Alternating copolymers of an oligopeptide (N3‐GVGV‐N3, where G: glycine; V: valine) and an oligothiophene (5,5′‐bis(ethynyl)‐3,3'‐dioctyltetrathiophene) are prepared by click chemistry. The experimental results discover that these copolymers exhibit strong molecular‐weight‐dependent self‐assembly behaviors. The copolymer P1 with the lowest weight‐average molecular weight ( = 7400 g mol?1), assembles into well‐ordered fibrous nanostructures. P3 ( = 16 980 g mol?1) assembles into nanoballs. P2, which has the medium between P1 and P3, ( = 14 800 g mol?1), exhibits more‐complicated self‐assembly behaviors, more like a transition state between the other two. All of the results suggest the self‐assembly ability of these oligopeptide segments might be the major reason for the nano‐structure evolution.
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.
Reverse iodine transfer polymerization (RITP) of 1,1,2,2‐tetrahydroperfluorodecyl acrylate (FDA) is successfully performed in supercritical carbon dioxide (scCO2) at 70 °C under a CO2 pressure of 300 bar. PolyFDA (PFDA) of increasing molecular weights (from 10 000 to 100 000 g mol?1) is synthesized with good agreement between theoretical, 1H NMR spectroscopy and and size exclusion chromatography/refractive index/right‐angle laser‐light scattering/differential viscometer (SEC/RI/RALLS/DV)‐estimated molecular weights (). Furthermore, the increase of goes with a decrease of the dispersity of the polymers (? from 2.06 to 1.33), which is consistent with a controlled radical polymerization (CRP). Lastly, the structure of final PFDA and therefore the RITP process are confirmed by matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) analyses.
Flame‐retardant polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites influenced by surface functionalization and surfactant molecular weights are studied. 3‐Aminopropyl‐triethoxysilane (APTES) is utilized to modify the CNTs (f‐CNTs), and maleic‐anhydride‐grafted PP (MAPP) with two molecular weights ( of 800 and 8000 g mol?1) is used to further improve the dispersion of f‐CNTs in the PP matrix. Thermal gravimetric analysis (TGA) and microscale combustion calorimetry (MCC) reveal that the molecular weight of MAPP directly affects the thermal stability and flammability of PP/f‐CNTs PNCs: both MAPP polymers ( of 800 and 8000 g mol?1) increase the thermal stability of PP; however, the heat release rate of PP/f‐CNTs is reduced in the presence of MAPP ( of 800 g mol?1) and increased in the presence of MAPP ( of 8000 g mol?1). MAPP ( of 800 g mol?1) also results in a lower viscosity of the PP/f‐CNTs PNCs compared with pure PP.
This study the impact of different catalytic systems on the formation of structural defects among the macromolecular chain, in the molecular characteristics (average molecular weights per number (), per weight (), and polydispersity index (Đ )), along with the composition ratio of the two monomeric units within the main chain for a specific class of conjugated polymers through the utilization of size exclusion chromatography and proton nuclear magnetic resonance (1H‐NMR) spectroscopy, respectively is examined. From the obtained results, the formation of the structural defects in the studied “donor–acceptor” polymers is visualized and quantified by 1H‐NMR. The alternating polymers containing the lower percentage of chemical defects demonstrate increased and values and increased absorption co‐efficiency as recorded by UV–vis absorption spectroscopy. Therefore, it is evident that this work highlights optimum Stille cross‐coupling polymerization conditions, which can be a guide rule for the synthesis of defect‐free conjugated polymers. 相似文献
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%).
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.
Imidazolium alcohols, [R‐Im‐Z‐OH]+[X]?, are investigated as initiators for ring opening polymerization (ROP) of ε‐caprolactone (CL). Two monomeric imidazolium alcohols { I [R = HOOC(CH2)5, Z = (CH2)11, X = Br] and III [R = n‐Bu, Z = (CH2CH2O)3CH2CH2, X = bis(trifluoromethylsulfonyl)imide (TFSI)]} are successfully utilized as initiators for ROP of CL, yielding corresponding polycaprolactones (PCL) Ia‐Br and IIIa‐TFSI . The oligoester II derived from I also acts as an initiator, providing block copolymer IIa‐Br . By anion exchange Ia‐Br and IIa‐Br are converted to Ia‐TFSI and IIa‐TFSI . The TFSI polymers have lower glass transition temperatures (Tg), resulting in higher conductivity, compared to the Br polymers. The ionic conductivities of the PCL block copolymers are higher than those of the PCL homopolymers, despite the similar Tg, because of their higher ionic content. Their static dielectric constants () increase linearly with ion content and exhibit the temperature dependence expected by Onsager, in the liquid state. The semicrystalline PCL homopolymers, upon crystallization, undergo a significant increase in , owing to a Maxwell–Wagner–Sillars interfacial polarization. The present results demonstrate that with proper design, block copolymers have the potential to provide high ionic conductivities combined with good mechanical strength, key attributes for application of these materials in mechanical actuators.
