Shape Fixity Rate Research Articles

Synthesis and Characterization of Three-Arm Poly(ε-caprolactone)-Based Poly(ester−urethanes) with Shape-Memory Effect at Body Temperature

Novel biodegradable star poly(ester−urethanes) containing three-arm poly(ε-caprolactone) (PCL) as switching segment were prepared as shape-memory polymers (SMPs) with switching temperature (Ts) around body temperature. PCL-triols with molecular weight (Mn) of 2700−4200 g/mol and Tm of 45−47 °C were synthesized in 55−67% yield by Novozym 435-catalyzed ring-opening polymerization of ε-caprolactone with glycerol as initiator, and their three-arm structures were confirmed by 1H and 13C NMR analysis. Reaction of the PCL-triols with methylene diphenyl 4,4′-diisocyanate isocynate and 1,6-hexanediol gave three-arm PCL-based poly(ester−urethane)s (tPCL-PUs) in 83−92% yield, with 65−75% soft segment. The structure of tPCL-PUs was confirmed by 1H NMR analysis, and the thermal properties were analyzed by DSC with Ts of 36−39 °C. tPCL-PUs showed excellent shape-memory effects at 38 °C during cyclic thermomechanical tensile tests: shape recovery within 10 s, shape fixity rate of 92%, and shape recovery rate of 99%. The novel biodegradable star SMPs are potentially useful in biomedical applications.

Shape-Memory Properties of Radiopaque Micro-Composites from Amorphous Polyether Urethanes Designed for Medical Application

AbstractBiocompatible shape-memory polymers are of high significance for application in medical devices or instruments for minimally invasive surgery. To follow the medical device placement or changes in shape of the device in vivo by imaging methods like X-ray techniques, radiopacity of the polymer is required. In this work, we explored the shape-memory properties of radiopaque polymer composites prepared by incorporation of barium sulphate micro-particles in a biomedical grade polyether urethane (PEU) by co-extrusion technique. The filler content was varied from 5 wt% to 40 wt%, which was confirmed by thermal gravimetric analysis (TGA) measurements, while the particle distribution was visualized by scanning electron microscopy (SEM). The thermal and mechanical properties of the composites were investigated by means of dynamic mechanical analysis at varied temperature (DMTA) and tensile tests. The shape-memory properties of PEU composites were quantified in cyclic, thermomechanical experiments. A significant increase in Young’s modulus and a decrease in elongation at break were observed for PEU composites with increasing content of BaSO4, while the DMTA results were not affected by incorporation of the fillers. All samples exhibited excellent shape-memory properties with shape fixity rates (Rf) above 98% and values for shape recovery rate (Rr) in the range of 81% to 93%. The maximum stress (σmax) obtained under constant strain recovery conditions increased from 0.6 MPa to 1.4 MPa with raising amount of BaSO4, while the corresponding temperature (Tσ,max) as well as the switching temperature (Tsw) determined under stress-free conditions remained constant for all polymer composites.

Effect of comonomer on thermal/mechanical and shape memory property of L‐lactide‐based shape‐memory copolymers

AbstractIn this study, three kinds of L‐lactide‐based copolymers, poly(lactide‐co‐glycolide) (PLGA), poly(lactide‐co‐p‐dioxanone) (PLDON) and poly(lactide‐co‐caprolactone) (PLC), were synthesized by the copolymerization of L‐lactide (L) with glycolide (G), or p‐dioxanone (DON) or ε‐caprolactone (CL), respectively. The copolymers were easily soluble in common organic solvents. The compositions of the copolymers were determined by 1H‐NMR. Thermal/mechanical and shape‐memory properties of the copolymers with different comonomers were compared. Moreover, the effect of the chain flexibility of the comonomers on thermal/mechanical and shape‐memory properties of the copolymers were investigated. The copolymers with appropriate lactyl content showed good shape‐memory properties where both the shape fixity rate (Rf)and the shape recovery rate (Rr) could exceed 95%. It was found that the comonomers with different flexible molecular chain have different effects on their thermal/mechanical and shape‐memory properties. Among them, PLGA has the highest mechanical strength and recovery rate while PLC copolymer has high recovery rate when the lactyl content exceeded 85% and the lowest transition temperature (Ttrans). Copyright © 2007 John Wiley & Sons, Ltd.