Chemistry Reference
In-Depth Information
2.7. Thermal analysis
Differential scanning calorimetry (DSC) was employed for the measurement of
the glass transition temperatures and detection of any other thermal transitions.
For this purpose, a TA Instruments, DSC 2910, was used with a heating rate of
10
C/min for samples weighing 5-15 mg. Decomposition onset temperatures were
determined by thermogravimetric analysis (TGA) employing a TA Instruments,
TGA 2950. The in-plane coefficients of thermal expansion (CTE) of the copoly-
mers were measured as a function of temperature via thermomechanical analysis
(TMA). The technique utilized a TA Instruments, TMA 2940, in tensile film
mode with a heating rate of 4°C/min and typical sample dimensions of 100
°
m
thick x 15 mm long x 5 mm wide. The CTE's were determined from the slopes of
the resultant expansion-temperature plots.
µ
2.8. Dynamic mechanical analysis
Dynamic mechanical analysis (DMA) was performed in order to determine the in-
fluence of the copolymer constitution on tensile modulus and on mechanical re-
laxation behavior. For this purpose a Perkin Elmer DMA-7 was run in tensile
mode, at an oscillation frequency of 1 Hz with a static stress level of 5
10
5
Pa and
×
10
5
Pa. With this stress controlled instrument,
the strain and phase difference between stress and strain are the measured outputs.
Typically, the resulting strain levels ranged from 0.05% to 0.2% while sample
dimensions were 8 mm long, 2 mm wide, and 0.1 mm thick. A gaseous helium
purge and a heating rate of 3°C/min were employed. The temperature scale was
calibrated with indium, and the force and compliance calibrations were performed
following conventional methods.
a superposed oscillatory stress of 4
×
2.9. Dielectric spectroscopy
Dielectric measurements were made mainly with an EG&G Model 398 Imped-
ance System over a frequency range from 0.1 Hz to 5 MHz, using an amplitude of
5 mV rms. The sample holder consisted of two stainless steel circular plates of
12.7 mm diameter pressed against each side of the polymer film. Sample thick-
nesses as measured by a digital micrometer, an optical microscope and scanning
electron microscopy ranged from 38
µ
m to 134
µ
m, insuring that the dielectric
constants were bulk values.
Certain samples were also selected for the in-plane dielectric constant determi-
nation by the interdigitated comb method [10, 11]. These measurements were per-
formed on a TA Instruments, DEA 2970 Dielectric Analyzer, over a frequency
range from 3x10
-2
Hz to 10
5
Hz.
Waveguide coupling was employed to measure the refractive index of selected
polymer films of 4
m thickness at optical frequencies and to determine the ani-
sotropy of the polymer films [12-14]. For these measurements, a Metricon Model
2010 Prism Coupler was employed at 632.8 nm and 1152 nm wavelengths. The
µ
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