High‐temperature thermal gradient interaction chromatography (HT‐TGIC) fractionates polyolefins based on an adsorption–desorption mechanism. Several factors influence the shape and position of HT‐TGIC chromatograms, notably polymer microstructure, analytical conditions, and, to a lesser extent, solvent type. This article investigates the joint influence of chain length and comonomer content of a series of polyethylene and ethylene/1‐octene copolymers having similar 1‐octene fractions (0–13 mol%) and a wide range of molecular weights on HT‐TGIC fractionation. For each series of copolymers having similar 1‐octene fraction, the elution peak temperature decreases exponentially and the profiles become increasingly broader below a critical number average chain length value. The authors use Monte Carlo simulation and Stockmayer distribution to explain the observed behavior, finding that no simple correlation exists between ethylene sequences in the copolymers and peak elution temperature, but that there is strong evidence that axial dispersion is responsible for symmetrical broadening of the HT‐TGIC profiles. The authors also study the HT‐TGIC of binary blends, finding that components with similar 1‐octene contents and dissimilar chain lengths tend to increase co‐adsorption/co‐desorption effects.
The isotropic melt of poly(l ‐lactic acid) (PLLA) and random l /d ‐lactide copolymers with 2% and 4% d ‐isomer co‐units in the chain has been crystallized at 90 °C, which leads to growth of α′‐crystals. The maximum melting temperature of the α′‐crystals is around 150 °C in case of the homopolymer, and decreases by about 10 and 15 K in the random copolymers containing 2% and 4% d ‐isomer co‐units, respectively. Analysis of the stability of the α′‐crystals requires suppression of formation of α‐structure, which is achieved by fast heating using a fast scanning chip calorimeter. For the PLLA homopolymer, the critical heating rate above which the α′/α‐transition is completely suppressed is around 30 K s–1, which significantly decreases in the copolymers due to the presence of d ‐isomer co‐units. The slower kinetics of the melting‐recrystallization process in such random l /d ‐lactide copolymers is explained by the required segregation of the chain defects.
Four monomers of the bis(pyridyl)acetylene and bis[(pyridyl)ethynyl]benzene types containing either 2‐pyridyl or 4‐pyridyl groups are polymerized into respective networks of the conjugated polyelectrolyte (CPE) type by catalyst‐free polymerization via activation with 1,4‐bis(bromomethyl)benzene as quaternization agent (QA). Prepared CPE networks are characterized by elemental analysis (EA), TGA analysis, 13C cross‐polarization magic‐angle spinning NMR, IR, UV/vis, and photoluminescence spectroscopies. Highly cross‐linked network structure containing both π‐conjugated polyacetylene type chains and ionic alternating type chains is proposed. According to EA analysis, the mole ratio of units derived from monomer molecules and QA molecules is close to unity in all prepared networks. The CPE networks based on 4‐pyridyl monomers exhibit strong photoluminescence in the visible region after irradiation with light of wavelength of 378 nm. Prepared CPE networks also show moderate efficiency in CO2 sorption up to 13.6 cm3 g?1 (STP) and exceptionally high ethanol vapor capture efficiency up to 24.5 wt% (293 K). The specific interactions of ionic network and adsorbed molecules and also temporary pores formation are assumed to play important role in sorption processes.
Inspired by the well‐known amphiphilic block copolymer platform known as Pluronics or poloxamers, a small library of ABA and BAB triblock copolymers comprising hydrophilic 2‐methyl‐2‐oxazoline (A) and thermoresponsive 2‐n‐propyl‐2‐oxazoline (B) is synthesized. These novel copolymers exhibit temperature‐induced self‐assembly in aqueous solution. The formation and size of aggregates depend on the polymer structure, temperature, and concentration. The BAB copolymers tend to agglomerate in water, with the cloud point temperature depending on the length of poly(2‐n‐propyl‐2‐oxazoline) chain. On the other hand, ABA copolymers form smaller aggregates with hydrodynamic radius from 25 to 150 nm. The dependence of viscosity and viscoelastic properties on the temperature is also studied. While several Pluronic block copolymers are known to form thermoreversible hydrogels in the concentration range 20–30 wt%, thermogelation is not observed for any of the investigated poly(2‐oxazoline)s at the investigated temperature range from 10 to 50 °C.
