4种低密度聚乙烯树脂的链结构及其性能

选用4种商品化的具有不同熔体流动速率的低密度聚乙烯(LDPE),利用高温凝胶渗透色谱仪(HT-GPC)、碳核磁共振谱仪(¹³C NMR)、差示扫描量热仪(DSC)和流变仪研究其链结构特点及其流变性能。 按照相对分子质量的差异分成两组,D-1和Q-1,D-3和Y-1,每组的两个样品具有相近的平均相对分子质量。 ¹³C NMR的结果表明,4种LDPE都既含有短链支化又含有长链支化,且短链支化含量均高于长链支化含量;而短链支化中丁基含量最多。 连续自成核退火热分级(SSA)结果表明,树脂中均含有不同长度的可结晶的亚甲基序列,即每种树脂分子链内的短链支化分布不均匀。 探讨了相对分子质量及其分布、亚甲基序列长度及其分布、支化含量、结晶度等因素对树脂熔融行为、流变行为和薄膜力学性能的影响,发现Q-1的低相对分子质量尾端和Y-1的长链支化含量均影响熔体流动速率,平均亚甲基序列长度决定熔融峰的位置,结晶度直接影响薄膜的力学性能。 基于上述结果,建立结构与性能的关联。

Chain Structure and Properties of Four Commercial Low Density Polyethylene Resins

Four commercial low density polyethylene(LDPE) resins with different melt flow rates were selected and their chain microstructures and the rheological properties were studied by high-temperature gel permeation chromatography(HT-GPC), ¹³carbon nuclear magnetic resonance spectroscopy(¹³C NMR), differential scanning calorimetry(DSC) and rheometer. The above resins are divided into two groups, D-1 and Q-1, D-3 and Y-1. Two resins in the same group have similar relative molecular mass. The results of ¹³C NMR spectroscopy show that the four LDPE resins not only contain short chain branches(SCB), but also have long chain branches(LCB), and the content of SCB is much higher than that of LCB, while the butyl branch in SCB is the highest one. The thermal fractionation(successive self-nucleation/annealing, SSA) results show that every resin contains different crystallizable methylene sequence lengths, i.e., the distribution of SCB in the intramolecular chain exhibits heterogeneity. The effects of molecular mass and its distribution, methylene sequence length and its distribution, branching content and crystallinity on melting behavior, rheological behavior and mechanical properties of the films were investigated. It is found that the low relative molecular mass end in Q-1 and LCB content in Y-1 influence their melt flow rate, the average methylene sequence length determines the melt temperature peaks, and the crystallinity influences the mechanical property of films. Based on the above results, the relationship between structure and property is established.