Shape Memory Behavior of Emulsion-Templated Poly(ε-Caprolactone) Synthesized by Organocatalyzed Ring-Opening Polymerization

Petra Utroša,Sebastijan Kovačič,David Pahovnik,Ema Žagar,Ozgun Can Onder

doi:10.1021/acs.macromol.9b01780

Petra Utroša, Sebastijan Kovačič + Show 3 more

Open Access

https://doi.org/10.1021/acs.macromol.9b01780

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Journal: Macromolecules	Publication Date: Nov 26, 2019
Citations: 34	License type: cc-by

Affiliation: National Institute of Chemistry

Abstract

Organocatalyzed ring-opening polymerization (ROP) of e-caprolactone (CL) and 4,4′-bioxepanyl-7,7′-dione as a bis-lactone cross-linker was performed within the oil-in-oil high internal phase emulsions (HIPEs) at 50 °C. In this way, the cross-linked poly(e-caprolactone) (PCL) polyHIPE foams of ∼85% porosity were synthesized. Thermomechanical properties of the prepared polyHIPEs were studied and proved to greatly depend on a degree of PCL cross-linking. The melting and crystallization temperatures as well as the degree of crystallinity of PCL polyHIPE foams decrease with an increasing cross-linking degree. Semi-crystalline polyHIPEs demonstrate shape memory behavior with excellent shape fixity and shape recovery. At an appropriate degree of PCL cross-linking, the polyHIPE temporary shape can be fixed at room temperature, while a transition to the permanent shape occurs upon heating at 40 °C. Moreover, a two-way shape memory behavior of the PCL polyHIPEs under constant stress was observed.

Highlights

High internal phase emulsion (HIPE) templating offers a route to produce highly interconnected porous polymer foams
PolyHIPE synthesis has been extended to other polymerization mechanisms, such as controlled radical polymerizations,[3,4] ring-opening metathesis polymerization (ROMP),[5,6] chain-growth insertion polymerization,[7] transition metal-catalyzed cross-couplings,[8] ring-opening polymerization (ROP),[9−11] and step-growth polymerizations
Degradable polyHIPEs based on poly(ε-caprolactone) (PCL) were synthesized, as PCL is an attractive and promising material for biomedical applications due to its good biocompatibility, degradability, and control over mechanical properties.[14,15]

Summary

Introduction

High internal phase emulsion (HIPE) templating offers a route to produce highly interconnected porous polymer foams. Polymerized HIPEs (polyHIPEs) are typically prepared via free-radical polymerization of vinyl monomers in aqueous emulsions.[1,2] Lately, polyHIPE synthesis has been extended to other polymerization mechanisms, such as controlled radical polymerizations,[3,4] ring-opening metathesis polymerization (ROMP),[5,6] chain-growth insertion polymerization,[7] transition metal-catalyzed cross-couplings,[8] ring-opening polymerization (ROP),[9−11] and step-growth polymerizations (thiol-ene[12] and thiol-yne[13]). HIPE templating produces highly interconnected porous structures, especially suitable for tissue engineering scaffolds.[1] Degradable polyHIPEs based on poly(ε-caprolactone) (PCL) were synthesized, as PCL is an attractive and promising material for biomedical applications due to its good biocompatibility, degradability, and control over mechanical properties.[14,15] PCL is a semi-crystalline polymer and as such can exhibit shape memory behavior. The shape memory phenomenon of polyHIPEs was reported only for the (meth)acrylate-based polyHIPEs, bearing the crystalline long side chains,[27,28] and for the polyHIPEs based on acrylamide and sodium acrylate that are capable of reversible metal coordination cross-linking.[29]

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