The limits of precision monomer placement in chain growth polymerization.

Guillaume Gody,Simon Harrisson,Sébastien Perrier,Per B Zetterlund

doi:10.1038/ncomms10514

Abstract

Precise control over the location of monomers in a polymer chain has been described as the ‘Holy Grail' of polymer synthesis. Controlled chain growth polymerization techniques have brought this goal closer, allowing the preparation of multiblock copolymers with ordered sequences of functional monomers. Such structures have promising applications ranging from medicine to materials engineering. Here we show, however, that the statistical nature of chain growth polymerization places strong limits on the control that can be obtained. We demonstrate that monomer locations are distributed according to surprisingly simple laws related to the Poisson or beta distributions. The degree of control is quantified in terms of the yield of the desired structure and the standard deviation of the appropriate distribution, allowing comparison between different synthetic techniques. This analysis establishes experimental requirements for the design of polymeric chains with controlled sequence of functionalities, which balance precise control of structure with simplicity of synthesis.

Highlights

Precise control over the location of monomers in a polymer chain has been described as the ‘Holy Grail’ of polymer synthesis
Our results are applicable to all chain polymerizations, which are carried out under living or near-living conditions, including ring-opening metathesis polymerization (ROMP)[24], the various types of reversible deactivation radical polymerization (RDRP, known as controlled/‘living’ radical polymerization)[25], and ionic polymerizations[26,27]
Our results demonstrate that the level of control over monomer placement is quite limited, even under ideal conditions, and that multiblock copolymers comprised of many short blocks will inevitably contain a large proportion of defective chains

Summary

Introduction

Precise control over the location of monomers in a polymer chain has been described as the ‘Holy Grail’ of polymer synthesis. The degree of control is quantified in terms of the yield of the desired structure and the standard deviation of the appropriate distribution, allowing comparison between different synthetic techniques This analysis establishes experimental requirements for the design of polymeric chains with controlled sequence of functionalities, which balance precise control of structure with simplicity of synthesis. This question is crucial to the synthesis of aperiodic copolymers: ‘copolymers in which monomer sequence distribution is not regular but follows the same arrangement in all chains’[1] Included in this definition are polymers that contain an ordered sequence of distinct blocks, and polymers that contain specific monomers at precisely defined locations[2,3,4]. The degree of control required can be interpreted with varying degrees of severity, corresponding to the sequencedefined, multisite and multiblock copolymers considered by Lutz[1] (Fig. 1): (a) control over the absolute position of a monomer with respect to the chain end, or the absolute separation between two monomers (sequence-defined copolymers); (b) control over the relative position of a monomer with respect to the total chain length, or the relative separation between two monomers (multisite copolymers) or (c) control over the number and order of blocks in a multiblock copolymer, without regard to the distribution of each individual block (multiblock copolymers)

Methods

Results

Conclusion