Bulk homopolymerizations of vinyl acetate and vinyl pivalate are studied by EPR experiments between ?65 °C and 60 °C with dicumyl peroxide acting as the photoinitiator. No mid‐chain radicals are seen, which demonstrates that backbiting plays no role. The chain‐length dependence of the termination rate coefficients measured up to 13% monomer conversion is adequately represented by the composite model. The power‐law exponents αs and αl for short‐chain and long‐chain radicals are: αs(VAc) = 0.57 ± 0.05, αs(VPi) = 0.67 ± 0.15, αl(VAc) = 0.16 ± 0.07, and αl(VPi) = 0.16 ± 0.07. The crossover chain lengths differ largely: ic(VAc) = 20 ± 10 and ic(VPi) = 110 ± 30. The rate coefficient for termination of two radicals of chain length unity, , which is the fourth composite‐model parameter, depends on temperature, as does the monomer fluidity.
A novel symmetrical selenium‐based reversible addition‐fragmentation chain transfer (RAFT) agent, Se,Se’‐dibenzyl carbonodiselenothioate (Se‐RAFT), is synthesized and used in the RAFT polymerization of styrene. The results obtained show that the Se‐RAFT agent is involved in the polymerization of styrene, as evidenced by narrow molar‐mass distributions (/ < 1.6) and the incorporation of the Se‐RAFT moiety into the resultant polymer. The latter is confirmed by aminolysis, NMR spectroscopy, size‐exclusion chromatography (SEC) and UV spectroscopy. This work provides detailed insight into the Se‐RAFT polymerization mechanism. The Se‐RAFT agent is unique in that the stabilizing and leaving groups are identical.
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.
Synthesis of complex macromolecular architectures exhibiting no chain ends such as flower‐like polymers is still of interest in the aim of investigating their physicochemical properties. For this purpose, poly(3,4‐dimethyl maleic imidoethyl acrylate)‐block‐polybutadiene‐block‐poly(3,4‐dimethyl maleic imidoethyl acrylate) triblock copolymer is synthesized in a convergent manner using a combination of living polymerization (anionic polymerization), reversible deactivation radical polymerization, and click chemistry. This copolymer is self‐assembled in a selective solvent (heptane/THF mixture) of the polybutadiene block leading to the formation of flower‐like micelles in thermodynamic equilibrium in dilute solution. These resulting transient architectures are fixed by covalently crosslinking the micelles core by inducing [2+2] cyclodimerization of the 3,4‐dimethyl maleic imidoethyl groups borne by the short solvophobic blocks under UV irradiation. Single flowers are isolated from residual non‐crosslinked chains by semipreparative size exclusion chromatography (SEC) and characterized by 1H NMR, SEC, dynamic light scattering (DLS), and transmission electron microscopy (TEM).
Molecular‐recognition‐responsive characteristics of a novel poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) (PNB12C4) hydrogel have been investigated. In the prepared PNB12C4 hydrogel, benzo‐12‐crown‐4 (B12C4) groups act as guest molecules and γ‐cyclodextrin (γ‐CD)‐receptors, and poly(N‐isopropylacrylamide) (PNIPAM) networks act as phase‐transition actuators. The formation of stable γ‐CD/B12C4 complexes enhances the hydrophilicity of the PNB12C4 hydrogel networks, and induces positive shift of the volume phase transition temperature (VPTT) of PNB12C4 hydrogel. Moreover, the PNB12C4 hydrogel also shows thermoresponsive adsorption property selectively towards γ‐CD. The γ‐CD‐recognition sensitivity of PNB12C4 hydrogel can be dramatically improved by increasing γ‐CD concentration in solution or B12C4 content in PNB12C4 copolymer networks. The results in this study provide valuable information for developing crown ether‐based smart materials in various applications.
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.
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.
