Semicrystalline Copolymers Research Articles

Fluorinated thienyl-quinoxaline-based D–π–A-type copolymer toward efficient polymer solar cells: synthesis, characterization, and photovoltaic properties

A tailor-made donor–π–acceptor copolymer comprising of a medium electron-donating alkylthienyl-benzodithiophene (BDTT) moiety and a strong electron-accepting fluorinated thienyl-quinoxaline (TTFQ) segment with thiophene π-bridge units has been synthesized by Stille coupling polymerization and thoroughly characterized for use as a p-type semiconducting polymer. The semicrystalline copolymer PBDTT-TTFQ shows a broad visible-near-infrared absorption band with an optical bandgap of 1.67 eV and possesses a relatively low-lying HOMO level at −5.34 eV. In addition, the PBDTT-TTFQ neat film reveals a highly dense fibrillar nanostructure with a certain degree of long-range order, suggesting the nanoscale self-assembly of PBDTT and TTFQ segments. A bulk-heterojunction polymer solar cell based on the blend of 1 : 1 PBDTT-TTFQ:PC71BM shows an open circuit voltage of 0.75 V, a short circuit current density of 14.6 mA cm−2, and a fill factor of 56.1%, achieving a power conversion efficiency of 6.1% under the illumination of AM 1.5G, 100 mW cm−2. The results unambiguously indicate that the PBDTT-TTFQ is an auspicious candidate for next-generation solar cell materials.

Physicochemical and mechanical properties of mixed culture polyhydroxyalkanoate (PHBV)

The mechanical properties of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) copolymers with 3HV unit content ranging from 12mol% to 72mol% were evaluated. Samples were produced using a naturally enriched mixed culture fed with acetic and propionic acids. A range of feeding strategies was used to explore the manipulation of comonomer composition and sequence distribution of the monomeric units in order to influence mechanical properties. GC/MS, 13C NMR and DSC analysis of the resulting solvent cast films revealed that the as-produced PHAs were a mixture of copolymers distinct in microstructure and/or composition. Atomic force microscopy demonstrated the formation of varying phase structures as well as surface morphologies. In spite of the range of microstructure or compositional variation that was achieved through feeding strategies, all samples but one exhibited mechanical properties similar to the homopolymer P(3HB). The one distinct copolymer, with 43mol% 3HV content, showed significantly increased elongation to break, as assessed after 2weeks of ageing. These results were attributed to the formation of different phase structures arising from the competition between cocrystallisation and phase segregation in blends of semicrystalline copolymers.

Mathematical Modeling of Temperature Rising Elution Fractionation (TREF) of Polyethylene and Ethylene/1‐Olefin Copolymers

AbstractTemperature rising elution fractionation (TREF) is a characterization technique widely used to estimate chemical composition distribution (CCD) of semicrystalline copolymers. Although several mathematical models have been previously proposed to elucidate the TREF fractionation mechanism, all previous TREF models assume equilibrium fractionation; thus, they cannot describe important kinetics effects observed in TREF experiments. In this work, a new TREF model is developed incorporating crystallization and dissolution kinetic models during the fractionation process. The proposed model describes the effects of molecular weight, comonomer content, cooling rate, heating rate, and solvent flow rate on experimental TREF profiles for both polyethylene and ethylene/1‐olefin copolymers very well.

Structure and Molecular Dynamics in Renewable Polyamides from Dideoxy–Diamino Isohexide

The chemical structure, the conformation, and the flexibility of the polymer chain fragments present in the polyamides synthesized from 2,5-diamino-2,5-dideoxy-1,4;3,6-dianhydrosorbitol, 1,4-diaminobutane, and either sebacic or brassylic acid have been studied by liquid-state 2D NMR spectroscopy viz. correlation spectra (COSY) and heteronuclear multiple-bond correlation spectra (gHMBC), by 13C cross-polarization/magic-angle spinning (CP/MAS) NMR, by X-ray scattering, and by FT-IR spectroscopy. The presence of 2,5-diamino-2,5-dideoxy-1,4;3,6-dianhydrosorbitol in the crystal phase of the polyamides was probed by wide-angle X-ray diffraction (WAXD), FT-IR, and solid-state 13C NMR. The incorporation of dideoxy–diamino isohexide into the backbone of PA 4.10 or PA 4.13 induces formation of gauche type conformers and gives rise to pseudohexagonal packing of the polymer chains in these semicrystalline copolymers. The experimental determination of the polymer chain structure combined with ab initio calculations revealed the presence of three most abundant diaminoisosorbide (DAIS) conformers. The combination of the 13C chemical shifts of these three conformers could explain all experimental resonances in the region of 50–90 ppm. WAXD and DSC analysis show that the crystallinity, and hence the physical properties of the investigated compositions, can be tailored by the content of the bicyclic diamine in the backbone of the polyamides.

