted by theoretical conduction model. Molecular simulations are used to demonstrate switching mechanism and the memory effects. The experimental results provide a sight for the design‐adjustable switching voltage of memory devices. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1630–1644