Ts. Petrova

Synthesis and characterization of poly(oxyethylene)–poly(caprolactone) multiblock copolymers

Novel poly(oxyethylene)/poly(caprolactone) POE/PCL copolymers were synthesized by step growth polymerization of poly(e-caprolactone) diols and poly(ethylene glycol) diacids using dicyclohexylcarbodiimide as coupling agent. The reaction was performed at room temperature and yielded multiblock copolymers with predetermined POE and PCL block lengths. The resulting copolymers were characterized by various analytical techniques including SEC, IR, 1H NMR, DSC and X-ray diffractometry. Data showed that the properties of these polymers can be modulated by adjusting the chain lengths of the macromonomers. In particular, one or two crystalline structures can exist within the copolymers of various crystallinities.

Homopolymers of 5-chloro-8-quinolinyl acrylate and 5-chloro-8-quinolinyl methacrylate and their copolymers with acrylic and methacrylic acid

Abstract Optimal conditions for the preparation of 5-chloro-8-quinolinyl acrylate (AQ) and 5-chloro-8-quinolinyl methacrylate (MQ) were found. Homopolymers were obtained by radical polymerization of AQ and MQ. Copolymers were obtained by copolymerization of AQ with acrylic acid (AA) and MQ with methacrylic acid (MA). The obtained monomers and polymers were characterized by spectroscopic methods (i.r., 1 H and 13 C-NMR), gel-permeation chromatography (GPC) and differential scanning calorimetry (DSC). It was shown that the water-soluble copolymers of AA and AQ (AQ content 5 or 14 mol%) form interpolymer complexes with poly(N-vinyl-2-pyrrolidone).

pH-sensitive hydrogels composed of chitosan and polyacrylamide: Preparation and properties

Three types of polymer networks of chitosan and polyacrylamide (PAAm) – semi-interpenetrating networks (semi-IPNs) of chitosan and crosslinked PAAm (net-PAAm–t-chitosan), semi-IPNs of PAAm and crosslinked chitosan (net-chitosan–t-PAAm), and interpenetrating networks (IPNs) of crosslinked chitosan and crosslinked PAAm (net-PAAm–net-chitosan) were prepared. Chitosan, in a two-fold molar excess to PAAm, provided pH-sensitivity to hydrogel networks. The amount of the crosslinking agent did not have much influence on the microhardness of network films, while higher contents of PAAm increased it. The equilibrium degree of swelling of the hydrogels had the highest values at pH 4 and decreased on increasing pH (pH 7, pH 9) or the ionic strength of the medium as well as with increasing of the degree of crosslinking. The networks in which chitosan was crosslinked, – semi-IPNs net-chitosan–t-PAAm and IPNs net-chitosan–net-PAAm, showed five cycles of completely reversible swelling.

5-Chloro-8-quinolinyl acrylate and n-vinyl-2-pyrrolidone copolymers: Synthesis, characterization and complexes with poly(methacrylic acid)

Abstract New copolymers of 5-chloro-8-quinolinyl acrylate (AQ) and N-vinyl-2-pyrrolidone (VP) were obtained by radical copolymerization in benzene or in DMF. Values of reactivity ratios for VP (M1) and AQ (M2) were r1 = 0.11 and r1 = 0.35 according to the Fineman-Ross method and 0.09 and 0.29 according to the Kelen-Tudos method, respectively. The product of the reactivity ratios, r1 × r1, was less than unity indicating a tendency towards alternation in the formation of copolymers. At considerable excess of VP and by the “compensation” method of polymerization, it was possible to obtain polymers, containing blocks of VP repeating units. It was shown that polymers with high VP content did not form interpolymer complexes in DMF with poly(methacrylic acid) and did not form interpolymer complexes with poly(acrylic acid). The polycomplexes were stable in the temperature range 20–80 °C. On increasing AQ content in the copolymers, the stability of the polycomplexes decreased and copolymers with AQ content higher than 30 mol% did not form interpolymer complexes.

