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](HTPEcarboxyl),α,ω-dihydroxyl-poly[(methylpropionatethio)methinetrimethylene](HTPEester)and α,ω-dihydroxyl-poly[(butylthio)methinetrimethylene](HTPEbutane),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 13C-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 Tg was in the order of HTPEbutane＜HTPEester＜HTPEcarboxyl.Greater interaction between side groups resulted in higher Tg.Moreover,all the functional PE samples exhibited poor thermostability as compared to HTPB.Finally,the promising applications for functional PEs were explored.HTPEcarboxyl can be utilized as a smart material with pH-responsive properties due to its pH-dependent ionization of carboxyl side groups.HTPEbutane can be employed as a macro-initiator for building the triblock copolymer due to the presence of active hydroxyl end groups.HTPEester can serve as a plasticizer for PVC which can enhance the ductility of PVC without obviously sacrificing strength.