The nature of bonding matters: Benzoxazine based shape memory polymers

Thermosetting Shape Memory Polymers and Composites Based on Polybenzoxazine Blends, Alloys and Copolymers

“…SEM images of fractured surfaces before and after extraction are presented in Figure . As described by the groups of H. Ishida, S. Zheng and K. Koschek PCL/PBA‐a blends (represented here by the sample Bz‐OH‐70) show a strong phase separation evidenced by a rough fractured surface . Extraction of free PCL leaves solely an agglomerated PBA‐a particle structure.…”

“…Thus, in PCL/PBA-a alloys both network density and free PCL are crucial for high shape fixity and recovery ( Figure 6). [32][33][34] Comparing the properties of the PCL/epoxy and PCL/benzoxazine based SMPs,t he overall shapem emory properties (S f and S r )a re similar.W ith respect to the mechanical properties, PBA-a features ap ronounceds tiffness with am ore than two times highers toragem odulus at RT (987 MPa vs. 236 MPa, Ta ble 2) and as hiftt oe levated temperatures at al ow storage modulus( shapeabilityt emperature).I nc ontrastt ot he PCL/ epoxy based SMP hydroxyl end group modification is required for covalent incorporation of thermoplastic oligomers into the PBA-a network. Despitet he additional manufacturing step, benzoxazine chemistry allows for af lexible material design as the epoxy based approach is limited to cycloaliphatic epoxy monomers and their need of thermolatent initiators restricts the use of high T m thermoplastics.…”

“…Thus, attempts to alloy hydroxyl‐terminated PCL with bisphenol A based benzoxazine resulted immiscible blends due to strong phase separation. That could be overcome by end group tosylation of PCLs hydroxyl end groups, leading to a covalent incorporation of the polyester by a nucleophilic attack of the benzoxazine onto the tosylated polyester . Gel content determinations proved that the neat hydroxyl‐terminated PCL oligomers form phase separated blend like samples, whereas the tosyl bearing PCL resulted copolymer like materials as depicted in Figure .…”

“…The authors concluded that the network density of PBA‐a can be adjusted by covalent incorporation of PCL oligomeric chains allowing for shapeability and recovery, whereas free partially crystalline PCL stabilizes the network and fixes the new, temporary shape. Thus, in PCL/PBA‐a alloys both network density and free PCL are crucial for high shape fixity and recovery (Figure ) …”

“…As described by the groups of H. Ishida, S. Zheng and K. Koschek PCL/PBA-a blends (represented here by the sample Bz-OH-70) show as trongp hase separation evidenced by ar ough fractured surface. [31,33,35] Extraction of free PCL leaves solely an agglomerated PBA-a particles tructure. In contrast, the copolymer like alloys exhibited as mooth surface pointingt oh omogenous distribution and incorporation of PCL before and after extraction.…”