Comonomer Units Research Articles

Influence of fluorination on the microstructure and performance of diketopyrrolopyrrole‐based polymer solar cells

The solar cell performance and microstructure of DPP-based polymers with different degrees of fluorination are reported. DPP-based polymers with thiophene–phenyl–thiophene comonomer and thiophene flanking units are studied, with the degree of fluorination of the phenyl unit varied. With bifluorination of the phenyl ring, a higher open circuit voltage is achieved whilst maintaining or even improving the overall solar cell efficiency. While tetrafluorination leads to a further 0.1 V increase in VOC, reaching a high photo voltage of 0.81 V, overall solar cell performance significantly drops. Microstructural studies using AFM, TEM, Grazing incidence wide-angle X-ray scattering (GIWAXS), and Resonant soft X-ray scattering (R-SoXS) reveal that bifluorination largely preserves the microstructure of the nonfluorinated system, whereas tetrafluorination results in coarse phase separation between the polymer donor and the fullerene acceptor. Our results demonstrate that the use of an extended comonomer is a promising strategy for optimizing the beneficial effects of fluorination for DPP-based polymer solar cells, especially in improving the open circuit voltage. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 49–59

Trigonal δ form as a tool for tuning mechanical behavior in poly(propylene-co-1-pentene-co-1-heptene) terpolymers

Abstract Terpolymers based on propylene with 1-pentene and 1-heptene as comonomeric units are satisfactorily synthesized containing distinct overall compositions in comonomers as well as three different 1-pentene/1-heptene ratios at a given global composition. The effect of total content in counits and ratio between comonomers on polymerization activity, intrinsic viscosity, molecular weights and microstructural details has been analyzed. In addition, their influence on the mechanical response has been preliminary checked. The results show that rigidity related parameters, like Young’s modulus and yield stress, are mainly dependent on overall composition, but comonomer ratio becomes also a primary variable for the terpolymers with a global counit content higher than 10 mol %. This fact is ascribed to the capability or inability of developing the trigonal polymorph as function of which counit (1-pentene or 1-heptene) is in majority or minority.

Oxidized Polyethylene Wax as a Potential Carbon Source for PHA Production.

We report on the ability of bacteria to produce biodegradable polyhydroxyalkanoates (PHA) using oxidized polyethylene wax (O-PEW) as a novel carbon source. The O-PEW was obtained in a process that used air or oxygen as an oxidizing agent. R. eutropha H16 was grown for 48 h in either tryptone soya broth (TSB) or basal salts medium (BSM) supplemented with O-PEW and monitored by viable counting. Study revealed that biomass and PHA production was higher in TSB supplemented with O-PEW compared with TSB only. The biopolymers obtained were preliminary characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The detailed structural evaluation at the molecular level was performed by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The study revealed that, when TSB was supplemented with O-PEW, bacteria produced PHA which contained 3-hydroxybutyrate and up to 3 mol % of 3-hydroxyvalerate and 3-hydroxyhexanoate co-monomeric units. The ESI-MS/MS enabled the PHA characterization when the content of 3-hydroxybutyrate was high and the appearance of other PHA repeating units was very low.

Ultrasensitive pH-Induced Water Solubility Switch Using UCST Polymers

For some thermosensitive polymers, the absence of an upper critical solution temperature (UCST) in water in an accessible temperature range (say, 5–90 °C) can be attributed to the influence of charged groups in the polymer structure. This property was exploited in the present study to achieve ultrasensitive pH-induced water solubility switch of UCST polymers in physiological medium. By incorporating either acrylic acid (AAc) or 4-vinylpyridine (4VP) comonomer units in the random copolymer of acrylamide and acrylonitrile (P(AAm-co-AN-co-AAc) or P(AAm-co-AN-co-4VP)), the pH-induced shift of UCST was investigated by monitoring the solution cloud point. The results revealed an unusually large shift of the cloud point upon pH variation over a small range. In particular, one P(AAm-co-AN-co-4VP) sample exhibited a cloud point drop from 72 °C at pH 4.75 to 15 °C at pH 4.50 (i.e., 57 K shift over 0.25 pH units), and its transition from soluble to insoluble state at room temperature was visually observable over a p...

