Investigation On Shape Memory Properties Of Composites And Nanoparticle Based On Poly(ε-Caprolactone)

Shape-memory polymers (SMPs) have been applied or displayed great potential in biomedical fields and some other fields. The environment that they stayed in is generally under normal conditions at room temperature and atmospheric pressure, however, sometimes they can be applied under extreme conditions such as high temperature and high pressure. To the best of our knowledge, the influence of the high pressure on the shape memory function of SMPs has received little attention. Cross-linked poly(ε-caprolactone) (PCL) and PCL-based nanocomposites have a good shape memory function upon a temperature stimulus, which belong to the Tm-type (the melting temperature type) dependent shape recovery. More importantly, maintaining and/or improving the shape memory function of SMPs under an extreme condition is very critical to expand their applications. Shape memory properties of SMPs can be influenced by the glass transition temperature (Tg) or the melting temperature (Tm), and the Tm is tunable by controlling the crystallinity of the SMPs.In this study, we developed a new method to improve the shape memory properties of PCL-NCC (PCL-nanocrystalline cellulose) nanocomposites via the recrystallization under a high-pressure environment. The nanocomposites were obtained first by mixing PCL, benzoyl peroxide (BPO) as the initiator, and NCC as nanofillers in N,N-dimethylformamide (DMF); second, they were dried and loaded into a mold; finally recrystallized at 140℃ under a high pressure environment. By increasing the pressure during the recrystallization of PCL matrix in the nanocomposites, the crystal parameters of PCL including the grain size, the degree of crystallinity and the melting temperature all produced a decreased change. Interestingly, these variations lead to an improvement of shape memory function of PCL-NCC nanocomposites.Additionally, the morphologies of nanocarriers for controlling drug delivery system have a certain effect on the long cycle in the blood. In order to achieve a better therapeutic effect by regulating the nanoparticle morphologies intelligently, shape memory polymers may be used to prepare nanoparticles. Based on this, cross-linked six arm poly(ethylene glycol)-poly(ε-caprolactone) (c-6 arm PEG-PCL) nanoparticle with shape memory effect was also prepared.The ellipsoidal nanoparticle was achieved by stretching polyvinyl alcohol (PVA) film. Atomic force microscope (AFM) was employed to observe the shape memory effect of c-6 arm PEG-PCL nanoparticle, which recovered to initial shape at 45℃. We can know that the nanoparticle of c-6 arm PEG-PCL has a good shape memory effect by calculating the aspect ratio of nanoparticle in the shape memory process.