Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.
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).
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.
In this study, the bifunctional hydroxyketone based photoinitiator (PI) 1,1′‐{[(2,3‐dihydroxybutane‐1,4‐diyl)bis(oxy)]bis(4,1‐phenylene)}bis(2‐hydroxy‐2‐methylpropan‐1‐one) (Di‐PI) is synthesized with the aim to facilitate a highly photoactive water‐soluble PI which offers high migration stability. Di‐PI provides a five times higher water‐solubility than the state of the art water soluble PI 2‐hydroxy‐1‐[3‐(hydroxymethyl)phenyl]‐2‐methyl‐1‐propanone (I2959). Photo differential scanning calorimetry (Photo‐DSC) measurements reveal that the curing speed and conversion of N‐acroylmorpholine (NAM) in aqueous solution containing 0.5 mol% of Di‐PI are only slightly lower than formulations containing the reference PI I2959 in a concentration of 1 mol%. Most importantly, Di‐PI offers almost identical activity in dipropylene glycol diacrylate (DPDA) as I2959, although its migration from cured DPDA is significantly reduced by a factor of 7.6 compared to I2959.
The thermostable α‐glucan phosphorylase‐catalyzed enzymatic α‐glucuronylation and subsequent α‐glucosaminylation of glycogen using α‐d ‐glucuronic acid 1‐phosphate (GlcA‐1‐P) and α‐d ‐glucosamine 1‐phosphate (GlcN‐1‐P), respectively, produce amphoteric glycogens. The products exhibit the inherent isoelectric points, which change depending on the GlcA/GlcN ratios. Chain elongation of amyloses from the nonfunctionalized, nonreducing ends of the products through the thermostable α‐glucan phosphorylase‐catalyzed enzymatic polymerization of α‐d ‐glucose 1‐phosphate monomers is demonstrated to yield amphoteric glycogen hydrogels. The produced hydrogels exhibit pH‐responsive behavior.
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.
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.
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.
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.
Melting and reorganization of conformationally disordered crystals (α′‐phase) of poly(l ‐lactic acid) (PLLA) are analyzed as a function of the rate of heating in a wide range between about 10?1 and 103 K s?1. It is found for the first time that the reorganization of conformationally disordered α′‐crystals into stable α‐crystals can be suppressed by fast heating. Heating of α′‐crystals of PLLA at a constant rate, faster than 30 K s?1, leads to its complete melting between 150 and 160 °C and suppression of formation of α‐crystals on continuation of heating. Non‐isothermal reorganization of α′‐crystals into α‐crystals only occurs when heating at a rate slower than 30 K s?1. It is evidenced that isothermal reorganization of α′‐crystals into α‐crystals at 150–160 °C proceeds via melting followed by recrystallization rather than a solid–solid phase transition.
Star‐shaped poly(2‐isopropyl‐2‐oxazolines) with dramatically hydrophobic dendrimer core are synthesized using carbosilane dendrimers of first to third generations as macroinitiators. It is observed that half of the initiator functional groups are incorporated in polymerization process. The polymerization degree of polyoxazoline arms is about 25. Strong arm folding results in small molecule dimensions in both aqueous and organic solutions. Thermosensitive properties are studied for second generation‐based star solution with the concentration of 0.00095 g cm−3. Model linear poly(2‐isopropyl‐2‐oxazolines) are investigated for comparison. Carbosilane dendrimer core interaction leads to the formation of different types of aggregates at low temperatures. The temperatures of the beginning (T 1 = 42–43 °C) and finishing (T 2 = 50 °C) of phase separation are determined. It is shown that macromolecule compactization and aggregation take place even far from the phase transition interval and alternately prevail on heating.