Synthesis and characterization of multiblock semi-crystalline hydrophobic poly(ether ether ketone)–hydrophilic disulfonated poly(arylene ether sulfone) copolymers for proton exchange membranes

Multiblock copolymers based on alternating segments of telechelic phenoxide terminated hydrophilic fully disulfonated poly(arylene ether sulfone) (BPS100) and decafluorobiphenyl (DFBP) terminated hydrophobic poly(arylene ether ketimine) (PEEKt), were synthesized from the hydrophilic and ketimine-protected amorphous hydrophobic telechelic oligomers by nucleophilic coupling reactions. After film formation from DMSO, the copolymer was acidified, which converted the ketimine to semi-crystalline ketone segments and the sulfonate salts to disulfonic acids. A semi-crystalline phase with a Tm of 325 °C was confirmed. The semi-crystalline multiblock copolymer membranes were tough, ductile and solvent resistant. Fundamental properties as proton exchange membranes (PEMs) showed enhanced conductivities under fully hydrated and reduced humidity conditions. These multiblock copolymers exhibited low in-plane anisotropic swelling behavior, in contrast to the random copolymers.

Dynamics of Water Absorbed in Polyamides

We investigate the dynamics of water absorbed in amorphous and semicrystalline aromatic polyamide copolymers. The combination of dielectric spectroscopy and quasi-elastic neutron scattering experiments allows us to characterize the water dynamics over a wide range of temperatures (dielectric spectroscopy) and at microscopic length scales (neutron scattering). The dielectric investigation evidences two relaxations associated with water motions: a fast process corresponding to motions of loosely bonded water molecules and a slower process corresponding to motions of amide–water complexes. While the slower process presents the characteristic Arrhenius temperature dependence of a secondary local relaxation over the whole temperature range, the fast process shows a crossover from Arrhenius to Vogel–Fulcher–Tamman (VFT) behavior at T ≈ 225 K, characteristic of confined water dynamics. The microscopic investigation by neutron scattering shows than in the VFT regime of the fast process the dynamics present a diff...

Synthesis and characterization of semicrystalline triblockcopolymers of isotactic polystyrene and polydimethylsiloxane

iPS-b-PDMS-b-iPS triblock copolymers were prepared by hydrosilylation of vinyl-terminated isotactic polystyrenes (iPS) with α,ω-bis(dimethylsilane)-terminated poly(dimethylsiloxane)s (PDMS). As a function of the molecular weights of the two components, the triblock copolymer composition was varied between 9.0 and 98 wt % iPS. The resulting triblock copolymers remained soluble during block copolymer synthesis due to slow iPS crystallization in solution. At iPS content exceeding 31 wt %, the iPS crystallization was achieved by postpolymerization annealing and melt processing. The triblock copolymers melted above 200 °C with melting temperatures very similar to those of the corresponding iPS homopolymers. Nanostructure and microstructure formation of both amorphous and semicrystalline triblock copolymers were examined by means of light microscopy, atomic force microscopy, and TEM measurements. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Homogeneous Phase Copolymerizations of Vinylidene Fluoride and Hexafluoropropene in Supercritical Carbon Dioxide

Copolymerizations of vinylidene fluoride (VDF) and hexafluoropropene (HFP) were carried out in homogeneous phase with supercritical carbon dioxide up to complete VDF conversion using conventional peroxide initiators. The HFP monomer feed ratios, fHFP, were varied between 0.65 and 0.20. Depending on fHFP amorphous or semi-crystalline copolymers were obtained. fHFP also determines the minimum pressure required to allow for homogeneous phase reactions. For example, HFP-rich copolymerizations in 70 wt.-% CO2 at 100 °C require a pressure of around 500 bar. Further, bulk copolymerizations in homogenous phase were feasible for fHFP = 0.65 at 900 bar up to complete VDF conversion. Copolymerizations in the presence of perfluorinated hexyl iodide carried out at 75 °C gave access to low dispersity polymers. Due to homogeneous phase conditions the use of any surfactants or fluorinated cosolvent is avoided.

