Hydroxyl-terminated Polyethylenes Bearing Functional Side Groups: Facile Synthesis and Their Properties

A series of hydroxyl-terminated polyethylenes (HTPE) bearing various functional side groups (e.g. carboxyl, ester and butane groups) were synthesized by the combination of ring-opening metathesis polymerization (ROMP) and visible light photocatalytic thiol-ene reaction. The products are named as α,ω-dihydroxyl-poly[(propionyloxythio)methinetrimethylene] (HTPE_(carboxyl)), α,ω-dihydroxyl-poly[(methylpropionatethio) methinetrimethylene] (HTPE_(ester)) and α,ω-dihydroxyl-poly[(butylthio) methinetrimethylene] (HTPE_(butane)), respectively. The investigation of ROMP indicated that the molecular weight of resultant hydroxyl-terminated polybutadiene (HTPB) can be tailored by varying the feed ratios of monomer to chain transfer agent (CTA). The exploration of the photocatalytic thiol-ene reaction between HTPB precursor and methyl 3- mercaptopropionate revealed that blue light as well as oxygen accelerated the reaction. ~1H-NMR and ~(13)C-NMR results verified all the double bonds in HTPB can be modified, and the main chain of resultant polymer can be considered as polyethylene. Subsequently, relationship between the structure of side groups and the thermal properties of functional PEs was studied. And the results suggested that the T_g was in the order of HTPE_(butane)<HTPE_(ester)<HTPE_(carboxyl). Greater interaction between side groups resulted in higher T_g. Moreover, all the functional PE samples exhibited poor thermostability as compared to HTPB. Finally, the promising applications for functional PEs were explored. HTPE_(carboxyl) can be utilized as a smart material with pH-responsive properties due to its pH-dependent ionization of carboxyl side groups. HTPE_(butane) can be employed as a macro-initiator for building the triblock copolymer due to the presence of active hydroxyl end groups. HTPE_(ester) can serve as a plasticizer for PVC which can enhance the ductility of PVC without obviously sacrificing strength.

通过开环易位聚合（ROMP）和可见光光催化硫醇 - 烯反应相结合的方法，合成了一系列带有各种官能侧基（例如羧基、酯基和丁基）的端羟基聚乙烯（HTPE）。产物分别命名为α,ω - 二羟基 - 聚[（丙酰氧硫基）甲叉三亚甲基]（HTPE_（羧基））、α,ω - 二羟基 - 聚[（丙酸甲酯硫基）甲叉三亚甲基]（HTPE_（酯））和α,ω - 二羟基 - 聚[（丁硫基）甲叉三亚甲基]（HTPE_（丁烷））。对ROMP的研究表明，通过改变单体与链转移剂（CTA）的进料比，可以调整所得端羟基聚丁二烯（HTPB）的分子量。对HTPB前体与3 - 巯基丙酸甲酯之间光催化硫醇 - 烯反应的探索表明，蓝光以及氧气可加速反应。~1H - NMR和~(13)C - NMR结果证实HTPB中的所有双键都可被修饰，所得聚合物的主链可视为聚乙烯。随后，研究了侧基结构与功能性聚乙烯热性能之间的关系。结果表明，玻璃化转变温度（T_g）的顺序为HTPE_（丁烷）< HTPE_（酯）< HTPE_（羧基）。侧基之间相互作用越强，T_g越高。此外，与HTPB相比，所有功能性聚乙烯样品都表现出较差的热稳定性。最后，探索了功能性聚乙烯的潜在应用。由于羧基侧基的pH依赖性电离，HTPE_（羧基）可用作具有pH响应特性的智能材料。由于存在活性羟基端基，HTPE_（丁烷）可用作构建三嵌段共聚物的大分子引发剂。HTPE_（酯）可用作PVC的增塑剂，它可以在不明显牺牲强度的情况下提高PVC的延展性。