3D‐Printable Shape‐Memory Polymers Based on Halogen Bond Interactions

Abstract

The supramolecular halogen bonding (XB) is utilized for the first time for the preparation of shape‐memory polymers. For this purpose, an iodotriazole‐based bidentate XB donor featuring a methacrylamide is synthesized. Free radical polymerization of the XB donor monomer together with butyl methacrylate, triethylene glycole dimethacrylate, and methacrylic acid results in covalently cross‐linked polymer networks bearing both, halogen bond acceptors and donors, in their side chains. While the reversible halogen bond interactions can act as switching unit, the required stable phase of the shape‐memory polymers is formed by covalent cross‐links. The successful formation of the supramolecular cross‐links is proven via Fourier‐transform Raman spectroscopy. Furthermore, the thermal properties are investigated via differential scanning calorimetry and thermo gravimetric analysis. Thermo‐mechanical analysis reveals excellent shape‐memory abilities with fixity rates above 95% and recovery rates up to 99%. Moreover, it is possible to 3D‐print this kind of material exhibiting the ability to recover its shape within a few seconds at 130 °C.

Exploring the principles of self-healing polymers based on halogen bond interactions

“…For this purpose, XB-MA, a methacrylamide-based monomer featuring a XB donor, was prepared according to the literature. (Meurer et al, 2022) Subsequently, the XB donor polymer (P1) was synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization of the monomer XB-MA and butyl methacrylate (BMA) as comonomer (Scheme 1a). A monomer ratio of BMA to XB-MA of 20:1 was utilized for the polymerization to guarantee a suitable degree of crosslinking.…”

“…(Messina et al, 2000;Wang et al, 2019) It has successfully been applied in the past to investigate specifically XB in self-healing (Tepper et al, 2017;Dahlke et al, 2018b) as well as in shape-memory polymers. (Meurer et al, 2022) Based on earlier investigation of the XB-MA donor (Meurer et al, 2022), characteristic Raman bands (ca. 282 cm −1 (ν(C-X)) and 1,534, 1,580, 1,608 cm −1 (ν(C-C/N ar )) could be identified, which shift in position upon binding to a XB acceptor.…”

“…While this makes it impossible to definitely confirm the presence of XBs within the polymer, this observation is in line with previous results on XB-based polymers. (Meurer et al, 2022) Since XBs formed with free carboxylic acids are much weaker compared to ionic species (Lieffrig et al, 2013), less changes to the electronic structure and, thus, the vibrational structure are expected. While in previous works, a small shift of ca.…”

“…(Auguie et al, 2015) 4.2 Polymer synthesis XB-MA was synthesized according to literature. (Meurer et al, 2022) P1: 0.129 g XB-MA (1.41 mmol), 4.00 g BMA (28.13 mmol) and 52 mg 2-cyanopropan-2-yl benzodithioate (CPDB) (0.24 mmol) were combined in a round bottom flask. Subsequently, 9.7 mg (0.06 mmol) 2,2′azobis (2-methylpropionitrile) (AIBN) were added via a stock solution in DMF, further DMF was added up to a total of 15 ml DMF (2 mol/L) and the solution was degassed with nitrogen for 50 min.…”

“…(Bulfield and Huber, 2016;Sutar and Huber, 2019) A rather new field for XBs are supramolecular-driven smart polymer materials. (Vanderkooy and Taylor, 2015;Kampes et al, 2021;Meurer et al, 2022) Despite their analogies to HB-based materials, there are only very few reports on designing such materials. Hereby two different approaches have been utilized for the preparation of self-healing XB-based polymers.…”