A study of diazonium couplings with aromatic nucleophiles both in solution and on a polymer surface

Photochromic Materials by Postpolymerisation Surface Modification

“…In general, the n → π* transition of an isolated azo group (R–N  NR) has λ max around 340 nm, but the extra conjugation of an adjacent aromatic ring leads to a bathochromic shift; for this reason, all of samples XAD4.A1–B x ′ have λ max greater than 340 nm (Table S2 and Figure S1a,b, Supporting Information). Importantly, the use of NaOAc gave better azo-coupling efficiency, as indicated from a hyperchromic effect consistent with a greater density of chromophores at the polymer surface, an outcome which was similar to reactions in solution . In some cases, attenuated total reflection-infrared (ATR-IR) spectroscopic analysis was sufficiently sensitive to give conclusive evidence for modification (e.g., XAD4.A2–B2 and XAD4.A2–B4 from the presence of a carbonyl group at around 1701 and 1744 cm –1 , respectively).…”

“…The diazonium salts were generated from the required amines 4a–e by stirring with NaNO 2 in THF/H 2 O = 1:1 in acidic conditions at 0 °C for 30 min and were used in situ; this step was done in the absence or presence of NaOAc, since buffering has been found to be beneficial for coupling in some cases. 52 Controls derived from blank XAD4 beads ( XAD4.B x ′ , x ′ = 1–5), which omitted the intermediate carbene step, were prepared for comparison purposes (Table S2, Supporting Information). The visible color of the beads gave an immediate indication of modification, and this was confirmed by diffused reflectance UV–vis (absorbance mode) spectroscopy, which gave spectra with absorbances less than 520 nm for the most intensely colored materials.…”

“…Importantly, the use of NaOAc gave better azo-coupling efficiency, as indicated from a hyperchromic effect consistent with a greater density of chromophores at the polymer surface, an outcome which was similar to reactions in solution. 52 In some cases, attenuated total reflection-infrared (ATR-IR) spectroscopic analysis was sufficiently sensitive to give conclusive evidence for modification (e.g., XAD4.A2–B2 and XAD4.A2–B4 from the presence of a carbonyl group at around 1701 and 1744 cm –1 , respectively). Both combustion and XPS analysis confirmed the presence of nitrogen; the former indicated loading levels of 4.8 × 10 12 up to 3 × 10 13 molecules cm –2 , and in the latter a surface loading value of up to 78% assuming full monolayer formation was observed.…”

“…Ax ( x = 1, 2) and this gave the surface-modified beads XAD4.A x –B x ′ ( x = 1–2, x ′ = 1–5, Scheme and Table S2, Supporting Information). The diazonium salts were generated from the required amines 4a–e by stirring with NaNO 2 in THF/H 2 O = 1:1 in acidic conditions at 0 °C for 30 min and were used in situ; this step was done in the absence or presence of NaOAc, since buffering has been found to be beneficial for coupling in some cases . Controls derived from blank XAD4 beads ( XAD4.B x ′ , x ′ = 1–5), which omitted the intermediate carbene step, were prepared for comparison purposes (Table S2, Supporting Information).…”

Chemical functionalization of polyethylene surfaces by plasma-assisted carbene insertion

“…3; we have recently reported a correlation of solution and diffuse reflectance UV behavior using this technique. [37] Without modification, the pristine PE does not show an obvious UV absorption (Fig. 3a, PE blank).…”