Structure and prolonged transport in a biodegradable poly(R-3-hydroxybutyrate)-drug system

In order to create new biodegradable systems for the targeted transport of drugs, poly(3-hydroxy-butyrate) films containing the antibiotic rifampicin in an amount of 5–15 wt % as a model drug are prepared. Film surfaces are studied via scanning electron microscopy, and various structural elements (globules and fibrils) are found. Polymer samples isolated from melt or solution feature different degrees of porosity. It is shown that the kinetic profiles of rifampicin release are of an abnormal character. An analysis of the profiles shows that the release of rifampicin is controlled by the superposition of two processes: its desorption via the diffusion mechanism (the nonlinear segment) and hydrolytic degradation of poly(3-hydroxybutyrate) (the extended linear segment), which becomes well defined after completion of the diffusion stage. The diffusionkinetic model of the process is developed.     

Local mobility of micelles of new cationic surfactants and their interactions with hydrophobically modified polyacrylamides

The local dynamics and organization of micelles of new long-chain cationic surfactants with saturated hydrocarbon fragments (from C₁₆ to C₂₂) are investigated via the EPR spin-probe technique. The local mobility of spin probes in the hydrocarbon core of a micelle changes insignificantly, while the order parameter noticeably increases with lengthening of the hydrocarbon fragment of the surfactant molecule. The specific features of the interaction of the surfactants with network junctions of the gels formed by two types of hydrophobically modified polyacrylamides??either containing charged groups (sodium acrylate) in the backbone or lacking these groups??are studied. In both cases, the local mobility of network junctions of the gel increases after the introduction of the surfactant (C₁₈). Moreover, for surfactant with a long alkyl group (C₂), the microscopic viscosity of the gel based on the uncharged polymer decreases, although the local mobility of the network junctions increases. Possible causes of the observed specific features are discussed.     

Synthesis and investigation of polyethylene blends with natural polysaccharides and their derivatives

Powder blends of LDPE with cellulose, ethyl cellulose, starch, chitin, and chitosan have been prepared under shear deformation in a rotor disperser at different initial-component ratios. The composition of powder fractions is identical to the original composition of the blends. The studied polymer blends demonstrate high mechanical characteristics. X-ray diffraction analysis and DSC studies show that the blending of LDPE with polysaccharides under shear deformations results in changes in the polymer structure and leads to a decrease of their degree of crystallinity. The maximum intensity of mold fungi growth is observed in starch-LDPE (50: 50, wt/wt) and chitin-LDPE (50: 50, wt/wt) blends.     

Kinetics of epoxide resins formation from epichlorohydrin and bisphenol-A

The kinetics of formation of epoxide resins based on epichlorohydrin and bisphenol-A via synthesis with one- or two-step addition of alkali are considered. The kinetics of the reaction were studied by taking into account the consumption of the alkali added and the change of molecular mass and epoxide value of epoxide oligomers. The results obtained are satisfactorily explained within the framework of a model containing the following postulates: all the alkali is bound as phenolate ions; all phenolic groups are of equal reactivity; the reactivity of epichlorohydrin is higher than that of glycidyl ethers; the stage of dehydrochlorination of chlorohydrin ethers in the synthesis with one-step addition of alkali is rapid and does not limit the process; the first stage of the two-step synthesis is the formation of chlorohydrin ethers and the second stage their consumption. The factors leading to differences between the experimentally obtained parameters of the resulting epoxide resins (molecular weight, epoxide value) and their calculated values are discussed. The synthesis of epoxide resins with two-step alkali addition is shown to possess certain advantages over the one-step process.     

Exchange reaction between epoxides and chlorohydrins

Conclusions We determined the equilibrium constant of the exchange reaction between epichlorohydrin and 1-chloro-2-hydroxy-3-phenoxypropane, which leads to the formation of phenyl glycidyl ether and glycerol 1,3-dichlorohydrin.Translated from Izvestiya Akademii Nauk SSR, Seriya Khimicheskaya, No. 2, pp. 450–451, February, 1979.     

