Design and structural study of a triple-shape memory PCL/PVC blend

- Facile preparation of a new triple-shape memory polymer material, PCL/PVC blend, was achieved.
- The PCL-30% had a broad glass transition and displayed the mechanical properties like an elastomer.
- The nano-scale PCL crystals and chain entanglements served as the physical networks.
- The amorphous PVC and PCL regions acted as the reversible phase at high and low switch temperatures respectively.

Poly(ε-caprolactone) (PCL) and poly (vinyl chloride) (PVC) are miscible with each other, and their glass transition temperatures differ a lot. With this feature, we tried to design a triple-shape memory material by simply blending them together. After carefully examining the glass transition broadness and the tensile behavior of various PCL/PVC blends, PCL-30% (the weight fraction of PCL was 30%) was picked out as the best candidate. It fulfills two criterions that it has a wide glass transition range and it has no strain or stress induced crystallization. Subsequent triple-shape memory procedure proves that it could function as an effective shape memory blend. The structure was studied by SAXS/WAXS and nano-scale periodic structure was found, which was composed of crystalline and amorphous PCL regions of 4.7 nm and 8.4 nm respectively. Such periodic domains would orient along the stretch direction, but it kept stable and could restore to its original state after the stress was released. Dichromic FTIR discerned the orientation of PCL chains at low temperature and PVC chains at high temperature. It can be concluded that both the nano-scale PCL crystalline structures and physical entanglements served as the fixed phase, while the amorphous PVC and PCL regions played as the reversible phase at high and low switch temperatures respectively.