The radical copolymerization of N‐substituted maleimides containing polymethylene and poly(ethylene oxide) side chains as the N‐substituent groups with isobutene, styrene, and α‐methylstyrene as the electron‐donating monomers is carried out in order to investigate the structure and thermal properties of the resulting comb‐like copolymers. The obtained copolymers show excellent thermal stability and their glass transition temperatures vary depending on the chain length of the introduced N‐substituents. The main‐ and side‐chain motions of the copolymers are investigated by dynamic mechanical analysis at various frequencies over the temperature range of ?150 to 100 °C.
Novel branched polyoxymethylene copolymers are synthesized by cationic copolymerization of 1,3,5‐trioxane (TOX) with 3‐(alkoxymethyl)‐3‐ethyloxetane (ROX) using BF3·Et2O as an initiator. Four oxetane derivatives with different side‐chain lengths (from 1 to 6 carbons) are tested for copolymerization. The copolymer composition is controlled by the feed ratio of ROX, and influenced by the chain length of alkyl group on ROX. The incorporation ratio and side‐chain length of the ROX unit have great influence on the thermomechanical properties and crystallinity of the copolymers.
The crystal structure of poly(4,4′‐diphenylsulfonyl terephthalamide) (pt‐PSA) is studied by X‐ray diffraction and molecular simulation. Although the number of observed reflections is limited to warrant a precise determination of the unit cell structure and symmetry, a reasonable monoclinic unit cell is suggested with dimensions of a = 0.645 nm, b = 0.488 nm, c = 3.010 nm, and γ = 122.5°. A twofold molecule with two monomeric units forming a large zigzag conformation satisfies the X‐ray diffraction data. A layer structure is formed in the crystal phase, which is stabilized by the hydrogen bond between ? NH and ? C?O and the parallel‐displaced π–π stacking from the distortional coplanarity of the benzene rings and amide group.
Three novel dithieno[3,2‐b:2′,3′‐d]thiophene‐based low‐bandgap polymers are synthesized by a Suzuki–Miyaura coupling reaction or by direct arylation polycondensation. The polymers present a high molecular weight (26–32 kDa) and narrow polydiversity (1.3–1.7). With a highest occupied molecular orbital (HOMO) energy level around ?5.20 eV, these polymers exhibit a narrow bandgap of 1.75–1.87 eV. All the polymers display strong absorption in the range of 350–700 nm. Bulk‐heterojunction (BHJ) solar cells are further fabricated by blending the as‐prepared polymer with (6,6)‐phenyl‐C61‐butyric acid methyl ester (PC61BM) at different weight ratios. The best devices contribute a power conversion efficiency (PCE) of 0.73% under AM 1.5 (100 mW cm?2).
A series of highly branched star‐comb poly(ε‐caprolactone)‐block‐poly(l ‐lactide) (scPCL‐b‐PLLA) are successfully achieved using star‐shaped hydroxylated polybutadiene as the macroinitiator by a simple “grafting from” strategy. The ration of each segment can be controlled by the feed ratio of comonomers. These star‐comb double crystalline copolymers are well‐defined and expected to illustrate the influences of the polymer chain topology by comparing with their counterparts in linear‐shaped, star‐shaped, and linear‐comb shape. The crystallization behaviors of PCL‐b‐PLLA copolymers with different architectures are investigated systematically by means of wide‐angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscopy analysis. It is shown that the comb branched architectures promote the crystallization behavior of each constituent significantly. Both crystallinity and melting temperature greatly raise from linear to comb‐shaped copolymers. Compared to linear‐comb topology, the star‐comb shape presents some steric hindrance of the graft points, which decrease the crystallinity of scPCL‐b‐PLLA. Effects of copolymer composition and chain topology on the crystallization are studied and discussed.
