One Dimensional Tautomerizable Styrenic Copolymers and Polymer Behavour under Confinement

JUAN M. GIUSSI; IWONA BLASZCZYK LEZAK; PATRICIA E. ALLEGRETTI; M. SUSANA CORTIZO; CARMEN MIJANGOS

Praga

Conferencia; 7th International Conference on nanostructured polymers and nanocomposites; 2012

Simple fabrication of polymers, copolymers and polymer based composites nanostructures by so called template synthesis method, has attracted increasing interest due to the possibility of obtaining polymers with different morphologies, i.e. nanorods, nanotubes or nanospheres with new or improved properties. Due to this fact those special behaviors seem to hold out a new perspective to deal with some classical problems in polymer physics, i.e. chain dynamics, the early stages of the crystallization etc. Moreover, one-dimensional polymer nanostructures (1DPNs) are of execeptional interest due to their potential applications in sensors, photonics, electronics, coatings, catalysis or ceramics. Also, some examples of ordered arrays of 1DPNs with potential application in field of magnetic labeling and biomedicine have been described in literature. Until the present, different homopolymers and block copolymer have been nanostructured by this method and studied the polymer properties under confinement. Nevertheless, tautomerizable copolymers have never been nanostructured and neither the resulting properties reported. The aim of the present work is to report the study carried out on infiltration of new tautomeric styrene copolymers (coStMOP, co-styrene-2-methyl-3-oxo-5-phenyl-4-pentenonitrile) nanostructures of different F (F:St/MOP) values into porous aluminum oxide (AAO) templates and to establish a comparison between the properties of this copolymer in bulk and nanostructures. Moreover, another aim which has been studied is if tautomeric equilibria exiting in coStMOP affects or may have influence on the properties of 1DPN copolymer and bulk copolymer. The presence of the tautomeric equilibrium could make these materials a specific substrates according to the environment in which they exist. This feature could make them interesting in biomedicine. Tautomerizable styrene copolymers, co-styrene-2-methyl-3-oxo-5-phenyl-4-pentenonitrile (coStMOP), were used for preparing polymer nanostructures. The chemical composition and molecular weight of the three copolymers are: coStMOP1, FMOP = 0.17 and Ww= 82000 g/mol; coStMOP2, FMOP = 0.38 and Ww= 64000 g/mol and coStMOP3, FMOP = 0.62 and Ww= 37000 g/mol). Anodized aluminium oxide templates (AAO) have been prepared via a two-step electrochemical anodization process of aluminum plates as described elsewhere. A first set of anodizations was carried in oxalic acid 0.3 M at a controlled temperature of 2-3 ºC. The obtained AAO templates have an average pore diameter of 35 nm and pore length of 80 μm. The infiltration of coStMOP copolymers into the AAO nanocavities was carried out via the melt precursor film wetting method, as described by Martín at al.1 For that, solid copolymer in powder: coStMOP1, coStMOP2 and coStMOP3, was placed on the AAO surfaces and then infiltrated at the corresponding temperatures (217, 220 and 230 ºC, respectively) and time (225, 300 and 360 min, respectively). Pore diameter and the length of AAO templates and of obtained copolymer nanofibers were characterized by scanning electron microscopy (SEM) spectroscopy. Chemical characterization of copolymer nanofibers has been carried out by Raman spectroscopy and thermal properties of copolymers have been examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Morphological studies by SEM have been conducted to establish the structure of infiltrated copolymers. Unlike the morphological study using SEM, Raman spectroscopy has enabled to evaluate the chemical structure of copolymers along the cavity of AAO template through the confocal methodology. The thermal properties of obtained materials showed differences between the nanostructured and bulk copolymers. For all polymers the values of Tg are higher in the nanostructured coStMOP than corresponding bulk polymers. The presence of two thermal events in air in TG spectra is probably caused by the presence of tautomeric forms of polymers. CoStMOP 1DPN have been prepared by infiltration of the copolymers into AAO template. SEM micrographs demonstrate the regularity of obtained nanofibers and also show the appropriate filling of the cavities. Raman spectra prove the presence of polymer characteristic bonds trough pores of AAO template until 60 μm of profundity. The thermal properties of these materials present differences between the nanostructured and bulk polymers.