Random Copolymers from Polyamide 11 and Polyamide 12 by Reactive Extrusion: Synthesis, Eutectic Phase Behavior, and Polymorphism

Random copolymers from polyamide 11 (PA11) and polyamide 12 (PA12) were obtained from the parent homopolymers by transamidation reactions during high-temperature reactive extrusion. Concomitantly, the product molecular weight increased by postcondensation reactions. With both species being crystallizable, eutectic phase behavior was observed and explained in terms of the Flory theory for random copolymer melting. Close to the eutectic composition, both species crystallize in a competitive mode, which induces mesomorphic phase formation. Although the crystal centers most likely remain PA11 or PA12 pure, it is argued that foreign comonomer units might be tolerated at the crystal borders, at least for PA11 crystals. To understand the copolymer crystallization behavior in general, large amounts of rigid amorphous material need to be created alongside the crystallites. Because of their low melting point and since the crystallinity and mechanical performance typical of the parent homopolymers are preserved, ran...

Chain microstructure and specific features of excitation energy transfer in solution and films of poly(9,9-dioctylfluorene) doped with 2,1,3-benzothiadiazole comonomer units

Spectral, luminescent and electro-optical properties of poly(9,9-dioctylfluorene), containing small quantity (1–2mol%) of 2,1,3-benzothiadiazole comonomer units, obtained by means of either Suzuki or Yamamoto polycondensation reactions were studied and compared. The difference of luminescent properties of the two copolymers with nearly identical chemical compositions was explained by different molecular structure of their macromolecules. The films of Yamamoto type copolymer, containing, obviously, microblock sequences of 2,1,3-benzothiadiazole units, exhibit a nearly white electroluminescence (CIE x=0.276, y=0.274) with a high brightness (3747cd/m2 at 10V), while the films of Suzuki type copolymer with randomly distributed isolated 2,1,3-benzothiadiazole fragments – green electroluminescence.

Rheological properties of thermoresponsive nanocomposite hydrogels

ABSTRACTHighly elastic and robust nanocomposite hydrogels based on N‐isopropylacrylamide (NIPAM) and cationic (3‐acrylamidopropyl) trimethylammonium chloride (AMPTMA) were synthesized by photopolymerization. Nanoscopic clay, laponite XLS, was added in the gels during the synthesis. The effect of a hydrophobic salt, lithium bis(trifluoromethane) sulfonimide (LiNTf2), and clay content on the viscoelastic properties, swelling ratio, and stiffness of the nanocomposite hydrogels were investigated as a function of temperature. Synthetic clay served as a multifunctional cross‐linker, producing hydrogels with enhanced elastic properties. Anionic NTf2 binds to the cationic comonomer units and significantly affected the viscoelasticity and thermal properties. DSC measurements showed that the volume phase transition temperature and its enthalpy changed with the clay content and with introducing the cationic comonomer (AMPTMA) in the PNIPAM network. With the addition of either laponite XLS or the comonomer and 5 mM solution of LiNTf2, a fourfold and fivefold increase in elastic modulus was obtained, respectively, compared to that of the homopolymer PNIPAM hydrogel. With increasing the temperature from 20 to 45°C for the copolymer gel with 10% AMPTMA in 5 mM LiNTf2, the elastic modulus grew 15 times larger. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43123.

Terthiophene-based D-A polymer with an asymmetric arrangement of alkyl chains that enables efficient polymer solar cells.

