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.
Novel self‐healing silicone rubbers are prepared by a two‐step procedure: aminopropyl methyl phenyl polysiloxanes is first reacted with salicylaldehyde and then with copper acetate. The reversible nature of the metal–ligand coordination interaction between polysiloxanes with pendent Schiff‐base groups and Cu2+ has endowed silicone rubbers with superior self‐healing properties. As compared with other self‐healing silicone rubbers based on hydrogen bonds or Diels–Alder reaction, this cross‐linked system shows high healing power. The materials are cut into two parts and put together in a mold for 1 h at 30 °C, observing a macroscopic healing and a strength recovery up to 87.0%.
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.
Novel nitrogen‐doped graphene nanoribbons (GNR‐Ns) are synthesized by the coupling reaction between a pyrazine (or benzene) derivative and naphthalene followed by cyclodehydrogenation. The amount of nitrogen doping in the GNR‐Ns is controlled by changing the monomer feed ratio of pyrazine to benzene for polymerization. The electron mobility of the GNR‐Ns increases while the hole mobility decreases, as the amount of nitrogen doping in the GNR increases, indicating that the charge‐transport behavior of GNRs is changed from ambipolar to an n‐type semiconductor. The threshold voltage of the GNR‐Ns also shifts from 20 to ?6 V as the amount of nitrogen doping increases.
Dendrigraft poly(l ‐lysine) (DGL) polyelectrolytes, obtained by iterative polycondensation of N‐trifluoroacetyl‐l ‐lysine‐N‐carboxyanhydride, constitute very promising candidates in many biomedical applications. In order to get a better understanding of their structure–property relationships in these applications, their absolute average molecular weights have to be accurately measured. Size‐exclusion chromatography coupled to a multi‐angle laser‐light‐scattering detector (SEC‐MALLS) is known to be the most appropriate analytical tool. These measurements require the determination of the refractive index increment, dn/dc, of these highly branched polycationic macromolecules in aqueous solution. This optical property has to be measured in the same aqueous conditions as SEC‐MALLS eluents. Consequently, data are determined and discussed as a function of different aqueous SEC‐MALLS eluents, as well as different counter‐ions of the many ammonium groups of DGL (generation 3, DGL‐3, used as a model herein). The resulting number‐average molecular weights, , are found to be very dissimilar when the measured dn/dc values are directly considered. In contrast, very close values are obtained (average = 18 700, standard error of 1110 g mol?1) with a low coefficient of variation for such data (ca. 6% for six analyses), when the dn/dc are corrected by the exact lysine amount (measured by the total Kjeldahl nitrogen method).
Graft polymers with poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as backbones are successfully prepared via two convenient steps. The utilization of semiflexible PPO as backbones offers unique properties for the graft polymers. Thermal, rheological, and phase behaviors of these new graft polymers are well controlled via the precise design of architectural parameters. The disordered microphase separation in melt state and the proper composition of side grafts provide the ease of thermal processing for these graft polymers. The graft density shows impact on the relaxation and mechanical properties of the thermoplastics. This work shows the possibility to use lots of semiflexible engineering polymers as backbones to construct new thermoplastics.
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.
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 fluorine‐containing difunctional benzoxazine is synthesized by hydrosilylation of a monofunctional benzoxazine based on o‐allylphenol and p‐fluoroaniline. Besides the intramolecular and intermolecular hydrogen bonding associated with the nitrogen and oxygen atoms in the oxazine ring, specific self‐complementary intermolecular Ar F···HO hydrogen bonding is formed in the polymerization of the benzoxazine, which leads to the resultant polybenzoxazine possessing a broad glass transition temperature range and showing two not well‐separated transitions. Based on the two glass transition temperatures, the polybenzoxazine exhibits triple‐shape‐memory behaviors by manipulating temperature and strain in the shape fixing process under tensile and bending modes. The dynamic mechanical and shape‐memory properties of the polybenzoxazine are influenced by the combined effect of the cross‐linking density and the Ar F···HO hydrogen bonding.
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.
Anionic polymerization of n‐butyl acrylate (nBA) in toluene initiated with a binary initiator, isopropyl α‐lithioisobutyrate/ethylaluminum bis(2,6‐di‐tert‐butylphenoxide) at ?60 °C, is terminated with ethyl α‐(chloromethyl)acrylate (ECMA) to afford a poly(nBA) possessing an acryloyl group at the terminal with 80% of termination efficiency. The reactivity of nBA against a polymer anion of methyl methacrylate formed under identical conditions is estimated relative to the termination with ECMA by reacting a mixture of nBA and ECMA followed by 1H NMR spectroscopic chain‐end analysis; the relative reactivity of nBA is found 80 times or more higher than ECMA.
