高分子分子链构象对高分子结构和结构形成的影响

The atomistic molecular dynamics method simulation of the melting behaviors of α (stable) and β (metastable) isotactic polypropylene (iPP) crystals at ultrafast heating rates clearly showed that α form has a little larger density than β form and lower energy at the same temperature. It indicated that α-iPP crystal with a lower energy is more stable than β-iPP. In the melting process, the right-handed helix ratio in α-iPP does not change while that of β-iPP decreases from 100% to 50%. It is reasonable because the helix ratio of the melting state equals 0.5 same with that of α-iPP crystal. The homocrystals formed by either PLLA or PDLA have a melting point of 160−180 °C, depending on the molecular weight and optical purity. However, blending of PLLA and PDLA can result in the formation of stereocomplex with a melting point of about 50 °C higher than that of homocrystals. The extremely high melting point of stereocomplex is originated from the strong interactions, i.e., hydrogen bonding in the unit cell. Thus, stereocomplexation opens a new way to enhance the properties such as thermal resistance, which benefits broader applications of polylactides. The helix effects on iPP and PLA crystallization structures and the mechanism of polymer structure formation will be investigated with X-ray scattering, laser scattering and dielectric spectroscopy technologies. New concept and mechanism of polymer structure formation would be proposed.

计算机模拟iPP结晶快速熔融结果表明：iPP的alpha晶型熔体由各占50%的左旋和右旋构象的分子链组成，beta晶型熔体由100%的左旋或右旋构象的分子链组成；各占50%的左旋和右旋聚乳酸形成的立构复合物结晶熔点比均聚物形成的结晶熔点高50度左右。虽然二者分子螺旋构象的稳定性不同，但是共混手性构象都形成更稳定的结构。本课题拟通过X射线散射、激光光散射和介电谱仪等原位、离位技术，研究调控聚丙烯和聚乳酸的分子构象对其凝聚态结构和性能的影响，尝试提出高分子结构形成新机理。

计算机模拟iPP结晶快速熔融结果表明：iPP的alpha晶型熔体由各占50%的左旋和右旋构象 的分子链组成，beta晶型熔体由100%的左旋或右旋构象的分子链组成；各占50%的左旋和右旋聚乳酸形成的立构复合物结晶熔点比均聚物形成的结晶熔点高50oC度左右。虽然二者分子螺旋构象的稳定性不同，但是共混手性构象都形成更稳定的结构。我们通过光射线散射、红外光谱和介电谱仪等原位、离位技术，研究了调控聚丙烯、聚乳酸和聚丁烯的分子螺旋构象对结晶结构和结构转变的影响，尝试认识和高分子结晶成新机理。我们发现聚丙烯、聚乳酸、聚丁烯稳定和亚稳结晶结构的形成和转变和非晶态温度依赖的构象熵有关，即高分子结晶的形成决定于结晶过程的焓变而形成不同晶型取决于熵变。在此基础上我们设计、制备了一系列高分子结晶结构调控剂并和相关生产企业开展了合作。