Redox polymerisation, 6. Kinetics of the polymerisation of acrylonitrile initiated by the systems glycerol-Mn(III) and allyl alcohol-Mn(III) in aqueous sulfuric acid

Polymerisation of acrylonitrile initiated by the redox systems glycerol-Mn(III) and allyl alcohol-Mn(III) is investigated in the temperature range 25-45°C in aqueous sulfuric acid/acetic acid and aqueous sulfuric acid, respectively. Oxidation of both glycerol and allyl alcohol proceeds through an intermediate complex. Decomposition of the complex is reversible with glycerol, whereas with allyl alcohol it is irreversible. Addition of Mn(II) retards both oxidation and polymerisation in the former system, while with the latter oxidation in the absence of monomer is unaffected, although polymerisation rates are retarded. Mutual termination predominates with the system glycerol-Mn(III), whereas primary radical termination accounts for the kinetics of polymerisation with the system Mn(III)-allyl alcohol. Rate and equilibrium parameters are evaluated and their significance is discussed

Redox polymerization-kinetics of the reaction inititated by the system CH<SUB>2</SUB>(CH)<SUB>2</SUB>-MN(III) in aqueous H<SUB>2</SUB>SO<SUB>4</SUB> and the system CH<SUB>2</SUB>(CN)<SUB>2</SUB>-MN(OAC)<SUB>3</SUB> in DMF and acetic acid

Polymerization of acrylonitrile and methyl methacrylate by the redox systems propanedinitrile-Mn(III) in aqueous sulfuric acid and propanedinitrile-Mn(OAc)3 in DMF and glacial acetic acid was investigated in the temperature range 20-40&#176;C. The kinetics are consistent with the formation of an intermediate complex whose irreversible decomposition yields the initiating radical. With both monomers mutual termination predominates. The main difference between aqueous H2SO4 and acetic acid compared with DMF lies in the ease of oxidation of the primary radicals by the oxidant. Rate and equilibrium parameters were estimated and their significance discussed

Polymerization of acrylonitrile initiated by the redox system 2,2'-thiodiethanol/Ce<SUP>4+</SUP> in aqueous sulfuric acid

The polymerization of acrylonitrile initiated by the redox system 2,2'-thiodiethanol/Ce4+ in dilute sulfuric acid was investigated in the temperature range of 15-25&#176;C. Oxidation of the substrate in the absence of the monomer has also been studied. The reaction involves the formation of an intermediate complex between the metal ion and the protonated species of the reductant, whose decomposition gives rise to the initiating free radicals. Multual interaction of the growing macroradicals accounts for the termination of polymerization. A suitable kinetic scheme has been proposed and rate and equilibrium constants evaluated

Redox polymerization: kinetics of polymerization of acrylonitrile initiated by the system 2,2'-thiodiethanol/trichloroaquobipyridylmanganese(III) in dilute sulfuric acid

The kinetics of polymerization of acrylonitrile and methyl methacrylate initiated by the redox system 2,2'-thiodiethanol/trichloroaquobipyridylmanganese(III) have been investigated in the temperature range 20-35&#176;C in dilute sulfuric acid. The oxidation of the substrate in the absence of monomer has also been studied. A third-order reaction involving the complex, the substrate, and H+ leads to the production of primary radicals which initiate polymerization of the monomers. The primary radicals are more reactive towards methyl methacrylate than towards acrylonitrile. The termination of polymerization with both monomers is by mutual interaction between the growing radicals. A suitable kinetic scheme has been proposed, and the rate constants evaluated

A photochemical method for immobilization of azidated dextran onto aminated poly(ethylene terephthalate) surfaces

