Facile Synthesis of Functional Periodic Copolymers: A Step toward Polymer-Based Molecular Arrays

A step-growth strategy was investigated for preparing functional periodic copolymers. Functional heterotelechelic α-alkyne, ω-azido poly(styrene-co-N-substituted maleimide) precursors (M n ≈ 2500 g·mol−1) have been prepared and subsequently polymerized by copper-catalyzed azide−alkyne cycloaddition (CuAAC). These precursors have been first synthesized by sequential atom transfer radical copolymerization of styrene and a N-substituted maleimide (i.e., benzyl maleimide, N-(2-(amino-tBOC)-ethylen)-maleimide, or benzyl N,N-maleoylglycinate) initiated by 3-(1,1,1-trimethylsilyl)-2-propynyl 2-bromo-2-methylpropanoate. In this approach, styrene homopolymerization was first started, and a discrete amount of the maleimide comonomer (e.g., 1 equiv as compared to initiator) was added when styrene half-conversion was reached. This controlled maleimide addition resulted in the formation of well-defined polystyrene segments containing a functional maleimide in the middle of their chains (i.e., in average 1 unit per chain). Subsequently, the sequence-controlled copolymers poly(styrene-co-N-substituted maleimide) have been transformed into reactive heterotelechelic polymers. Various synthetic pathways have been compared for preparing these reactive intermediates. Ultimately, these heterotelechelic precursors were polymerized by CuAAC. 1H NMR and SEC evidenced the formation of high-molecular-weight periodic copolymers.