Copolymerization of carbon dioxide (CO2) and propylene oxide (PO) is employed to generate amphiphilic polycarbonate block copolymers with a hydrophilic poly(ethylene glycol) (PEG) block and a nonpolar poly(propylene carbonate) (PPC) block. A series of poly(propylene carbonate) (PPC) di‐ and triblock copolymers, PPC‐b‐PEG and PPC‐b‐PEG‐b‐PPC, respectively, with narrow molecular weight distributions (PDIs in the range of 1.05–1.12) and tailored molecular weights (1500–4500 g mol?1) is synthesized via an alternating CO2/propylene oxide copolymerization, using PEG or mPEG as an initiator. Critical micelle concentrations (CMCs) are determined, ranging from 3 to 30 mg L?1. Non‐ionic poly(propylene carbonate)‐based surfactants represent an alternative to established surfactants based on polyether structures.
Polyacrylonitrile (PAN) with high molecular weight and low dispersity is successfully synthesized by visible‐light‐induced metal‐free radical polymerization at room temperature. This polymerization technique uses organic dye Eosin Y as photocatalyst and benzenediazonium tetrafluoroborates as initiator. Gel permeation chromatography‐multiangle laser light scattering shows the absolute molar weight of the PAN more than 1.50 × 105 g mol−1 with a polydispersity index < 1.3 while MALDI‐TOF MS and 19F NMR spectroscopy indicate the F‐chain‐end process. The first‐order kinetic behavior, molecular weight distributions shifting, and “ON/OFF” experiment results suggest this reaction may follow the atom‐transfer‐like radical polymerization mechanism. In addition, this new approach allows for the efficient synthesis of well‐defined random copolymers.
Two star‐shaped tris(4‐(thiophen‐2‐yl)phenyl)amine derivatives, namely tris(4‐(5‐(3‐pentylthieno[3,2‐b]thiophen‐5‐yl)thiophen‐2‐yl)phenyl)amine and tris(4‐(5‐(3‐pentyl‐2‐(thiophen‐2‐yl)thieno[3,2‐b]thiophen‐5‐yl)thiophen‐2‐yl)phenyl)amine, are developed as photoinitiators for radical and cationic polymerizations under near‐UV and visible light‐emitting diodes (LEDs) (e.g., 385, 405, and 455 nm). When used in combination with an iodonium salt (and optionally N‐vinyl carbazole) or an amine/alkyl halide couples, they lead to excellent photoinitiating abilities for the polymerization of epoxides or (meth)acrylates under air. Compared with commercial photoinitiators, i.e., camphorquinone‐based systems or bis(2,4,6‐trimethylbenzoyl)‐phenylphosphineoxide, the novel photoinitiators exhibit noticeably higher polymerization efficiencies under air (epoxide conversions = 41–57% vs ≈0%, halogen lamp exposure; methacrylate conversions = 50–55% vs 44%, LED at 405 nm exposure; methacrylate conversions = 34–42% vs 0–8%, LED at 455 nm exposure). These systems are also interesting in overcoming oxygen inhibition. The photochemical mechanisms are studied by steady‐state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry, and laser flash photolysis techniques.
A new D–A copolymer ( PBDT‐DTQx) based on the 2,3‐di(5‐hexylthiophen‐2‐yl)quinoxaline acceptor unit and a bithienyl‐substituted benzodithiophene (BDT) donor unit is designed and synthesized for application as the donor material in polymer solar cells (PSCs). The polymer film shows a broad absorption band covering the wavelength range from 300 to 720 nm and a low highest occupied molecular orbital (HOMO) energy level at ?5.35 eV. A device based on PBDT‐DTQx :PC70BM ([6,6]‐phenyl‐C71‐butyric acid methyl ester) (1:2.5, w/w) with chloronaphthalene as a solvent additive displays a power conversion efficiency (PCE) of 3.15%. With methanol treatment, the PCE of the PSCs is further improved to 3.90% with a significant increase of the short‐circuit current density, Jsc, from 10.10 mA cm?2 for the device without the methanol treatment to 11.71 mA cm?2 for the device with the methanol treatment.
