Concepts for controlling nucleation in systems of biodegradable polymers

生物可降解聚合物由于其对环境的友好性和来源于生物基资源而引起了人们的广泛兴趣，其中许多是半结晶的。然而，导致缓慢结晶的低成核速率、相应地长的加工时间和最终不利的结晶形态，导致不令人满意的物理性质，并基本上限制了它们在工业应用中的使用。在这种情况下，通过提高成核速率并因此改善特别是机械性能，预期会有很大的改进。在这项联合提案中，两个在基础研究和应用方面都有很强背景的团队将合作研究生物可降解聚合物的成核过程。我们的目标是加深我们的理解成核机制，并在开发的方法，增加在生物可降解聚合物成核的可能性。加速的成核和相应的更快的整体结晶以及因此缩短的加工时间将导致更均匀的结晶形态和上级机械性能。其目标是将来自模型系统（如纳米薄膜）的成核和结晶的基本概念转化为用于处理和改善大块材料宏观物理性能的指导规则。其中心思想是局部操纵链构象，调整特定的分子相互作用，并建立分子水平上的特征与成核速率，结晶形态和最终材料性能之间的相关性。三个互补和相互交织的策略将遵循：i）化学合成具有可调链柔性、各种侧基和特定相互作用的可生物降解聚合物，ii）设计具有不同分子晶格参数的聚合物成核剂，以及iii）通过在成核剂表面上的吸附、自引晶、局部摩擦和宏观拉伸来改变聚合物链构象。此外，我们试图建立一个理论模型，以定量关联链构象和结构信息的分子水平与成核速率。

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.