Liquid Crystal Ordering on Conjugated Polymers Film Morphology for High Performance

The electronic performance of conjugated polymers depends on the microstructure of the polymer films. A percolated network morphology with high crystallinity, ordered intermolecular packing and long‐range order is beneficial for charge transport. In recent reports, some conjugated polymers have been shown to exhibit liquid crystallinity. The appearance of liquid crystalline ordering provides a new solution to solve the difficulties in microstructure manipulation. In this review, we summarize how liquid crystallinity can assist molecular arrangement and guide long‐range orientation during film processing, leading to high charge mobility. We expect that this article could draw more attention to the liquid crystallinity of conjugated polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1572–1591     

Relationships between nanostructure and thermomechanical properties in poly(vinyl alcohol)/montmorillonite nanocomposite with an entrapped polyelectrolyte

Poly(vinyl alcohol)/montmorillonite (PVA/MOM) hydrogels containing coacervated microparticles of sulfonated polyester (PES) were prepared by direct mixture of the components in water. The system was characterized by using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamical mechanical analysis (DMA). The influence of PES and MOM on the microstructure of the nanocomposite hydrogels was established. The presence of PES causes a significant change on the crystallinity of PVA. Furthermore, the presence of MOM leads to a hierarchical nanostructure that also contributes to change the crystallinity of PVA. The results of structural investigation are correlated with the mechanical properties of the composites obtained by DMA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2618–2629, 2008     

Infrared spectroscopic characterization of oriented polyamide 66: Band assignment and crystallinity measurement

Having found much ambiguity in the infrared band assignments for polyamide 66 (PA66), we revisited some of these assignments before using infrared spectroscopy to assess microstructure changes resulting from multiple thermal treatments. We discovered that earlier assignments of the 1144 and 1180 cm⁻¹ bands to the amorphous (noncrystalline) phase were incorrect, whereas the bands at 924 and 1136 cm⁻¹ can be attributed unambiguously to the noncrystalline phase. We also confirmed that PA66 bands at 936 and 1200 cm⁻¹ are crystalline bands. The normalized absorbance of the 1224‐cm⁻¹ fold band increases in proportion to crystallinity, indicating that chain folding is the predominant mechanism of thermal crystallization in PA66. We demonstrated that infrared spectroscopy can be used to estimate the degree of crystallinity of PA66, and two methods were explored. One is a calibration method in which the band ratio of 1200 and 1630 cm⁻¹ is plotted against crystallinity measured by density. The other is an independent infrared method based on the assumption that PA66 satisfies a two‐phase structure model. The crystallinity determined by the independent infrared method showed good agreement with the crystallinity obtained from density measurements. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 516–524, 2000     

Correlation of charge transport with structural order in highly ordered melt‐crystallized poly(3‐hexylthiophene) thin films

A series of well‐defined poly(3‐hexylthiophene)s (P3HT) of different molecular weight (MW) and high regioregularity was investigated for charge transport properties in as‐cast and melt‐crystallized films. The semicrystalline structure of the P3HT was characterized by X‐ray scattering and Atomic force microscopy. Crystallization by cooling from the melt led to a substantial increase in crystallinity and a stronger alignment of the crystals in comparison to as‐cast films. The increase in crystallinity went along with an increase in hole mobility of up to an order of magnitude as measured by the space charge limited current method. Additionally, the hole mobility depended on the long period of P3HT lamellae and consequently on the MW. In compliance with the long period, the charge carrier mobility first increased with the MW before decreasing again at the onset of chain folding. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 943–951     

Effect of the microstructure on the dye diffusion and mechanical properties of polyamide‐6 fibers

