Polyethyleneimine (PEI), a potent architecture backbone was explored for the synthesis of novel polymeric ionic liquids (PolyE-ILs) with protagonist properties. The simple quaternization of PEI dendrimer with Bronsted acids (H 2 SO 4 , H 3 PO 4 , CH 3 SO 3 H, CF 3 COOH and TsOH) leads to formation of series of protic PolyE-ILs with corresponding counter anions [HSO 4 ] À , [H 2 PO 4 ] À , [CH 3 SO 3 ] À , [CF 3 COO] À and [TsO] À. The physicochemical properties of synthesized PolyE-ILs were studied by using TGA, Hammett acidity, hydrodynamic radii, solubility, and elemental analysis. PolyE-ILs showed characteristic Hammett acidity (0.94-1.78), good thermal stability (< 250°C) and enhanced hydrodynamic radii. However, use of PolyE-IL can be promoted for their wide applications as an acid catalysts. The reported PolyE-IL-1 with sulfonic acid counter ion was explored as catalyst for esterification of (E)-cinnamic acids and it showed good catalytic activity. The enhanced hydrodynamic radii due to the branched architecture of PEI dendrimers facilities the separation process via Nanofiltration (NF) membrane with no membrane fouling. Thus, PolyE-ILs can be highly active, easily recoverable, and reusable catalyst for esterification reactions with superior sustainability and economics. In addition to this the present one pot PolyE-IL synthesis process is non-complex and simple as compared to conventional post polymerization, ion exchange, and nucleophilic addition etc., strategies for synthesis of PILs.

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k-Carrageenan is a major constituent of red seaweeds composed of inherent repeating sulfated galactan units having potential to produce 5-hydroxymethyl furfural (5-HMF). The presence of inherent alkali sulfate functionality generates catalytically active acid sites on the backbone of k-carrageenan. In the present study, catalyst-free synthesis of 5-HMF was studied by inducing acid active sites on alkali-sulfated functionalities of k-carrageenan. The presence of −SO 3 H active sites on acid-imparted k-carrageenan were accountable for the self-catalytic property to deconstruct k-carrageenan into galactose units and further dehydration into 5-HMF. A plausible mechanism for the self-catalytic deconstruction of k-carrageenan into 5-HMF has been proposed. The comparative study of catalytic and noncatalytic reactions in DMSO resulted 43% and 41% yield of 5-HMF, respectively. Of the tested solvents (DMF, DMSO, IPA, TBA, and IAA), DMSO was found as the best solvent for deconstruction. Furthermore, the ease of solvent recovery is achieved by using IPA as a green solvent in combination with DMSO, which resulted in 50% yield of 5-HMF. The use of a catalyst-free protocol by using IPA as a green and low boiling reaction medium promotes development of green processes.