Summary: Although controlled/living radical copolymerization has been extensively studied, the control of copolymer composition distribution receives little attention. In this paper, taking RAFT copolymerization as an example, we develop a mathematical model and simulate copolymerization systems with various reactivity ratios. It is demonstrated that through semi‐batch operations with programmed profiles of slow monomer feeding rate, precise control over copolymer composition distribution (uniform and designed gradient distributions) along polymer chain can be achieved. It is also found that the semi‐batch operations have lower rates of polymerization than their batch counterparts. The reason for this difference is analyzed, and the magnitude depends on the reactivity ratios and targeted copolymer composition. The improvement of the semi‐batch rate by distributing a part of the initiator amount to the monomer feeding tank is found to be minor.
Model‐based design and control over composition distribution of gradient copolymers implemented by semi‐batch operations. 相似文献
The photomechanics of azobenzene LCNs is modeled using a nonlinear continuum mechanics approach that couples photoisomerization of liquid crystal domain structures with light absorption and deformation of a glassy polymer network. The effects during UV‐stimulated trans–cis photomechanical deformation versus blue‐green light (trans–cis–trans) photomechanical deformation are simulated. Different bending deformation is predicted by assuming liquid‐crystal order/disorder behavior during trans–cis photoisomerization in comparison to light‐polarization‐driven reorientation of the trans phase during potential trans‐cis‐trans photoisomerization. Light‐controlled deformation mechanisms offer support for improved control of photo‐responsive morphing structures with a single blue‐green polarized light source.
We report for the first time the preparation of single polypyrrole (PPy) molecule chains using a “metal‐organic framework” with 1 nm channels as a template. The obtained one‐dimensional (1‐D) PPy has highly structure order and excellent conductivity, which has improved by as much as five orders of magnitude in comparison with that of 2‐D PPy.
The copolymerization parameters of N‐(isopropyl)acrylamide ( 1 ) and N‐(2‐hydroxy‐5‐(1‐(4‐hydroxyphenyl)‐3‐oxo‐1,3‐dihydroisobenzofuran‐1‐yl)benzyl)acrylamide ( 2 ) are determined. For both monomers, the homoaddition proceeds slightly faster than the heteroaddition step; however, the polymer formation occurs in a statistic fashion. Copolymers of different compositions are prepared and the cloud points are determined. Thereby, a significant influence of the concentration of monomer 2 and the pH value is found. For the first time, the complexation of polymer attached phenolphthalein by β‐cyclodextrins is shown. Furthermore, it is possible to achieve a decomplexation by the addition of suitable guest molecules. Both procedures can be followed with the naked eye.
Summary: The glass transition temperatures of conducting composites, obtained by blending carbon nanotubes (CNTs) or polypyrrole (PPy) particles with epoxy resin, were investigated by using both differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). For both composites, dc and ac conductivity measurements revealed an electrical percolation threshold at which the glass transition temperature and mechanical modulus of the composites pass through a minimum.
DC conductivity, σdc, as a function of the conducting filler concentration of the CNT– (▪) and PPy– (○) epoxy resin composites. 相似文献
Frontal photopolymerization has attracted much attention in the last decade as it allows the curing of thick films. Unfortunately, the use of peroxides, which feature appropriate storage stability, also requires inappropriately high initiation temperatures. Here, a new approach involving a copolymerisation‐induced destabilization of (meth)acrylate‐based peroxides that allows lower front temperatures is presented. The increasing degree of branching next to the carbonyl group lowers the decomposition temperature by at least 20 °C. In classical monomer formulations, sufficient storage stability is confirmed.
Melts of symmetric three‐arm stars are generated using a novel iterative method. In this method, an equilibrated low molecular weight configuration is used to generate progressively higher molecular weights by affine scaling and equilibration. At each stage in the progression, the synthetically lowered entanglement density allows bypassing of the exponentially large relaxation times of branched polymers. The quality of equilibration was assessed by measuring the mean dimensions, distribution of dimensions, and internal length scales of the polymers. The total time required to generate the progression of equilibrated configurations was seen to scale as the Rouse time of the highest molecular weight.
Summary: Polypyrrole nanotubes with high electric conductivity and azo function have been fabricated in high yield via an in‐situ polymerization. During the process fibrillar complex of FeCl3 and methyl orange (MO), acting as a reactive self‐degraded template, directed the growth of polypyrrole on its surface and promoted the assembly into hollow nanotubular structures.
TEM image of uncompleted PPy nanotubes synthesized in MO solutions after reaction for 40 min. 相似文献
Summary: Thermogravimetry and differential scanning calorimetry have been used to study the thermal and thermo‐oxidative degradation of polystyrene (PS) and a PS–clay nanocomposite. An advanced isoconversional method has been applied for kinetic analysis. Introduction of the clay phase increases the activation energy and affects the total heat of degradation, which suggests a change in the reaction mechanism. The obtained kinetic data permit a comparative assessment of the fire resistance of the studied materials.