The morphology, mechanical properties, and dye diffusion of drawn and heat‐set polyamide‐6 (PA6) yarns were examined. Correlations between the microstructure of PA6 yarns and the dye diffusion coefficients and mechanical properties were established. The crystallinity of PA6 yarns was estimated with density and Fourier transform infrared spectroscopy measurements. A decrease in the γ crystallinity and an increase in the γ‐crystallite size with the draw ratio were observed and attributed to the disappearance of small crystallites and an increase in the average γ‐crystallite size population during the deformation process. The scouring treatment increased the total crystallinity, almost entirely as a result of an increase in the α fraction. Thermally induced crystallization involved increases in both crystalline phases (α and γ) and did not involve crystal‐to‐crystal transformation, whereas drawing PA6 yarns involved both crystallization of the amorphous phase in the α form and γ→α transformation. A sharp decrease in the diffusion coefficient with an increasing draw ratio of PA6 yarns was correlated with an increasing amorphous orientation. The influence of thermally induced crystallinity on the diffusion coefficient seemed exceptionally strong. The mechanical properties of PA6 yarns were examined and correlated with structural changes. It was demonstrated that the crystallinity had a direct correlation with the terminal modulus and extension at break, whereas there was no correlation with the initial modulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 349–357, 2007     

Microstructure analysis and thermal property of copolymers made of glycolide and ϵ‐caprolactone by stannous octoate

Glycolide (GL) and ?‐caprolactone (CL) were copolymerized in bulk at relatively high temperatures using stannous octoate as a catalyst. To investigate the relationship among microstructure, thermal properties, and crystallinity, three series of copolymers prepared at various reaction temperatures, times, and comonomer feed ratios were prepared and characterized by ¹H and ¹³C NMR, DSC, and wide‐angle X‐ray diffraction (WAXD). The 600‐MHz ¹H NMR spectra provided information about not only the copolymer compositions but also about the chain microstructure. The reactivity ratios (r_G and r_C) were calculated from the monomer sequences and were 6.84 and 0.13, respectively. In terms of overall feed compositions, the sequence lengths of the glycolyl units calculated from the reactivity ratios exceeded those measured from the polymeric products. Mechanistic considerations based on reactivity ratios, monomer consumption data, and average sequence lengths are discussed. The unusual phase diagram of GL/CL copolymers implies that the copolymer melting temperature does not depend on its composition alone but rather on the nature of the sequence distribution. The DSC and WAXD measurements show a close relationship between polymer crystallinity and the nature of the polymer sequence. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 544–554, 2002; DOI 10.1002/pola.10123     

Influence of monomer type on miniemulsion polymerization systems stabilized by graphene oxide as sole surfactant

Based on a recent report [J. Polym. Sci. Part A. Polym. Chem. 2013 , 51, 47–58] whereby we demonstrated the synthesis of polystyrene nanoparticles by miniemulsion polymerization stabilized by graphene oxide (GO) nanosheets as sole surfactant, we hereby report the synthesis of hybrid polymer nanoparticles of several members of the (meth)acrylate family as well as the cross‐linker divinylbenzene via the same approach. The nature of the resultant emulsion is strongly linked to the polarity of the monomer used; monomers with a relatively small polar component (based on Hansen solubility parameters) such as lauryl methacrylate and benzyl methacrylate, in addition to styrene, generate stable emulsions that can be effectively polymerized. Particularly polar monomers (e.g., methyl acrylate and methyl methacrylate) formed kinetically stable emulsions in the presence of GO, however rapid coagulation occurred during polymerization. Electron microscopy analysis reveals the formation of polymer nanoparticles with size distribution between 200 and 1000 nm with roughened surface morphologies, indicative of GO sheets adsorbed at the interface. The results of this work demonstrate the applicability of this synthetic route for specific monomers in the preparation of novel graphene‐based polymeric materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5153–5162     

Effect of multiple adduct fullerenes on charge generation and transport in photovoltaic blends with poly(3‐hexylthiophene‐2,5‐diyl)

