It is well known that viscoelastic behavior strongly affects the properties of lightly crosslinked cellular polymers (e.g., thermoformability, primary and secondary foamability). Polyolefin foams, crosslinked to equivalent gel levels by either irradiation (< T_m) or peroxide (>T_m) processes, exhibit different viscoelastic characteristics in the melt state. This implies that polymer crosslinking and foam expansion dynamics play critical and sometimes interrelated roles in defining material properties, and that sol/gel measurements alone cannot adequately characterize these networks due to entropic (i.e., network order) effects. The effect of network order on the viscoelastic properties of crosslinked cellular polyethylene was systematically studied as described herein.
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