Core-First Synthesis of Three-Armed Star-Shaped Polymers by Rare Earth Metal-Mediated Group Transfer Polymerization

Abstract

Addressing polymer topologies is one of the key methods for tailoring polymer properties. Herein, we report for the first time on the core-first synthesis of three-armed star-shaped polymers with adjustable molecular weights via rare earth metal-mediated group transfer polymerization (REM-GTP). Based on the versatility of REM-GTP, enabling polymerization of a broad variety of functional monomers not accessible via conventional techniques, a novel and fast method toward directed polymeric structures was established. Therefore, the trinuclear catalyst was synthesized by 3-fold C–H bond activation of 1,3,5-tris­(3,5-dimethyl-4-pyridinyl)­benzene using Cp2YCH2TMS­(THF) as precursor complex. Kinetic investigations in comparison to monometallic Cp2Y­(sym-collidinyl) on the polymerization of diethyl vinylphosphonate (DEVP) and 2-isopropenyl-2-oxazoline (IPOx) evidenced activity of all three metal centers. However, in REM-GTP generally occurring incomplete initiation provoked by the interaction of initiators and monomers, potential impurities, and applied reaction conditions led to a distribution of stars, long linear, and short linear polymers originating from chain growth in three, two, and one direction, respectively. For further visualization PIPOx produced by the trinuclear complex was converted into P­(IPOx-graft-2-ethyl-2-oxazoline) using living cationic ring-opening polymerization. AFM scans confirmed the occurrence of the three types of polymer. Additionally, comparable solely linear PDEVP and PIPOx were synthesized by dinuclear complexes generated by C–H bond activation of 1,3-bis­(3,5-dimethyl-4-pyridinyl)­benzene and 1,4-bis­(3,5-dimethyl-4-pyridinyl)­benzene using Cp2YCH2TMS­(THF) as precursor. In the case of PDEVP, the mass fraction of the low molecular weight polymer, being formed by chain growth in one direction, was accessible via GPC analysis. Further stochastic examinations on the incomplete initiation for multinuclear complexes corroborated our findings accurately.

Metal‐Catalyzed Group‐Transfer Polymerization: A Versatile Tool for Tailor‐Made Functional (Co)Polymers

“…The latest research with Cp 2 YCH 2 TMS(THF) as precursor complex gave a trinuclear catalyst by three‐fold C−H bond activation of 1,3,5‐tris(3,5‐dimethyl‐4‐pyridinyl)benzene. This catalyst allowed the fast catalytic synthesis of star‐shaped polymeric structures (vide infra) …”

“…Visualization was achieved by transformation of PIPOx into P(IPOx‐g‐EtOx) and subsequent analysis with AFM. Based on the findings a detailed study on the initiator efficiency of multinuclear complexes was conducted …”

C–H Bond Activation of Silyl-Substituted Pyridines with Bis(Phenolate)Yttrium Catalysts as a Facile Tool towards Hydroxyl-Terminated Michael-Type Polymers

“…Further to this, the synthesis of block copolymers was facilitated due to the living character of this polymerization type by simple sequential addition of different monomers with respect to their coordination strength to the metal center [7,25,26]. Additionally, C-H bond activation gave access to post-polymerization functionalization and facilitated the synthesis of new block copolymer structures and polymer architectures [7,18,[27][28][29][30][31][32][33][34].…”

Differences and similarities between mono-, bi- or tetrafunctional initiated cationic ring-opening polymerization of 2-oxazolines

“…It imposes the need to choose suitable cores to act as multifunctional initiators in polymerization processes in which the synthesis conditions must be well defined to promote the formation of polymeric products with fitting properties for concrete applications, and for instance a minimization of star coupling. 14,18 Additionally, characterizing the final multi-arm polymers can be very challenging, and generally, only limited molecular information is available on the polymer products.…”