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  • Author or Editor: B. Gaur x
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A computer assisted heat capacity measuring system has been designed from commercial components. A differential scanning calorimeter of type Perkin-Elmer DSC-2 forms the basis for measurements from 100 to 1000 K. A Hewlett-Packard calculator (minicomputer) of type 9821 is the data handling system. The data are collected and permanently stored on teletape. The program has been written to govern measurement and final computation, tabulation, plotting, and curve fitting. Calibration is done by comparison with benzoic acid or aluminium oxide (sapphire). Zinc heat capacities have been measured as an example and for evaluation of accuracy. Accuracies of better than ± 0.5% have been achieved, an improvement of approximately a factor 3 to 5 over a similar system without computer assist. The system will be used mainly for heat capacities of linear macromolecules.

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Abstract  

The paper describes the synthesis of low molecular mass poly(allyl chloride) (PAC) (M n= 856-3834 g mol-1) using Lewis acid (ALCL3, FeCL3, TiCL4) and al powder. Branching in PAC was indicated on the basis of elemental analysis and 1H-NMR spectroscopy. azidation of pac could be carried out at 100°C by using NaN3 and DMSO as solvent. Curing of poly(allyl azide) (PAA) by cyclic dipolar addition reaction with EGDMA (ethylene glycol dimethacrylate, 5-45 phr) was investigated by differential scanning calorimetry and structure of cured polymer was confirmed by FTIR. A two-step mass loss was exhibited by uncured and cured PAA in nitrogen atmosphere. A mass loss of 20-28% (155-274°C) and 50-61% (330-550°C) was observed.

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It is shown that heat capacities of linear macromolecules consisting of all-carbon single-bonded backbones can be calculated from the appropriate contributions of substituted carbon atoms to a precision of about − 0.2±2.5% (155 data points), which is similar to the experimental precision. Heat capacity contributions of 42 groups are given over the full range of measurement and reasonable extrapolation. The quality of the addition scheme is tested on 16 series of measurements on homopolymers, copolymers and blends. The addition scheme works for all these different states of aggregation of the constituent groups. The basis of the addition scheme is discussed.

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The thermal behavior of poly(2,6-dimethyl-1,4-phenyiene oxide) (PPO R resin), poly(3-bromo-2,6-dimethyl-1,4-phenylene oxide), and a series of their statistical copolymers with identical average molecular lengths has been characterized by thermogravimetry and computer-interfaced differential scanning calorimetry. The heat capacities are found to be additive with respect to the concentrations of the two components. The change in heat capacity at the glass transition (Δ C p) is independent of composition for bromination of up to 75% of the repeat units. At higher bromine levelsΔ C p decreases abruptly. This behavior is attributed to the temperature dependence ofΔ C p for the two components. The glass transition temperature (T g) of the copolymers varies nearly linearly with composition. A comparison of the experimental values ofT g is made with various equations derived for statistical copolymers and homogeneous polymer blends. A modification of the Couchman equation is presented taking into account the temperature dependence ofΔC p.

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The low temperature heat capacities of 13 group IV chalcogenides are examined. The heat capacity of crystals with largely isotropic structure (GeTe, SnSe, SnTe, PbS, PbSe, PbTe) can be represented within ±3% by a three-dimensional Debye function (θ 3=205, 230, 175, 225, 150 and 130, respectively). The heat capacity of crystals with anisotropic structures (GeS, GeSe, SnS, GeS2 and SnS2) could only be represented by pairs of two-dimensional Debye functions for the longitudinal and transverse lattice vibrations (error ±0.5 to 3%;θ 2 (l)=505, 345, 400, 705, 480 and 570, respectively, andθ 2 (t)=200, 185, 160, 175, 100 and 265, respectively).

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