Summary: A new approach to the preparation of water soluble polymer in inverse miniemulsions is proposed. A redox initiation system consisting of ceric ions and carbohydrate‐based surfactant Span 60 as a reducing agent is successfully used for the polymerization of AAm. This initiation system provides chain nucleation and growth near interfacial boundaries. As a result, stable uniform latex with particle radius of about 50–70 nm is obtained. The prepared PAAm has a rather high of up to about 2 × 106 Da.
In this communication, β‐cyclodextrin modified quantum dots were used as a water‐soluble “supramolecular” cross‐linker (SCL) because of its surface's supramolecular activity. The guest monomer‐loaded SCL (mSCL) can be used to copolymerize with water‐soluble monomers leading to transparent hybrid supramolecular hydrogels. This simple and versatile method opens new venues for the preparation of hybrid supramolecular hydrogels and the host–guest chemistry of cyclodextrins.
The use of decatungstate in combination with silanes to generate silyl radicals under green fluorescence bulb irradiation as well as sunlight exposure is described. The mechanisms are investigated by ESR and laser flash photolysis experiments. The high potential of this reaction is evidenced here when using a decatungstate/silane/diphenyl iodonium salt combination as an initiating system for the ring opening photopolymerization of epoxides.
Summary: Dienic elastomers are highly sensitive towards oxidation. During UV exposure, both scission and/or recombination reactions compete which involves an evolution of the molecular structure of the material. We developed an in situ technique to monitor the viscoelastic property changes upon UV irradiation of polymers in a single experiment. We illustrated this photorheology technique in the case of two kinds of elastomers. From our findings, this method is assumed to bring significant new advantages.
Photograph of the photorheometer used in this study. 相似文献
A novel helical poly(macromonomer) [poly(M‐PS): absolute = 82 800–252 000, determined by GPC/RALLS] with a polyacetylene main chain and polystyrene (PS) side chains was synthesized by the polymerization of acetylene‐terminated M‐PS [ = 2 000, / = 1.20, = 18] with an Rh catalyst. M‐PS was prepared by ATRP of styrene using the acetylene‐containing initiator 2‐bromo‐2‐methylpropionic acid (S)‐1‐methylpropargyl ester ( l ). In solutions, poly(M‐PS) exhibited an intense CD signal at 345–355 nm, indicating that it possessed a predominantly one‐handed helical conformation. Poly(M‐PS) had a stable helical conformation irrespective of solvents and temperature.
Kinetic Monte Carlo studies (confirmed by integration of the corresponding differential equations) are used to demonstrate the fundamental differences between the two most often accepted schemes of segmental exchange. Modeling of reshuffling systems, originally composed of homopolymers of various , various mass distributions, and different compositions, is carried out until the equilibrium copolymers are obtained. It is shown that one of the schemes leads always to a random microstructure (Bernoulli statistics) whereas modeling of the other one indicates possibility of formation of all achievable distributions of comonomer units (from multiblock to nearly alternate). The concepts of the degrees of randomness and reshuffling are discussed and new definitions are proposed.
Summary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non‐fractionated polymer. The Δnind value decreases by increasing the degree of polymerization ( ) within the oligomeric range but becomes independent of molecular weight starting from a of ≈70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording.
Birefringence induced after 10 min, Δnind(600) and its growth rate at the same moment versus molecular weight. 相似文献
Polyaniline nanodisks have been synthesized successfully by the chemical oxidation polymerization of aniline by a self‐assembly process without the use of any acid. The thickness and lateral dimensions of the polyaniline nanodisks are in the range of 20–30 nm and 1–2 µm, respectively. The influence of synthetic parameters, such as the concentration of ammonium peroxydisulfate and pH, on the morphologies of polyaniline nanostructures have been investigated.
Summary: RAFT is applied to the dendronized macromonomers of the first and second generation, 1 and 2 , respectively. Good results are obtained in the presence of AIBN as radical initiator, with compound 6 as mediator and at mediator to monomer ratios of 2:200 for monomer 1 ( = 320 000, PDI = 1.24) and monomer 2 ( = 178 000, PDI = 1.20). The common characteristics of a controlled polymerization are reasonably met. The more sterically demanding G2 monomer 2 requires higher polymerization temperatures.
Summary: We study the impact of topological disorder on the mechanical response of hyperbranched macromolecules from a theoretical and numerical perspective. The polymer models are generated using a bond switching algorithm, and the emerging systems are described within the Zimm and Rouse pictures of macromolecular dynamics. The topological disorder is manifest in the frequency‐dependent dynamic moduli, . These are clearly distinct from that of regular hyperbranched fractals of the same size, and they do not obey simple scaling rules. The dynamic moduli reflect the short‐range order inherent in the model, and we thus suggest that the extent of disorder in branched tree‐like polymers may be well‐estimated experimentally using .
Summary: Magnetic nanoparticles have been prepared by a co‐precipitation method and modified with methacryloxypropyltrimethoxysilane. Magnetic molecularly imprinted polymer particles have been prepared by suspension polymerization in silicone oil. The particles possess a high affinity to the template molecules and are rapidly separated under a magnetic field.
Summary: A p–n di‐channel copolymer based on polyfluorene (PF) has been designed and prepared. Branches containing oxadiazole units are attached to the PF backbone through the spiro‐structure and act as channels to improve the electron affinity; these branches form a steric ‘di‐channel’ framework with the polymer backbone. The polymer possesses excellent thermal stability. The lowest unoccupied molecular orbital energy level of the polymer is significantly altered in comparison with poly(9,9‐dioctylfluorene‐2,7‐diyl).
Schematic of the di‐channel polyfluorene synthesized here and the mechanism of energy transfer through the structure. 相似文献
Summary: A new strategy was developed to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight‐average molecular weight ( ) of 1 900 was adopted to modify the clay. The modified clay slurry was then mixed with silicone rubber by hand, and exfoliation was achieved. The proposed mechanism thereof was verified by TEM and XRD. The physical entanglement of the soft siloxane surfactant plays a vital role in the diffusion and intercalation of the matrix molecules during the compounding of the slurry‐polymer mixture. This simple method is applicable to other silicone‐based materials reinforced by clay.
TEM micrograph of silicone rubber/clay‐sil nanocomposite. 相似文献
The synthesis of hyperbranched poly(ethylene glycol) (hbPEG) in one step was realized by random copolymerization of ethylene oxide and glycidol, leading to a biocompatible, amorphous material with multiple hydroxyl functionalities. A series of copolymers with moderate polydispersity ( < 1.8) was obtained with varying glycidol content (3–40 mol‐%) and molecular weights up to 49 800 g mol−1. The randomly branched structure of the copolymers was confirmed by 1H and 13C NMR spectroscopy and thermal analysis (differential scanning calorimetry). MTS assay demonstrated low cell toxicity of the hyperbranched PEG, comparable to the highly established linear PEG.
A fast method is presented for the calculation of the MSD and the MWD of polymers obtained via step‐growth polymerization of polyfunctional monomers bearing identical reactive groups (i.e., systems of type “Afi”). Using this method, the complete distribution can be calculated rapidly, not just the statistical averages of the polymer population such as or . The computed MSD and MWD give more insight than these averages and can be compared to similar data measured on actual polymer systems. The low‐ and intermediate molecular size/weight part of the distribution curves are calculated using a recurrence scheme, while the high‐molecular tail (large and very large polymers) of the distributions is derived from an asymptotic approximation of the associated generating functions.