High-temperature two-dimensional liquid chromatography of ethylene-vinylacetate copolymers

Temperature rising elution fractionation hyphenated to size exclusion chromatography (TREF × SEC) is a routine technique to determine the chemical heterogeneity of semicrystalline olefin copolymers. Its applicability is limited to well crystallizing samples. High-temperature two-dimensional liquid chromatography, HT 2D-LC, where the chromatographic separation by HPLC is hyphenated to SEC (HPLC × SEC) holds the promise to separate such materials irrespective of their crystallizability. A model blend consisting of ethylene-vinyl acetate (EVA) copolymers covering a broad range of chemical composition distribution including amorphous and semicrystalline copolymers and a polyethylene standard was separated by HT 2D-LC at 140 °C. Both axes of the contour plot, i.e. the compositional axis from the HPLC and the molar mass axis from the SEC separation were calibrated for the first time. Therefore, a new approach to determine the void and dwell volume of the developed HT 2D-LC instrument was applied. The results from the HT 2D-LC separation are compared to those from a cross-fractionation (TREF × SEC) experiment.

Pyroelectric scanning probe microscopy: A method for local measurement of the pyroelectric effect in ferroelectric thin films

This work demonstrates a surface scanning method for the quantitative determination of the local pyroelectric coefficient in ferroelectric thin films. It allows generating a map of the pyroelectric response with very high spatial resolution. In domains of previously aligned dipole moments (achieved by tip-assisted poling) small heat fluctuations are achieved by laser diode excitation from the sample's bottom side thus inducing changes in the surface potential due to the pyroelectric effect. Simultaneously, the surface potential variations are detected by scanning surface potential microscopy thus forming the base for the pyroelectric coefficient map. The potential of the method is demonstrated on the basis of ferroelectric semicrystalline copolymer thin films yielding local maxima of the pyroelectric coefficients up to $40\text{ }\ensuremath{\mu}\text{C}/{\text{m}}^{2}\text{ }\text{K}$. Another promising feature is the ability to visualize ``screened'' polarization thus enabling in-depth profiling of polarization distributions and domain formation and to study the composition dependence of ferroelectric nanodomains.

Poly(acrylonitrile-co-methyl acrylate) copolymers: Correlation between copolymer composition, morphology and positron annihilation lifetime parameters

A series of poly(acrylonitrile-co-methyl acrylate) copolymers of differing copolymer compositions are synthesized through free radical emulsion copolymerisation of methyl acrylate (MA) and acrylonitrile (AN) and by variation of the monomer feed ratios. The copolymers are characterized by NMR, SEC, WAXD, DMA, and positron annihilation lifetime spectroscopy. Results show that, there is a linear decrease in the glass transition temperature (Tg) of the copolymers and the MA content. There is also a progressive decrease in the crystallinity of the copolymers with increasing MA content. Positron results show a sigmoidal variation in the ortho positronium lifetime with an increasing MA content. The low MA content, semi-crystalline copolymers show a positive deviation from the linear additive relationship between the o-Ps lifetime and MA content, whereas the higher MA content amorphous copolymers show a negative deviation from the linear additive behavior. The o-PS intensity shows a linear behavior with MA content with a slight deviation from the additive linear behavior for the very high-content MA copolymer. These variations in the measured positron lifetime parameters are interpreted in terms of the copolymer morphology. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Modifying an amorphous polymer to a fast crystallizing semi-crystalline material by copolymerization with monodisperse amide segments

Segmented block copolymers of polysulphone with monodisperse amide segments were synthesized by a melt and a solution polymerization method. Both triblock and multiblock copolymers were prepared. The length of the difunctional polysulphone was varied from 2000 to 20,000 g/mol. The monodisperse amide segment was the tetra-amide T6T6T based on terephthalic acid (T) and hexamethylene diamine (6) units. The main goal of this work was to study if the high Tg amorphous polysulphone could be modified to a high Tg semi-crystalline PSU-T6T6T copolymer. The copolymers were characterized by viscosity measurements, NMR, FTIR, MALDI-TOF, DSC, and DMA. Depending on the amide concentration in the copolymers the T6T6T melting temperatures ranged between 220 and 270 °C and thus the crystallization window was small 50–100 °C. From the FTIR results, it was revealed that the crystallinity of the T6T6T segments in the copolymer could be very high, up to 92–97%. The T6T6T has crystallized out into nanoribbons with a high aspect ratio. These high Tg semi-crystalline copolymers had a high dimensional and solvent resistance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 63–73, 2010

Crystallization of poly( l-lactide-dimethyl siloxane- l-lactide) triblock copolymers and its effect on morphology of microphase separation