We report a series of difluorobenzothiadizole (ffBT) and oligothiophene-based polymers with the oligothiophene unit being quaterthiophene (T4), terthiophene (T3), and bithiophene (T2). We demonstrate that a polymer based on ffBT and T3 with an asymmetric arrangement of alkyl chains enables the fabrication of 10.7% efficiency thick-film polymer solar cells (PSCs) without using any processing additives. By decreasing the number of thiophene rings per repeating unit and thus increasing the effective density of the ffBT unit in the polymer backbone, the HOMO and LUMO levels of the T3 polymers are significantly deeper than those of the T4 polymers, and the absorption onset of the T3 polymers is also slightly red-shifted. For the three T3 polymers obtained, the positions and size of the alkyl chains play a critical role in achieving the best PSC performances. The T3 polymer with a commonly known arrangement of alkyl chains (alkyl chains sitting on the first and third thiophenes in a mirror symmetric manner) yields poor morphology and PSC efficiencies. Surprisingly, a T3 polymer with an asymmetric arrangement of alkyl chains (which is later described as having an "asymmetric bi-repeating unit") enables the best-performing PSCs. Morphological studies show that the optimized ffBT-T3 polymer forms a polymer:fullerene morphology that differs significantly from that obtained with T4-based polymers. The morphological changes include a reduced domain size and a reduced extent of polymer crystallinity. The change from T4 to T3 comonomer units and the novel arrangement of alkyl chains in our study provide an important tool to tune the energy levels and morphological properties of donor polymers, which has an overall beneficial effect and leads to enhanced PSC performance.

Copolymerization of N -(prop-1-yne-3-yl)-4-(piperidine-1-yl)-1,8-naphthalimide with Arylacetylenes into Fluorescent Polyacetylene-Type Conjugated Polymers

N-(prop-1-yne-3-yl)-4-(piperidine-1-yl)-1,8-naphthalimide (PNPr), i.e., the monomer with a terminal ethynyl group and 1,8-naphthalimide fluorophore, has been successfully copolymerized with a series of monoethynylarenes into well-soluble high-molecular-weight (Mw up to 210 000) linear polyacetylene-type copolymers containing from 14 to 51 mol% units derived from PNPr. The copolymerization of PNPr with bifunctional 4,4′-diethynylbiphenyl provides polyacetylene-type micro/mesoporous fluorescent network containing 8 mol% PNPr units and exhibiting the Brunauer–Emmett–Teller surface of ≈1000 m2 g−1. The copolymerizations (catalyzed with acetylacetonato(norborna-2,5-diene)rhodium complex, [Rh(nbd)acac]) proceed smoothly despite the fact that the homopolymerization of PNPr fails. The fluorescence of PNPr (emission at ≈ 510 nm) has been retained after the incorporation of PNPr into the copolymers. The fluorescence of the copolymers can be induced by a direct excitation of PNPr units or via an energy transfer mechanism. In the latter case, the comonomeric units with aromatic hydrocarbon fluorophores (e.g., of the biphenyl-type) emitting at 380–400 nm (after irradiation with 300 nm UV radiation) serve as energy donors for fluorescent PNPr acceptors. The difference between the wavelengths of the primary absorbed radiation and the finally emitted radiation is 210 nm.

Preferential Incorporation of Azelaic Acid Units into the Crystalline Phase of the Copoly(Alkylene Dicarboxylate) Derived from 1,9-Nonanediol and an Equimolar Mixture of Pimelic and Azelaic Acids

The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate) (PES 9,7) and poly(nonamethylene azelate) (PES 9,9)) was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio that was strongly depended on the supercooling degree. The crystalline structure of both homopolyesters was defined by an orthorhombic P21ab space group and a large unit cell containing four molecular segments with an all-trans conformation. Nevertheless, the structure in the chain axis projection was equivalent to a simpler cell containing only two segments. Crystalline lamellae were effectively degraded by lipases, starting the enzymatic attack on the lamellar surfaces. The random copolymer constituted by an equimolar amount of pimelate and azelate units (COPES 9,7/9) crystallized according to regular lamellae with a similar molecular arrangement in the chain axis projection. The structure of this copolymer was preferably conditioned by the azelate component as could be deduced from both, diffraction and spectroscopic data. Analysis of small angle X-ray scattering patterns pointed out that less crystalline lamellae with higher amorphous thickness had developed in the copolymer. This feature was interpreted as a consequence of the preferential incorporation of pimelate comonomer units in the folding surface.

