The cationic polymerization of 1,3‐pentadiene using a tert‐butyl chloride (tBuCl)/TiCl4 initiating system in CH2Cl2 at different reaction conditions is reported. It is shown that the reaction rate increases with the increase of the tBuCl/TiCl4 molar ratio, while the molecular weight distribution becomes narrower. Well‐defined oligo(1,3‐pentadiene)s ( ≤ 3500 g mol?1; / ≤ 3.0) are obtained at high tBuCl/TiCl4 molar ratio (340) and low temperature (–78 °C). 1H and 13C NMR spectroscopy studies reveal the presence of tert‐butyl head and –CH2–Cl end groups. The number‐average functionalities (Fns) at the α‐ and ω‐ends are calculated to be Fn(tBu) > 1 and Fn(Cl) < 1, respectively. The general mechanism of 1,3‐pentadiene polymerization is proposed.
The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)3] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)3/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 105 g mol‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)3/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).
This study reports the synthesis and characterization of poly(3‐hexylthiophene) (P3HT) from a direct heteroarylation polymerization of two isomeric monomers, 2‐bromo‐3‐hexylthiophene (monomer 1 ) and 2‐bromo‐4‐hexylthiophene (monomer 2 ). Using the Herrmann–Beller catalyst along with P(o‐NMe2Ph)3, the resulting polymers are obtained in excellent yields and exhibit a good number‐average molecular weight (Mn of 33 and 16 kDa, respectively). Detailed 1H NMR analyses reveal less than 1% of homocouplings and no evidence of β‐branching. Dehalogenation is identified as the main chain termination step and preferentially occurs on monomer 2 . The melting temperature (237 °C) and hole mobility (up to 0.19 cm2 V?1.s?1) of the nearly defect‐free P3HT obtained from this simple polymerization of monomer 1 are comparable, if not superior, to those obtained with commercially available GRIM and Rieke samples.
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.
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.
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.
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).
The Janus polymerization combines cationic and anionic polymerizations into growing chains with two different chain ends. This provides a novel pathway to produce topologically interesting polymers. Here this polymerization is applied to allow the synthesis of branched polytetrahydrofuran (bPTHF) and poly(tetrahydrofuran‐co‐ε‐caprolactone) (bPTC). Rare earth triflates [RE(OTf)3] (RE = Lu, Sc, and Y) are used as catalyst, and small amounts (0.10–0.15 mol%) of ethylene glycol diglycidyl ether act as both initiator and comonomer due to the different reactivities of the two epoxide groups. The poly(ε‐caprolactone) block in bPTC provides crystalline domains and potential degradation under acidic conditions. The products of bPTHF show unusual tensile properties with a high strain at break of 1070% differing greatly from linear PTHF. Due to the large number of terminal hydroxyl groups and their strong hydrogen bonding, bPTHF has self‐healing properties with potentially promising applications.
Two carbazole derivatives with terpyridine units attached to the 3,6‐positions are synthesized, 1 with a hydrogen at the 9‐position and 2 bearing a dodecyl chain there, to evaluate the influence of H‐bonds on their self‐assembly behavior with metal ions. The unalkylated derivative 1 assembles with zinc ions to form a single product identified by NMR, electrospray ionisation mass spectrometry (ESI‐MS), and X‐ray photoelectron spectroscopy (XPS) as a pentametric metallocycle ( Zn‐1 ), whereas 2 forms a mixture of two assemblies ( Zn‐2 ). The pentamer Zn‐1 shows tunable dual emission in the blue and green regions by varying the solvent and excitation wavelength, and molecular packing studies by powder X‐ray diffractometry (XRD), transmission electron microscopy (TEM), polarising optical microscopy (POM), and atomic force microscopy (AFM) reveals a high propensity to form ordered layers. A fluorescence quenching experiment of electron‐rich Zn‐1 with C60 shows a high association constant of Ksv = 3.2 × 105m ?1, suggesting effective charge transfer between Zn‐1 and C60 molecules.