Three medium‐bandgap polymers based on a 4,5‐ethylene‐2,7‐dithienyl carbazole as the electron‐donating unit and different 5,6‐dialkoxy‐2,1,3‐benzothiadiazoles as the electron‐accepting units, are synthesized as polymer donors for photovoltaic applications. The three copolymers possess highest occupied molecular oribital (HOMO) levels around ?5.47 eV and medium bandgaps of about 1.94 eV. The solar cells with polymer:[6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) = 1:4 as the active layer, show an especially high open‐circuit voltage (Voc) of 0.95 V and attain good power conversion efficiency up to 5.91%. The hole mobilities of the active layer films, measured by space‐charge‐limited current (SCLC), are up to 3.5 × 10?4 cm2 V?1 s?1. Given the favorable medium bandgaps, low‐lying HOMO levels, and good hole mobilities, these copolymers are promising candidates for the construction of a highly efficient front cell to harvest the shorter wavelength band of the solar radiation in a tandem solar cell with high Voc.
In order to regulate the electronic ability of benzo[1,2‐b:4,5‐b′]dithiophene (BDT), the new electron‐donating unit (BDTOT) is designed and synthesized which consists of a BDT backbone with conjugated 2‐(2‐ethylhexyl)‐3,4‐dimethoxythiophene side chains. By alternating copolymerization of BDTOT with electron‐accepting units of fluorinated benzothiadiazole (FBT), benzothiadiazole (BT), and pyrrolo[3,4‐c]pyrrole‐1,4‐dione (DPP), three donor–acceptor (D‐A) copolymers (PBDTOT‐FBT, PBDTOT‐BT, and PBDTOT‐DPP) have been developed for PSC applications. The impact of dimethoxythiophene substituent and the electron‐accepting strength of the acceptor units on the absorption, HOMO/LUMO energy levels, and photovoltaic properties of the resultant polymers is investigated in detail. PBDTOT‐BT and PBDTOT‐DPP exhibit relatively narrower bandgaps and PBDTOT‐FBT possesses a down‐shifted HOMO energy level as compared to their corresponding analogs without methoxy groups onto the conjugated thiophene side chains. The screening of the different blend ratio, the processing additive, and polar solvent post‐treatment is conducted to optimize the polymer solar cell (PSC) devices. PSCs with PBDTOT‐FBT as donor deliver a power conversion efficiency (PCE) of 2.55%. By treatment of the active layer with methanol to tailor the morphology, the solar cell based on PBDTOT‐FBT exhibits the remarkably improved PCE of 4.84% with a Voc of 0.92 V, a Jsc of 8.71 mA cm?2, and an FF of 60.3%.
A diamine monomer with trifluoromethyl groups, 3,3′‐bis(trifluoromethyl)‐4,4′‐diamino‐1,1′‐biphenyl, is synthesized from 5‐bromo‐2‐nitrobenzotrifluoride with two steps. The model reaction with monofunctional benzoyl chloride at room temperature gives the model compound with a quantitative yield. The results of the model reaction indicate that the amine groups have sufficient reactivity in spite of the presence of electron‐withdrawing and bulky trifluoromethyl group at the ortho position. The monomer is polymerized with terephthaloyl chloride and isophthaloyl chloride in N,N‐dimethylacetamide (DMAc) or DMAc containing LiCl using pyridine as an acid acceptor at room temperature. All synthesized polymers are somewhat crystalline and colorless. While the meta‐linked polyamide ( PA2 ) shows excellent solubility in polar aprotic solvents, the para‐linked one ( PA1 ) is dissolved in polar aprotic solvents containing LiCl and concentrated H2SO4. They show good thermal and thermooxidative stability as well as high melting temperatures.