Crystallization behavior and mechanical properties of copolymers of isotactic poly(1-butene) with 1-octene from metallocene catalysts

The crystallization behavior and the mechanical properties of random isotactic butene–octene copolymers (iPBC8) prepared with a metallocene catalyst are presented. Samples with low octene concentrations, up to nearly 6 mol%, crystallize from the melt in form II. In these samples octene units stabilize the tetragonal form II, decelerating or even preventing the transformation of form II into the trigonal form I. Octene concentrations higher than 7 mol% prevent crystallization of the samples from the melt and the obtained amorphous samples crystallize by aging at room temperature in mixtures of form II and form I'. The sample with the highest octene concentration of 11.5 mol% crystallizes surprisingly from the amorphous phase directly in the pure form I'. In these samples, form I' crystallized from the amorphous phase transforms into form II by stretching. Form II transforms back into form I' upon releasing the tension. Therefore, in samples where form I' is favored in powder samples, form II is favored in stretched fibers. The transformation of form I into form II by stretching and the back transformation of form II into form I after releasing the tension is unusual for isotactic polybutene (iPB) and rather unexpected. The presence of octene comonomer units also affects the mechanical behavior of iPB and produces increase of flexibility and ductility with increasing comonomer content, and samples with octene concentration higher than 6–7 mol% show unexpected remarkable elastomeric properties. The formation of crystals of form II or form I' during aging allows development of elastomeric properties and enhancement of mechanical strength. The elastic properties are associated to the reversible crystal–crystal phase transition between form II and form I occurring during stretching and when the tension is removed.

Thermoresponsive Polymer Micelles as Potential Nanosized Cancerostatics.

An effective chemotherapy for neoplastic diseases requires the use of drugs that can reach the site of action at a therapeutically efficacious concentration and maintain it at a constant level over a sufficient period of time with minimal side effects. Currently, conjugates of high-molecular-weight hydrophilic polymers or biocompatible nanoparticles with stimuli-releasable anticancer drugs are considered to be some of the most promising systems capable of fulfilling these criteria. In this work, conjugates of thermoresponsive diblock copolymers with the covalently bound cancerostatic drug pirarubicin (PIR) were synthesized as a reversible micelle-forming drug delivery system combining the benefits of the above-mentioned carriers. The diblock copolymer carriers were composed of hydrophilic poly[N-(2-hydroxypropyl)methacrylamide]-based block containing a small amount (∼ 5 mol %) of comonomer units with reactive hydrazide groups and a thermoresponsive poly[2-(2-methoxyethoxy)ethyl methacrylate] block. PIR was attached to the hydrophilic block of the copolymer through the pH-sensitive hydrazone bond designed to be stable in the bloodstream at pH 7.4 but to be degraded in an intratumoral/intracellular environment at pH 5-6. The temperature-induced conformation change of the thermoresponsive block (coil-globule transition), followed by self-assembly of the copolymer into a micellar structure, was controlled by the thermoresponsive block length and PIR content. The cytotoxicity and intracellular transport of the conjugates as well as the release of PIR from the conjugates inside the cells, followed by its accumulation in the cell nuclei, were evaluated in vitro using human colon adenocarcinoma (DLD-1) cell lines. It was demonstrated that the studied conjugates have a great potential to become efficacious in vivo pharmaceuticals.

Cocrystallization of monomer units in lactic acid-based biodegradable copolymers, poly(l-lactic acid-co-l-2-hydroxybutanoic acid)s

The copolymers of l-lactic acid (LLA) and l-2hydroxybutanoic acid (L-2HB) [P(LLA-co-L-2HB)s] having relatively random monomer sequences were synthesized by polycondensation. It was first revealed that the cocrystallization of LLA and L-2HB units occurs in P(LLA-co-L-2HB) copolymers for a wide comonomer unit (L-2HB unit) content range of 27–74 mol% during precipitation and melt-crystallization. The interplane distance values of the precipitated and melt-crystallized P(L-2HB), PLLA, and P(LLA-co-L-2HB) samples increased monotonically with an increase in L-2HB unit content, whereas the Tm values of the P(LLA-co-L-2HB) copolymer samples decreased with the deviation of L-2HB unit content from 0 or 100% and became minimum at the L-2HB unit content of 74 mol%. In melt-crystallized P(LLA-co-L-2HB) copolymer samples, crystallites were formed by random incorporation of monomer units without selecting the types of monomer units, whereas in precipitated P(LLA-co-L-2HB) samples, the crystallites were formed by the rather predominant incorporation of L-2HB units having a larger side chain. The cocrystallization of P(LLA-co-L-2HB) copolymers is expected to provide the versatile biodegradable materials having a wide variety of degradation rates and behavior by altering the monomer unit contents and also by crystallinity and crystalline size which cannot be attained by non-crystallizable biodegradable copolymers and will thereby widen the applications of LLA-based polymers.

