Summary: Here we report about the synthesis of colloidal particles of nematic and smectic liquid‐crystalline polymers. For this purpose mesogen‐containing acrylate monomers were synthesized and polymerized in a special modification of a precipitation polymerization called dispersion polymerization. By variation of the polymerization conditions colloidal particles of different size and polydispersity could be obtained including very narrowly distributed samples in optimized batches. On azobenzene‐containing colloidal particles switching experiments with polarized light were performed. It could be observed that the nematic director of the mesogens within the colloidal particles can be rotated due to the photochemical trans‐cis‐isomerization of the azobenzene chromophores.
The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous‐flow processes involving microreactors found various applications in chain growth polymerization, their influence on step‐growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from = 1 900 to 11 000 g · mol?1. Thus, the microreactor setup offers for the first time the possibility to synthesize PSSQ with adjustable properties.
Summary: Stabilized nanoparticles functionalized with carboxy groups were synthesized directly from dextran and acrylic acid (AA), without using any organic solvent and surfactant. The composition and morphology of these dextran‐based nanoparticles, as well as the mechanism of this one‐pot synthesis, were also investigated in this paper. This approach is anticipated to be applicable to various water‐soluble polysaccharides to fabricate nanoparticles facilely.
Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA. 相似文献
The present article briefly reviews research developments in the area of biomacromolecules and bio‐related macromolecules, whose research papers have been published for several decades preferably in the Macromolecular Journals. The area covers the important classes of macromolecules, polysaccharides (cellulose, amylose, chitin, etc.), polyesters (poly(lactic acid), poly(hydroxyalkanoate)s, etc.), and phenolic polymers (lignin, urushi, etc.). These polymers and their derivatives are very important for scientific interests as well as for industrial applications. Their synthesis, structure, reactions, and properties are mainly mentioned, and important topics of the target polymers are selected and mostly chronologically reviewed.
Summary: Degradation studies of cis‐1,4‐polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end‐functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well‐defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a range of from 10 000 to 30 000, with a polydispersity index of around 2.5.
Structure produced by the metathetic depolymerization of hydroxy telechelic cis‐1,4‐polyisoprene. 相似文献
The concept of micellar catalysis was transferred to the hydroaminomethylation of 1‐octene with N,N‐dimethylamine. In the first series of experiments a rhodium(I ) complex with amphiphilic triphenylphosphane functionalized poly(2‐oxazoline)s as macroligand was applied as catalyst. Results obtained under standard hydroformylation conditions (T = 100 °C, p = 50 bar) were not satisfying with regard to activities and selectivities of the hydroaminomethylation reaction. Rising the temperature to 150 °C increased the yield of amine to 22% with a corresponding n/iso selectivity of 7.5 and a TOF number of 461 h?1. Best results were obtained by applying a dual Rh/Ir catalyst within the polymeric micelles leading at lower temperature of 130 °C to an amine yield of 24% with a corresponding n/iso selectivity of 11 and TOF numbers of about 600 h?1.
A microwave‐assisted method of synthesizing high‐molecular‐weight PLA using SSA as green catalyst was developed. Yellowish PLA with above 2.0 × 104 g · mol?1 was obtained when the reaction was run at 260 °C within 60 min under microwave irradiation with 0.4 wt.‐% SSA. This method used only 10% of the energy consumption necessary for conventional heating, and the catalyst could be used five times without losing catalytic activity. The improvement in and the decrease in the energy consumption under microwave irradiation suggested that selective heating and hot spots effects played a crucial role. The method was shown to be a time‐saving, green and a promising way to lower the cost and spread the application of PLA.
