Number Average Molecular Weight Measurements Research Articles

Polybithiophene and its bilayers with polyaniline coatings on stainless steel by electropolymerization in aqueous medium

For the first time, electrosynthesis of polybithiophene (PBTh) and its bilayers with polyaniline (PAni) coatings on stainless steel (SS) in aqueous oxalic acid solutions containing monomer and sodium dodecyl sulfate (SDS) was carried out by potentiodynamic synthesis technique. Smooth and adherent films were obtained on the steel surfaces. Homopolymers and bilayers were characterized by cyclic voltammetry, FTIR, UV–vis spectroscopies and SEM. Homopolymers were also characterized by means of conductivity and the number average molecular weight measurements. The effects of the scanning potential limits on electrosynthesis of PBTh and its bilayer coatings were investigated. The test for corrosion protection of the polymer coated and uncoated SS substrates were performed in highly aggressive 0.5 M NaCl and 0.5 M HCl solutions by linear potentiodynamic polarization and Tafel test technique, respectively. Corrosion test revealed that among the protective coatings obtained, PBTh as homopolymer and PAni/PBTh as bilayer exhibited the most effective anticorrosive properties. According to linear potendynamic polarization test, the dissolution current of these coatings at 1.6 V decreased to 99.8% and 99.6% in NaCl solution, respectively, when compared to that of uncoated SS surfaces.

Kinetics and Modelling of Bulk and Solution Diallyl Terephthalate Polymerization

Free radical polymerization kinetics of diallyl terephthalate (DAT) in solution was investigated with two different peroxide initiators: dicyclohexyl peroxydicarbonate (CHPC) and benzoyl peroxide (BPO) in temperature range from 50°C to 110°C, where ortho-xylene was used as a solvent. Conversion points were measured using Fourier Transform Infrared (FTIR) measurements. Previously developed kinetic model for bulk DAT polymerization, was extended to solution DAT polymerization. The ratio of solvent chain - transfer rate constants to propagation rate constants of the polymerization system were found between 1.25 10-4 to 1.68 10-4 for various reaction conditions. They were obtained using the calculated initial polymerization rates and the number average molecular weight measurements made by GPC. The effect of different solvent fractions and initiator concentrations on the diffusion limitations were investigated. Only two kinetic parameters, kpd0 and ktd0 were obtained by fitting the kinetic model onto measured conversions for various reaction conditions at 0.2, 0.5 and 0.8 solvent fractions. Thus obtained kpd0 and ktd0 kinetic parameters were extrapolated to zero solvent fractions and from obtained values of kinetic parameters the conversion points for bulk DAT polymerization were calculated and compared to measured conversion points.

Structural Analysis by NMR and FIMS of the Tar-Sand Bitumen of Bemolanga (Malagasy)

The detailed characterization of the tar-sand bitumen of Bemolanga (Malagasy) was performed with the aid of NMR and FIMS techniques. After precipitation of the asphaltenes an elaborate separation of maltenes was carried out by HPLC. The number average molecular weight measurements indicate that this bitumen is much heavier than American bitumens (MW = 900 against 534 for the Athabasca bitumen for example). The modeling shows that the average length of the alkyl chains and the ratio of the number of naphthenic rings to that of aromatic rings increase from the aromatic fractions to the resin fraction and then decrease for the asphaltenes. Moreover, the average length of the alkyl chains is always larger than that in the corresponding fraction of American bitumens.

NMR and intrinsic viscosity study of two different phenol-formaldehyde resol resins

Two different phenol-formaldehyde (PF) resol resins used as binders in wood products manufacture were subjected to acetylation and fractionation, and the fractions were studied by quantitative NMR, intrinsic viscosity, and number average molecular weight measurements

The thermal degradation of polysiloxanes: Part 5—Synthesis, characterisation and thermal analysis of poly(tetramethyl- p-silphenylene siloxane) and copolymers with dimethylsiloxane

Poly(tetramethyl- p-silphenylene siloxane) and a series of copolymers with dimethylsiloxane have been prepared and characterised by means of ir and nmr spectroscopy and number average molecular weight measurements. Thermal gravimetry (TG) and Thermal Volatilisation Analysis (TVA) have been used to demonstrate the relationships which exist between stability and composition.

Synthesis of a polytitanocarbosilane and its conversion into inorganic compounds

The novel polytitanocarbosilane, formed by the cross-linking of polycarbosilane with titanium tetra-alkoxide, was synthesized to examine the process of converting a multielement organometallic polymer into an inorganic compound. The chemical structure of this polymer was investigated by the techniques of infra-red spectroscopy (IR), gel permeation chromatography (GPC), number average molecular weight measurements and29Si nuclear magnetic resonance (NMR) measurements. The pyrolysis products in N2 gas at 1400° C and 1700° C were the microcrystalline and crystalline states of silicon carbide and titanium carbide, respectively.

The influence of the tacticity on thermal degradation of PVC. III. Verification by ozonization of degraded samples

AbstractTwo sets of ozonization reactions, for 1 h and 24 h respectively, have been carried out at −20°C on degraded samples of PVC having different contents of tactic sequences. The evolution of the polyene sequences distribution with the ozonization was followed by UV‐Visible spectroscopy. The number of chain scissions of ozonized samples was calculated from the number average molecular weight measurements before and after ozonization.The observed increase of short polyenes relative to the long polyenes with ozonization was found to depend markedly on the content of syndiotactic sequences. On the other hand, the number of chain scissions after total ozonization was found to be the higher the lower the content of tactic sequences in PVC samples is.