Role of Chain Structure and Melt Topology in Polymer Crystallization

链结构和熔体拓扑在聚合物结晶中的作用

• 批准号: 1607786
• 负责人: Rufina Alamo
• 金额: $ 56.09万
• 依托单位: Florida State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1607786&HistoricalAwards=false
• 关键词: Role; Chain; Structure; Melt; Topology

NON-TECHNICAL SUMMARY:Most commercial polymers are processed into useful materials by cooling them from a high temperature. During this process, a fraction of the long polymer molecules self-assemble in ordered crystalline regions connected by regions where the molecules remain disordered. The speed of the solidification process depends on the liquid phase structure of the melt and the entanglements (topology) that long polymer molecules adopt during heating. Molecules that retain memory of the ordered state in the melt act as seeds to speed up the crystallization. This project addresses how the seeded melt structure changes in polymers with short or long branches, or with polar or non-polar branches and their role on crystallization. Studies of model blends, and polyethylenes with pendant groups, either random or at a precise distance will enable building of fundamental relations between molecular structure and properties to predict the behavior of commercial complex polyethylene materials. These studies are significant also because the great expansion of shale gas extraction has placed the US as a very highly competitive provider of derivatives such as polyethylenes. Hence, advances in the understanding of the state of the melt and the crystallization of polyethylenes are of major relevance as they could lead to improved processing technologies and to reduced costs and energy utilization. The proposed research is also aimed at providing learning and training opportunities for graduate and undergraduate students, many of them underrepresented minorities.TECHNICAL SUMMARY:The proposed research program builds on recent developments on the strong melt memory of crystallization of random ethylene copolymers, and the unique layered crystallization of precision halogen substituted polyethylenes to further address the role of chain structure in the evolution and final crystal morphology of semicrystalline polymers with various types of short and long-chain branching. Models for random copolymers will be used to address: (a) the effect of branch length (ethyl to hexyl), chain architecture (stars, H-type, comb, pom-pom), and branch polarity (acetoxy) on melt diffusion, and self-nucleation; (b) the effect of comonomer content distribution on co-crystallization in model blends, and the interplay between sequence segregation and LLPS; (c) the generality of the role of sequence selection in crystalline melt memory. A second thrust aims to advance understanding of the evolution of the crystalline state of polyethylenes with pendant groups placed at the same equidistant length along the backbone. Taking advantage of model systems with pendant groups with controlled tacticity, the origin and drive for the formation of lamellar crystallites from isotactic as well as from atactic systems will be sought. Differences in sublamellar structure, and crystallization kinetics are of special interest as they relate to novel crystallites formed from ethylene-like copolymers with controlled tacticity that are not accessible in classical random ethylene copolymers. Molecular details at the crystal growth front will be extracted from the unique temperature gradient of growth rate kinetics.

非技术摘要：大多数商业聚合物都是通过高温冷却来加工成有用的材料的。在这个过程中，一部分长的聚合物分子在有序的结晶区域中自组装，这些区域由分子保持无序的区域连接。凝固过程的速度取决于熔体的液态结构和长聚合物分子在加热过程中采用的缠结(拓扑)。在熔体中保持有序状态记忆的分子就像种子一样加速结晶。本项目研究了具有短或长支链、或具有极性或非极性支链的聚合物中种子熔体结构的变化及其在结晶中的作用。对模型共混物和具有随机或精确距离的侧基的聚乙烯的研究将能够建立分子结构和性能之间的基本关系，以预测商业复杂聚乙烯材料的行为。这些研究具有重要意义，还因为页岩气开采的大幅扩张使美国成为聚乙烯等衍生品的极具竞争力的供应国。因此，在了解聚乙烯熔体和结晶状态方面的进展具有重大意义，因为它们可以改进加工技术，降低成本和能源利用。这项拟议的研究还旨在为研究生和本科生提供学习和培训的机会，其中许多人代表的少数族裔。技术摘要：拟议的研究计划建立在无规乙烯共聚物结晶的强烈熔体记忆和精密卤素取代聚乙烯的独特分层结晶的最新进展基础上，以进一步研究链结构在具有各种类型的短链和长链支化的半结晶聚合物的演化和最终结晶形态中的作用。随机共聚物的模型将被用来解决：(A)支链长度(乙基到己基)、链结构(星形、H型、梳状、POM-POM)和支链极性(乙酰氧基)对熔体扩散和自成核的影响；(B)共单体含量分布对模型共混物中共结晶的影响，以及序列分离和LLP之间的相互作用；(C)序列选择在结晶熔体记忆中作用的一般性。第二个推力旨在促进对侧基沿主链等距离放置的聚乙烯结晶状态演变的理解。利用具有可控规整性的侧基的模型体系，将从全同立构体系和非同立构体系中寻找形成片状微晶的来源和驱动力。膜下结构和结晶动力学的差异是特别令人感兴趣的，因为它们与由具有受控规整性的乙烯类共聚物形成的新型微晶有关，而这些微晶在经典的无规乙烯共聚物中是无法获得的。晶体生长前沿的分子细节将从生长速率动力学的独特温度梯度中提取出来。