Shape memory induced structural evolution of high performance copolyimides

Abstract

In this work, two kinds of high temperature shape memory copolyimides were prepared and the shape memory cycles induced structural evolution of macromolecular chains was investigated in detail. The glass transition temperature (T g ) of poly(benzoxazole-co-imide) (PI1) and poly(benzimidazole-co-imide) (PI2) are 280 8C and 355 8C, respectively. The results show that PI1 could keep stable macromolecular chain structure under shape memory cycles and exhibit outstanding shape memory performance (R f > 98%, R r > 97%) under different stretch condition. Whereas, shape memory cycles induced orientation with more ordered macromolecular chains packing is formed for PI2 after several thermal mechanical cycles,

Transparent, High Glass-Transition Temperature, Shape Memory Hybrid Polyimides Based on Polyhedral Oligomeric Silsesquioxane

“…Optically transparent PIs with high thermal resistance have drawn great attention due to their extensive applications as transparent flexible substrates of optoelectronic devices, such as image displays, organic photovoltaics, printing circuit boards, and touch panels [4]. High temperature-resistant transparent PIs with shape memory effect, which involve conversion into a temporary shape and restoration to the original shape under external stimuli, have potential in advanced adaptive optoelectronic and deployable aerospace structural applications [2,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. However, the trade-off between good transparency and thermal stability of PI films remains challenging due to the contradiction between the two properties in many instances [4].…”

The retarding effects and structural evolution of a bio‐based high‐performance polyimide during thermal imidization

“…Due to the excellent thermal and mechanical properties, good electrical properties, and a series of outstanding performances under extreme conditions, aromatic PI films have attained much attention over the past decades, which have been used in optics, aerospace, and microelectronic fields . Recently, PIs were also used in synthesis of aerogel and got a noticeable ability of oil absorbance even in harsh environment and showed extraordinary potential in shape‐memory materials as well …”

High-Temperature-Induced Shape Memory Copolyimide

“…Shape fixity (R f ) and shape recovery (R r ) of the polyimide films were calculated according to the recorded spline deformation following Equations (1) and (2) [ 17 ] where ε f represents the strain of the spline at the fixed temporary shape after removing the stress, ε m represents the maximum strain under stress, ε p represents the residual strain in the sample after the shape memory test, and N represents the number of cycles.…”

“…Then, lowering the temperature to freeze the chain segments fixes the material’s shape. When heating the material above the glass transition temperature, entropic elasticity allows the chain segments to return to the equilibrium position under the action of the crosslinking network so as to trigger the shape recoveries [ 16 , 17 ]. For instance, Kong and Xiao [ 18 ] added ether bonds and flexible segments to the molecular chain by simultaneously employing 4,4′-(1,1′-biphenyl-4,4′-diyldioxy)dianiline (BAPB) and bis phenol A dianhydride (BPADA) to provide the macromolecules with a large number of entanglements and strong π–π interactions between the chains that function as a stationary phase.…”