Two new donor/acceptor copolymers PBDTPhBT1 and PBDTPhBT2 with alternating benzodithiophene ( BDT ) and bisthiophene‐phthalimide ( PhBT ) units were synthesized by Stille coupling reaction. The copolymers showed identical optical bandgaps of 1.98 eV. The HOMO energy levels are ?5.35 and ?5.32 eV for PBDTPhBT1 and PBDTPhBT2 , respectively. The bulk heterojunction solar cell devices based on these copolymers as donors and PC71BM as acceptor displayed high open‐circuit voltages of 0.90–0.93 V and achieved power conversion efficiency of 1.54% under the illumination of AM 1.5, 100 mW · cm?2.
Summary: A dipolar filter pulse sequence combined with cross‐polarization‐MAS is applied to characterize the phase distribution, morphology, and spin diffusion within a high‐density polyethylene sample. A new method to obtain quantitative 13C NMR by combining cross‐polarization‐MAS and spin diffusion NMR is presented. The derived crystallinity is consistent with the corresponding crystallinity obtained by 1H NMR.
Illustration of the pulse sequence(s) applied in the present work. 相似文献
Summary: Solid‐state olefin metathesis of rigid‐rod acyclic diene metathesis (ADMET) polymers and ring‐closing metathesis (RCM) have been investigated. 1,4‐Dipropoxy‐2,5‐divinylbenzene ( 4 ) was synthesized and used in a bulk ADMET polymerization to produce oligomers of dialkoxy poly(phenylene vinylene). The reaction was continued in the solid state, effectively doubling the molecular weight. Solid‐state RCM was investigated with a variety of solid dienes and metathesis catalysts, and demonstrated in low conversions using amide diene 5 with catalysts 9 , 13 , and 14 .
Summary: A new method for the measurement of monomer partitioning for emulsion polymerisation is presented. The method is based on measuring the partition coefficients for films cast from different latexes. Its validity was demonstrated for methyl methacrylate (MMA) and butyl acrylate (BA), as well as for mixtures of these two species, by comparing the data to model predictions using literature data. The model predictions and experimental results agreed quite well for MMA, but less so for BA due to its extremely low water solubility.
pH‐sensitive micelles formed by interchain hydrogen bonding of poly(methacrylic acid)‐block‐poly(ethylene oxide) copolymers were prepared and investigated at pH < 5. Both and Rh of the micelles increase with decreasing pH of the solution, displaying an asymptotic tendency at low pH values. The observed micelles are well‐defined nanoparticles with narrow size distributions (polydispersity ΔRh/Rh ≤ 0.05) comparable with regular diblock copolymer micelles. The CMCs occur slightly below c = 1 × 10?4 g · mL?1. The micelles are negatively charged and their time stability is lower than that of regular copolymer micelles based purely on hydrophobic interactions.
Summary: The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymers based on poly(ethylene glycol) and poly(ε‐caprolactone) were synthesized. Micelles of star‐shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady‐state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di‐, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4‐arm star‐shaped block copolymers than for di‐ and 3‐arm star‐shaped block copolymers, which qualitatively agrees with the experiments.
Ozonolysis of unsaturated polymers produced useful telechelic oligomers that can form building blocks for networks and block copolymers. The unsaturated polymers can be prepared by semicontinuous emulsion polymerization with dienes, and here it is shown that the addition of cyclodextrins enhanced the incorporation of these comonomers. Both α‐ and β‐cyclodextrin provide copolymers with higher fractions of butadiene (BD) incorporated into the chain but α‐cyclodextrin had the highest levels of incorporation. Oxidative work up after ozonolysis produced latexes of carboxylic acid oligomers of different molar masses. A clear effect of polymer size on toxicity was observed with the oligomers with < 2 700 g · mol.?1 proving to have similar cytotoxic effects to lactic acid. However, oligomers with above 2 700 g · mol.?1 were cytocompatible and gave similar results to a polylactide control material.
A historical overview of the role of NMR spectroscopy in macromolecular science in general and its coverage in “Macromolecular Chemistry and Physics” in particular is given. In the early days physics‐application to study molecular dynamics, partial alignment of macromolecules and phase separation prevailed, deduced from broad‐line solid‐state NMR. Only somewhat later, high‐resolution NMR in solution was established as an important tool for elucidating the chain microstructure. In the future, these two aspects are expected to merge.