This investigation characterizes the molten morphologies following isothermal crystallization of poly( l-lactide- block-dimethyl siloxane- block- l-lactide) triblock copolymers, which were synthesized by ring-opening polymerization of l-lactide using hydroxyl-telechelic PDMS as macroinitiators, via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The break-out and preservation of the nanostructure of the triblock copolymer depended on the segregation strength, which was manipulated by varying the degree of polymerization. The crystallization kinetics of these semicrystalline copolymers and the effect of isothermal crystallization on their melting behaviors were also studied using DSC, FT-IR and WAXS. The exclusive presence of α-phase PLLA crystallite was verified by identifying the absence of the WAXS diffraction signal at 2θ = 24.5° and the presence of IR absorption at 1749 cm −1 when the PLLA segment of the block copolymers was present as a minor component. The dependence of the crystallization rate (Rc) on the chemical composition of the triblock copolymers reveals that the Rc of the triblock copolymers was lower than that of PLLA homopolymer and the Rc were substantially reduced when the minor component of the crystallizable PLLA domains was dispersed in the PDMS matrix.

Comparison of High‐Temperature HPLC, CRYSTAF and TREF for the Analysis of the Chemical Composition Distribution of Ethylene‐Vinyl Acetate Copolymers

AbstractThe chemical composition distribution (CCD) is a fundamental molecular parameter of copolymers. High‐temperature interactive liquid chromatography (HT‐HPLC) has recently emerged as a new analytical technique for determination of the CCD of semicrystalline copolymers of ethylene and polar comonomers. With the aim of comparing the results of HT‐HPLC with those from the traditionally used temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) techniques, three ethylene‐vinyl acetate (EVA) copolymers were fractionated by TREF and the fractions were analyzed by HT‐HPLC. HT‐HPLC‐Fourier transform‐infrared (FT‐IR) spectroscopy showed that individual fractions of different VA‐content coelute in the HPLC. While the separation in TREF and CRYSTAF is mainly the result of the overall effect of alkyl branches and VA‐comonomer units, in HT‐HPLC it is the polar comonomer that selectively contributes to the adsorption. Thus, HT‐HPLC leads to a much more detailed knowledge of the distribution of the structured units; in addition, it saves time.magnified image

Influence of chain microstructure on the hydrolytic degradation of copolymers from 1,3‐trimethylene carbonate and L‐lactide

AbstractRing‐opening copolymerization of L‐lactide (LLA) and 1,3‐trimethylene carbonate (TMC) blends with LLA/TMC feed ratios from 90/10 to 50/50 was realized at 110 or at 180 °C for various time periods, using low toxic zirconium (IV) acetylacetonate (Zr(Acac)4) as initiator. The resulting copolymers exhibit different chain microstructures. Copolymers obtained at 110 °C exhibit a gradient chain structure with the presence of lactidyl sequences next to very short ones, and are semicrystalline. In contrast, copolymers obtained at 180 °C are amorphous because of a more random chain microstructure with the presence of larger amounts of medium sequences. Degradation of the copolymers was carried out in pH 7.4 phosphate buffer at 37 °C. Analytical techniques such as 1H NMR, DSC, GPC, and XRD were used to monitor the degradation. Initially amorphous copolymers can remain amorphous during degradation because of the highly random unit's distribution, and equivalent LLA and TMC contents. However, initially amorphous copolymers containing larger amounts of lactidyl units are able to crystallize during degradation because of the presence of relatively long LLA blocks. Insofar, as initially semicrystalline copolymers are concerned, degradation occurs preferentially in the amorphous zones. Therefore, various degradation behaviors and degradation rates can be obtained by varying the chemical composition, chain microstructure, and morphology of PLLA‐PTMC copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3869–3879, 2009

Adhesion control for injection overmolding of polypropylene with elastomeric ethylene copolymers

AbstractTwo types of random semicrystalline copolymers (ethylene–octene and ethylene–butene) were overmolded on a core polypropylene. Maximum solid–liquid interface temperature achieved for the overmolding injection process is used as the key parameter for adhesion control. The main bonding process is shown to be a Rouse‐type fingering mechanism that develops in short time scales. Normalized peel tests were conducted on overmolded samples to measure the resulting polypropylene copolymers' bonding strength. All the ethylene random copolymers used for this study give good adhesion to polypropylene in overmolding processes, provided the right range of interface temperature is reached. Adhesion strength can be easily controlled for efficient debonding and recycling of used overmolded parts. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Molecular Dynamics of PEGylated Multifunctional Polyhedral Oligomeric Silsesquioxane

