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- Author or Editor: I. Popovic x
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Abstract
Non-isothermal thermogravimetry was performed in a dynamic nitrogen atmosphere, on a series of poly(di-n-propyl itaconates) (PDnPI) and poly(di-iso-propyl itaconates) (PDiPI) which had been prepared in the presence of various amounts of the chain transfer agentn-dodecyl mercaptan (DDM). Differential thermogravimetry (DTG) showed that both polymers degraded in two stages. The DTG curve of PDnPI had a large first peak followed by a smaller shoulder, whereas the DTG curve of PDiPI was composed of two peaks of almost equal heights. The addition of DDM during the polymerisations in both cases resulted in a similar decrease in the relative area of the first peak.
Abstract
The non-oxidative thermal degradation of poly (di-2-chloroethyl itaconate) (PD2CEI) was studied by TG and by analysing the thermal products. The major processes occurring during thermal analysis are crosslinking, depolymerisation and carbonisation. The thermal degradation activation energy increased with increasing sample mass loss. The thermal degradation of PD2CEI was compared to that of the structurally similar poly(2-chloroethyl methacrylate) (P2CMA).
Abstract
Polymethacrylonitrile (PMAN) was prepared by bulk, solution and precipitation polymerization. The thermal stability of the polymer, which is affected by the structure of the chain end groups, was studied by non-isothermal thermogravimetry (TG). On the basis of the differential TG curves of samples prepared by polymerization in the presence of chlorinated solvents, it may be concluded that, in addition to end-chain and random main chain scission initiated depolymerization, hydrogen chloride evolution also occurs during the thermal degradation of PMAN.
Abstract
The thermal stability of poly(methyl methacrylate) (PMMA) photopolymerised using colloidal cadmium sulphide as the photoinitiator was studied by thermogravimetry (TG) and differential TG (DTG). The thermal stability of the CdS initiated PMMA was greater than that of conventional radically polymerised PMMA and approached that of anionically prepared PMMA. The DTG curve of the CdS initiated PMMA was a composite of four peaks, three of which correspond to the three peaks observed in the DTG curve of standard radically prepared PMMA. It is suggested that the additional peak arises from a new mode of depolymerisation initiation, that is, from chain end unsaturation introduced into the polymer chain during polymerisation initiation with the colloidal CdS.
Abstract
The effect of molar mass and, in the case of dextran, of the degree of branching on the thermal degradation kinetics of dextran and pullulan was studied in the presence and absence of oxygen. Although the initial mass loss of the dextran samples occurred at higher temperatures than that of the pullulan samples, the overall thermal degradation activation energies were lower for dextran than for pullulan. In the case of dextran the thermal stability was found to decrease with molar mass and degree of branching. The molar mass of pullulan, in the range of 104 to 105 g/mol, appeared to have no significant influence on the thermal characteristics of the samples.
Abstract
A coincidence method for measuring 137Cs, 40K, 226Ra and 232Th decay products activity in soil, vegetation and fish samples, was applied to the six-crystal gamma-coincidence spectrometer PRIPYAT-2M. In this way, some problems appeared in simultaneous measurement of 137Cs, 226Ra and 232Th by NaI(Tl) detectors and the PRIPYAT-2M spectrometer were solved. The obtained results were agreeable with the HPGe spectrometer ones.
Summary
A simple and reliable TLC method for analysis of -lipoic acid (LA) with post-chromatographic derivatisation with palladium(II) chloride immersion reagent has been developed and evaluated. Separation of LA was performed on 20 cm × 10 cm RPTLC plates with 2-propanol-methanol-acetone-water-acetic acid 6:4:2:8:0.2 (v/v) as mobile phase. Yellow complexes formed in situ were scanned at 375 nm. The migration distance of LA was 43.0 mm. The relationship between peak area and amount of LA applied was evaluated by use of linear (1.0–3.0 µg per band) and second-degree polynomial (0.5–5.0 µg per band) regression functions. The correlation coefficient (r = 0.999), the limit of quantification (0.39 µg per band), recovery (98.5–105.2%), and precision (1.8–2.9%) obtained by use of the procedure were satisfactory. The method was used for analysis of LA in several drug formulations and selected dietary supplement preparations. The LA content was 99.5–101.0% in the drug formulations, 98.8–99.5% in three of five dietary supplements tested, and 48.0–185.0% in two other dietary supplements.
Abstract
The application of derivativ thermogravimetry (DTG) to investigate polymerisation mechanisms is illustrated using the radical polymerisation of di-n-alkyl itaconates as well as the photoinitiated polymerisation of methyl methacrylate by colloidal CdS. The thermal properties of the resulting polymers are described. The advantages and disadvantages of DTG are discussed.
Abstract
The thermal behaviour of three aromatic polymers, poly(3,3-dioxy-4,4-diphenylmethane) (POA), poly(2,2-m-phenylene-5,5-dibenzoxazolemethane) (PBO) and a commercial poly-(phenyleneisophthalamide) (Phenylon) was studied by thermal analysis, i.e. DSC and TG. PBO was formed by the progressive thermocyclization of POA. By transforming POA into PBO the thermal stability was increased proportionally to the degree of cyclization, due to the stiffening of the polymer chain. PBO was found to be more thermally stable than Phenylon. The activation energies of the desorption of moisture, cyclization and thermal degradation of the polymers in both nitrogen and air were determined from non-isothermal TG data.