The change in activation energy for the degradation of PS and the PS–clay nanocomposite with the extent of polymer conversion. 相似文献
Summary: Physico‐chemical interactions between hydrophobic polyolefin materials and hydrophilic inorganic nanoparticles such as surface‐hydroxylated SiO2 have not been well understood so far. In this study, the effects of particle size and content of SiO2 nanoparticles on isothermal growth rate of PP spherulites in various PP/SiO2 nanocomposites were investigated by polarized optical microscopy. It was unexpected to find that hydrophilic SiO2 nanoparticles can be homogeneously dispersed in a PP matrix. Spherulite growth rates of PP in PP/SiO2 nanocomposites decrease significantly with increasing SiO2 content and decreasing particle size. Most interestingly, the spherulite growth rate was zero for PP/16 nm‐SiO2 nanocomposites with SiO2 content above 2.5 wt.‐% resulting in a highly transparent film.
Photographs of 200 µm‐thick PP and PP/16 nm‐SiO2 (5 wt.‐%) sheets in front of a graphic pattern. 相似文献
Porous surface patterns are used in a wide variety of practical applications. Honeycomb‐patterned porous polymer films are good templates for preparing porous surfaces due to their simple fabrication and the arrangement of pores on the surface. Catechol groups include in adhesive protein of mussels have attracted much attention due to their highly and substrate‐independent adhesive properties. In this paper, highly and substrate‐independent adhesive honeycomb‐patterned porous polymer films are prepared by using amphiphilic copolymer having catechol moieties. Furthermore, porous surface patterns are transferred on various organic or inorganic substrates by wet etching with using adhesive honeycomb films as templates.
The preparation of a bisphenol‐A carbonate copolymer, containing Cu‐diimine units with nonlinear optical (NLO) properties, and its MALDI‐TOF mass spectrometric characterization are reported. Contrary to the usual synthetic method, NLO groups were inserted directly into a commercial polycarbonate by prolonged heating at 250 °C. This innovative procedure allows to obtain a Cu/diimine‐containing polymer of high molecular weight.
A clickable alkyne monomer, PgMA, was successfully polymerized in a well‐controlled manner via single electron transfer initiation and propagation through the radical addition fragmentation chain transfer (SET‐RAFT) method. The living nature of the polymerization was confirmed by the first‐order kinetic plots, the linear relationships between molecular weights and the monomer conversions while keeping relatively narrow (≤1.55), and the successful chain‐extension with MMA. The better controllability of SET‐RAFT than other CRP methods is attributed to the less competitive termination in view of the presence of the CTA as well as the Cu(II) that is generated in situ. Moreover, a one‐pot/one‐step technique combining SET‐RAFT and “click chemistry” methods has been successfully employed to prepare the side‐chain functionalized polymers.
An amphiphilic biodegradable polymer, poly(aspartic acid‐co‐lactic acid) (PAL), was synthesized by simply heating a mixture of aspartic acid (Asp) and L ‐lactide without additional catalysts or solvents. The unique branched architecture comprising succinimide units and lactic acid units was confirmed by IR and NMR spectroscopy. A copolymer of sodium aspartate and lactic acid (PALNa) was prepared by reacting PAL with an aqueous sodium hydroxide solution. The PAL was soluble in many organic solvents, while the PALNa was soluble in methanol and water. The hydrolytic degradation behavior of PAL varied with the copolymer composition. A higher Asp content resulted in a faster molecular weight decrease, and introducing glycolic acid units accelerated the degradation rate.
Spherical polyelectrolyte brushes consisting of a magnetite/polystyrene nanocomposite core and a poly(acrylic acid) brush shell were prepared by photo‐emulsion polymerization. They are narrowly dispersed, superparamagnetic and redispersible after aggregating by external magnetic field, as determined by transmission electron microscopy, dynamic light scattering, thermal gravimetric analysis and a vibrating sample magnetometer. Magnetic control is thus introduced into nano‐sized spherical polyelectrolyte brushes to achieve recovery and controllable delivery in applications. This approach opens up the way for cost‐effective applications of spherical polyelectrolyte brushes.
Poly[2‐(methacryloyloxy)ethyl phosphorylcholine] ‐modified gold surfaces, which have been newly prepared by a ‘grafting to’ method using a series of monosulfanyl‐terminated PMPC, are characterized by protein adsorption experiments based on surface plasmon resonance spectroscopy and ellipsometry measurements. The extent of BSA adsorption on PMPC‐modified surfaces was systematically reduced for thicker PMPC layers, thus the number of MPC units on the gold surface appears to be an important factor for the excellent protein resistance offered by PMPC‐modified gold surfaces fabricated by the ‘grafting to’ method, which is sharp contrast to that of PEG tethered chains.
Highly efficient formation of poly(propylene carbonate) can be achieved in the coupling of CO2 and propylene oxide assisted by 4‐(N,N‐dimethylamino)pyridine (DMAP) and catalyzed with salen chromium(III) chloride by using DMAP/Cr ratios of less than 2. Under these conditions a possible backbiting mechanism is suppressed, leading to only minor amounts of cyclic carbonate as a side product.
Synthesis of a water‐soluble polydiacetylene has been achieved by topochemical polymerization in the solid state of the bis(N‐methylimidazolium)diacetylene monomer. Structural characterization for the monomer by X‐ray diffraction and NMR spectroscopy supports a photopolymerization initiated at the surface. Characterization of the polymer (NMR, UV and Raman spectroscopy, and dynamic light scattering) is given along with a molecular modelling interpretation of the polymerization in the solid state.
