ABSTRACT
Completely amorphous copoly(ether)ester networks based on oligo(propylene glycol) and oligo[(rac-dilactide)-co-glycolide] segments were synthesized by crosslinking star-shaped hydroxyl-telechelic cooligomers using an aliphatic low-molecular weight diisocyanate. Two different network architectures were applied exhibiting differences in the phase-separation behavior. For networks from oligo(propylene glycol)-block-oligo[(rac-lactide)-co-glycolide] triols (G(3)OPG-bl-OLG) only one glass transition was obtained. However, networks from a mixture of oligo(propylene glycol) triols (G(3)OPG) and oligo[(rac-lactide)-co-glycolide] tetrols (P(4)OLG) with a ratio of components in a certain range show two glass transition temperatures (T (g)) being attributed to two segregated amorphous phases. In this way a wide spectrum of mechanical properties can be realized and adjusted to the requirements of a specific application.
Subject(s)
Isocyanates/chemistry , Polyesters/chemistry , Polyglactin 910/chemistry , Propylene Glycol/chemistry , Urea/chemistry , Urethane/chemistry , Chemistry/methods , Cross-Linking Reagents/chemistry , Crystallization , Glass , Materials Testing , Models, Chemical , Polyesters/chemical synthesis , Polymers/chemistry , Stress, Mechanical , Temperature , Urethane/chemical synthesisABSTRACT
Biodegradable shape-memory polymers have attracted tremendous interest as potential implant materials for minimally invasive surgery. Here, the precise control of the material's functions, for example, the switching temperature T(sw), is a particular challenge. T(sw) should be either between room and body temperature for automatically inducing the shape change upon implantation or slightly above body temperature for on demand activation. We explored whether T(sw) of amorphous polymer networks from star-shaped rac-dilactide-based macrotetrols and a diisocyanate can be controlled systematically by incorporation of p-dioxanone, diglycolide, or epsilon-caprolactone as comonomer. Thermomechanical experiments resulted that T(sw) could be adjusted between 14 and 56 degrees C by selection of comonomer type and ratio without affecting the advantageous elastic properties of the polymer networks. Furthermore, the hydrolytic degradation rate could be varied in a wide range by the content of easily hydrolyzable ester bonds, the material's hydrophilicity, and its molecular mobility.