The effect of replacing [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) by its multiadduct analogs (bis‐PCBM and tris‐PCBM) in bulk heterojunction organic solar cells with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) is studied in terms of blend film microstructure, photophysics, electron transport properties, and device performance. Although the power conversion efficiency of the blend with bis‐PCBM is similar to the blend with PCBM, the performance of the devices with tris‐PCBM is considerably lower as a result of small photocurrent. Despite the lower electron affinity of the fullerene multiadducts, μs‐ms transient absorption measurements show that the charge generation efficiency is similar for all three fullerenes. The annealed blend films with multiadducts show a lower degree of fullerene aggregation and lower P3HT crystallinity than the annealed blend films with PCBM. We conclude that the reduction in performance is due largely to poorer electron transport in the blend films from higher adducts, due to the poorer fullerene network formation as well as the slower electron transport within the fullerene phase, confirmed here by field effect transistor measurements. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Thermal and mechanical properties of syndiotactic polystyrene/organoclay nanocomposites with different microstructures

The fabrication of syndiotactic polystyrene (sPS)/organoclay nanocomposite was conducted via a stepwise mixing process with poly(styrene‐co‐vinyloxazolin) (OPS), that is, melt intercalation of OPS into organoclay followed by blending with sPS. The microstructure of nanocomposite mainly depended on the arrangement type of the organic modifier in clay gallery. When organoclays that have a lateral bilayer arrangement were used, an exfoliated structure was obtained, whereas an intercalated structure was obtained when organoclay with a paraffinic monolayer arrangement were used. The thermal and mechanical properties of sPS nanocomposites were investigated in relation to their microstructures. From the thermograms of nonisothermal crystallization and melting, nanocomposites exhibited an enhanced overall crystallization rate but had less reduced crystallinity than a matrix polymer. Clay layers dispersed in a matrix polymer may serve as a nucleating agent and hinder the crystal growth of polymer chains. As a comparison of the two nanocomposites with different microstructures, because of the high degree of dispersion of its clay layer the exfoliated nanocomposite exhibited a faster crystallization rate and a lower degree of crystallinity than the intercalated one. Nanocomposites exhibited higher mechanical properties, such as strength and stiffness, than the matrix polymer as observed in the dynamic mechanical analysis and tensile tests. Exfoliated nanocomposites showed more enhanced mechanical properties than intercalated ones because of the uniformly dispersed clay layers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1685–1693, 2004     

Effect of a post‐annealing process on microstructure and mechanical properties of high‐density polyethylene/silica nanocomposites

High‐density polyethylene (HDPE) and nanosilica nanocomposites were prepared for SiO₂ content up to 15 wt%. Microstructural characterization evidenced a homogenous distribution of silica aggregates with a mean size increasing with the filler content finally resulting in a rheological percolation between 7.5 and 10 wt%. Nanoparticles did not induce any significant impact on the matrix crystallinity but led to a real improvement on elastic properties accompanied with a large embrittlement above the percolation threshold. The effect of annealing near HDPE melting temperature was studied. Differential scanning calorimetry, X‐ray diffraction, and small‐angle X‐ray scattering analyses showed a significant change in the HDPE microstructure after annealing at 125°C. A large increase in the crystallinity (from 68 to 76%) and a clear improvement of Young's modulus (by 55%) were observed prior to polymer degradation. A valuable impact of silica particles on thermal stability was also obvious regarding the evolution of elastic properties for extended exposure times (850–1,200 h). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 535–546     

Synthesis of head‐to‐tail polyurethanes from nonsymmetric diisocyanate and ethylene glycol with organotin catalysts

An ordered head‐to‐tail (HT) polyurethane was successfully prepared by the polyaddition reaction of p‐isocyanatobenzyl isocyanate with ethylene glycol with dibutyltin dilaurate as a catalyst. Furthermore, the HT regularity of polyurethane was improved to 83% with 1,1,3,3‐tetraphenyl‐1,3‐dichlorodistannoxane. The polymerization was conducted in N,N‐dimethylformamide at 30 °C with both monomers mixed at once. The microstructure of the polymer was investigated by ¹H and ¹³C NMR spectroscopy, and the polymer obtained by the polyaddition reaction had the expected HT linkages. The constitutional regularity of the polymers influenced the thermal properties and crystallinity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 416–429, 2001     

