Thermally-Induced Actuation of Magnetic Nanocomposites Based on Oligo(ω-Pentadecalactone) and Covalently Integrated Magnetic Nanoparticles

Abstract

The incorporation of inorganic particles in a polymer matrix has been established as a method to adjust the mechanical performance of composite materials. We report on the influence of covalent integration of magnetic nanoparticles (MNP) on the actuation behavior and mechanical performance of hybrid nanocomposite (H-NC) based shape-memory polymer actuators (SMPA). The H-NC were synthesized by reacting two types of oligo(ω-pentadecalactone) (OPDL) based precursors with terminal hydroxy groups, a three arm OPDL (³ AOPDL, M_n = 6000 g mol•1⁻¹ ) and an OPDL (M_n =3300 g • mol⁻¹ ) coated magnetite nanoparticle (Ø = 10 ± 2 nm), with a diisocyanate. These H-NC were compared to the homopolymer network regarding the actuation performance, contractual stress (σ_contr) as well as thermal and mechanical properties. The melting range of the OPDL crystals (ΔT_m,OPDL) was shifted in homo polymer networks from 36 ºC − 76 ºC to 41ºC − 81 °C for H-NC with 9 wt% of MNP content. The actuators were explored by variation of separating temperature (T_sep), which splits the OPDL crystalline domain into actuating and geometry determining segments. T_sep was varied in the melting range of the nanocomposites and the actuation capability and contractual stress (σ_contr) of the nanocomposite actuators could be adjusted. The reversible strain (ε_rev) was decreased from 11 ± 0.3% for homo polymer network to 3.2±0.3% for H-NC9 with 9 wt% of MNP indicating a restraining effect of the MNP on chain mobility. The results show that the performance of H-NCs in terms of thermal and elastic properties can be tailored by MNP content, however for higher reversible actuation, lower MNP contents are preferable.