Comparison of Swollen vs. Compounded Cross‐linked High‐Cis‐1,4‐Polybutadiene/n‐Tetracosane Shape Memory Polymers

Abstract

Blending elastomers with phase change materials offers a modular approach to fabricating smart materials, such as shape memory polymers. This study compares shape memory polymers prepared by peroxide cross‐linking a blend of polybutadiene and n‐tetracosane (compounded samples) versus swelling peroxide cross‐linked polybutadiene in n‐tetracosane (swollen samples). Characterization of the thermal, thermomechanical, and shape memory behavior of the two types of samples show very similar behavior as a function of polybutadiene content. The sample with ca. 30% polybutadiene displayed shape memory metrics of ~90% fixity and ~99% recovery at 25% applied strain. The main difference in the samples was the change in fixity and recovery with cycling where they were heated and cooled using water baths. The compounded samples exhibited a 1.4% decrease in fixity, 0.2% decrease in recovery, and 2.25% weight loss over 20 cycles. In contrast, the swollen samples have a 4.2% decrease in fixity, 0.4% decrease in recovery, and 5.63% weight loss over 20 cycles. This weight loss was attributed to the expulsion of the n‐tetracosane that experienced a higher driving force in the swollen sample with stretched chains. The cyclic and long‐term aging of these polymers is different depending on the preparation method to incorporate the n‐tetracosane into the material.