Exploring Dynamic Equilibrium of Diels-Alder Reaction for Solid State. Plasticity in Remoldable Shape Memory Polymer Network

Transcription

1 Supporting Information Exploring Dynamic Equilibrium of Diels-Alder Reaction for Solid State Plasticity in Remoldable Shape Memory Polymer Network Guogao Zhang, Qian Zhao*, Lipeng Yang, Weike Zou, Xiangyi Xi, Tao Xie* State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou , China. Materials: Furfurylamine (FA), 2,2-Bis(4-glycidyloxyphenyl)-propane (BGPP) were purchased from TCI. 1,1 -(Methylenedi-4,1-phenylene)bismaleimide (BM) was procured from Sigma-Aldrich. Anhydrous N N-Dimethylformamide (DMF) was obtained from Aladdin. All the reagents were used as received without further purification. Polymer Network Synthesis: Stoichiometric amounts of FA and BGPP were mixed in DMF to form a 30 wt% solution, then reacted in a closed vessel at 120 C for 12 h. The obtained solution was mixed with BM to form a clear solution, which was then poured into an open PTFE round mold with a diameter of 80 mm. The solution was allowed to react at 70 C for 10 h with solvent partially evaporated to yield a gel. Afterwards, the gel was dried at 70 C under vacuum for another 50 h. Dynamic mechanical analysis (DMA) was conducted in a TA Q800 instrument in Multi-frequencystrain mode (frequency: 1 Hz; heating rate: 5 C min -1 ). Static thermo-mechanical tests including shape memory cycles and stress relaxation were carried out at a Strain rate mode. Shape fixity and recovery were calculated by Equation 1, where ε load represents the maximum strain under load, ε rec is the recovered strain, and ε d is the fixed strain after cooling and restriction removal.

2 R = and R = (1) Shape retention ratio (R ret ) for plasticity cycles were calculated from Equation 2, with ε load and ε ret representing strain before and after load removal, respectively. R ret = (2) The values of strain at break (ε b ) were measured under a tensile test condition using a universal material testing machine (Zwick/Roell Z005, 50 C, 5 mm min -1 ) equipped with a thermal chamber. Samples in dogbone shapes with the neck dimensions of 0.5*4.5mm were used. At least five specimens were tested for each sample. Young s modulus and tensile strength of DA0.2 were measured at 60 C, 90 C, and 120 C, at strain rates of 50 mm min -1. The crosslinking degree of DA0.2 at different temperatures was calculated by the Equation 3 where d is the crosslinking degree, E is the Young s modulus, R is the gas constant and T is the absolute temperature. d= (3) Gel permeation chromatography (GPC) was conducted with a Waters 2414 instrument with a refractometric detector. The solvent was THF and the calibration was done with monodisperse polystyrene. Liquid state remolding was conducted by placing the polymer sample between two clean polyimide films with a round steel spacer (diameter of 28 mm and thickness of 1.7 mm). The sample was heated to 140 C under 0.5 kn of pressure for 8 min, and quenched in air to room temperature. The obtained round disk was further compressed against a coin at the same temperature and pressure. The molded polymer coin (thickness: 1.7 mm) was subsequently annealed at 70 C for 2 hours. Differential scanning calorimetry (DSC) was conducted in a TA Q200 instrument. In the first heating process, samples were equilibrated at -20 C, then heated to 200 C at a rate of 10 C min -1. After 2

3 cooling to -20 C, the samples were heated to 200 C again at a rate of 10 C min -1 in a second heating process. Fourier transform infrared (FTIR) spectra were recorded with a ThermoFisher Nicolet5700 Fourier transformation infrared spectrometer. A mixture of FA-BGPP and BM was dissolved in dichloromethane, and then the solution was coated on the surface of a KBr tablet. FTIR spectra were recorded right now after the coating was dried at room temperature, and other spectra were recorded after heating the coating at 70 C for 2 h and 8 h. Figure S1. 1 H-NMR spectra of (A) a mixture of FA and BGPP and (B) FA-BGPP oligomer show the complete reaction of FA and BGPP as indicated by the disappearance of the peak 1, 2. 3

4 Figure S2. FTIR spectra of a mixture of FA-BGPP and BM treated at 70 C for 0 h (A), 2 h (B), 8 h (C). The peak at 1775 cm -1 is specific to DA adducts of maleimide and furan. The DA reaction in this system can be finished completely within 2 hours, since there is no visible difference between the FTIR spectra after the reaction at 70 C for 2 h and 8 h. 4

5 Figure S3. DSC heating traces of (a) DA0, (b) DA0.1, (c) DA0.2, (d) DA0.3. The solid lines represent the first heating trace, and the dash lines represent the second heating trace. The endothermic peaks come from the retro-da reaction at elevated temperature, which confirms the formation of DA adducts in DA0.1, DA0.2, DA0.3. Table S1. Mechanical properties of DA0.2 at different temperatures. Temperature ( C) Young s modulus (MPa) Tensile strength (MPa) Crosslinking density (10-4 mol/cm 3 )