Background: Dextran, a bacterial polysaccharide, has been reported to be as good as poly(ethylene glycol) in its protein-rejecting and cell-repelling abilities. In addition, the multivalent nature of dextran is advantageous for surface grafting of biologically active molecules. We report here a method to photochemically bind dextran hydrogel films to aminated poly(ethylene terephthalate) (PET) surfaces in aqueous media using a heterobifunctional crosslinker, 4-azidobenzoic acid. In order to achieve this, dextran was first functionalized with the crosslinker using carbodiimide chemistry followed by photo-crosslinking and immobilization onto the nucleophile-rich aminated PET surfaces. Results: The presence of the immobilized dextran on PET was verified by attenuated total-reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and contact angle measurements. The grafted surface was highly hydrophilic due to the heavily hydrated polysaccharide network on the surface as demonstrated by the near zero water contact angle. Conclusion: A photochemical method for surface immobilization of dextran onto aminated PET using aryl azide chemistry is a facile technique to generate highly hydrophilic and more hemocompatible surfaces. The aryl nitrenes generated by photolysis produce a metastable, electron-deficient intermediate, azacycloheptatetraene, which is believed to be responsible for the simultaneous crosslinking of dextran and its immobilization onto the aminated PET surface. The aryl azide chemistry reported here for dextran could be useful as a versatile technique for surface modification of other nucleophile-rich polymers to create dextran- or similar polysaccharide-immobilized surfaces

Degradable alginate hydrogels crosslinked by the macromolecular crosslinker alginate dialdehyde

Alginate dialdehyde (ADA) biopolymers possessing a degree of oxidation of either 10 or 50% (10-ADA and 50-ADA, respectively) were characterized using FTIR, XPS and SEC. The aldehyde vibrational mode at 1740 cm(-1) was observed only in ADA which had been equilibrated under ambient conditions while dry samples did not display this band. Spectral changes, both FTIR and XPS, were consistent with formation of hemiacetal moieties. The two types of ADA (10-ADA and 50-ADA) were used as macromolecular crosslinkers to form labile covalent crosslinks in alginate hydrogels. The compositions and properties of the hydrogels were explored through measurement of water uptake and stability in aqueous solution, and characterising the internal structure and mechanical properties by cryogenic scanning electron microscopy and tensile testing, respectively. A decrease in water content was observed when using 50-ADA as compared to 10-ADA correlating with a higher number of crosslinks formed in the hydrogel incorporating 50-ADA. Water uptake also correlated with the amount of 50-ADA incorporated. All ADA-alginate hydrogels displayed short term stability of 3 days after immersion in aqueous solution. The stability of the 50-ADA containing hydrogel was enhanced by introducing ionic crosslinking. Tensile properties of the hydrogels were found to be dependent on the overall polymer density and uniformity of the crosslinking

Doxorubicin-Polysorbate 80 Conjugates: Targeting Effective and Sustained Delivery to the Brain

Targeting therapeutic agents to the brain to treat the central nervous system (CNS) diseases is a major challenge due to the blood-brain-barrier (BBB). In this study, an attempt was made to deliver a model drug such as doxorubicin (DOX) to the brain in a mice model through DOX-Polysorbate 80 (DOX-PS80) conjugates. DOX was successfully conjugated with the non-ionic surfactant Polysorbate 80 (PS80) by carbamate linkage and the conjugate was characterized by different spectroscopic techniques such as FTIR, UV-Visible and NMR. The DOX conjugation efficacy was found to be 43.69 ± 4.72 %. The in vitro cumulative release of DOX from the conjugates was found to be 4.9 ± 0.8 % in PBS of pH 7.3 and 3.9 ± 0.6 % in simulated cerebrospinal fluid (CSF) of pH 7.3 at the end of 10 days. In vitro BBB permeability assay was carried out using bEnd.3 cells and DOX-PS80 conjugate showed a 3-fold increase in BBB permeability compared to controls. In vitro cytotoxicity assay using U251 human glioblastoma cells showed an IC50 value of 38.10 µg/mL for DOX-PS80. Cell uptake studies revealed that DOX-PS80 was effectively taken up (90%) by the bEnd.3 and U251 cells and localized in cytoplasm at the end of 24 h. Tumor spheroid assay and in vivo experiments in Swiss albino mice demonstrated the possibility of DOX-PS80 conjugate crossing the BBB and delivering the drug molecules to the target site for treating CNS disorders