Summary: The fracture properties of polymers are one of the key parameters that define their service life and limit their applications. One of the most interesting and important questions is how the molecular architecture and the structure of polymers at nanolength scales influence their fracture properties. X‐ray scattering is a powerful means of probing bulk structures at the nanometre scale. It can therefore provide a wealth of information relating to such structure‐property relationships. In the present study, synchrotron radiation microfocus small‐angle X‐ray scattering is used to investigate the damage area ahead and around the crack tip in polyamide 6 (PA6). The results reveal that the damage area propagates far beyond the visible crack, and inside the damaged zone platelet‐shaped cracks/voids are formed.
We propose a theoretical explanation of the parallel and perpendicular lamellar orientations in free surface films of symmetric polystyrene‐block‐polybutadiene diblock copolymers on silicon substrates (with a native SiOx layer). Two approaches are developed: A correction to the strong segregation theory and a qualitative analysis of the intermediate segregation regime. We show that the perpendicular orientation of the lamellae formed by the molecules of high molecular weight is stabilized by A–B interfacial interactions. They are weaker in the case of the perpendicular orientation of the lamellae, whereas the surface tension coefficient of the A–B interface decreases with the increase of the molecular weight.
Sixteen parallel polymerization reactions of 2‐ethyl‐2‐oxazoline have been performed at different temperatures in an automated synthesizer that allowed individual heating of each reactor. During the reactions samples were taken automatically, which were characterized by means of both online GPC and offline GC, in order to optimize the reaction temperature and to determine the activation energy of the polymerization.
Summary: Amphiphilic graft polyphosphazenes (EtTrp/PNIPAm‐PPP) with different mole ratios of hydrophobic groups to hydrophilic segments were synthesized by ring‐opening polymerization and subsequent substitution reactions. The self‐assembly behavior of these graft copolymers was studied in detail by TEM, SEM, CLSM, and AFM. Depending on the copolymer composition and common organic solvent employed in dialysis process, supramolecular aggregates ranging from network, nanospheres, high‐genus particles to macrophage‐like aggregates were produced with graft copolymers.
Transparent film materials with excellent mechanical and thermal properties were elaborated by drying a latex suspension of armored polymer/Laponite composite particles. Low‐temperature TEM observation of ultrathin cross‐sections of the films indicated a unique network morphology characterized by a “honeycomb” distribution of the Laponite platelets remindful of the original particles morphology.
We describe an enzyme‐responsive polymeric vehicle, which is of great interest in controlled drug delivery, biosensing, and other related areas. The polymer synthesized using lipase as catalyst in DMSO has a favorable molecular structure that is quickly hydrolyzed by lipase in aqueous phase, and allows a fast release of encapsulated molecules.
Polymerizable vinylimidazolium ionic liquids (ILs) that contain mesogenic coumarin and biphenyl units, respectively, have been synthesized. The N‐alkylation of N‐vinylimidazole with bromoalkylated mesogenic units 7‐(6‐bromohexyloxy)coumarin ( 1 ) and 4,4′‐bis(6‐bromohexyloxy)biphenyl ( 2 ) was then carried out. The thermal behavior of the obtained ILs 3 and 4 was investigated by differential scanning calorimetry and polarizing optical microscopy. These measurements showed that the attached mesogenic units induce the self‐assembly of ILs and, therefore, the occurrence of liquid crystalline phases. Subsequently, the ionic liquid crystals (ILCs) 3 and 4 were polymerized by a free‐radical mechanism.
Mussel adhesives function as tools for surface modifications of a wide variety of materials due to their remarkable adhesion properties. Herein, a combination of bioinspired mussel adhesives based on a dopamine derivative, polymer chemistry, and well‐established Diels–Alder (DA) chemistry leads to a bioinspired switchable surface system that possesses the capability of attaching and detaching specific polymers on demand. A dopaminemaleimide compound, which has been attached to a gold surface under maritime conditions undergoes DA‐ and retro‐DA‐click‐conjugations with cyclopentadiene‐carrying PEG chains. The surface attachment and the subsequent DA/rDA cycles are evidenced via XPS analysis.
Summary: Tetraaniline‐block‐poly(L ‐lactide) diblock oligomers are synthesized via ring‐opening polymerization. The diblock oligomers cast from an L ‐lactide selective solvent (chloroform) show spherical aggregates for the leucoemeraldine state, and ring‐like structures that are composed of much smaller spherical aggregates for the emeraldine state. The formation mechanisms of the two different surface morphologies are discussed in detail.
