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Isothermal crystallization kinetics of low‐density polyethylene (LDPE) were measured from 96°C‐103°C using a power‐compensating differential scanning calorimetry (DSC). Crystallization kinetics were measured using different sample thicknesses and on samples compounded with nickel, a filler with high thermal conductivity. For the unfilled material, sample thickness and temperature had a significant effect on the rate of crystallization as measured by the Avrami rate constant K, but had no effect on the nucleation mechanism and dimensionality of growth, as measured by the Avrami constant n. The crystallization growth rate as expressed by K1/n scaled approximately with the thickness of the sample. For the filled material, K was much higher and independent of nickel content, suggesting a limiting growth rate for polyethylene at a given temperature in this equipment. The dependence of crystallization rale on sample thickness indicates that barriers to heat transfer can be important. This work shows that for most crystallization rates, thermal conductivity, rather than interfacial resistance between sample and pan, limits heat transfer. Even though thermal conductivity typically dominates heat‐transfer resistance, sample‐pan thermal contact is still important, and some guidelines are given to determine whether good contact is being made.

A new liquid crystal monomer, the diacrylate of a bis phenyi diazene, was synthesized. It was polymerized to form both unoriented and oriented polymer solids --the latter in the presence of a magnetic field. The millimeter wave birefringence was measured for a polymeric rod, whose macroscopic orientation was perpendicular to its long axis, using a waveguide version of the Mach-Zehnder interferometer, and the measured An was 0.075 at 30 GHz. The mechanical strength of oriented and unoriented polymer plates was measured. The tensile modulus in the direction parallel to the oriented axis was 6.8~108 N/m2, which was about 4 times that of the same material without macroscopic orientation. The torsional rigidity modulus of a thin rod (orientation perpendicular to its length) was measured to be of the order 107 N/m4. Both the large dielectric anisotropy and high mechanical strength make the oriented polymer potentially suitable for application in a novel class of millimeter wave modulation devices.

Conductive polymer matrix composites have been a focus of research for the past 30 years, due to applications such as electromagnetic shielding. The electrical resistance of these materials can be broken into three major categories: the intrinsic resistance of the filler and matrix, the particle‐particle contact resistance, and the tunneling resistance. Both the particle‐particle contact and tunneling resistance in nickel filled low density polyethylene (LDPE) composites can be reduced by the addition of an ultrathin polypyrrole (PPy) coating on the nickel surface. Coating the nickel particles with PPy leads to increases in conductivity as much as three order of magnitude at concentrations well above the percolation threshold without significantly changing the mechanical properties. We believe at concentrations above the critical region PPy forms “molecular wires” reducing the loss of conductivity associated with the uniaxial orientation of the polymer matrix.