Miscibility in crystalline/amorphous blends of poly(3-hydroxybutyrate)/DGEBA

A differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) study of miscibility in blends of the semicrystalline polyester poly(3-hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) was performed. Evidence of the miscibility of PHB/DGEBA in the molten state was found from a DSC study of the dependence of glass transition temperature (T_g) as a function of the blend composition and isothermal crystallization, analyzing the melting point (T_m) as a function of blend composition. A negative value of Flory–Huggins interaction parameter χ_PD was obtained. Furthermore, the lamellar crystallinity in the blend was studied by SAXS as a function of the PHB content. Evidence of the segregation of the amorphous material out of the lamellar structure was obtained. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Morphology of polyanhydride copolymers: Time‐resolved small‐angle X‐ray scattering studies of crystallization

Synchrotron small‐angle X‐ray scattering (SAXS) was used to study the isothermal crystallization kinetics of a family of polyanhydride copolymers consisting of 1,6‐bis(p‐carboxyphenoxy)hexane and sebacic acid monomers. In situ SAXS experiments permitted the direct observation of the crystallization kinetics. The structural parameters (the long period, lamellar thickness, and degree of crystallinity) were obtained from Lorentz‐corrected intensity profiles, one‐dimensional correlation functions, and interface distribution functions to form a comprehensive picture of the crystal morphology. The combination of these three analyses provided information not only on the lamellar dimensions but also on the polydispersity (nonuniformity) of these dimensions. Where possible, the crystallization kinetics were interpreted with a modified version of the Avrami equation. The results can be used to perform the rational design of controlled‐drug‐release formulations because crystallinity affects drug‐release kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 463–477, 2005     

Influence of deformation on irreversible and reversible crystallization of poly(ethylene‐co‐1‐octene)

The effect of uniaxial deformation and subsequent relaxation at ambient temperature on irreversible and reversible crystallization of homogeneous poly(ethylene‐co‐1‐octene) with 38 mol % 1‐octene melt‐crystallized at 10 K min was explored by calorimetry, X‐ray scattering, and Fourier transform infrared spectroscopy. At 298 K, the enthalpy‐based crystallinity of annealed specimens increased irreversibly by stress‐induced crystallization from initially 15% to a maximum of, at least, 19% when a permanent set of more than 200% was attained. The crystallinity increased by formation of crystals of pseudohexagonal structure at the expense of the amorphous polymer, and as a result of destruction of orthorhombic crystals. The stress‐induced increase of crystallinity was accompanied by an increase in the apparent specific heat capacity from 2.44 to about 2.59 J g^?1 K^?1, which corresponds to an increase of the total reversibility of crystallization from, at least, 0.10 to 0.17% K^?1. The specific reversibility calculated for 100% crystallinity increased from 0.67 to 0.89% K^?1 and points to a changed local equilibrium at the interface between the crystal and amorphous phases. The deformation resulted in typical changes of the phase structure and crystal morphology that involve orientation and destruction of crystals as well as the formation of fibrils. The effect of the decrease of the entropy of the strained melt on the reversibility of crystallization and melting is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1223–1235, 2002     

Photophysics and morphology of a polyfluorene donor–acceptor triblock copolymer for solar cells

We present a study of the optical, structural and device properties of a polyfluorene (PFM)‐based (PFM‐F8BT‐PFM) donor–acceptor triblock copolymer for use in an organic solar cell. Neutron reflectivity is employed to probe the vertical composition profile before and after thermal annealing while the crystallinity was examined using grazing incidence wide‐angle X‐ray. The absorption spectra and photoluminescence emission for the triblock and analogous blend of PFM with F8BT reveal a greater degree of intermixing in the triblock. However, the triblock copolymer exhibits exciplex emission, which necessitates a geminate polar pair; long‐lived exciplex states are detrimental in organic photovoltaic devices. The triplet yield in the triblock and the blend is estimated using photoinduced absorption, with the triblock copolymer generating a triplet population 20 times that of the blend. This is far from ideal as triplets are wasted states in organic photovoltaic devices and they can also act as scavengers of polarons reducing the efficiency even more. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1705–1718     