Side group liquid crystalline polymers: 2H NMR has elucidated alignment and dynamics of these complex materials. 相似文献
Novel polymer cladding materials were synthesized and their potential for use in optical waveguide devices was investigated. 9‐[2‐(2,3,5,6‐Tetrafluoro‐4‐vinylphenoxy)ethyl]‐9H‐carbazole and 1‐pentafluorophenylpyrrole‐2,5‐dione were used as comonomers for preparing the acrylic cladding copolymers. These showed a low resistivity (≈2 × 1013 Ω · cm) at room temperature and a low optical loss (?0.6 dB · cm?1) at a wavelength of 1.55 µm. The refractive indexes and the glass transition temperatures of the polymer cladding materials can be controlled by the composition of the copolymers. The resulting polymers are good candidates for cladding materials for practical applications in devices.
Summary: A novel copolymer containing perylene bisimide and porphyrin units was synthesized through a Wittig‐type coupling reaction and characterized. An electrochemical experiment showed its electronic properties. Optoelectronic measurements showed a steady and rapid cathodic photocurrent response of the polymer film. The features of copolymer colloids were also studied by UV‐Vis spectrometry and TEM. A large quantity of nanoparticles were observed with TEM, with a mean diameter of 200 nm. The size effect leads the absorption wavelength of the nanoparticles to be red‐shifted, which is consistent with the results of UV‐Vis spectrometry.
Poly(ethylene azelate) (PEAz) was synthesized and its melting behavior was studied with DSC and Step Scan DSC. The equilibrium melting point of PEAz was found 62 °C and the heat of fusion of 100% crystalline polymer was estimated at 160 J · g?1. Polarized light microscopy showed mixed birefringence. From isothermal crystallization DSC study, after self‐nucleation, crystallization rates were estimated. The Lauritzen–Hoffman plots showed crystallization regime I to II and II to III transition at 34 and 19 °C respectively. Non‐isothermal crystallization was studied. The activation energy was calculated applying the isoconversional method of Friedman. Chemical hydrolysis of PEAz was very slow, while enzymatic hydrolysis showed comparable rates with PCL.
Summary: Latent reactivity has been employed to create processable elastomers constructed of carbosilane and either carbosiloxane or polyether segments. Two types of latent modes have been introduced: “chain‐internal” and “chain‐end” sites through the use of labile silicon methoxy and trifunctional olefinic functionalities. These latent reactive sites remain inert during formation of the linear copolymer; subsequent exposure to moisture triggers hydrolysis of the methoxy group and formation of a chemically crosslinked thermoset. These “chain‐end” sites limit the formation of dangling chains improving the overall mechanical properties of the material. The thermoset's mechanical response can be potentially varied from plastic to elastic behavior, depending on the ratio of hard and soft monomers employed. The concentration of “chain‐internal” and “chain‐end” crosslink sites enhances strength; modification to the run length and structure of the soft phase enhances elasticity, generating samples having moduli of 6 MPa, tensile strengths of 0.6 MPa and elongations of 400%.
Summary: The average lateral dimensions of cellulose microfibrils in paper sheets can be determined from the width of X‐ray Bragg peaks at half the maximum height. The method assumes it is the finite size of the crystallite which is the main contributor to peak broadening in the directions orthogonal to the long axis of the crystallite. This assumption is examined in the context of samples from different botanical sources, of varying crystallinity and cellulose content and the various instrumental sources of broadening X‐ray powder patterns. Excellent fits to the data from paper samples can be obtained by using five Voigt functions to the powder diffraction patterns, for the 101, , 021, 002 and 040 reflections. Of these reflections, the 020 is the clearest, and the best able to determine the lateral dimension of the crystallite. Results indicate that the size of microfibrils is dependent on the botanical source of the fibres.
