Block Copolymer Synthesis

Block copolymers are a class of linear copolymers consisting of two or more homopolymer subunits linked by covalent bonds and can be divided into diblock copolymers, triblock copolymers and multiblock copolymers according to the number of homopolymer subunits. Block copolymers play a critical role in many fields such as chemistry, physics, biological, and medical fields. Many methods have been developed for block copolymer synthesis. The most convenient method is the sequential polymerization for two or more monomers without purification of intermediate compounds. However, this method is strongly limited to a few monomers, usually with the same chemical and physical properties, which make them often inadequate for material synthesis by self-assembly^[1]. The emergence of click chemistry provides a versatile tool for block copolymer synthesis because of its simplicity, selectivity, efficiency, and tolerance to various functional groups.

Applications

• Block co-polypeptide synthesis by CuAAC click reaction

Block co-polypeptides, typical block copolymers, have been widely used in biosensing, tissue engineering and selective drug delivery due to their optically active and biocompatible. Agut et al^[2]. reported a straightforward synthetic method of block co-polypeptides by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction that couples synthetic polypeptide precursors carrying antagonist alkyne and azide functional groups in α-position. In this method, no interference by azide or acetylene group was found during the synthesis of the block co-polypeptides.

• Conjugated block copolymer synthesis by CuAAC click reaction

Conjugated block copolymers have the potential to improve solution-treated optoelectronic devices such as organic photovoltaics (OPVs), but there are significant synthetic challenges. Smith et al. demonstrated a new route to synthesize conjugated block copolymers via CuAAC click reaction and a series of poly (3-hexylthiophene)-block-poly (9,9-dioctylfluorene) (P3HT-b-PF) conjugated block copolymers with varying block weight fractions were synthesized by this method (Scheme 1)^[3]. The main advantage of this synthetic route is the ability to characterize or purify the starting materials fully before the coupling reaction, and a single starting polymer may be coupled with multiple different products to give a variety of conjugated block copolymers.

Scheme 1. Preparation of P3HT-b-PF by CuAAC click reaction.

What Can We Do?

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References

1. Que´mener, D.; et al. RAFT and click chemistry: a versatile approach to well-defined block copolymers. Macromolecules. 2007, 40: 5653-5661.
2. Agut, W.; et al. Synthesis of block co-polypeptides by click chemistry. Macromolecular Rapid Communications. 2008, 29: 1147-1155.
3. Smith, K.A.; et al. Synthesis and crystallinity of conjugated block copolymers prepared by click chemistry. Macromolecules. 2013, 46: 2636-2645.