Facile control of high temperature shape memory polymers

Abstract

Glass transition temperature (Tg) is crucial in determining application areas of high temperature shape memory polymers (SMPs), but some Tgs are difficult or uneconomic to be obtained. Here we introduce a facile way to prepare high temperature SMPs with controllable Tgs from 183 to 230 °C by copolymerization of polyimides, and relationships between Tgs and diamine components of the shape memory copolyimides agree with Fox Equation. These copolyimides can fix temporary shape and return to original shape nicely, and the possible mechanisms of their high shape fixity and shape recovery are analyzed on the basis of thermomechanical properties and molecular structures. The copolymerization of shape memory polyimides has offered an effective way to obtain high temperature SMPs with desired properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44902.

Electroactive High‐Temperature Shape Memory Polymers with High Recovery Stress Induced by Ground Carbon Fibers

“…The shape memory of EASMPI is activated by the most common direct heat at first, as shown in Figure . It can fix the temporary U shape with high R f of 96.3% (Figure a), and the high R f is mainly due to the fact that E′ in glassy state is much higher than that in rubbery state, and the large difference in E′ during cooling can efficiently freeze chain mobility and fix the temporary shape very well . The images showing shape recovery of EASMPI on 322 °C hot‐stage at 2, 3, 6, 9, and 18 s are manifested in Figures b–f, respectively.…”

“…The peak of tan δ is usually taken as T g of polyimides, and T g of pure SMPI and EASMPI are 295 and 302 °C (Figure a) . T g is related with chain segmental motions, and EASMPI exhibits enhanced T g because GCFs can obstruct chain movements of the polyimide chains and more heat energy is required to overcome the friction among macromolecules and GCF . The decreased peak height of tan δ demonstrates that EASMPI possesses lower damping capability than pure SMPI due to the existence of carbon fibers.…”

“…It can fix the temporary U shape with high R f of 96.3% (Figure 6a), and the high R f is mainly due to the fact that E′ in glassy state is much higher than that in rubbery state, and the large difference in E′ during cooling can efficiently freeze chain mobility and fix the temporary shape very well. [33] The images showing shape recovery of EASMPI on 322 °C hot-stage at 2, 3, 6, 9, and 18 s are manifested in Figures 6b-6f, respectively. R r of SMP is mainly determined by the permanent phase, while GCF can reduce the permanent phase of EASMPI by interrupting the poly imide chain entanglements and destroying the intermolecular π-π interactions.…”

“…[28][29][30] T g is a most critical parameter for SMPs stimulated with direct heating, and T g of SMPI can be higher than 300 °C by adjusting molecular structure, molecular weight, crosslink density, etc. [31][32][33][34][35] From the viewpoint of applications, electroactive SMPI (EASMPI) that can be activated conveniently with electricity is strongly desired, but the SMPIs reported are just activated with direct heat until now. [36] During the exploration, we have observed that it is very difficult for some conductive fillers such as silver nanowires, carbon nanotubes, carbon black, and graphene to produce EASMPI, although they have produced other electroactive SMPs.…”

“…As a kind of typical high temperature SMP with extraordinary mechanical properties and excellent thermal stability, shape memory polyimide (SMPI) has vast potential in applications subjected to severe conditions such as high temperature actuators, deployable space structures, and smart jet propulsion systems . T g is a most critical parameter for SMPs stimulated with direct heating, and T g of SMPI can be higher than 300 °C by adjusting molecular structure, molecular weight, crosslink density, etc . From the viewpoint of applications, electroactive SMPI (EASMPI) that can be activated conveniently with electricity is strongly desired, but the SMPIs reported are just activated with direct heat until now .…”