Aperiodic Copolymers

Abstract

Current polymer terminology only describes very simple copolymer structures such as block, graft, alternating periodic, or statistical copolymers. This restricted vocabulary implies that copolymers exhibit either segregated (i.e., block and graft), regular (i.e., alternating and periodic), or uncontrolled (i.e., statistical or random) comonomer sequence distributions. This standard classification does not include many new types of sequence-controlled copolymers that have been reported in recent years. In this context, the present viewpoint describes a new category of copolymers: aperiodic copolymers. Such structures can be defined as copolymers in which monomer sequence distribution is not regular but follows the same arrangement in all chains. The term aperiodic can be used to describe encoded comonomer sequences in monodisperse sequence-defined copolymers but also the block sequence of some multiblock copolymers. These new types of copolymers open up very interesting perspectives for the design of complex materials. Some recent relevant literature on the topic is discussed herein.

Figure 1

(a) Proposed definition for sequence-controlled and sequence-defined copolymers. (b) Some official (blue), nonofficial (gray), and nonexisting (red) terms to denote synthetic copolymers. Note that the color code is only valid for (b). The colors displayed in (a) are used for aesthetic reasons only.

Figure 2

Schematic representation of different types of aperiodic copolymers: multiblock copolymers (left), multisite copolymers obtained using time-controlled monomer additions (middle), and monodisperse sequence-defined copolymers (right). The ellipse points displayed at the extremities only mean that the sequences can be longer than shown.