Herein we present the first smart polyvinylphosphonate-bioconjugates obtained via an efficient modular synthetic route.

Accommodating the increasing demand for tailor-made polymers is a major goal in polymer chemistry. Therefore, the investigation of polymerization techniques, which allow the precise synthesis of macromolecules is of exceptional interest. Ionic or controlled radical polymerization are capable living-type methods for the generation of uniform polymers. However, even these approaches reach their limits in certain issues. In the last decades, group-transfer polymerization (GTP) and especially metal-catalyzed GTP have proven to give access to a plethora of tailor-made homo- and copolymers based on α,β-unsaturated monomers. Thereby, GTP has established its potential in the development of functional and smart polymers. This concept article highlights the most significant progress in metal-catalyzed GTP with a focus on functional (co)polymers including different polymeric architectures and microstructures.

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.

Control of stereoregularity is an integral part of a precision polymerization method and for the development of functional materials. Yttriumand aluminum-based catalysts are known for converting diethyl vinylphosphonate (DEVP) into its stimuli-responsive polymer in a precise but stereoirregular way. Herein, we present Y-and Al-based constrained geometry complexes (CGCs) to induce isotacticity without losing control over other macromolecular parameters. After having established convenient synthesis routes and detailed structural analyses, these CGCs showed exceedingly high turn-over frequencies (up to 45 000 h −1 ) in the group-transfer polymerization of DEVP. The initiator efficiencies (≤99%) and dispersities (≤1.02) strongly depended on the substitution pattern of the applied ligands. An analysis of the microstructure using multidimensional NMR ( 1 H− 1 H and 1 H− 13 C(− 31 P)) correlation experiments demonstrated significant disparities for the stereospecificity of the CGCs and enabled a reliable signal assignment. The yttrium catalysts produced highly isotactic poly(diethyl vinylphosphonate), likely following a chain-end control mechanism, whereas the aluminum complexes produced less defined polymers.

Multifunctional silacyclopropanes act as universal crosslinkers for PDMS-elastomers, which can react via ring-opening or silylene insertion.