(327g) Well-Defined Polymeric Structures Bearing Degradable Branching Points: Synthesis, Characterization and Stability

Polymer networks (gels) and other branched polymers containing cleavable points are modern materials with unique structure and properties. These polymeric materials can have their cross-links degraded and branches removed under the appropriate chemical or physical stimuli, and they can be converted to lower molecular weight products with different properties (e.g. mechanical strength and solubility) from those of the parent materials. This behavior renders them ideal for use in biomedical applications as erodable matrices for controlled protein and drug delivery, and tissue engineering, and also in the electronics industry as thermolyzable polymers for removal and re-attachment of components. Of special interest to many researchers have been branched polymers with labile dimethacrylates as degradable branching points, i.e. bifunctional monomers that are polymerized alone or with monofunctional monomers by ?non-living? (synthetically easier) or ?living? methods that secure better structural control of the resulting branched polymer. In these polymeric systems, the chemistry of the cleavable branching points is important, allowing for defining the degradation conditions and fine-tuning the rate of degradation.

Our study is the first to address the preparation of polymer networks and star polymers bearing degradable dimethacrylate cross-linkers by using a ?living? polymerization method, group transfer polymerization (GTP), the characterization and the degradation of these materials. The novelty of this investigation is two-folded and lies on: (1) the control of the architecture, molecular weight and polydispersity of the synthesized degradable polymers ? neat cross-linker networks, randomly cross-linked networks, star polymers and cross-linked star polymer model networks and their degradation products; and (2) the use of novel cleavable cross-linkers for the polymer preparation that bear different labile groups and therefore can be degraded under different conditions.

A variety of techniques including Gel Permeation Chromatography (GPC), Dynamic and Static Light Scattering (DLS and SLS), Nuclear Magnetic Resonance (NMR) spectroscopy and Thermogravimetric Analysis (TGA) were used to support the synthesis and degradation (hydrolysis or thermolysis) of the well-defined polymer structures of this work and to establish structure-property relationships.