Two benzodithiophene (BDT)‐based broad absorbing low band gap random copolymers, P1 and P2 , incorporating electron accepting imide functionalized pyrrolo[3,4‐c]pyrrole‐1,3‐dione (TDPPDT) and lactam functionalized pyrrolo[3,4‐c]pyrrole‐1,4‐dione (DKPP) derivatives are prepared. The copolymerization of differently alkylated two TDPPDT derivatives with both of BDT and DKPP offers random copolymers P1 and P2 . The absorption bands of polymers P1 and P2 cover the region from 300 to 900 nm and the estimated band gaps of P1 and P2 are 1.43 and 1.39 eV, respectively. The highest occupied molecular orbital energy levels of P1 and P2 are identical, at –5.25 eV. The organic field effect transistors made from P1 and P2 provide a hole mobility μ of 3.0 × 10?4 and 3.6 × 10?5 cm2 V?1 s?1, respectively. Polymer solar cells (PSCs) prepared from P1 and P2 afford a maximum power conversion efficiency of 1.64% and 2.14%, respectively.
Core–corona inversion of micelles of diblock copolymer poly(acrylic acid)‐block‐poly(N‐isopropylacrylamide) (PAA‐b‐PNIPAM), has been successfully realized by switching either pH or temperature. The strong interaction of doxorubicin with the PAA block and the pH‐sensitive drug release from the polymer make the system very useful as a controlled drug delivery system. The encapsulation of hydrophobic Nile Red molecules above the lower critical solution temperature of PNIPAM suggests that this polymer may be useful for removing hydrophobic pollutants.
A set of copolyesters (PHTxGluxy) with compositions ranging between 90/10 and 50/50 in addition to the parent homopolyesters poly(hexamethylene terephthalate) (PHT) and PHGlux, are prepared by the melt polycondensation of 1,6‐hexanediol (HD) with mixtures of dimethyl terephthalate (DMT) and dimethyl 2,4:3,5‐di‐O‐methylene‐d ‐glucarate (Glux). The copolyesters have in the 35 000–45 000 g mol?1 range, their microstructure is random, and they start to decompose at a temperature well above 300 °C. Crystallinity of PHT is repressed by copolymerization so that copolyesters containing more than 20% of sugar‐based units are essentially amorphous. On the contrary, PHTxGluxy displays a Tg that increases monotonically with composition from 16 °C in PHT up to 73 °C in PHGlux. Compared with PHT, the copolyesters show an accentuated susceptibility to hydrolysis and are sensitive to the action of lipases upon incubation under physiological conditions. The degradability of PHTxGluxy increases with the content in Glux units.
A perylene bisimide derivative of N,N′‐diisopropylphenyl‐1,6,7,12‐tetrachloroperylene‐3,4,9,10‐tetracarboxyl bisimide (PBI) is synthesized and used as a sensitizer for a photorefractive (PR) polymer composite. Small amount (0.1 wt%) of PBI sensitizer gives the maximum PR performance of composite based on poly(4‐(diphenylamino)benzyl acrylate) (PDAA) (45 wt%), 2‐(4‐(azepan‐1‐yl)benzylidene)malononitrile (35 wt%), and (4‐(diphenylamino)phenyl)methanol (24.9 wt%). High external diffraction efficiency of 49%, response time of 47 ms, and sensitivity of 28 cm2 J?1 are obtained under an applied electric field of 40 V μm?1 at writing beam of 532 nm. PBI sensitizer effectively forms a charge‐transfer complex with PDAA, which favors the generation of the charge carriers followed by the space‐charge formation. Furthermore, low PBI concentration contributes to low absorption coefficient at 532 nm, which leads to better PR performance.
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