Synthesis of amphiphilic block-gradient copolymers of styrene and acrylic acid by Nitroxide Mediated Polymerization

We present an overview on synthesis of amphiphilic ionic block-gradient copolymers of styrene and acrylic acid by means of one step direct Nitroxide Mediated Polymerization (NMP) and their characterization. The copolymers comprise a block of poly(acrylic acid) and one or two terminal blocks that include co-monomer units of styrene and acrylic acid in variable proportion. Using 1H NMR the gradient sequence of the poly(acrylic acid-co-styrene) copolymer block has been confirmed. In contrast to diblock copolymers of styrene and acrylic acid, that are known to form in aqueous environment “frozen” aggregates with glassy poly(styrene) core, the novel block gradient copolymers exhibit stimuli-responsive aggregation behavior, as was demonstrated by subsequent studies. This feature makes them very promising for design of a large variety of smart functional materials.

Poly(hexamethylene succinate) copolyesters containing phosphorus pendent group: Retarded crystallization and solid-state microstructure

Crystallization behavior and solid-state microstructure of poly(hexamethylene succinate) (PHS) and its phosphorus-containing copolyesters with bulky pendent group (DDP) have been investigated. The molecular weight, chemical structure and composition of the copolyesters were characterized and confirmed by GPC, 1H and 31P NMR. WAXD results suggest that the bulky DDP comonomer units in the copolyesters are noncrystallizable and are extruded from the crystal lattice of PHS. POM observations indicate that the spherulitic morphology becomes irregular and blurry with an increase of the DDP content. The kinetics analysis of isothermal crystallization shows that the crystallization of the copolyesters is retarded by the presence of the bulky DDP comonomer units. The observed crystallization and melting temperatures of the copolyesters are progressively depressed with the increase of DDP. SAXS quantitative analysis provides a proof that the significant increase in the long period of the copolyesters mainly arises from the increase in the amorphous layer, because the thickness of the lamellar increases slightly. A model of the lamellar crystal structure of the copolyester is proposed for its depression of the equilibrium melting temperature.

Synthesis of rotaxane cross-linked polymers derived from vinyl monomers using a metal-containing supramolecular cross-linker

An effective method for the synthesis of the rotaxane cross-linked polymers (RCPs) was developed using a metal-containing supramolecular cross-linker (MSC). Radical polymerization of several vinyl monomers and bulky end-capped comonomer afforded RCPs in high yields. The obtained RCPs exhibited thermal properties corresponding to their respective polymer skeletons. Swelling ratio gradually increased with the decreasing amount of the steric comonomer units, indicating that the sliding ability of the movable cross-linker is strongly related to the swelling ability.

Synthesis and Characterization of Gallafluorene-Containing Conjugated Polymers: Control of Emission Colors and Electronic Effects of Gallafluorene Units on π-Conjugation System

We present synthesis and characteristics of the conjugated polymers involving organogallium complexes. A series of alternating copolymers composed of gallafluorene were prepared with diverse comonomers through various types of cross-coupling reactions such as Suzuki–Miyaura, Sonogashira–Hagihara, and Stille reactions. It was confirmed that the synthesized polymers possess solubility in common organic solvents and stability toward air and moisture. Significantly, optical properties originating from the electronic interaction between gallafluorene and various comonomers were observed. For example, vivid color emissions were demonstrated in the blue, green, yellow, orange, and red regions depending on the chemical structures of the comonomer units. In addition, it was eventually found that the benzotriazole-containing polymer showed significant optical properties originating from aggregation in the film state. From the electrochemical measurements, it was indicated that the energy levels of their frontier orbitals were varied by the comonomer units. Indeed, it is supported that the gallafluorene polymers have higher energy levels of HOMOs (highest occupied molecular orbitals) than those of the fluorene-based conjugated polymers instead of gallafluorene. Finally, it is suggested that the gallafluorene unit could work as an electron-donating group in the polymer main chain.

