Polymer on Top: Current Limits and Future Perspectives of Quantitatively Evaluating Surface Grafting

Abstract

Well-defined polymer strands covalently tethered onto solid substrates determine the properties of the resulting functional interface. Herein, the current approaches to determine quantitative grafting densities are assessed. Based on a brief introduction into the key theories describing polymer brush regimes, a user's guide is provided to estimating maximum chain coverage and-importantly-examine the most frequently employed approaches for determining grafting densities, i.e., dry thickness measurements, gravimetric assessment, and swelling experiments. An estimation of the reliability of these determination methods is provided via carefully evaluating their assumptions and assessing the stability of the underpinning equations. A practical access guide for comparatively and quantitatively evaluating the reliability of a given approach is thus provided, enabling the field to critically judge experimentally determined grafting densities and to avoid the reporting of grafting densities that fall outside the physically realistic parameter space. The assessment is concluded with a perspective on the development of advanced approaches for determination of grafting density, in particular, on single-chain methodologies.

Simultaneous Electro‐Click and Electrochemically Mediated Polymerization Reactions for One‐Pot Grafting from a Controlled Density of Anchor Sites

“…0.8 nm −2 , lower than the theoretical maximum grafting density for PNIPAM chains on a flat surface (ca. 1.2 nm −2 ) …”

“…The properties described above for the PNIPAM layers point to a relatively low grafting density of polymer chains on the surface . Although the density of H−Eth−Ar anchor points is somewhat lower than the maximum theoretical packing density of PNIPAM brushes, the H‐ Eth‐Ar density is significantly higher than typical estimated densities of PNIPAM achieved experimentally . Thus based on the H−Eth−Ar layer, the maximum possible density of grafted polymer is known but the actual grafting density is unknown.…”

“…Poly‐NIPAM (PNIPAM) is a well‐studied thermo‐responsive polymer with lower critical solution temperature (LCST) close to 32 °C . Its temperature‐induced conformation changes depend on the brush density, thereby allowing us to gain qualitative information on this property. Utilizing the similarity of the catalyst system for the electro‐click and SI‐eATRP reactions, we use a simple and convenient one‐pot reaction in which the H−Eth−Ar modified substrate is immersed in a solution containing azide‐functionalized initiator (bromo‐2‐methylpropionic acid 3‐azidoprophyl ester, APBiB), monomer (NIPAM) and CuBr 2 / N , N , N′ , N , N′′ ‐pentamethyldiethylenetriamine (PMDETA) as catalyst.…”

“…In addition to the composition of polymers, the density of polymer chains grafted from a surface can determine the final properties of the polymer‐coated material . Controlling and measuring the density of grafted polymers can be difficult yet is important for the preparation of reproducible materials.…”

Synthetic Methodologies for Chelating Polymer Ligands: Recent Advances and Future Development

“…Depending on the grafting density of the polymer, fixed chains take the so‐called mushroom or brush configurations (Figure ) . In this case, their mutual transitions are observed depending on various conditions.…”