Temperature-sensitive hydrogel beads were prepared by radiation crosslinking of poly(vinyl methyl ether) PVME spheres wrapped in Ca-alginate. The obtained gel beads have diameters in the sub-millimeter or millimeter range (depending on the PVME concentration). They were characterized by sol-gel analysis, swelling measurements, and differential scanning calorimetry. The gel content g increases with increasing radiation dose D. The swelling degree Qv decreases with increasing PVME concentration cp and increasing D. In comparison to PVME bulkgels the phase-transition temperature of the synthesized PVME gel beads is a little decreased. 相似文献
Hydrophilic polymeric films based on blends of poly(acrylic acid) and poly(vinyl methyl ether) (PVME) were prepared by casting technique and were cross-linked by gamma-radiation. The films are soft and elastic in a dry state and form hydrogels upon immersion in water. Effect of absorbed dose on the gel fraction as well as on the swelling of the films in aqueous solutions of different pH is studied. It was found that addition of lower molecular weight PVME decreases the gelation dose, which is likely related to a decrease in glass transition temperature of the blends. In acidic media the films have low swelling degree because of suppression of carboxylic groups ionisation and formation of additional physical cross-links via interpolymer hydrogen bonding. 相似文献
Some possibilities of NMR spectroscopy (mainly spin-spin relaxation) in investigations of hydration and other polymer-solvent interactions during the temperature-induced phase separation in aqueous polymer solutions are described. A certain portion of water molecules bound in phase-separated mesoglobules was revealed. The residence time of the bound HDO for poly(vinyl methyl ether) (PVME)/D2O solution (c = 6 wt%) is 1.2 ms. With time a slow release of originally bound water from the respective mesoglobules was observed. For highly concentrated PVME/D2O solutions (c = 20–60 wt%), the residence time of bound HDO ≫ 2.7 ms and fractions of bound water unchanged even for 70 h were found. A similar behaviour as described above for water (HDO) was also found for EtOH molecules in PVME/D2O/EtOH solutions. 相似文献
Summary: NMR relaxation and diffusion coefficient measurements revealed that a portion of water molecules is bound in mesoglobules formed in poly(N-isopropylmethacrylamide) (PIPMAm) and poly(vinyl methyl ether) (PVME) aqueous solutions above the LCST, with fast exchange between bound and free states (residence time ∼1 ms). Two types of bound water molecules were assigned to water bound inside mesoglobules and on their surface. For highly concentrated PVME/D2O solutions (c ≥ 20 wt%) a slow exchange was detected by NMR for bound water (residence time = 2.1 s). For PIPMAm aqueous solution IR spectra indicate a two-steps character of the phase transition. For PIPMAm in D2O/ethanol (EtOH) mixtures the globular structures were observed by NMR at 298 K for certain compositions of the mixed solvent (cononsolvency effect). Virtually no EtOH is bound in these globular structures, in contrast to the temperature-induced globular structures. 相似文献
Some possibilities of 1H NMR spectroscopy in investigations of structural-dynamic changes and polymer-solvent interactions during the temperature-induced phase transitions in aqueous polymer solutions are described. Results obtained recently on D2O solutions of poly(vinyl methyl ether) (PVME), poly(N-isopropylmethacrylamide) (PIPMAm), negatively charged copolymers of N-isopropylmethacrylamide and sodium methacrylate, and PIPMAm/PVME mixtures are discussed. A markedly different rate of dehydration process in dilute solutions on the one hand, and in semidilute and concentrated solutions on the other hand, was revealed from 1H spin-spin relaxation measurements. 相似文献
Phase separation of polystyrene/poly (vinyl methyl ether) (PS/PVME) blends was induced and controlled by irradiation with linearly polarized light. The PS component was made photosensitive by chemically labeled with either anthracene or trans‐stilbene. The former was used to crosslink the PS component whereas the latter induces phase separation by changing polymer segmental volumes. The phase separation and reaction kinetics were observed and discussed in terms of mode‐selection process. 相似文献
The structural‐dynamic changes and polymer‐solvent interactions during temperature‐induced phase transition in poly(vinyl methyl ether) (PVME)/D2O solutions in a broad range of concentrations (0.1‐30 wt.‐%) were studied by 1H NMR methods. In the whole concentration range the phase transition is manifested by line broadening (linewidth 350‐500 Hz) of a major part of PVME units, evidently due to the formation of globular‐like structures. Above the LCST transition, the fraction of phase‐separated PVME segments is equal to 0.8±0.1, independent of polymer concentration. While at low concentrations the transition is virtually discontinuous, at high concentrations the transition region is ∼ 3 K broad. Measurements of nonselective and selective 1H spin‐lattice relaxation times T1 of solvent (HDO) molecules evidenced that at elevated temperatures, where most PVME forms globular structures, a part of solvent molecules is bound to PVME forming a complex; the lifetime of the bound water (HDO) molecules is ≤2 s. 相似文献
