Publication date: 7 April 2017
Source:Polymer, Volume 114
Author(s): Sravan Baddi, Rati Ranjan Nayak, Aruna Palanisamy
Segmented poly(urethane acylsemicarbazides) carrying aromatic groups in the hard segments were synthesized by two step polymerization technique using commercially available, cost effective raw materials. The resulting polymers with specific ratios of NCO/OH were found to gel organic solvents like dimethylformamide, dimethylacetamide and N-methylpyrrolidone and their corresponding gels were thermoreversible. Tuning of the gelation behaviour and gel properties have been achieved by varying the polyol molecular weight (polypropylene glycol - 1000 and 2000) and NCO/OH ratio. Influence of hard segment content on the gel-sol transition as studied by DSC showed that increasing hard segment content led to stronger gelator-gelator interactions and hence higher Tgel. Broad tanδ peaks of films of xerogels reflected a network kind of structure due to physical crosslinks in the self-assembled state in DMA analysis. The films of xerogels of PPG1000 based gelators exhibited higher tensile strength but lower elongation compared to PPG2000 based gelators. Viscoelastic nature of the supramolecular elastomeric gels was confirmed by dynamic oscillatory studies and stability of the gel was found to increase with increase in hard segment content. H-bonding between the urethane moieties as confirmed by IR spectroscopy and hydrophobic interactions between the PPG units in the soft segments lead to a phase separated structure. Hence phase separation induced gelation mechanism has been proposed and supported by SEM images and XRD data. Both the gelators and xerogels had capability of adsorbing crystal violet from their aqueous solutions and desorbing in organic solvents like acetone and methanol.
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