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 ).
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.
In this work, an oxidation‐responsive thioether‐functionalized poly(N‐isopropylacrylamide) is reported, which is synthesized via reversible‐addition fragmentation transfer (RAFT) polymerization using 6‐(methylthio)hexyl acrylate or 2‐(methylthio)ethyl acrylate as comonomers and S‐ethyl‐S ′‐(a ,a ′‐dimethyl‐a ″‐acetic acid)trithiocarbonate as RAFT agent, investigating the influence over the lower critical solution temperature (LCST) of the random thioether functionalities, prior and upon oxidation. The hydrophobic thioethers shift the LCST values of the resulting copolymers to very low temperatures, but the value could be regulated upon oxidation due to the huge increase in dipolar moment. The resulting copolymers containing hydrophilic sulfoxides show much higher LCST values, reaching a difference of up to 23 °C after oxidation. Results are supported by 1H NMR, size exclusion chromatography, and turbidimetry measurements.
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).
Here, the synthesis, characterization, and photovoltaic properties of four new donor–acceptor copolymers are reported. These copolymers are based on 4,4‐difluoro‐cyclopenta[2,1‐b:3,4‐b′] dithiophene as an acceptor unit and various donor moieties: 4,4‐dialkyl derivatives of 4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene and its silicon analog, dithieno[3,2‐b:2′,3′‐d]‐silol. These copolymers have an almost identical bandgap of 1.7 eV and have a HOMO energy level that varies from ?5.34 to ?5.73 eV. DSC and X‐ray diffraction (XRD) investigations reveal that linear octyl substituents promote the formation of ordered layered structures, while branched 2‐ethylhexyl substituents lead to amorphous materials. Polymer solar cells based on these copolymers as donor and PC61BM as acceptor components yield a power conversion efficiency of 2.4%.
In this study, an effective way is presented to synthesize a mussel‐inspired adhesive from two inexpensive commercially available materials: polyvinyl alcohol (PVA) and 3,4‐dihydroxybenzoic acid via the esterification reaction and deprotection technology. This bioinspired adhesive exhibits good bonding ability on metal, glass, plastic, and wood, and the maximum bonding strength can be up to 4.0 MPa at dry conditions on glass substrate. Meanwhile, this adhesive can also be used as a wet/underwater adhesive. Such a PVA‐based bioinspired adhesive may be used as a potential candidate for applications in industrial field.
The development of chemicals from renewable sources as replacements for current toxic and unsustainable petrochemicals is an area of expanding study and interest. Phenolic epoxies derived from lignin, an underutilized resource generated as waste by the pulp and paper industry, and furanyl–amine epoxy curing agents derived from cellulosic biomass, are already proven independently to yield thermosetting resins possessing adequate thermal and thermomechanical properties. In this work, the union of the aforementioned technologies is examined to determine the properties and characteristics of such highly bio‐derived epoxy and amine thermosets. Resins with bio‐derived carbon content greater than 97% are synthesized and characterized via Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Lignin‐derived epoxy resins are found to be compatible with a cellulose‐derived furanyl diamine curing agent to produce thermosetting resins with good thermomechanical and thermogravimetric properties, rivaling the levels of properties exhibited by similar commercial petroleum‐derived systems, indicating viability for replacing petroleum‐based polymers in high‐temperature applications.
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.
A series of well‐defined hydroxypropyl methyl cellulose‐block‐poly(l ‐lactide) (HPMC‐b‐PLLA) diblock copolymers are synthesized via UV‐initiated thiol‐ene click reaction of thiol‐terminated HPMC with different block lengths and allyl‐terminated PLLA, using 2,2‐dimethoxy‐2‐phenylacetophenone as photocatalyst. The former is obtained by coupling the reducing aldehyde endgroup of short chain HPMC with the amine group of cysteamine, and the latter by ring‐opening polymerization of l ‐lactide in the presence of allyl alcohol. Fourier transform infrared (FT‐IR), nuclear magnetic resonance (1H NMR), and diffusion ordered spectroscopy NMR confirm the successful coupling of both blocks. The molar mass of the resulting copolymers ranges from 7000 to 12 800 g mol−1 as determined by size exclusion chromatography. The copolymers are able to self‐assemble in aqueous medium, yielding micelles of 50–100 nm with core–shell structure as evidenced by dynamic light scattering, transmission electron microscopy, and 1H NMR. The critical micelle concentration of copolymers ranges from 0.12 to 0.15 mg mL−1. Last but not the least, the copolymers exhibit thermoresponsive behavior with a lower critical solution temperature around 80 °C.
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