The importance of taking into account the principle of microscopic reversibility in the analysis of complex copolymerization systems is demonstrated. The analysis of a reversible copolymerization system in which segmental exchange is possible from the point of view of the reaction microreversibility proves that hetero‐reshuffling rate constants depend on homo‐reshuffling rate constants and copolymerization thermodynamics.
The adhesion and fracture of styrene‐acrylonitrile random copolymer and poly(methyl methacrylate) (PMMA/SAN) laminates were studied. They showed a drastic transition from brittle to ductile on varying the acrylonitrile (AN) content in SAN, with changes in the fracture mode from interfacial failure to cohesive fracture. Energy‐filtering transmission electron microscopy (EFTEM) and scanning electron microscopy (SEM) with an in‐lens detector system were employed to study the interface and adhesion of the laminates. The effect of the AN content in SAN on the PMMA/SAN interfacial structures could be revealed by imaging of the interfaces using elemental mapping and electron energy loss spectroscopy (EELS). The in‐lens detector system in the SEM enabled the differentiation of thin interfaces with poor adhesion strength, yielding smooth and flat fracture surfaces, where numerous nanosized fibrils were formed normal to the surfaces.
A generalized silica coating scheme is used to functionalize and protect sub‐micron and micron size dicyclopentadiene monomer‐filled capsules and polymer‐protected Grubbs' catalyst particles. These capsules and particles are used for self‐healing of microscale damage in an epoxy‐based polymer. The silica layer both protects the capsules and particles, and limits their aggregation when added to an epoxy matrix, enabling the capsules and particles to be dispersed at high concentrations with little loss of reactivity.
Summary: Laser‐induced fluorescence spectroscopy of the optical probe Nile Blue A in polymer clay nanocomposites is described. Concentration quenching of the fluorescence dominates the probe behavior until the clay platelets are physically separated by polymer intercalation. Further separation into an exfoliated structure results in an intense increase in probe fluorescence. Preliminary results indicate the ability to discriminate between intercalated and exfoliated structures in nanocomposites formed by melt processing.
Are hyperbranched polymers capable of forming entanglements? This is the central issue of this contribution. Hyperbranched polyglycerol (hbPG) samples with different molecular weights (600–106 000 g · mol−1), narrow polydispersities (1.2–1.8) and high degrees of branching (≈0.6) were prepared by anionic ring‐opening polymerization. The viscoelastic properties of these polymers with respect to molecular architecture and molar mass were investigated. At low molecular weights “classical” scaling behavior between zero shear viscosity and molecular weight can be observed, whereas between 3 000 and 10 000 g · mol−1 a plateau‐like area is found. The results indicate entanglement dynamics when exceeding a critical molar mass ( ≈ 20 000 g · mol−1) due to entangled hyperbranched polyglycerols.
The addition of a new mechanism to the Leonov model is described to capture the energy dissipation observed for highly filled systems even at very low strain values. By considering that flocs can undergo deformation before rupture, an internal reorganization within the agglomerates is introduced as a dissipative mechanism. The present improved model describes both oscillatory and strain sweep experimental results with only one additional, physically meaningful parameter: the number of hopping particles in the flocs which may be obtained from microscopic observations. Consistent values of this number are found in agreement with the histograms of the particle dispersion.
Summary: Nitroxide‐mediated polymerization of styrene in a continuous tubular reactor has been demonstrated for the first time. The polymerization kinetics in the tubular reactor are similar to those in a batch reactor. The number average molecular weight increases linearly with conversion, and chain extension experiments were successful, indicating that the living nature of the polymerization is maintained in the tubular reactor.
Evolution of molecular weight as measured by GPC for chain‐extended latex in continuous tubular reactor. 相似文献
Commercially available 1,2‐PB was transformed into a well‐defined reactive intermediate by quantitative bromination. The brominated polymer was used as a polyfunctional macroinitiator for the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline to yield a water‐soluble brush polymer. Nucleophilic substitution of bromide by 1‐methyl imidazole resulted in the formation of polyelectrolyte copolymers consisting of mixed units of imidazolium, bromo, and double bond. These copolymers, which were soluble in water without forming aggregates, were used as stabilizers in the heterophase polymerization of styrene and were also studied for their ionic conducting properties.
We reveal that a beam of low‐energy electrons (18 eV) can directly trigger long‐range molecular ordering of an amorphous, semi‐flexible oligomer in a few minutes without the prerequisite of pre‐orientation. A strong endothermic transition was detected with a micro‐thermal analyzer on the areas that had been exposed to the electron irradiation while the areas that were shielded from the irradiation by a protective mask remained amorphous as usual. This result suggests that long‐range molecular ordering only develops in the area of the oligomer film under electron irradiation. This is the first‐time effort to use electron irradiation to control the long‐range ordering of an amorphous organic thin film above the glass transition temperature.
