Role of Topological Repulsive Forces in Polymer Crystallization

在半晶状的聚合物,ciystalline阶段与非晶相共存,但后者的性质尚未熟悉在这个工作中,我们提出一个新的hyposesis,在结晶融化,纠葛在聚合物驱逐形成结晶相并累积到非晶相,se,非晶相的自由能增加,ciystallization停止点的驱动力ciystallization平衡自由能的增加。为了证明这一假设，我们对纠缠高度凝聚的非晶态聚合物进行了计算机模拟。作为这种系统的一个模型，永久纠缠的环状聚合物，通常被称为连环网络，被考虑。在保持体系的纠缠态、聚合物数目和元素浓度不变的情况下，研究了体系的热力学和力学性能与聚合物结晶的关系。发现了以下内容。1)数值计算了非晶相中元素的化学势作为纠缠浓度的函数，表明化学势来源于“局域结”之间的排斥相互作用。2)利用文献中发现的化学势和结晶熵，我们发现结晶温度与结晶相比之间的关系，很好地解释了已知的实验结果。3)在非晶相中，聚合物链呈不寻常的构象，在整体范围内是正常的，但在局部高度延伸。

In semi-crystalline polymers, ciystalline phase coexists with amorphous phase, but the nature of the latter has not yet been known well In this work, we propose a new hyposesis that, in crystallizing from melts, entanglements among polymers are expelled form the crystalline phase and accumulated into the amorphous phase, se that the free energy of the amorphous phase increases and ciystallization stops at point where driving force of ciystallization balances the increase of the free energy. To prove the hyposesis, we have performed computer simulations of amorphous polymers in which entanglements are highly condensed. As a model of such systems, permanently entangled cyclic polymers, which are usually called catena networks, are considered. Changing the concentration of entanglements, while keeping the entanglement state, the polymer number and the element concentration of the systems, the thermodynamic and mechanical properties of the systems are studied in relation to the crystallization of the polymers. The following are found.1)The chemical potential of elements in the amorphous phase is computed numerically as function of the concentration of entanglements, and it is shown that the chemical potential comes from repulsive interaction among "local-knots".2)With use of this chemical potential and the entropy of crystallization found in the literature, we have found a relation between the crystalline temperature and the ratio of crystalline phase, which explain well the known experimental results.3)In the amorphous phase, polymer chains take an unusual conformation, which is normal in global scale, but highly extended locally.