聚乙烯链段生长的休眠机制与聚集态结构调控

Chain entanglement is an important topology structure in the condensed state of polymer, which endow effects on the synchronous increment of processability and performance. In terms of the entangled formation during the polymerization, the structural and dynamic characterization of the entanglements are revealed, which aims to gain the methods for the synthesis of disentangled ultra-high molecular weight polyethylene (UHMWPE). A micro-zone of active sites with controllable structure is synthesized according to the self-assembly of POSS and the interaction among the POSS, MgCl2 and catalytic molecules, which is used to demonstrate and control the structural characterization of entanglements. Furthermore, N2/Ar nanobubbles are arranged surround the active sites, which will disperse concentrated inert components around the active sites, according to the fragmentation and disappearance of the nanobubbles. This will make the chain growth dormancy and also make propagated chains preferentially crystallizing. Subsequently, the chains growth will be awaken, followed by the diffusion of ethylene. An alternated micro-flow field will be built up based on the fragmentation of nanobubbles and the diffusion of ethylene, which will effectively work in controlling the dynamic characterization of entanglements. From the view of synergistic effect of monomer diffusion – polymerization - chain crystallization, the matching criterion of “dormancy-awaken” behavior and the chain crystallization will be revealed. This will intensify the decrement of entanglements in the high temperature polymerization. Finally, a nano-bubbling bed polymerization process will be established for the synthesis of weakly entangled UHMWPE, synchronously increasing the processability and performance of UHMWPE.

链缠结是高分子聚集态结构中十分重要的拓扑结构，影响着材料加工和使用性能的同步提升，对于聚烯烃高性能化至关重要。有关链缠结的调控理论和技术历来广受人们关注。本申请针对初生态聚乙烯链缠结的动态形成这一关键过程，利用POSS分子的自组装行为及其与氯化镁、催化剂分子的相互作用，构建空间结构和活性中心聚集程度均可控的催化颗粒，研究链穿插、交叠的空间尺度对链缠结结构的影响，建立链缠结结构属性的调变机制；通过在催化颗粒引入惰性气体纳米气泡，利用气泡对催化颗粒的间歇性撞击，在活性中心周围营造惰性气体/乙烯交变交替的微观流场，研究链段生长过程的休眠-激活方法以及链缠结等聚集态结构的响应规律。从传质-反应-结晶的耦合作用出发，揭示链段生长的休眠-激活行为与链结晶行为的匹配准则，建立链缠结动态属性调控的过程强化机制。最后，建立适应工业生产的链缠结调控理论和技术，指导UHMWPE加工和使用性能的大幅提升。

为降低初生态UHMWPE的链缠结程度，改善其加工性能并充分发挥其优异的力学性能，本项目首先基于通过含硅羟基POSS分子与格氏试剂之间的化学反应，充分发挥了笼状POSS分子的自聚效应、空间位阻效应和电荷效应，构建了分散暴露式的“活性微区单元”，设计了产物形貌、堆密度和聚合动力学满足工业装置要求的解缠结Ziegler-Natta催化剂；随后，提出了惰性微气泡/微液滴（氮气、丙烷、氟硅油）辅助的乙烯淤浆聚合方法，通过惰性氮气微气泡或惰性微液滴以及惰性制冷剂丙烷与颗粒的间歇接触，使活性链在“激活”和“休眠”的两个状态间不断切换，为初生链段提供了一个亚稳态的结晶环境，从工艺上实现了初生态聚乙烯分子链的解缠结；最后，研究了低缠结催化剂在惰性微气泡/微液滴辅助的淤浆聚合行为，通过催化剂和工艺的协同实现了低缠结UHMWPE的解缠结。完成了300 L工业中试实验和高强UHMWPE纤维新产品的开发。中试结果表明，工业聚合温度下（60-85℃），POSS改性的催化剂可高效地制备低缠结UHMWPE，聚合活性是现有商业催化剂的2倍，达2万gPE/g Cat。氮气微气泡辅助的乙烯淤浆聚合可利用工业催化剂稳定地控制初生态UHMWPE的低缠结程度，从工艺上解决缠结的问题。所得低缠结UHMWPE具有优异的可牵伸性，首次在工业纺丝线上开发了强度达43.2cN/dtex超细、高强UHMWPE纤维。.本项目发表了13篇SCI文章，申请专利5项，授权专利4项，参加国际国内学术会议6次，培养博士生4名、硕士生5名，顺利完成了申请书中的内容。