Here we report a study of molecular dynamics of (1) four different poly(propylene oxide)/poly(ethylene oxide) (PPO/PEO) copolymers, two amorphous and two semicrystalline, and (2) the product of the chemical reaction between these copolymers and a multifunctional polyhedral oligomeric silsesquioxane (POSS). We refer to the latter group of compounds as “PEGylated POSS”. Experimental results were generated using broadband dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS) over a wide range of frequencies and temperatures. Amorphous copolymers exhibit the segmental process (α), the normal mode process (αN), and two local processes (β and γ), while semicrystalline copolymers possess segmental (α) and two local relaxations (β and γ). The β process is a secondary relaxation and the γ process is due to the combination of the local motions in PPO and PEO blocks. PEGylated POSS was synthesized by chemical reaction between the functional end groups on the PPO block (amine) and the POSS side chain (epoxy). Dynamics of PEGylated POSS were investigated and contrasted with the dynamics of the corresponding neat copolymers. Covalent bonding between POSS and copolymer slows down the segmental and the normal mode process but does not affect the time scale of the β or the γ process. A detailed account of the effect of molecular weight, PPO/PEO mole ratio, copolymer morphology and covalent bonding between POSS and copolymer on the molecular origin, temperature dependence, and spectral characteristics of relaxation processes in copolymers and PEGylated POSS is provided.

Application of a crystallization kinetics model to simulate the effect of operation conditions on Crystaf profiles and calibration curves

AbstractCrystallization analysis fractionation (Crystaf) is a polymer characterization technique used to estimate chemical composition distributions (CCDs) of semicrystalline copolymers. The Crystaf profile can be transformed into a CCD using a calibration curve that relates average comonomer content to peak crystallization temperature. The calibration curve depends on copolymer molecular properties and Crystaf operation conditions. In this investigation, we applied a crystallization kinetics model to simulate Crystaf calibration curves and to quantify how Crystaf calibration curves depend on these factors. We applied the model to estimate the CCDs of three ethylene/1‐hexene copolymers from Crystaf profiles measured at different cooling rates and showed that our predictions agree well with the CCDs described by Stockmayer's distribution. We have also used this new methodology to investigate the effects of cooling rate, molecular weight, and comonomer type on Crystaf profiles and calibration curves. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 866–876, 2009

Dynamic stress relaxation of thermoplastic elastomeric biomaterials

In this paper we present the results of comparative dynamic stress relaxation studies performed with poly(styrene-b-isobutylene-b-styrene) (SIBS), polyurethane (PU) and polyester (PED) biomaterials in air and simulated body fluid (SBF) at 24°C and 37°C. SIBS showed the highest value of relieved stress under constant strain (24.1% after 100,000 cycles in air) with PED and PU having similar relative change (12.2% and 10.5%). In spite of its softness (Shore A 56 vs. 80), the dynamic modulus (Edyn) and stiffness of SIBS were in between PED and PU. The behavior of the materials was correlated to their structure: SIBS is an amorphous block copolymer with a long elastomer midblock, while PU and PED are semicrystalline segmented copolymers with much shorter soft blocks, and hydrogen bonding. SIBS and PED were relatively insensitive to SBF and temperature changes, while PU experienced the largest changes in physical properties in vitro (simulated body fluid, 37°C).

Enhanced organic ferroelectric field effect transistor characteristics with strained poly(vinylidene fluoride-trifluoroethylene) dielectric

Poly(vinylidene fluoride-trifluoroethylene) (70–30 mol%) was used as the functional dielectric layer in organic ferroelectric field effect transistors (FeFET) for non-volatile memory applications. Thin P(VDF-TrFE) film samples spin-coated on metallized plastic substrates were stretch-annealed to attain a topographically flat-grain structure and greatly reduce the surface roughness and current leakage of semi-crystalline copolymer film, while enhancing the preferred β-phase of the ferroelectric films. Resultant ferroelectric properties ( P R = |10| μC/cm 2, E C = |50| MV/m) for samples simultaneously stretched (50–70% strain) and heated below the Curie transition (70 oC) were comparable to those resulting from high temperature annealing (>140 oC). The observed enhancements by heating and stretching were studied by vibration spectroscopy and showed mutual complementary effects of both processes. Organic FeFET fabricated by thermal evaporating pentacene on the smooth P(VDF-TrFE) films showed substantial improvement of semiconductor grain growth and enhanced electrical characteristics with promising non-volatile memory functionality.