Nanostructuration by self-assembly in N-alkyl thiazolium and triazolium side-chain polymethacrylates

Amphiphilic polymers are tunable systems to construct supramolecular hierarchically self-assembled structures. Six families of heterocyclic polymethacrylates (PMTAs) bearing 1,3-thiazole and 1,2,3-triazole pendant groups with alkyl and succinate spacers were chemically modified by quaternization reaction of the azole heterocycles with five alkylating agents (methyl, butyl, octyl, dodecyl, and hexadecyl iodide) leading to a library of 30 different amphiphilic poly(ionic liquid)s (PMTAs-RI). These polymers have been characterized in bulk by small- and wide-angle X-ray scattering (SAXS, WAXS) and differential scanning calorimetry (DSC). Quaternization induces a dramatic effect (increase) on the glass-transition temperature Tg, being strongest for methyl iodide members. Increasing the length of the quaternizing agent, plasticization is first observed, followed by a further increase of Tg. This effect, together with evidence of a second Tg and crystallization for the members with the longest quaternizing agents, could be attributed to the presence of well-developed alkyl nanodomains evidenced by the structural investigation. WAXS and SAXS results have been consistently interpreted by assuming nanostructuration driven by the amphiphilicity balance of poly(ionic liquid)s. The different morphologies revealed by SAXS have been characterized, assigning a plausible chemical nature to the phases involved in each case. The nonpolar fraction has been considered as the control parameter defining the main features of the achieved morphology. By increasing this parameter, structures ranging from hexagonally packed nonpolar cylinders in a polar matrix to the inverse situation have been found, passing through lamellar phases. Under some conditions, within the polar lamellae a third phase formed by cylinders of heterocycles has even been determined. We have checked the validity of the scenario proposed by comparing the sizes deduced from the SAXS analysis with the expected characteristic lengths of the associated moieties, inferring thereby how alkyl side groups arrange within the nanodomains. On the basis of the complete picture achieved, the type of nanostructures formed by this class of polymers can be predicted, if the chemical composition including the quaternization degree is known.This work has been supported by MAT2013-47902 and MAT2011-24797 (Spanish-MINECO and EU). R.T. acknowledges CSIC for his JAE-Pre grant. A.A. acknowledges financial support from the Projects MAT2012-31088 (Spanish-MINECO and EU) and IT-654-13 (Basque Government).Peer Reviewe