The new aluminum compounds 1–3 modified by unsaturated alcohol, Me3−nAl(O(CH2)4OCHCH2)n (n = 1 ( 1 ), 2 ( 2 ), 3 ( 3 )), are synthesized and investigated by multinuclear (1H, 13C, 27Al) NMR spectroscopy. The compounds 1 – 3 initiate living ring‐opening polymerization of ε‐caprolactone in bulk at 40–80 °C to afford polyesters with controlled molecular weight (M n up to 35 000 g mol−1) and relatively narrow molecular weight distribution (M w/M n < 1.8). Among initiators studied here, aluminum trialkoxide shows the highest activity, whereas aluminum dialkoxide is a less active. In all cases, the fragment of unsaturated alcohol is transferred to the end of the polymeric chain with high degree of functionality (>85%) yielding macromonomers. These macromonomers are copolymerized with maleic anhydride to give poly(vinyl ether‐co‐maleic anhydride)‐g‐poly(ε‐caprolactone) graft copolymers.
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 convenient one‐pot method for the controlled synthesis of polystyrene‐block‐polycaprolactone (PS‐b‐PCL) copolymers by simultaneous reversible addition–fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) processes is reported. The strategy involves the use of 2‐(benzylsulfanylthiocarbonylsulfanyl)ethanol (1) for the dual roles of chain transfer agent (CTA) in the RAFT polymerization of styrene and co‐initiator in the ROP of ε‐caprolactone. One‐pot polymerizations using the electrochemically stable ROP catalyst diphenyl phosphate (DPP) yield well‐defined PS‐b‐PCL in a relatively short reaction time (≈4 h; = 9600?43 600 g mol?1; / = 1.21?1.57). Because the hydroxyl group is strategically located on the Z substituent of the CTA, segments of these diblock copolymers are connected through a trithiocarbonate group, thus offering an easy way for subsequent growth of a third segment between PS and PCL. In contrast, an oxidatively unstable Sn(Oct)2 ROP catalyst reacts with (1) leading to multimodal distributions of polymer chains with variable composition.
The controlled radical polymerization of 2‐vinylpyridine is reported using commercial blue light‐emitting diodes as visible light source in the presence of S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐aceticacid) trithiocarbonate without exogenous initiators or photocatalysts. With this system, poly(2‐vinylpyridine) with well‐regulated molecular weight and narrow dispersity (?) (? = 1.13) and a conversion efficiency of 84.9% is obtained after 9 h irradiation. The polymerization can be instantly switch “on” or “off” in response to visible light while maintaining a linear increase in molecular weight with conversion and first order kinetics. These results demonstrate the simplicity and efficiency of the photocatalysts‐free, visible light mediated reversible addition fragmentation chain transfer polymerization as a platform to achieve well‐defined poly(2‐vinylpyridine) under mild conditions.
Cationic polyelectrolytes find potential applications in electronic device fabrication, biosensing as well as in biological fields. Herein, a series of cationic main‐chain polyelectrolytes with pyridinium‐based p ‐phenylenevinylene units that are connected via alkylene spacers of varying lengths are synthesized by a base‐catalyzed aldol‐type coupling reaction. Their mean average molecular weights range from 15 000 to 32 000 g mol‐1, corresponding to about 16–33 repeat units. Due to the presence of alkyl side‐chains and alkylene spacers as well as cationic hard‐charges the polymers are endowed with amphiphilic character and hence, aggregation of these polyelectrolytes at high concentration leads to thermoreversible physical gel formation in dimethyl sulfoxide accompanied by interchain interactions. Morphological analysis shows spherical aggregates in case of C16‐Poly‐S12 in dimethyl sulfoxide. Dependence of gelation behavior on the length of alkyl side‐chains and alkylene spacers of the polyelectrolytes are addressed.
A novel poly(phenylene ethynylene) containing 2‐thiohydantoin [poly( 1 )] is synthesized. The addition of F? quenches the fluorescence, while the fluorescence of the solution only changes slightly upon addition of other anions, indicating the sensing ability of poly( 1 ) toward F?. The addition of Ag+ quenches the fluorescence of the polymer, whereas the addition of other metal ions results in only slight changes to the fluorescence. Compared with its small‐molecule counterpart, the Stern–Volmer quenching constants of poly( 1 ) toward F? and Ag+ are 165 and 105 times greater, respectively. This result indicates the amplified quenching effect of poly( 1 ).
