Iterative Replacement of Functionality in Polymer Main Chain Based on Segment Reorganization via Cross-Metathesis Reaction
Ke He, Junpo He
Abstract
Polymer segment reorganization is capable of changing the chemical structure of the backbone, inserting a functionality into or removing a functionality from the chain, and replacing a specific moiety at the precise site of the chain. It is useful for the preparation of polymer samples with orthogonal structures of segments and functionalities, which is significant for the study of structure–property relationships. In the present work, we developed a strategy for iterative replacement of functional groups in the middle point of the polymer main chain. The strategy involves the “cutting-off” of the polymer precursor by a molecular “scissor”, a small molecular olefinic compound, through cross-metathesis (CM) reaction in the presence of Grubbs catalyst, followed by recombination of the cleaved products by a (functional) “binder”, a dithiol agent, via thiol-Michael addition reaction. The polymer precursors were prepared through atom transfer radical polymerization (ATRP) using an olefin-containing dibromide initiator to introduce an olefinic moiety in the middle of the chain. The key point of the present work is the use of the itaconic derivative ( Z )- O, O ′-(but-2-ene-1,4-diyl) 4-dimethyl bis(2-methylenesuccinate) (BES), an itaconic derivative containing one olefinic and two vinylic double bonds, as the molecular “scissor”. Owing to the high selectivity of the double bonds in CM and the thiol-Michael reaction, iterative replacement of functionalities at the middle of the main chain was achieved for the first time. The protocol can be useful for the preparation of arrays of polymer samples with orthogonal functionalities and building blocks, which is significant for the study of the structure–property relationship of polymers.