Semiconducting Polymers Consisting of Anthracene and Benzotriazole Units for Organic Solar Cells.

An alternating copolymer composed of 2,6-dibromo-9,10-bis(2-ethylhexyloxy)anthracene and benzotriazole units, poly(An-alt-BTz), was synthesized, through a Suzuki cross-coupling polymerization, for use in photovoltaic devices as a p-type electron donor. For the reduction of the bandgap energy of benzotriazole units, 5,5'-dibromo-2,2'-bithiophene, or 2,5-dibromothieno [3,2-b] thiophene units were introduced into the polymer. Poly(anthracene-co-benzotriazole-co-bithiophene(thienothiophene))s were synthesized using the same polymerization reactions. The measured optical bandgap energy of poly(anthracene-alt-benzotriazole) was 2.62 eV. As the contents of the flat comonomer units in the ter-polymers increased, the bandgap energies of the resulting polymers decreased up to 1.95 eV. The energy levels of the HOMO and the LUMO of the copolymers were determined from the cyclic voltammetry. Photovoltaic devices were fabricated with the polymers as electron donors and PC71 BM as an electron acceptor. One of the fabricated devices showed the maximum PCE of 0.74% with 0.57 V of VOC, 2.59 mA/cm2 of JSC, and 0.48 of FF under AM 1.5G (100 mW/cm2) condition.

Naphthodithiophene Diimide (NDTI)-Based Semiconducting Copolymers: From Ambipolar to Unipolar n-Type Polymers

A series of naphthodithiophene diimid (NDTI) based semiconducting polymers with various comonomer units, i.e., thienylenevinylene (TV), naphtho[1,2-b:5,6-b′]dithiophene (NDT), vinylene (V), benzo[c][1,2,5]thiadiazole (BTz), and naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NTz), were synthesized by Stille coupling or copper iodide-assisted Stille coupling using 2,7-dibromo-NDTI or 2,7-bis(trimethylstannyl)-NDTI, respectively. Their HOMO and LUMO energy levels were estimated by cyclic volttammetry and photoelectron spectroscopy. The HOMO energy levels of the NDTI-based polymers were strongly affected by the electronic nature of the comonomer units. In contrast, their LUMO energy levels were almost identical, likely owing to their localized LUMOs on the NDTI moiety. All the polymers showed air-stable electron transport in the field-effect transistors (FETs), thanks to their low-lying LUMO (∼−4.0 eV), as ambipolar (PNDTI-TV, -NDT, ∼0.082 cm2 V–1 s–1, μe = ∼0.029 cm2 V–1 s–1) or unipolar n-channel materials (PNDTI-V, -BTz, PNDTI-NTz, μe = ∼0.21 cm2 V–1 s–1), depending on their HOMO energy levels. These results indicate that the type of active carrier in the NDTI-based polymers can be controlled by the nature of comonomer units. Moreover, the two-dimensional grazing incidence X-ray diffraction (2D GIXD) indicated that the polymers with linear backbone structures and large space between the branched alkyl chains tend to afford well-organized crystalline thin film with the edge-on orientation, consistent with good transport characteristics in their FET devices.

Synthesis, molecular characterization, evaluation of polymorphic behavior and indentation response in isotactic poly(propylene-co-1-heptene) copolymers

Different polymorphs are developed in isotactic poly(propylene-co-1-heptene) copolymers depending on 1-heptene molar content and thermal history: monoclinic and orthorhombic crystallites as well as mesomorphic entities. Indentation hardness values and deformability are found to be related to those variables as well as to crystallinity degree. Consequently, mechanical behavior can be tailored mainly by varying all of these parameters and a range from rigid to soft and more easily deformable materials is attained by synthesis of copolymers based on isotactic propylene with 1-heptene as comonomeric unit. Evaluation of the influence of molecular weight, intrinsic viscosity and microstructural details is also performed.