The improvement in the power conversion efficiency (PCE) and performance of poly(3‐hexylthiophene) (P3HT)/[6,6]‐phenyl‐C61butyric acid methyl ester (PCBM) solar cells are reported by using dithiafulvalene (DTF)‐based conjugated oligomers ((poly[2‐(9H‐fluoren‐9‐ylidene)‐4,5‐bis(hexylthio)‐1,3‐dithiole‐ran‐(2,1,3‐benzothiadiazole)] (PTBT) and poly[2,7‐(9,9‐dihexylfluorene)‐ran‐(2‐(9H‐fluoren‐9‐ylidene)‐4,5‐bis(hexylthio)‐1,3dithiole]‐ran‐(2,1,3‐benzothiadiazole)] (PFTBT)) that contain a DTF unit, which serves as an electron‐rich donor, and a benzothiadiazole group, which serves as an electron‐deficient acceptor in the main chain. A P3HT/PCBM device with 5 wt% PTBT exhibits an efficiency of up to 1.78%, which is higher than that of a device composed only of a P3HT/PCBM blend (1.01%). Introducing 2 wt% PTBT into the P3HT/PCBM blend substantially increases the charge‐carrier mobility from 2.01 × 10?4 to 4.59 × 10?4 cm2 V?1s?1. The improvement of the PCE is attributed to improved charge transport in the device and an increased open‐circuit voltage, suggesting that blending PTBT increases the intermolecular interaction of the molecules. In addition, doping the oligomer in ambient atmospheric conditions enhances the stability of these devices.
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 grafting of well‐defined polystyrene to graphene oxide (GO) using nitroxide‐mediated polymerization (NMP) is demonstrated by a two‐step reaction. In the first step, GO is functionalized with glycidyl methacrylate (GMA) to yield GO‐GMA. Polystyrene (PS), previously synthesized via SG1‐based NMP, is then grafted to GO‐GMA by a simple reaction between the SG1 end group and the GMA double bond to yield GO‐GMA‐g‐PS. 1H, heteronuclear single‐quantum correlation (HSQC), nuclear magnetic resonance (NMR), X‐ray photoelectron spectroscopy (XPS), Raman, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA) are consistent with attachment of the GMA group to the GO surface and with polystyrene being grafted to the GO surface to form the GO‐GMA‐g‐PS nanocomposite (NC). GPC analysis shows a number‐average molecular weight of 3330 g mol?1 for the PS with molecular weight dispersity (Ð) of 1.13. Up to 28 mass% of PS has been introduced into the GO NC. The present “grafting‐to” methodology holds promise for the facile and clean synthesis of graphene oxide polymer NCs.
In the context of novel sustainable and structurally significant building blocks for polymer science, the synthetic routes are described to new oligoamide structures based on the terpenoid ketone (?)‐menthone. The basic concept is an oxime formation of this cyclic ketone followed by the Beckmann rearrangement, resulting in the corresponding lactams. These lactams are polymerized under anionic or acid‐catalyzed conditions (ring‐opening polymerization (ROP)) to give alkyl‐substituted and stereocenter containing oligoamide scaffolds that are assumed to be suitable for further copolymerizations and modifications and thus for a wide range of different applications. The regio‐ and the stereochemistry of the formed oximes and lactams as well as their impact on the polymerization behavior is discussed.
The synthesis of telechelic poly(ether sulfone)s with methoxy end groups is reported. Molecular weights ranging from 1600 to 2800 g mol?1 and polydispersities of 1.1–1.2 are synthesized by chain‐growth condensation polymerization. The initiator is chosen by using semiempirical calculations and 19F NMR spectroscopy measurements. The polymers are characterized by NMR spectroscopy and matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectrometry (MS), and are terminated by a methoxy group at one end and a fluorine at the other, and up to approximately 20% polymer of similar mass but slightly higher polydispersity, methoxy terminated at both ends, is present, along with less than 5% of polymer terminated at both ends by fluorine atoms. These do not need to be separated, and can be converted to methoxy‐ending telechelic blocks, yielding polyvalent, reactive rigid building blocks for copolymer synthesis.
下载免费PDF全文