The shape memory properties of polycaprolactone-based polyurethanes (PCLUs) synthesized via a novel route of reactive extrusion were investigated in terms of the deformation amplitude, temperature, and rate by differential scanning calorimetry (DSC), dynamic mechanical analyzer, and polarized optical microscopy (POM). DSC analysis shows that the crystalline melting temperature and crystallinity of PCLU increased monotonically with increasing the average polymerization degree ðDPnÞ of poly(e-caprolactone) (PCL) block. The retract force increased with increasing the temperature and reached the maximum (6-7 MPa) within 45-55 C. Furthermore, a modified model with two recovery stages was postulated to elucidate the shape memory process, which is visually presented by POM analysis. The two stages of tensile and compressive recovery are distinguished by the inflexion temperature, within 43-48 C and 64-66 C, respectively. The shape fixity is about 60-70% and can be improved to 100% by choosing proper deformation temperature. The tensile deformation recovery ratio was 80-98% due to the water absorption, whereas the compressive deformation recovery ratio was almost 100%. Besides, recovery tests show that the lowest recovery temperature ranged from 24 to 47 C was influenced by the deformation temperature, rate and the PCL block ðDPnÞ. Thus, the shape memory properties can be adjusted according to different purposes. INTRODUCTIONShape memory polymers, as novel smart materials, have attracted extensive interest 1-16 for their potential promising applications including biomaterials, 1,17 actuators, 5 sensors, 18 and smart textile. 19 In general, the shape memory effect was realized by the cooperation of the chemical or physical cross links and the reversible network chains, which can play the roles of fixed phase and molecular switch, 4,12,16 respectively. The cross links are employed in the course of shape memorization to memorize the original shape. Although the reversible network chains are designed to have a thermal transition at certain temperature, which can be either T g (the reversible network chains are amorphous) or T m (the reversible network chains are crystalline). The reversible network chains are flexible, and therefore the polymers can develop large deformation above the transition temperature. In contrast, they are frozen to lose mobility, and thus the polymers can fixed in a temporary shape below the transition temperature. Shape memory polyurethanes have been an important category in the shape memory polymer family because certain segmented polyurethanes were found to exhibit shape memory effect. 14,15,17 Due to the thermodynamical dissimilarity, the shape memory polyurethanes will separate into hard-segment and soft-segment microphases, which play the roles of fixed phase and reversible network chains for the shape memory effect, respectively. 4,16 Many attempts have been made to elucidate the relationship between the structure and shape memory effect of the polyurethanes. 14,15,[20][21][22][23][24][25] The...

Polyurethanes with multiblock copolymers of poly(e-caprolactone) (PCL) and poly(tetramethylene oxide) glycol (PTMG) or poly(ethylene glycol) (PEG) as a soft segment were synthesized in situ via reactive extrusion from e-caprolactone (CL) and 4,4 0 -diphenylmethane diisocyanate (MDI). The titanium alkoxide mixture generated from an ester-exchange reaction between titanium propoxide [Ti(OPr) 4 ], and excessive PTMG or PEG was used as an initiator and catalyst. Compared to the reported fabrication of polycaprolactone-based polyurethane (PCLU), the in situ reactive extrusion preparation not only explored a new rapid route for the fabrication of PCLU but also offered a simplified, controllable approach for the production of PCLU in a successive mass scale. A series of PTMG-PCLUs and PEG-PCLUs with different PCL block-average degrees of polymerization (DP n 's) were prepared by only an adjustment of the relative concentration of CL in the reaction system, with a certain constant molar ratio of MDI to titanium alkoxide.1 H-NMR, gel permeation chromatography, and differential scanning calorimetry results indicate that all of the CL monomers were converted in the polymerization, and the molecular weight of the copolymers was about 8 Â 10 4 g/mol with a polydispersity index of approximate 2.4. With an increase in the PCL block-average DP n in PTMG-PCLU from 25 to 40, the tensile strength increased from 16.5 to 22.7 MPa, and the melting point increased from 46.1 to 49.5 C. It was also verified by PEG-PCLU prepared with organic Ti of lowered content in the initiator mixture that the mechanical properties could be greatly affected and dropped with decreasing content of organic Ti in the initiator mixture.