Photoresponsive polyamides containing pentamethylated norbornadiene moieties: Synthesis and photochemical properties under sunlight irradiation

Abstract

Photoresponsive polyamides containing main‐chain pentamethylated norbornadiene (NBD) moieties are obtained in quantitative yields via the Yamazaki–Higashi reaction between a pentamethylated NBD dicarboxylic acid and a series of aromatic diamines. Chemical structures are confirmed by 1H and 13C NMR and weight average molar masses measured by SEC are in the range of 21,500–28,600 g mol−1 with chain dispersities close to 2. Physical properties are investigated by FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis, and viscosimetry. All obtained polyamides are amorphous with glass transition temperatures ranging from 68 to 124 °C. They are soluble at room temperature in common organic solvents and exhibit good thermal stabilities with Td10 values ranging from 175 to 276 °C. The photochemical isomerization of the NBD moiety into quadricyclane (QC) is studied by UV/vis spectroscopy after sunlight irradiation of polymer films. For all polyamides, a first‐order kinetic rate is observed for the conversion of NBD to QC. The thermal release of the stored energy associated to the reverse transformation of QC groups into NBD ones is about 90–95 kJ mol−1 as measured by DSC of the irradiated polymer films. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4650–4656

Photochemical isomerization of norbornadiene‐containing polytriazoles obtained by click chemistry polyaddition

“…48 The relatively moderate thermal stability of polytriazoles 11-20 most probably results from the thermally driven cleavage of NBD units as previously observed for NBD-containing polyimides (T d10 267-337 C), 24 and polyamides (T d10 175-276 C). 25 Hash residual values ranging from 33 to 41% were obtained in accordance with previously reported polytriazoles. 38,47,48 Photochemical Properties Polytriazoles 11-20 were characterized by UV-vis spectroscopy to determine their maximum absorption wavelengths (k max ).…”

“…These values are considerably lower than previously reported ester‐ or ether‐containing polytriazoles ( T d10 ∼ 330–380 °C), and aromatic polytriazole resins ( T d10 ∼ 400–570 °C) . The relatively moderate thermal stability of polytriazoles 11–20 most probably results from the thermally driven cleavage of NBD units as previously observed for NBD‐containing polyimides ( T d10 ∼ 267–337 °C), and polyamides ( T d10 ∼ 175–276 °C) . Hash residual values ranging from 33 to 41% were obtained in accordance with previously reported polytriazoles …”

“…The PVI experiments obey first‐order kinetics in the initial reaction stage as reported earlier in literature for NBD‐containing polymers [Fig. (b)] . The rate constants of NBD conversion ( k app ) were calculated from the slope of the linear fit of the first‐order plots (Table ).…”

“…4(b)]. [21][22][23][24][25] The rate constants of NBD conversion (k app ) were calculated from the slope of the linear fit of the first-order plots (Table 1). Obtained k app values suggest a strong influence of the chemical structure of both the dialkyne and the diazide monomers on the rates of NBD conversion.…”

“…20 Nishikubo and coworkers have developed the synthesis of poly(ester-amide)s, 21 and polyesters, 22 introducing the NBD in the main chain of the polymer by polyaddition of NBDdicarboxylic acid with secondary diamines and diepoxides, respectively. More recently Ben Romdhane and coworkers have detailed the synthesis and photochemical properties of imide-amide organic models based on pentamethylated-NBD units, 23 as well as polyimides, 24 and polyamides, 25 obtained by polyaddition of dianhydride and dicarboxylic acid NBD derivatives with different aromatic diamines.…”