A new block‐co‐polymer based on poly(arylene ether sulfone) and nitrile‐functionalized poly(phenylene oxide) is prepared via polycondensation. Upon swelling with Li triflate dispersed in succinonitrile, a polymer electrolyte suitable for application in secondary Li ion batteries is obtained, which at temperatures above 313 K exhibits conductivities of 10?4–10?3 S cm?1. The presence of distinct coordination modes of the Li ions (not discernible from inspection of 7Li chemical shifts) is revealed based on a dynamic contrast identified from a distribution of transverse relaxation times. Three relaxation components reflecting polymer‐bound, partially and fully solvated Li ion species are identified on the basis of Carr–Purcell–Meiboom–Gill NMR data after inverse Laplace transformation and multiexponential relaxation analysis toolkit analysis thus highlighting the versatility of the applied methods.
Histidine–zinc interactions are believed to play a key role in the self‐healing behavior of mussel byssal threads due to their reversible character. Taking this as inspiration, the authors synthesize here histidine‐rich copolymers, as well as model histidine compounds and characterize them using isothermal titration calorimetry (ITC). With this approach, the influence of two different zinc(II) salts and the role in the complex formation of the amine function of the imidazole ring are investigated in detail. The extracted metal–ligand ratios are utilized to design novel self‐healing metallopolymers. For this purpose, n‐lauryl methacrylate is copolymerized with the histidine monomer via reversible addition‐fragmentation chain transfer polymerization. The copolymers are crosslinked using different zinc salts, and the resulting coatings are characterized with Raman spectroscopy to investigate the metal coordination behavior and with scratch healing tests to investigate the self‐healing capacity. Finally, the self‐healing behavior of the different materials is correlated with the metal–ligand binding affinity measured by ITC.
Synthesis of densely grafted (co)polymer brushes, including poly(n‐butyl acrylate), poly(2‐dimethylaminoethyl methacrylate), poly(n‐butyl acrylate)‐block‐poly(tert‐butyl acrylate), and poly(2‐dimethylaminoethyl methacrylate)‐block‐poly(tert‐butyl acrylate) from silicon wafer surfaces via a simplified surface‐initiated electrochemically mediated atom transfer radical polymerization under constant potential/current conditions is reported. A sacrificial (nontethered) initiator is added to form free polymer chains in solution used to estimate the molecular weights and molecular weight distributions of chains attached to the surface. The polymers show narrow molecular weight distributions (Đ = 1.10–1.33). Water contact angle measurements and ellipsometry are used to characterize wettability and thicknesses of the modified surfaces. Grafting densities up to 0.93 nm−2 are obtained. The rate of the polymerization is controlled by applying more negative potential values, which results in an increase in the surface thickness (up to 116 nm). Finally, the poly(tert‐butyl acrylate) blocks are hydrolyzed to the poly(acrylic acid) blocks. These new, densely grafted brushes are promising candidates for applications in microelectronics, nanotechnology, tailoring of surface properties, nanopatterning, or antifouling coatings.
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).
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.
A family of novel (X‐TATAT)n‐type conjugated polymers based on the carbazole (X), thiophene (T), and benzoxadiazole (A) moieties is designed and explored as electron‐donor materials for organic bulk heterojunction solar cells. Incorporation of the branched side chains of different size and shape affects significantly the optoelectronic properties of the materials, particularly frontier energy levels of polymers translated to the open circuit voltages of the photovoltaic cells. The revealed unprecedented correlation between the parameters of the solar cells (V OC, fill factor (FF), J SC) and bulkiness of the alkyl side chains provides useful guidelines for rational design of novel materials for organic photovoltaics.
N‐vinylcaprolactam (NVCL) is modified via alkylation at the α‐position. The α‐substituents are ethyl (3‐ethyl‐1‐vinylcaprolactam), dodecyl (3‐dodecyl‐1‐vinylcaprolactam), octadecyl (3‐octadecyl‐1‐vinylcaprolactam), 1‐propanol (3‐(3‐hydroxy‐propyl)‐1‐vinylcaprolactam), and PEG3 bromide (3‐PEG3‐bromide‐1‐vinylcaprolactam). These monomers are homo‐ and copolymerized with N‐(4‐methylphenyl)maleimide by the free radical mechanism. The structures of the obtained polymers are characterized by means of 1H NMR and IR spectroscopy, gel permeation chromatography (GPC), and by use of differential scanning calorimetry (DSC) (Tg).
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.
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