Synthesis And Properties Of Linear Siloxane Side Chain Modified Diketopyrrolopyrrole Based Conjugated Polymers

In recent years,stretchable electronics are the mainstream direction of today's electronic devices,among which polymer semiconductors have received much attention as the key material for active devices.Side chain engineering has a profound impact on the performance of conjugated polymers.Siloxanes are an important class of side chains because of their unique physicochemical properties including high flexibility,thermal stability and weathering resistance.This thesis revolves around the engineering of siloxane side chains.Firstly,high-performance conjugated polymers modified with linear siloxane side chains of different lengths were designed and synthesized.Based on this study,the relationship between linear siloxane side chain structure and mechanical properties of semiconductor polymers is further explored to achieve synergistic optimization of high electrical properties and high mechanical properties of polymer semiconductors.The main contents of this thesis are summarized as follows.(1)A series of diketopyrrolopyrrole(DPP)and thiophene(TT)conjugated polymers with linear hybridized siloxane terminal side chains of different lengths were designed and synthesized.The number of silicon atoms in the side chains was 3,5 and 7(PTDPPTT-Si-3,PTDPPTT-Si-5 and PTDPPTT-Si-7,in contrast to the two reference polymers PTDPPTT-Ref-1 and PTDPPTT-Ref-2).Compared to PTDPPTT-Si-3,PTDPPTT-Si-5 and PTDPPTT-Si-7 have longer siloxane terminal groups and therefore have higher solubility and obtain higher molecular weights during polymerization reactions.The extended siloxane side chain polymers maintained higher transistor properties of 2.44 cm² V^-1 s^-1 and 2.18 cm² V^-1 s^-1,respectively,and the PTDPPTT-Si-7 polymers still showed higher carrier mobility when processed with the non-chlorinated solvents toluene and n-hexane.(2)The film morphology,mechanical properties,and electrical stability of the conjugated polymers with different lengths of siloxane side chains under stretching were investigated.Compared with PTDPPTT-Si-5 and PTDPPTT-Ref-2,PTDPPTT-Si-7 exhibited excellent ductility and low tensile modulus of 108�21 MPa,and retained80%of the initial mobility at 100%stretching.Meanwhile,PTDPPTT-Si-7 exhibits excellent fatigue resistance and retains stable mobility,threshold voltage and switching ratio under 400 cycles of stretching at 50%strain.In addition,the extended linear siloxane side chain reduces the contact angle of the polymer solution on hydrophobic surfaces and improves the solution processability of the conjugated polymer.This study provides important guidelines for the application of linear siloxane side chain-modified semiconductor polymers in wearable electronics.