玻璃化转变温度可区域数字化调控的形状记忆聚合物

Thermal transition temperatures (e.g. glass transition temperatures) play an important role in various applications of shape memory polymers that can recover from temporary shapes to original (permanent) shapes upon heating. This study reports a shape memory epoxy with unsaturated double bonds, enabling a secondary photocuring process. Dual-functional epoxy monomer, E44, and monofunctional epoxy monomer, glycidyl methacrylate, are first thermally cured via a polyether amine crosslinker. Properties of the cured epoxy can be finely tuned by controlling the feed compositions. The increase of feed ratio of glycidyl methacrylate will lead to lower glass transition temperature and elastic modulus, whereas larger strain at break. In the secondary photocuring process, the unsaturated bonds provided by glycidyl methacrylate are polymerized after light exposure, forming additional crosslinking points. As a result, the glass transition temperature of the material increases. Herein, digital photo-masking technique is applied for the photocuring process via a commercial projector. The regional exposure time of the material can be conducted, and thus, the local glass transition temperature can be controlled in a range of approximately 40 − 70 °C. Storage modulus at the rubbery state of the material increases from approximately 0.5 MPa to 8 MPa after photo exposure for 240 s, implying that there is a remarkable increase of the crosslinking density via the secondary photocuring. Both the materials before and after the secondary photocuring provide ideal shape memory performance. The shape fixity ratios and shape recovery ratios retain nearly 100% during six shape memory cycles, indicating good thermo-mechanical stability of the material. The material with regional controllable glass transition temperature enables a programmable multi-shape recovery process. Complex original shapes can be fabricated if the secondary photocuring is conducted towards a thermally cured epoxy. In addition, the material can be potentially applied as a novel substrate for stretchable electronics due to its strain isolation functionality.