A two‐step synthesis of high‐molecular‐weight and bio‐based poly(butylene succinate) (PBS) from succinic anhydride and butane‐1,4‐diol is established, in which the first step is a 12 h atmospheric polycondensation at 95 °C in the presence of succinic acid. The subsequent polymerization, catalyzed by Novozym 435 suspended in toluene, yields PBS with a molecular weight above 73 000 g mol?1. The recovered lipase catalyst appears to give similar performance after six cycles. The versatility of this atmospheric synthetic route to PBS copolymers is validated through the syntheses of poly(butylene succinate‐co‐butylene malate) (PBSM), poly(butylene succinate‐co‐butylene fumarate) (PBSF), and poly(butylene succinate‐co‐butylene terephthalate) (PBST), in which succinic acid is replaced by corresponding di‐acids as monomers.
A series of random binary poly(ethylene glycol) and fluoropolymer brushes (POEGMA‐PNCA‐F15) are grafted onto substrates via surface‐initiated polymerizations (atomic transfer radical polymerization and ring opening metathesis polymerization, respectively) from polydopamine based mix‐catecholic initiators. The chemical composition, surface morphology, swellability, and wettability of the as‐prepared surfaces are characterized by X‐ray photoelectron spectra (XPS), atomic force microscopy (AFM), and static water contact angle measurements, respectively. The antifouling properties are evaluated by settlement of spores and diatoms, the results indicate that the as‐prepared amphiphilic surfaces with random hydrophilic and hydrophobic polymer brushes can mitigate biofouling, and the ratio of the hydrophilic and hydrophobic polymer brushes is a key determinant factor in antifouling effect, the optimal ratio (1:1 initiator) of bipolymer brushes on surfaces exhibits good antiadhesion performance against both Chlorella spores and Navicula diatoms.
The ring‐opening polymerization (ROP) of a cyclic ester using alkyl acetate carbene (ROCOCH:) is generated from diazoacetate as organocatalyst under microwave irradiation, which enables the one‐pot preparation of copolymers of polyester and polyolefin. The chemical structure of the polymerized product is characterized by NMR, Fourier transformed infrared (FTIR), and UV–vis spectroscopy. The incorporation of the azo group into the obtained copolymer is determined by elemental analysis, which indicates that 1.38–6.21% nitrogen is contained in the obtained copolymers. The influences of catalyst and microwave irradiation parameters on the polymerization are investigated. Both the microwave power and irradiation time have great influences on the copolymerization. Moreover, the molar mass of the obtained polymers is calculated with polystyrene standards, which gradually increases from 600 to 36 100 g mol?1 as the reaction temperature increases from 60 to 120 °C. Polymer with of 36 100 g mol?1 and PDI of 1.86 is produced under optimized conditions. The combination of ROP and carbene polymerization offers a new and convenient pathway to synthesize copolymers of polyesters and polyolefins.
The preparation of stimuli‐responsive aminomethyl functionalized poly(p‐xylylene) coatings by chemical vapor deposition polymerization is reported. Modification of the paracyclophane precursor with ionizable aminomethyl groups leads to polymer coatings with pH‐responsive swelling properties. The swelling behavior is monitored in situ using spectroscopic ellipsometry and additional streaming potential measurements are performed. With decreasing pH‐value, the coating becomes increasingly charged and reversibly swells to several times its dry thickness. The swelling ratio is sensitive to the ionic strength of the solution. By using a mixture of unfunctionalized and functionalized precursors in the chemical vapor deposition process, the number of charges in the polymer layer can be tuned and with it the swelling ratio of the coating. As a proof‐of‐concept for possible applications, a commercial paper filter is coated. This results in a pH‐dependent wetting behavior and pH‐dependent transport through the capillaries of the paper.
In this work, an agarose/poly(acrylamide‐co‐acrylic acid) interpenetrating network hydrogel is prepared by the photopolymerization of acrylamide, acrylic acid, and N ,N ′‐methylenebisacrylamide within agarose network at its gel state. The as‐prepared hydrogel exhibits two independent kinds of shape memory effects. The thermal‐activated shape memory behavior is attributed to the reversible coil‐helix transformation of agarose, within the permanently cross‐linked poly(acrylamide‐co‐acrylic acid) network; the light triggered shape recovery is driven by the dissociation of the complexes between carboxyl groups and Fe(III) ions, due to the photoreduction of Fe(III) to Fe(II) in the presence of citric acid. The versatile and simple strategy as presented here should be beneficial for the design of dual‐activated shape memory hydrogels and foster their use in a number of fields such as biomaterials, soft robotics, smart actuators, and sensors.
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