Sequence-controlled polymers in which the monomer units get dispersed in an organized manner along the chain are extensively used in numerous applications due to their unique properties. Unfortunately, precise synthesis of these natural polymers is associated with several challenges. This is due to the difficulty in controlling the monomer distributions which is a critical factor in the synthesis of sequence-controlled polymers. Generally, it is perceived that both of the sequence distribution and monomer composition influence the properties and structure of synthetic polymers.
Among the many developed methods to effectively control monomer sequence distribution during sequence-controlled polymerization is the chain-growth polymerization. It utilizes reversible-deactivation radical polymerization (RDRP) and living anionic polymerization (LAP) to achieve good monomer sequence controllability. In conjunction with sequence monomer feeding, it has also enabled synthesis of periodic structures. However, little emphasis has been given to the impact of controlled polymer structures like monomer sequence on their properties.
Recently, Dalian University of Technology researchers led by Associate Professor Hongwei Ma developed a strategy for sequence regulation with living anionic polymerization. They syntheses three different sequence-defined polymers with different periodicities and same number of SiH functional groups per chain. They expected to obtain a periodic-controlled sequence-defined polymer. Their research work is currently published in the research journal, Macromolecules.
Briefly, the research team utilized one-pot living anionic copolymerization of styrene and dimethyl(4-(1-phenylvinyl) phenyl) silane (DPE-SiH), two-step polymerization followed by a coupled reaction after the polymerization process. Also, in situ HNMR was used to investigate the monomer sequence distribution in the three synthesized structures. Furthermore, living anionic polymerization technique was used to determine the sequence regulation strategy through synchronous regulation of the functional block and the monomer sequence. Eventually, they compared and contrasted the characteristics of the three resulting polymers.
The authors observed that the three synthesized synthetic polymers exhibited equal molecular weights in the chains but different periodicities and monomer sequence distributed as symmetrical structure, gradient and tandem. Additionally, it was necessary to apply the resulting polymers as backbones to synthesis corresponding bottlebrush polymers. They were conventionally grafted onto the backbones at conversion rates greater than 97% in the three cases. This resulted in an excellent solution and thermal properties of the three bottlebrush polymers. For instance, the gradient structure exhibited the highest hydrodynamic radii. Also, a significant increase in transition temperature was exhibited in the tandem and gradient polymers attributed to the incorporated DPE-SiH units.
According to the authors, block periodicities and the difference monomer sequence structures of the polymers significantly influences their properties. For instance, the developed method can effectively control the spacing branching to synthesis highly efficient bottlebrush polymers. Therefore, the study is a promising solution and will advance further the sequence regulation thus leading to the design and development of novel polymers.
Huang, W., Ma, H.*, Han, L., Liu, P., Yang, L., & Shen, H., Hao, X., & Li., Yang. (2018). Synchronous Regulation of Periodicity and Monomer Sequence during Living Anionic Copolymerization of Styrene and Dimethyl-[4-(1-phenylvinyl)phenyl]silane (DPE-SiH). Macromolecules, 51(10), 3746-3757.Go To Macromolecules