Precise Pentamers with Diverse Monomer Sequences and Their Thermal Properties

Sequenced-defined oligomer has been emerged as one of the hot topics in polymer chemistry due to its capability of precisely controlling both chain length and monomer sequence.Recent efforts have focused on development of synthetic methodologies using state-ofthe-art chemistry tools.However,investigating the impact of minor changes in monomer sequence on physical properties of these materials is still underdeveloped.Herein,four sequenced pentamers are synthesized by a reversible addition-fragmentation chain transfer(RAFT)single unit monomer insertion technique,in which a base pentamer possesses a relatively rigid backbone comprising of five cyclic monomer units.One of the cyclic units in this base pentamer is replaced by an acyclic monomer at different locations(the 1st,3rd and 5th unit)to produce three modified pentamers,which leads to a significant decrease of glass transition temperature(Tg)compared to the base pentamer.Meanwhile,the modified pentamers with identical primary structures but distinct monomer sequences also present different Tg values depending on the position of the acyclic monomer unit.The middle(3rd)position of the acyclic unit causes profound decrease of Tg due to its increased molecular flexibility.These synthetic pentamers have been demonstrated to be excellent oligomeric plasticizers to modulate thermal transitions of bulk polymer materials.