Concepts for controlling nucleation in systems of biodegradable polymers

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Biodegradable polymers, many of them being semi-crystalline, have attracted much interest due to their benignity to environment and derivation from bio-based resources. However, low rate of nucleation resulting in slow crystallization, correspondingly long processing times and final unfavorable crystalline morphologies, is causing unsatisfactory physical properties and substantially limit their use in industrial applications. In this context, great improvements are expected by enhancing the rate of nucleation and thus improving in particular mechanical properties. In this joint proposal, two teams having strong background in both fundamental research and application aspects will collaborate to investigate the processes of nucleation in biodegradable polymers. We aim at deepening our understanding of nucleation mechanisms and at developing methods for augmenting the probability of nucleation in biodegradable polymers. Accelerated nucleation and corresponding faster overall crystallization, and thus shortened processing time, will lead to a more homogeneous crystalline morphology and superior mechanical properties. The goal is to translate fundamental concepts of nucleation and crystallization derived from model systems like nanoscopic thin films into guiding rules for processing and improving macroscopic physical properties of bulk materials. The central idea is to manipulate chain conformations locally, to tune specific molecular interactions and to establish correlation between features on the molecular level with the rate of nucleation, crystalline morphology and final material properties. Three complementary and intertwined strategies will be followed: i) chemical synthesis of biodegradable polymers with tunable chain flexibility, various side groups and specific interactions, ii) designing polymeric nucleating agents with varying molecular lattice parameters, and iii) changing polymer chain conformation via adsorption on surfaces of nucleating agents, self seeding, local rubbing and macroscopic tensile drawing. In addition, we attempt to establish a theoretical model in order to quantitatively correlate chain conformations and structural information on molecular level with the rate of nucleation.