The well-ordered structures of block copolymer formed by self-assemble have attracted much attention as potentially interesting optical materials, especially as photonic crystals1,2. In order to achieve desirable photonic crystal properties, the morphologies of block copolymers should be controlled, including obtaining the correct size of domains for the optical frequencies of interest and attainment of long-range domain order and appropriate orientation. We know that the morphology of one blo… 相似文献
Liquid adsorption chromatography, in combination with full adsorption–desorption and precipitation–redissolution techniques, is a powerful procedure for the fractionation of mixtures in the synthesis of star polymers. An easy separation of 4‐ and 6‐arm star poly(methyl methacrylate)s from their single arm precursors could be carried out by both procedures, with differences of separation efficiency also depending on the molecular weight of the precursor and the number of arms.
Size exclusion chromatograms of retained and eluted fractions obtained by liquid adsorption chromatography/full adsorption–desorption separation with a tetrahydrofuran/cyclohexane eluent system (53:47 wt.‐%) for a crude reaction mixture (dotted line) containing a 4‐arm star PMMA polymer and a single‐arm precursor (solid lines a and b, respectively). 相似文献
The effect of nanoclay on the phase-separation behavior of poly（methyl methacrylate）/poly（vinyl acetate）（PMMA/PVAc） blends has been mainly investigated by small-angle laser light scattering. It is found that the effect of clay on the thermodynamics and kinetics of phase-separation for PMMA/PVAc blends seems inconsistent. The kinetics phaseseparation rate decreases, while the thermodynamics parameters, cloud points Tc and delay time tD of isothermal phaseseparation also decrease, and the variation amplitude depends on the matrix composition. The affinity of clay to PMMA results in the composition difference between the border layer and the polymer matrix and further causes the concentration fluctuation at the early stage of phase separation to reduce Tc and tD. On the other hand, the decrease of phase-separation rate is caused by the mechanical barrier effect of clay on the macromolecular diffusion of blend matrix. Hence, such seemingly counterintuitive results on the thermodynamics and kinetics of phase-separation are attributed to different dominant factors. 相似文献
Interpenetrating polymer networks (IPNs) of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) were prepared by simultaneous network formation. The PEO network was produced by acid-catlayzed self-condensation of α,ω-bis(triethoxysilane)-terminated PEO in the presence of small amounts of water. The PMMA network was formed by free radical polymerization of MAA in the presence of divinylbenzene as crosslinker. The reaction conditions were adjusted to obtain similar crosslinking kinetics for both reactions. An attempt was made to construct a phase diagram of the IPNs by measuring the composition of the IPNs at the moment of the appearance of the phase separation, as indicated by the onset of turbidity. This composition could be determined because the siloxane crosslinks of the PEO network could be hydrolyzed in aqueous NaOH with the formation of linear, soluble PEO chains. The phase diagram was compared with phase diagrams of blends of linear polymers and of semi-IPNs (crosslinked PMMA and linear PEO), obtained under similar conditions, i.e. polymerization of MMA in the presence of varying amounts of PEO. It was observed that the form of the phase diagrams of the linear polymers is similar to that of the IPNs, but is quite different from that of the semi-IPNs. Thus, homogeneous transparent materials containing up to 60% of PEO could be prepared in the blends and the IPNs, but in the semi-IPNs, phase separation occurred with PEO contents as low as 10%. 相似文献
Azo pigment yellow 14 (P.Y.14) was encapsulated into copolymer of styrene and maleic acid (PSMA) via phase separation technique followed by the preparation of composite dispersions. Herein, we mainly investigate its rheological properties. Our results showed that the apparent viscosity (na) of composite dispersion first decreased and then increased with an increase of molar content of maleic acid in PSMA (FM), intrinsic viscosity of PSMA ([n]), and the weight ratio of PSMA to P.Y.14 (RC/P), respectively. The composite dispersion with low na was more close to Newtonian fluid when FM, [n] and RC/P were equal to 0.53, 79.65 mL/g, and 12%, respectively. na of the composite would increase with increasing the pH value, and first decreased and then increased with a raising of the electrolyte and alcohol concentration, respectively, especially with AlCl3 and glycerol. 相似文献
Polysulfone (PSF) membranes have gained great attention in the fields of ultrafiltration,microfiltration,and thin film composite membranes for nanofiltration or reverse osmosis.For the first time,it is proposed to fabricate PSF membranes via thermally induced phase separation (TIPS) process using diphenyl sulfone (DPSO2) and polyethylene glycol (PEG) as mixed diluent.DPSO2 is chosen as a crystallizable diluent,while PEG is considered in terms of molecular weight (Mw) and dosage.We systematically investigate the interactions between PSF,DPSO2 and PEG based on the simulation calculations and solubility parameter theory.It is inferred that DPSO2 has an excellent compatibility with PSF,and the addition of PEG results in the ternary system thermodynamically less stable and then facilitates its liquid-liquid (L-L) phase separation.SEM images indicate that cellular-like pores are obvious throughout the membrane when the PEG content in the mixed diluent is 25 wt％-35 wt％.We can facilely manipulate the pore size,water flux and mechanical properties of PSF membranes with the dosage of PEG-200,the Mw of PEG or the cooling rate.The successful application of TIPS can provide a new approach for structure manipulation and performance enhancement of PSF membranes. 相似文献
