含咪唑离子聚乙烯离聚体的合成与性能

利用双(β-二酮单亚胺)钛催化乙烯和5-碘甲基降冰片烯(IMNB)的配位共聚, 高效合成了高分子量、 窄分子量分布和组分可控的烯烃共聚物. 将该含有碘甲基侧基的共聚物与N-甲基咪唑进行亲核取代反应, 然后再与有机金属盐进行离子交换, 制备了一系列带有甲磺酸根(CH₃SO{}_{\mathrm{3}}^{-})、 三氟甲磺酸根(CF₃SO{}_{\mathrm{3}}^{-})或双(三氟甲磺酰)亚胺负离子(Tf₂N^-)的聚乙烯离聚体. 研究表明, 离子基团的引入会破坏聚合物的结晶, 熔融温度和结晶度均随着离子含量的增加而降低. 但离聚体的玻璃化转变温度却高于乙烯/IMNB共聚物, 表明离子基团之间的强相互作用抑制了链段运动.与共聚物前体相比, 聚乙烯离聚体表现出更高的热稳定性、 更好的亲水性和更高的抗拉强度. 当离子含量相同时, 聚乙烯离聚体的抗拉强度顺序为: CH₃SO{}_{\mathrm{3}}^{-}>CF₃SO{}_{\mathrm{3}}^{-}>Tf₂N^-, 而断裂伸长率呈现相反的趋势.

Synthesis and Properties of Imidazolium-based Polyethylene Ionomer

The novel ethylene/5-iodomethyl norbornene(IMNB) copolymers with high molecular weight, narrow molecular weight distribution and different incorporation of comonomer were firstly synthesized by using titanium catalysts bearing two β-ketiminato chelate ligands, then iodine atoms distributed randomly along the copolymer chains were subsequently converted into ionic groups via nucleophilic substitution reaction with N-methylimidazole, followed by exchanging the I^- counteranions with CH₃SO₃^-, CF₃SO₃^-, or Tf₂N^-. Thus, a series of imidazolium-based polyethylene ionomers bearing different counteranions were readily obtained. As observed, the introduction of ionic groups destroyed the crystallization of copolymers, contribu-ting to the decrease of melting temperature and crystallinity. Such effect became more significant with increasing the ion content. Ionomers had higher glass transition temperature(T_g) than that of ethylene/IMNB copolymer, suggesting the interaction between ionic groups restricted the mobility of surrounding segments. Compared with copolymer, polyethylene ionomers exhibited better thermal stability, hydrophilic property and tensile strength. With the same ion content, the stress-at-break values of the ionomers followed the order: CH₃SO₃^- >CF₃SO₃^- >Tf₂N^-, whereas the strain-at-break values in the opposite order.