(a) Polyetherimide (PEI) (b) Experimental sequence: The polymer is compacted at the air-water interface. Next, reactants are injected and the layer is observed with interfacial rheology. Then, the layer is transferred to a solid substrate or grid. The solubility of the layers on solid substrates is assessed by washing with DMF, chloroform, and water. (c) Overview over four investigated functionalization procedures: (I) Direct amidation with and without Lewis acid catalyst. (II) Hydrolytic ring opening, (III) 3-step mechanism from hydrolytic ring opening via EDC/NHS activation of the generated carboxyl groups to amidation with (IIIa) EDA or (IIIb) TAPP. If the same amine reacts with two or more chains, cross-links are formed.

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... class of high-performance polymers that can be surface modified without oxidative pretreatment are polyimides (PIs) and the more easily processable polyetherimide (PEI) (Fig. 1a) [9]. Owing to the presence of phthalimide groups in the backbone, these polymers can react with nucleophiles in a polymer analogous reaction, meaning that the chain length remains unaffected. In addition to their excellent mechanical and thermal properties, PEI and PIs can be processed into porous devices such as particles [10] and ...

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... our previous study, we focused on the reaction of PEI with hydroxyl ions, which, under suitable conditions, leads to ring opening without chain cleavage [18]. Here, we focus on the functionalization with multivalent amines (Fig. 1c), either directly or in a process involving hydroxyl ions. As a first step, we investigate different approaches for a direct reaction with aqueous amine solution, where three different outcomes can be expected: In absence of pH control and at high amine content, the solutions are alkaline, and hydrolysis could be favored over amidation. ...

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... the solutions are alkaline, and hydrolysis could be favored over amidation. With pH control and an excess of amines, a high number of free amine groups are expected, whereas an excess of polymer could promote network formation when a multivalent amine reacts with several chains. The direct amidation of imides can be promoted by Lewis acids (Fig. 1c I). Here, Yb(III)triflate was chosen, which has shown both good activity [19] and water stability ...

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... three-step procedure is investigated as an alternative approach for amidation of PEI (Fig. 1c II). This procedure starts by ring opening of the phthalimide groups at pH 12.5, followed by activation with water-soluble carbodiimide and conversion to activated esters. Then, the activated esters react with bivalent ( Fig. 1c IIIa) and tetravalent amines (Fig. 1c IIIb). With appropriate stoichiometry, the multivalent amines can bridge ...

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... three-step procedure is investigated as an alternative approach for amidation of PEI (Fig. 1c II). This procedure starts by ring opening of the phthalimide groups at pH 12.5, followed by activation with water-soluble carbodiimide and conversion to activated esters. Then, the activated esters react with bivalent ( Fig. 1c IIIa) and tetravalent amines (Fig. 1c IIIb). With appropriate stoichiometry, the multivalent amines can bridge the chains, resulting in network formation. However, network formation requires reactive collisions between amidated and non-amidated monomers. With bulk PEI having a T g > 200 °C, a thermal activation is required. Here, we ...

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... procedure is investigated as an alternative approach for amidation of PEI (Fig. 1c II). This procedure starts by ring opening of the phthalimide groups at pH 12.5, followed by activation with water-soluble carbodiimide and conversion to activated esters. Then, the activated esters react with bivalent ( Fig. 1c IIIa) and tetravalent amines (Fig. 1c IIIb). With appropriate stoichiometry, the multivalent amines can bridge the chains, resulting in network formation. However, network formation requires reactive collisions between amidated and non-amidated monomers. With bulk PEI having a T g > 200 °C, a thermal activation is required. Here, we investigate whether the T g of ultrathin PEI ...

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... experimental procedure is shown in Fig. 1b. The film is formed by spreading droplets of diluted polymer in chloroform solution. After evaporation of the solvent, the PEI film is compacted and the reactants are injected in the liquid phase. The progress of the reaction is followed by interfacial rheology or surface potential measurements. The functionalized films are transferred ...