Amorphous, multi-phase polymer network systems with shape memory properties by photopolymerization

The thesis deals with the development and characterization of amorphous, covalent polymer network systems with shape-memory properties. The highest glass transition temperature of these networks serves as switching temperature Ttrans for the shape-memory effect. For potential applications in medicine, the material is designed to be degradable in physiological environments. The networks are obtained by UV irradiation of telechelic oligomers. In the polymer network system from oligo[(L-lactide)-ran-glycolide] segments, it is possible to obtain materials with different mechanical, but equal thermal properties just by varying the molecular weight of the network precursor. Cyclic, thermomechanical measurements which keep the network at 30% elongation during the fixing show that the increase of stress observed is higher the lower the fixing temperature is. Measurements which keep the network at constant stress during the fixing and at 0 stress during reheating show that the strain fixity rate (Rf) and strain recovery rate (Rr) are not influenced by the fixing temperature. The shape-recovery is investigated at different heating rates. Three different network systems are designed to toughen the brittle network system described above, and keep them elastic at room temperature. The goal is to obtain a phase-separated amorphous polymer network system in which the the higher Tg should serve as Ttrans for the shape-memory effect. The first concept involves the copolymerization of oligo[(L-lactide)-ran-glycolide]dimethacrylate with various acrylates to form an AB-network. The mechanical properties of all AB-network systems can be varied by the acrylate content. All systems have excellent shape-memory properties, showing Rf and Rr values of over 90%. The second concept involves the copolymerization of oligo[(L-lactide)-ran-glycolide]dimethacrylate with poly(ethylene glycol)dimethacrylate or poly(propylene glycol)dimethacrylate. This method presents difficulties because of the big difference in viscosity and hydrophilicity of oligo[(L-lactide)-ran-glycolide]dimethacrylate and polyether dimethacrylates. Homogeneous, amorphous networks can not be obtained. The third concept involves the synthesis of ABA triblockcopolymers with poly(ethylene oxide) or poly(propylene oxide) as block B, and oligo[(L-lactide)-ran-glycolide] segments as block A. In poly[(L-lactide)-ran-glycolide]-b-polyethylene oxide-b-oligo[(L-lactide)-ran-glycolide], crystallinity can not be avoided. In poly[(L-lactide)-ran-glycolide]-b-polypropylene oxide-b-oligo[(L-lactide)-ran-glycolide], the desired phase-separation can not be achieved. Therefore, the system is modified and oligo(rac-lactide) is used instead of oligo[(L-lactide)-ran-glycolide]. Macrodiols with three different molecular weight are prepared. The mechanical properties of the networks is adjusted by the oligo(rac-lactide) content, which also leads to variation in the crosslink density. The strain recovery rate Rr increases from 87,5% to 100% when the poly(rac-lactide) content of the network increases from 42% to 66%. In hydrolytical degradation experiments of the networks, it is shown that the degradation rate is influenced by the poly(rac-lactide) content. The networks stay amorphous during the degradation period investigated. This is a big advantage with regard to an application as implant material, since crystalline wear debris during degradation in vivo can cause foreign body reactions.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2003

Author dc:creator

• Choi, Nok-young

Contributors dc:contributor

• Höcker, Hartwig

• info:eu-repo/classification/ddc/540
• Chemie
• polymer network
• shape-memory
• photopolymerization

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123109%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61446