Surface morphology changes induced by oxidation of the aniline segment of tetraaniline‐block‐poly(L ‐lactate) and drying effects. 相似文献
The free volume (voids) distribution in the lamellae of the conventional symmetric and amphiphilic diblock copolymers is studied via Monte–Carlo simulation based on the standard bond fluctuation model. Both in the conventional and amphiphilic block copolymers the voids are found to concentrate on the interfaces between the incompatible units, the magnitude of the effect being unexpectedly significant. A crystalline‐like ordering of voids with increase of the incompatibility between the different repeated units in amphiphilic copolymers is first reported and implications of this peculiarity for the morphology and mechanical properties of the amphiphilic copolymers are discussed.
The mechanistic interpretation of kinetic anomalies in reversible addition–fragmentation chain transfer (RAFT)‐mediated polymerization is critically reviewed. The main conclusion of this exercise is that available data do not allow model discrimination between the two prevailing mechanistic schemes, i.e., the slow fragmentation model and the intermediate radical termination model. However, assessment of the rate parameters reveals that the incompatibilities may not be as large as previously reported in literature. Dedicated kinetic studies on model compounds should be performed to shed further light on the seemingly incompatible data that currently exists in literature.
Based on the Hammett equation, a general method is established to relate the polycondensation monomer reactivity with both the monomer structural parameters and the properties of the solvent used for the non‐equilibrium ternary copolycondensation to give copolyamides. Linear plots of the logarithm of the monomer reactivity ratio, log r, versus structure parameter ΔpK could be represented by the equation log r = ρΔpK.
Relationship between log r and ΔpK using THF as the solvent. 相似文献
Summary: We describe an interesting approach to the fabrication of wettability gradients from hydrophobicity to superhydrophobicity in low‐density polyethylene (LDPE) films by first forming high porosity surfaces and placing the specimens onto linear temperature gradients. While the polymer chosen for the study is non‐polar, its microporous layer provides sufficient superhydrophobicity. Lateral gradient heating of the layer results in partial melting of the polymer and correspondingly decreases porosity thus decreasing hydrophobicity.
A new sol‐gel hybrid film based on heterocyclic chromophore, namely 2‐[4′‐(N‐ethyl‐N‐hydroxyethyl)amino phenyl azo]‐4,5‐dicyanoimidazole (IZ), has been synthesized and characterized. The hybrid system possesses a high chromophore loading density up to 65 wt.‐% without observing a phase separation. The initial decomposition temperatures of the chromophore and hybrid material were determined to be 260 and 272 °C, respectively. Poled films show a fairly high and stable nonlinear optical (NLO) response, even at an elevated temperature.
Summary: In this study, a method for producing super‐amphiphobic surfaces through plasma modification of benzoxazine films is presented. Microroughening and fluorination of the benzoxazine films occurs during the plasma treatment process and a rugged surface with a micro/nano binary structure is formed. The combined effect of low surface energy and substrate roughness results in high advancing contact angles (157° for water, 152° for diiodomethane) and low contact angle hysteresis.
SEM image of a cross‐linked polybenzoxazine film treated with Ar plasma (7 min) heated to 200 °C (1 h) and treated with CF4 plasma for 30 s. 相似文献
Summary: A new class of poly(arylene ethynylene)s (PAEs) containing an electron‐deficient N‐alkylphthalimide unit was prepared by means of a Sonogashira reaction. Complete solubility of the PAEs was observed by utilizing a 2,6‐diisopropylphenyl side chain. The chemical structure of the novel soluble polymer 3c was confirmed by NMR spectra, whereas the insoluble polymers were characterized by elemental analysis and IR spectra. Fluorescence measurements of 3c indicate a rigid structure and high symmetry in the excited state.
One of the most important events in free‐radical emulsion polymerization is desorption of radicals from the polymer particles to the aqueous phase. Desorption takes place by diffusion of radicals inside the particle toward the surface and transfer to the aqueous phase. The rate of desorption can be determined theoretically for homogeneous spherical particles. For more complex cases, analytical solutions become difficult or impossible to obtain and a numerical approach is better suited for estimating desorption rate coefficients. In this paper, Brownian dynamics simulation is used for the estimation of desorption rate coefficients in emulsion polymerization systems of increased complexity, in particular for non‐homogeneous polymer particles.
One‐dimensional methyl orange fibrils can be easily prepared. They are stable in acidic aqueous solutions and soluble in neutral water. When used to synthesize conducting polymer microtubules, the fibrils act as “hard templates” formally but as “soft templates” effectively. Microtubular structures of polypyrrole, polyaniline, and poly(3,4‐ethylenedioxythiophene) have been achieved successfully via such water‐soluble versatile templates.