Temperature-dependent light intensity controlled optical switching in azobenzene polymers

We have investigated the dependence of the photoinduced birefringence in a low-molecular azopolymer on the exciting light intensity at elevated temperatures. We have found that in the temperature range 44–56 °C the stationary photobirefringence is higher for a low pump intensity(1 mW) than for a higher intensity (20 mW). At some fixed temperatures, the difference between the two values of the birefringence is as high as 0.07. By alternating the light intensity, the anisotropic phase shift in the polymer films can be switched repeatedly between two values differing by more than 130 deg. This can be used for light-intensity controlled optical switching.

Hydrolysis of chitosan, chitosan-polyoxyethylene and chitosan-poly(2-acryloylamido-2-methylpropanesulfonic acid) by a crude enzyme complex from Trichoderma viride

The degradation of chitosan using a crude enzyme complex from the soil fungus Trichoderma viride was examined in terms of temperature, pH, enzyme activity and the presence of a polymer partner. It was found that chitosan hydrolysis is not suppressed by combining it with polyoxyethylene or poly(2-acryloylamido-2-methylpropanesulfonic acid). The results on Trichoderma viride immobilized on beads imply that chitosan, as well as its polymer complexes are appropriate carriers for development of ecologically safe phytosanitary preparations.

Holographic multiplexing using photoinduced anisotropy and surface relief in azopolymer films

The properties of gratings in an azobenzene polymer inscribed with different combinations of the polarizations of the recording beams are investigated and the optimal conditions for polarization multiplexing are found. Two holograms are stored with the same spatial frequency and the same polarization of the reference beam, varying the polarization of the subject beam. Simultaneous and separate read-out of the reconstructed images is demonstrated.

Photoinduced processes and holographic storage in stilbene and stilbenecarboxaldehyde in a polymethylmethacrylate matrix

We report a spectrophotometric investigation of the photoprocesses in PMMA films containing stilbene or stilbenecarboxaldehyde. UV light induces trans–cis isomerization of the stilbene-type molecules accompanied by considerable changes in the absorption spectra. In the stilbenecarboxaldehyde/PMMA films these changes are anisotropic. The photoanisotropy strongly depends on the wavelength of the exciting light. We also report, for the first time to our knowledge, holographic storage in these materials. The recorded holographic gratings are stable for months.

Ultraviolet and 1H-NMR studies on the products of the chemical modification of α,ω-dichloropoly(oxyethylene) with potassium 5-nitro-8-quinolinolate

Abstract The products of the chemical modification of α,ω-dichloropoly(oxyethylene) (molecular weight of the polyether chain 200, 400 and 1000) with potassium 5-nitro-8-quinolinolate have been studied. Their structures have been established by u.v. and 1H-NMR spectroscopy. Additional evidence for the formation of poly(oxyethylene)s with 5-nitro-8-quinolinolate end-groups is provided by the similarity in the absorption spectra of the products and the model compound (5-nitro-8-ethoxyquinoline).

Synthesis and Characterization of Poly(Oxyethylene)S with (2-Benzoxazolon-3-yl)Acetyl End-Groups. Complex Formation with Polycarboxylic Acids

Abstract Chemical modification of poly(oxyethylene)s (MW from 600 Da to 3000 Da), leading to the obtaining of poly(oxyethylene)s with (2-benzoxazolon-3-yl)acetyl endgroups, is described. The corresponding diesters were synthesized in high yields-70—84% and degree of esterification-82—92% under mild conditions in the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine as catalyst. The diesters were characterized by 1H-NMR, 13C-NMR and IR spectra, and SEC analysis. The relatively narrow molecular weight distribution was retained in the process of chemical modification. The complex formation between polyacrylic or polymeth-acrylic acids and (2-benzoxazolon-3-yl)acetyl derivatives of poly -(oxyethylene)s was studied in dilute aqueous solutions by potentio-metric titration and viscometry. The presence of (2-benzoxazolon-3-yl)acetyl end groups attached to the poly(oxyethylene)s chains results in a significant decrease of the critical poly(oxyethylene) chain length necessary for the formation of sta...