The dynamic-structural changes and polymer - solvent interactions during the thermotropic phase transition in poly(vinyl methyl ether) (PVME)/D2O solutions in a broad range of polymer concentrations (c = 0.1-60 wt.-%) were studied combining the measurements of 1H NMR spectra, spin-spin (T2) and spin-lattice (T1) relaxation times. Phase separation in solutions results in a marked line broadening of a major part of polymer segments, evidently due to the formation of compact globular-like structures. The minority (∼15%) mobile component, which does not participate in the phase separation, consists of low-molecular-weight fractions of PVME, as shown by GPC. Measurements of spin-spin relaxation times T2 of PVME methylene protons have shown that globular structures are more compact in dilute solutions in comparison with semidilute solutions where globules probably contain a certain amount of water. A certain portion of water molecules bound at elevated temperatures to (in) PVME globular structures in semidilute and concentrated solutions was revealed from measurements of spin-spin and spin-lattice relaxation times of residual HDO molecules. 相似文献
Anisotropic phase separation of polystyrene/poly(vinyl methyl ether) (PS/PVME) blends was induced by photoisomerization of trans-stilbene moieties labeled on the PS chains (abbreviated hereafter as PSS chains) using linearly polarized light. As temperature increases, the anisotropy becomes weaker and eventually disappears at 10°C above the glass transition of the PSS component. It was concluded that the elastic stress associated with the spatial distribution of the reaction is responsible for this morphological anisotropy. 相似文献
Photooxidation of blends of polystyrene and poly (vinyl methyl ether) was studied at 30°C. The oxygen uptake by PS was negligible but PVME oxidized readily. The induction period of oxidation of PVME was prolonged by the presence of PS. The steady state rate of oxidation of the blend was strongly influenced by the segmental mobility of the blend which also governed the kinetics and morphology of phase separation. The molecular weight of PVME decreased more slowly in the blend as PS content increased. It was believed that the reaction between PVME radicals and PS resulted in less reactive PS radicals which retarded oxidation. The PS radicals eventually underwent chain scission reactions. 相似文献
We report the results of experimental infrared and thermal analysis studies of binary miscible blends of poly(vinyl methyl ether) (PVME) with an ethyl methacrylate-co-4-vinyl phenol (EMAVPh) copolymer. This is a complex blend system, involving multiple specific interaction sites. Using the concept of competing equilibria we show that the equilibrium constant describing hydrogen bonding between the OH group of EMAVPh and the ether oxygen of PVME can be determined from quantitative infrared spectroscopic analysis of the fraction of hydrogen bonded carbonyl groups present in miscible binary blends. 相似文献
Fourier transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) miscible blends as a function of temperature are presented. Below the lower critical solution temperature (LCST) little change is observed in the interaction spectrum obtained via digital subtraction techniques. Once above the LCST, the magnitude of the interaction spectrum decreases as a result of the phase separation process. Comparison of the behavior of the ether C? O stretching band in the reference PVME and in the blends has yielded a lower limit estimate for the interaction energy of about 0.15 kcal/mol. 相似文献
By fitting the spinodals of poly(vinyl methyl ether)/deuterated polystyrene (PVME/PSD) systems, the adjustable parameters ε*12 and δε* in the Sanchez‐Balasz lattice fluid (SBLF) theory could be determined for different molecular weights. According to these parameters, Flory‐Huggins and scattering interaction parameters were calculated for PVME/PSD with different molecular weights by means of the SBLF theory. From our calculation, Flory‐Huggins and scattering interaction parameters are both linearly dependent on the reciprocal of the temperature, and almost linearly on the concentration of PSD. Compared with the scattering interaction parameters, the Flory‐Huggins interaction parameters decreased more slowly with an increase in the concentration for all three series of blends. 相似文献
13C nuclear magnetic resonance (CMR) spectra were obtained for 2,4-dimethoxypentane, which is a model compound of poly(methyl vinyl ether), and the effects of the solvent and temperature on the chemical shifts were investigated. CMR spectra of poly-(alkyl vinyl ethers) were also determined and analyzed. The diad tacticities were obtained from β-methylene carbon resonances of poly(methyl vinyl ether), poly(ethyl vinyl ether), and poly(isobutyl vinyl ether), but not from those of poly(isopropyl vinyl ether) and poly(tert-butyl vinyl ether). The methoxyl carbon resonance of poly(methyl vinyl ether) and the ethoxyl methylene carbon resonance of poly(ethyl vinyl ether) showed splittings corresponding to pentad and triad sequences, respectively. The α-methine and quaternary carbon resonances of poly(tert-butyl vinyl ether) showed splittings corresponding to pentad and triad sequences, respectively. 相似文献
Summary: The thermosensitive phase‐separation of poly(vinyl methyl ether) in water has been investigated by micro‐Raman spectroscopy in the presence of tetraalkylammonium bromides. The equilibrium distribution of both polymer and salts to the polymer‐rich and solvent‐rich phases was determined as a function of temperature. Tetraalkylammonium ions with longer alkyl chains associate more strongly with PVME and raise the phase‐transition temperature due to an increase in hydrophilicity.
Fourier-transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends are presented. Both compatible (one-phase) and phase-separated blends were studied. In the case of compatible PS/PVME blends, there is strong evidence for molecular interactions. The interaction spectrum was obtained by digital subtraction techniques. In contrast, no interaction is detected for the phase-separated blends. In view of these results, molecular interactions must play a role in the compatibility of the two polymers. The merits of factor analysis and least-squares fit methods, as pertaining to our data, are also discussed. 相似文献