The molecular mechanism of the thermo-responsive shape memory effect of self-assembled poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} fiber

A new molecular mechanism is proposed to explain the shape memory effect of mesogen-jacketed liquid crystalline polymer fiber-poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} (PBPCS) fiber-designed in the molecular level. Due to the strong coupling effect between flexible backbone and rigid side mesogens, the molecular structure of PBPCS can be regarded as dual chains model that is constituted by a flexible backbone chain and a rigid side chain in parallel. The flexible backbone chains are reversible above the transition temperature and act as a switch structure, the physically cross-linked points caused by the pi-pi weak interactions between rigid side mesogens are responsible for memorizing a shape function and act as a fixing structure; therefore, the switch structure (flexible backbone) and the fixing structure (rigid mesogens) are found in each macromolecular chain. Furthermore, the shape memory behavior of PBPCS fibers is discussed by a viscoelastic molecular model consisting of two Maxwell models in parallel, the obtained theoretical values by dual chains model was in agreement with experimental results, very well. The viscoelastic molecular model described for shape memory process was correlated to the molecular mechanism explained for shape memory effect. This work provides a new idea and significant approach for design of new shape memory polymers.