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

Abstract

A step-growth strategy was investigated for preparing functional periodic copolymers. Functional heterotelechelic R-alkyne, ω-azido poly(styrene-co-N-substituted maleimide) precursors (M n ≈ 2500 g 3 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. 1 H NMR and SEC evidenced the formation of high-molecular-weight periodic copolymers.

Tailored Polymer Microstructures Prepared by Atom Transfer Radical Copolymerization of Styrene and N‐substituted Maleimides

“…This crucial concept was verified with model copolymerization experiments. [25,28] When added during the course of styrene homopolymerization, the MIs are usually incorporated in narrow regions of the growing polymer chains. For instance, a single maleimide unit can be placed in a chain section as short as 3-5 styrene units.…”

“…For instance, a single maleimide unit can be placed in a chain section as short as 3-5 styrene units. [28] Yet, it should be reminded that chain-to-chain sequence distribution still exists. Nevertheless, it is possible to create short local functional patches, constituted of 1 to 3 MI units, in a linear polystyrene chain.…”

“…[11] For example, we studied lately the periodic polymerization of short sequencecontrolled building-blocks containing positioned functional MI units (Scheme 4). [28] Functional heterotelechelic a-alkyne, v-azido poly(styrene-co-N-substituted maleimide) precursors (M n $ 2500 g Á mol…”

“…[5,13,15,20,[22][23][24][25][26][27][28][29][30][31][32] In particular, a few research groups investigated sequence-regulation in chaingrowths polymerizations. For instance, the innovative approaches recently reported by the research groups of Sawamoto, [26,29,32,33] Thomas, [10,27] and Kamigaito [20,30] have to be mentioned.…”

“…This aspect was also verified in our study. [28] 1 H NMR and SEC evidenced the formation of high-molecular weight periodic copolymers. Typically, after one day of CuAAC step-growth at room temperature, five to ten reactive copolymers were attached together.…”