Polymer-stabilized foams and foam films have received considerable attention during the past years. This review paper gives an overview of recent studies dealing with polyelectrolyte/surfactant mixtures, proteins, and microgels adsorbed at single air/water interfaces, in foam films and in macroscopic foams. These polymeric systems have in common that their structure or shape changes when adsorbing at an air/water interface. These structural changes in comparison to their bulk behavior greatly influence the properties of foam films and foams. Regarding the foam stability, formation of adsorbed layers or aggregates plays an important role. The discrepancy between stabilization of macroscopic foams and destabilization of single foam films might be attributed to the blockage of Plateau borders and, therefore, slowed down drainage. Another important parameter is the interfacial viscoelasticity. 相似文献
Homopolymeric microgels composed of PMMA were prepared by emulsion polymerization in the presence of 0.5 % 1,4-butanediol divinylether (BVE) in an aqueous medium followed by careful removal of the soap. The microgels were coated with polystyrene (PS) by anionic grafting of living PS chains onto the surface. Both types of microgels were characterized by GPC and by static and dynamic light scattering in several solvents. A special model consisting of a hard core and a seam of dangling chains has been developed and applied to interpreting the light scattering data from the various solvents. The model gives consistent results, e. g. the core radius agrees well with the radius of gyration. In the coated microgels a strong expansion of the core as a result of the PS/ PMMA incompatibility is observed.Dedicated to Prof. Dr. H.-G. Kilian on the occasion of his 60th birthday. 相似文献
The challenging task of characterizing polydisperse polymer mixtures possessing ultrahigh molecular weight (MW) polymers and microgels in organic solvents is addressed with thermal field-flow fractionation (ThFFF) and multiangle light scattering-differential refractive index (MALS-dRI) detection. In initial experiments, a 350,000 g/mol poly(methyl methacrylate) (PMMA) standard is used to evaluate the effects of temperature gradient and temperature gradient programming on the measurements. dRI baseline fluctuations caused by temperature programming were minimized by using a mobile phase heater to thermostat connecting tubing. ThFFF–MALS-dRI is then used to separate and characterize a complex polyvinyl acetate (PVAc) sample containing ultrahigh MW polymers and microgels. The open channel design employed by ThFFF allowed the PVAc sample to be analyzed with minimal sample preparation. Unfiltered PVAc sample showed components with MWs close to 109 g/mol and root mean square radius rrms values approaching 400 nm. The same sample, filtered through a 0.5 μm pore-size membrane, yielded a MW that was at least one order of magnitude lower. These results demonstrated that the common practice of prefiltering polymer samples prior to analysis can lead to erroneously low average MWs and polydispersities. The accuracy of MW and rrms calculated using standard light scattering equations developed for small scattering molecules and relatively high wavelengths is also examined. 相似文献
The goal of this study was to prepare and characterize water-soluble, high-molecular-weight microgels. N-Vinylpyrrolidone (NVP) and vinylacetate (VAc) in combination with cross-linkers diethylene glycol dimethacrylate (DEGDMA)
or diethylene glycol divinyl ether (DEGDVE) were copolymerized in solution to high conversion. Polymerization was performed
in different solvents or solvent mixtures, with solubility parameters ranging from 16.0 to 47.6 J0.5cm−1.5, and at different initial monomer concentrations. In solvent mixtures with solubility parameters of 20–40 J0.5cm−1.5, macrogelation did not occur below a critical gelation concentration and microgels were formed. For NVP/VAc/DEGDMA (85.0/10.0/5.0 wt%,
84.8/12.9/2.4 mol%) and NVP/VAc/DEGDVE (85.0/10.0/5.0 wt%, 84.8/12.9/3.5 mol%) the critical gelation curves were determined.
The molecular weights of the microgels depend on the solvent systems and the initial monomer concentration. Microgels of high
molecular weight but low cross-linking density gave aqueous solutions with high viscosities. Increasing the amount of cross-linker
to 20 wt% gave high-molecular-weight microgels with lower solution viscosity. Microgels with a monomer composition NVP/VAc/DEGDVE
(65.0/15.0/20.0 wt%, 66.2/19.5/14.3 mol%) were prepared in ethanol at different monomer concentrations (3–20 wt%). The molecular
weights were determined by a combination of field-flow fractionation and light scattering. By increasing the initial monomer
concentration, the molecular weight and the molecular-weight distribution as well as the intrinsic viscosity increased. The
exponent of the Mark–Houwink equation was 0.26.
Received: 19 March 2001 Accepted: 20 July 2001 相似文献
One of the most promising strategies in anticancer therapies is the targeted delivery through malignancy-associated cellular markers. The design of new synthetic devices with enhanced stimuli-responsive sensitivity and targeting ligands is a promising field for the development of cancer-specific delivery systems. One of the pathways to achieve this aim is the chemical functionalization of nanodevices such as microgels. The p-nitrophenyl acrylate (NPA) is an active ester molecule with a group that can be easily cleavaged by the nucleophilic attack of species such as amines. This modification consists of an easy chemical reaction that leads to several types of functionalized microgels, which are originally made up of NPA as one of their constituent monomers.
Here is reported the chemical functionalization of NPA-based microgels by incorporating pH-sensitive functional groups and folic acid as a tumor targeting ligand into the same initial polymer network. For this purpose, microgels of p-nitrophenyl acrylate (NPA)-co-methacrylamide (MeAM) synthesized by precipitation polymerization, were modified with two different pyridine derivatives: 2-aminomethylpyridine (2-AMP) and 2-aminopyridine (2-AP), thus pH-sensitive microgels with acid pH swelling capacity were obtained. The equilibrium swelling behaviour was studied as a function of pH, ionic strength, copolymer composition and type of pyridine derivative. In addition, the microgels were derivatized with ethylene diamine, to obtain amino-functionalized microgels to which the folic acid was subsequently attached as the targeting ligand. As final step, pH-sensitive groups and folic acid were equimolarly attached to the polymer chains to obtain the fully functionalized microgels. 相似文献