Photo-patternable Stretchable Electroactive Conjugated Polymers

Abstract

Stretchable electronics have attracted growing interests due to their potential to enable a wide variety of unprecedented device applications, including flexible displays, energy-storage devices, sensors and biosensors. More recently, next-generation stretchable electronics are emerging involving wearable and implantable devices towards integration with soft tissues and biological systems. To realise these frontier applications, the devices are required to adhere and conform to the human body or tissues, while being able to stretch and even self-heal like the human skin. π-Conjugated polymers (CPs) are considered promising candidates as stretchable and bio-integrated electrical materials owing to their advantages of good flexibility, electronic and mechanical tunability by molecular engineering, and ease of processing through large-area printing techniques. In this Thesis, the engineering of molecular structures through rational macromolecular design of side chains has been demonstrated to develop multifunctional CPs with intrinsic stretchability and other desired mechanical functionalities. Firstly, a series of poly(thiophene phenylene)-graft-poly(n-butyl acrylate) (PThP-g-PBA) CPs with varied side-chain lengths were designed and synthesised to investigate their structure-property relationships, including the morphological, optical, electrochemical, electrical and mechanical properties. Besides, the fabrication processability of electronic materials with micro- and/or nanoscale patterns is essential for practical and fine device fabrication. Therefore, CPs that can be post-crosslinkable and directly patternable are highly desirable. Herein, to address the patterning issue, glycidyl methacrylate (GMA) segments were employed which contain chemically and photochemically reactive epoxy rings. On one hand, a poly(3,4- ethylenedioxythiophene) (PEDOT)-based CP was functionalized with poly(BA-co-GMA) side chains to impart softness, adhesiveness as well as post-crosslinking functionality. On the other III hand, a poly(3-hexylthiophene) (P3HT)-based semiconducting polymer with poly(ethylene glycol)methyl ether methacrylate-co-GMA) (poly(PEGMMA-co-GMA)) grafts was synthesised, which integrates the advantageous mechanical features of PEGMMA (i.e., softness, mechanical stretchability, and water-swellability) with the good electrical conductivity of P3HT. More importantly, it was reported for the first time the micro-patterning of grafted conducting copolymer films through the photo-crosslinking ability of the epoxybearing GMA side chains. In this research, a conclusion was drawn that the molecular engineering of CPs would be a straightforward way towards the development of electrically conductive and multifunctional polymers for versatile stretchable and wearable electronics.