极少量1,5-己二烯改善聚丙烯树脂热稳定性研究

Improving Thermal Stability of Polypropylene by Tiny Amounts of 1,5-Hexadiene

在Ziegler-Natta丙烯聚合反应中,引入少量1,5-己二烯,在不明显改变聚丙烯链结构的基础上,通过可能的主链环化,提高其热稳定性.聚合反应由9,9-二(甲氧基甲基)芴为内给电子体的Mg Cl2/Ti Cl4催化剂在本体条件下进行,1,5-己二烯浓度控制在1.0 mol%以下.结果显示,在所控制的1,5-己二烯浓度下,虽然催化剂活性和聚合物分子量有一定程度的降低,但聚合物的熔点(Tm)和熔融焓(ΔHf)只略有下降,而结晶温度(Tc)基本保持不变.GPC和流变测试结果表明聚合物的链结构无变化,聚合过程无支化或交联结构生成.热重分析(TGA)结果显示,聚丙烯热稳定性有较大幅度的提高,初始分解温度(Tonset)从纯聚丙烯的460.6℃提高到482.3℃,聚合物在反应釜中呈良好的颗粒形态.

Tiny amounts of 1,5-hexadiene（1,5-HD） are introduced into propylene bulk polymerization using Ziegler-Natta catalyst.The thermal stability can be enhanced by possible backbone cyclization which has inconspicuous change to the backbone structures of polypropylene.Mg Cl2/ Ti Cl4 catalyst with 9,9-bis-（methoxymethyl） fluorine（BMMF） as internal electron donor is used for bulk polymerization and concentrations of 1,5-HD are controlled well below 0.1 mol / L.Nuclear magnetic resonance（NMR）,gel permeation chromatography（GPC）,differential scanning calorimetry（DSC）,dynamic shear rheology and scanning electron microscopy（SEM） are used to characterize the structures and morphology of the polymer.The results indicate that,albeit the catalytic activity and polymer molecular weight exhibit certain degrees of decrease due to 1,5-HD,the major crystallization properties of polypropylene including melting temperature（Tm）,fusion enthalpy during melting（ΔHf） and maximum crystallization temperature（Tc） remain almost unchanged.Because of the tiny amounts of 1,5-HD,the structure of 1,5-HD in PP cannot be detected by neither1H-NMR nor13C-NMR.The isotacticity of PP has little change by13C-NMR.The structure of polymer is linear which is characterized by GPC and dynamic shear rheology analysis and no branched or crosslinking structure is formed in polymerization.The insertion of 1,5-HD has little influence to the chain structure of polypropylene macromolecules.Thermogravimetric analysis（TGA） results indicate that the thermal stability of polypropylene is much improved by polymerizing with 1,5-HD.The onset degradation temperatures（Tonset） of polypropylenes obtained with the presence of 1,5-HD are increased by as much as 20 K,from 460.6 ℃ to482.3 ℃ under nitrogen atmosphere and 5% and 10% weight loss temperature increased about 30 degree.It indicates that tiny amounts of 1,5-HD is indeed inserted into the macromolecule chain as the cyclic structure which enhances the rigidity and improves the thermal stability of the polymer.Moreover,polymer particles in reactor are granule-like,which meets the demand of industrial polymerization process.Overall,this research provides new thinking to improving thermal stability of polypropylene resins.