Butyl rubber-based interpenetrating polymer networks with side chain crystallinity: Self-healing and shape-memory polymers with tunable thermal and mechanical properties

A self-healing and shape-memory interpenetrating polymer network (IPN) is produced by UV polymerization of n-octadecyl acrylate (C18A) monomer in a toluene solution of butyl rubber (isobutylene-isoprene rubber, IIR) using Irgacure 2959 photoinitiator at ambient temperature. IPNs containing 20-80 wt% IIR have crystalline domains formed by side-by-side packed octadecyl side chains aligned perpendicular to the poly(C18A) (PC18A) backbone. TEM images reveal that the morphology of IPNs consists of crystalline domains dispersed in a continuous amorphous matrix where the size of the dispersed phase could be adjusted between mu m and nm level by changing the amount of IIR. Calculations indicate that the effective cross-link density of IPNs is mainly determined by their crystalline domains followed by hydrophobic associations while the chemical cross-links between IIR and PC18A components are negligible. We also show that the crystalline domains acting as sacrificial bonds dissipate energy under strain leading to a significant toughness improvement. IPNs exhibit tunable melting temperature (46-50 degrees C), crystallinity (1.5-25%), Young's modulus (0.6-35 MPa), toughness (1.3-12 MPa), and a stretchability of up to 1200% by varying the amount of IIR component. What is more, they also exhibit temperature induced healing behavior with 59-77% efficiency, and an effective shape-memory function. The strategy presented here is applicable for the preparation of IPNs based on various rubbers and poly(n-alkyl (meth)acrylates) with long alkyl side chains.

Automated summary

In this study, a self-healing and shape-memory interpenetrating polymer network (IPN) was synthesized by UV polymerization. It was found that the physical properties of IPNs, including melting temperature, crystallinity, Young's modulus, toughness, and stretchability, could be tuned by varying the amount of isobutylene-isoprene rubber (IIR). The crystalline structure acted as sacrificial bonds to dissipate energy under strain, leading to improved toughness. Furthermore, the IPNs exhibited temperature induced healing behavior and effective shape-memory function.