The reversible network formation in polydimethyl-siloxanes with side carboxyl groups

The peculiarities of the structurisation of polydimethylsiloxane with carboxyl side groups are investigated by studying its viscosity, elasticity and thermomechanical behaviour over a large temperature interval. The structurisation exhibited in the transition from initial liquid to elastomeric state is shown to be thermoreversible. It occurs more intensively as temperature increases. The cooling of the polymer to room temperature leads to the liquefaction of the elastomer proceeding over a long time; this time depending on the temperature and the length of time of heating. The reasons for these peculiarities lie in the relation between intra- and intermolecular interactions between COOH-groups and the specific changes of polydimethylsiloxane conformations with temperature.     

The peculiarities of physical network formation in carboxyl-containing poly(dimethylcarbosiloxane)

An unusual effect of physical network formation during heating or at room temperature alter previous heating was found for originally liquid poly(dimethylcarbosiloxane) containing 0.5 – 2.5 mol% of side carboxyl groups by means of the measurement of its Theological properties. The reason for this behaviour is supposed to be the predominance of intramolecular hydrogen bonding of COOH groups in original polymer and the intra– to Intermolecular bonds rearrangement during heating. The alternative reason can be the microphase separation with domains of COOH groups. The reversibility of the network is confirmed by the decrease in the elasticity modulus, development of irreversible deformation on further heating and by break-up of Junctions on the addition of small amounts of polar liquids.     

Dynamic mechanical and thermal characteristics of homopolymers and copolymers containing arylene ether ketone units with carboxylic side groups and their salts

Properties of a poly(arylene ether ketone) with carboxyl side groups, copolymers containing units of this homopolymer, and their salts with different degrees of neutralization by alkali metals were studied by the methods of dynamic mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry. By varying the nature of a metal atom and the degree of neutralization of carboxylic groups of a homopolymer and their content in copolymers, one may change the properties of polymers, including their ability to form ion pairs and, hence, their glass transition temperatures. For polymer salts at the 100% neutralization of carboxylic groups, the storage modulus and the glass transition temperature are shown to increase with decreasing the radius of the metal ion. The thermal stability of poly(arylene ether ketone) with carboxylic side groups and copolymers with different contents of such groups may be controlled by varying the nature and content of the introduced metal.     

Conductivity of nonaqueous solutions of aromatic polymers containing ionizable side groups

The concentration dependence of the equivalent conductivity has been measured for dilute DMAc solutions of K, Na, and Li salts of aromatic polymers with ionizable side groups [poly(diphenylenesulfophthalide) and poly(arylene ether ketone) with side COOH groups]. A correlation between the concentration dependences of the equivalent conductivity and reduced viscosity shows that the first parameter initially sharply decreases with an increase in concentration and then achieves a limiting value at a rather low concentration and that precisely in this concentration range the polyelectrolyte effect manifests itself in the concentration versus reduced viscosity curve. With an increasing amount of metal ions incorporated into the polymer, the equivalent conductivity grows. It was demonstrated that the type of counterion affects the reduced viscosity and equivalent conductivity of salt solutions. This effect depends on the structure of the polymer backbone: for poly(arylene ether ketone) salts, the reduced viscosity and the equivalent conductivity increase in the sequence Li → Na → K, while for poly(diphenylenesulfophthalide) salts, the reduced viscosity increases in the reverse order and the equivalent conductivity remains almost invariable. The limiting values of the equivalent conductivity and the degree of association of polyelectrolytes have been estimated in terms of the Arrhenius-Ostwald theory. It has been shown that, in the case of poly(diphenylenesulfophthalide) salts, the equivalent conductivity and the degree of association are higher than those for poly(arylene ether ketone) salts with side COOH groups. This finding is indicative of a stronger binding of counterions by poly(arylene ether ketone).