Reactions and structural changes during thermal annealing in a semicrystalline,aromatic diacetylene‐containing polyester

Thermally induced solid‐state reactions and microstructure changes in a high molar mass, semicrystalline, aromatic diacetylene‐containing polyester, poly[2,4‐hexadiyn‐1,6‐ylene terephthalate], were investigated with a combination of laser Raman spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction analysis. The study has provided some new insights into the rather complex solid‐state reactions in the semicrystalline diacetylene‐containing polyester. Results suggest that, in addition to the usual desired solid‐state topochemical crosspolymerization in the crystalline region, a certain degree of random crosslinking reaction occurs in the amorphous region, especially when the annealing is carried out above the glass transition. After prolonged annealing or annealing at a higher temperature, a further reaction involving the formed polydiacetylene chains may occur, as evident from the reduction in crystallinity and even complete loss of crystallinity. An attempt has been made to separate the contribution of the topochemical reaction from the overlapping exothermic activities in the differential scanning calorimetry curves via subtraction. This allows the monitoring of the crystalline‐phase solid‐state topochemical crosspolymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2354–2363, 2002     

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     

Polyolefin soluble polyisobutylene oligomer‐bound metallophthalocyanine and azo dye additives

Metallophthalocyanines prepared with polyisobutyl (PIB) substituents have very high solubility in organic solvents including saturated hydrocarbons, toluene, and other low polarity organic solvents. In heptane, PIB‐bound metallophthalocyanines have solubility of about 0.1 g/mL at 25 °C, solubility values that are significantly higher than other substituted metallophthalocyanines. PIB terminally functionalized with metallophthalocyanines as well as PIB containing terminal azo dye groups also dissolve in molten hydrocarbon polymers like polyethylene or polypropylene. Thus, these highly chromogenic PIB‐bound dyes can be incorporated uniformly into the polyolefins to form colored polymer solids on cooling. Because only a low concentration of a highly hydrocarbon compatible dye is used, the crystallinity and thermal properties of the colored polyolefin products are not significantly affected. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 545–551     

Enhanced mechanical property of chitosan via blending with functional poly(ε-caprolactone)

Blends of chitosan and poly(ε-caprolactone-co-2-oxepane-1,5-dione) (PCO) were fabricated by solvent casting technique using 77% acetic acid as the cosolvent. The interactions between chitosan and PCO were analyzed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and differential scanning calorimetry. The miscibility became poorer with increase of PCO from 50% to 75%, which was supported by the Flory–Huggins interaction parameter and crystallinity of PCO. According to X-ray pattern, crystallinity of CS became weaker when PCO content was improved. Results indicated that there existed stronger interactions in comparison with PCL/CS blends. Therefore, the addition of functional polyester PCO made the brittle chitosan ductile. The elongation was significantly prolonged to 21.60 ± 4.92% with the break stress maintaining about 32 MPa, better than that of PCL blends. The degradation behavior showed slower degradation rate compared with pure CS and the morphology was illustrated by scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Use of polystyrene brushes to investigate the role of interface between substrates and thin homogeneous films

The viscoelastic properties of thin polystyrene (PS) films depend on confinement, as it can modify the molecular dynamics affecting the glass transition. In the recent past, the authors have investigated the region next to the free interface by means of an atomic force microscope suitably modified to monitor the indentation of a tip into a film during a given lapse of time while applying a constant load. Herein, to explore the interface with the substrate, the authors report on experiments in which PS brushes grafted to native silicon oxide were used. It was found that the film wettability on brushes and H‐terminated silicon can be highly improved when compared with native silicon oxide. In addition, the glass transition temperature of thin films increases up to the bulk value in the case of film/brush combinations with high molecular weight or films with high molecular weight on H‐terminated silicon. Data are discussed according to hypotheses such as residual solvent presence, interface free volume, and molecular mechanical coupling. These observations can be of great interest for nanotechnological applications, especially in those instances where one needs to tailor the temperature dependence of viscoelastic properties of thin films. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1149–1156