Self-organization of stack-up block copolymers into polymeric supramolecules

Nanoscale Research Letters, Jan 2007

Polyethylene oxide –b– polypropylene oxide -b- polyethylene oxide (EO106PO70EO106) block copolymer self-organizes into polymeric supramolecules, characterized by NMR as phase transition from the isotropic stack-up block structure to the ordered cubic polymeric supramolecular structure. Its dependence on both temperature and copolymer concentration is clearly shown by the changes in line shape and chemical shift of the PO70blockβ,γ resonances.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2Fs11671-007-9038-8.pdf

Self-organization of stack-up block copolymers into polymeric supramolecules

Nanoscale Res Lett Self-organization of stack-up block copolymers into polymeric supramolecules Yong J. Yuan 0 Ka-Wai Choi 0 Herbert Wong 0 0 Y. J. Yuan (&) K.-W. Choi H. Wong Industrial Research Ltd., Crown Research Institutes , 69 Gracefield Road, 31-310 Lower Hutt , New Zealand Polyethylene oxide -b- polypropylene oxide -b- polyethylene oxide (EO106PO70EO106) block copolymer self-organizes into polymeric supramolecules, characterized by NMR as phase transition from the isotropic stack-up block structure to the ordered cubic polymeric supramolecular structure. Its dependence on both temperature and copolymer concentration is clearly shown by the changes in line shape and chemical shift of the PO70 block b, c resonances. Self-assembly; NMR; Block co-polymer - Self-assembly of polymeric supramolecules is a powerful tool for producing functional materials that combine several properties [ 1 ]. Potential applications include: information storage, magnetic fluid, medical diagnosis, catalysis, ceramics, sensors, separations and reactions involving large molecules, chromatographic media, proton conducting materials, controlled release of agrochemicals, hosts for supramolecular assembly, and pigments/solubilising agent in paints and cosmetics [ 2 ]. Commercially available non-ionic Pluronics or Synperonics triblock copolymers [ 3 ] (polyethylene oxide– polypropylene oxide–polyethylene oxide, EOm POnEOm) are superior polymeric templates, which produce material of a wide pore diameter and wall thickness [ 4, 5 ]. The concept of stacking triblock copolymers [4] was proposed to produce very longrange linear nanostructures, due to extension more or less indefinitely in both directions. The synthesized conical molecules, which are shaped like a badminton shuttlecock, were reported to stack together in a directed manner [ 6 ]. The specific shapes open up the huge potential for directionalities of alignment, causing by hydrogen-bonding and/or weak van der Waals interactions. Pluronics F127 is the subject of interest for this study. It has the formula of EO106PO70EO106. As illustrated in Scheme 1, this triblock compound consists of a hydrophobic PO70 block sandwiched by two hydrophilic EO106 blocks. For simplicity, there are two different modes of interaction for self-assembled block copolymer, namely hydrophobic PO70 and hydrophilic EO106 packing segments. In both cases, the packing of large molecules, i.e., EO106PO70EO106, means that only a fraction of molecules will be in direct contact due to hydrogen-bonding, polar or van der Waals forces. Because of the unique amphiphilic property, the material self-assembles into stacking structures. Hydrogen-bonding among the PO70 units are expected to drive the triblock molecules to assemble into linearrotating cylinder structures [ 4 ]. Its phase behavior is temperature and concentration dependent, which relies on the level of dehydration of EO106 and PO70 block. An additional self- assembly process pushes the corona-surrounded domains into unusual anisotropic interactions, which was suggested to be a cubic phase [ 7 ]. NMR (nuclear magnetic resonance) for studying liquid crystalline systems was discussed, [ 8 ] to elucidate thermotropic and lyotropic phase transitions. The studies of the 13C NMR of EO61PO41EO61 (F87) at Scheme 1. Self-organization of stack-up EO106PO70EO106 into polymeric supramolecules low concentration less than 1% (w/w) have been documented previously, [ 9, 10 ] even the self-assembly behavior in water of a mixture of EO13PO30EO13 (L64) and EO37PO58EO37 (P105), was explored [11] by 2H NMR at 25 C. However, the experimental application of these techniques and the interpretation of their results are more complicated than in homogeneous systems [ 7, 12 ]. To date, no complete NMR study of F127 polymer has been published. This study is focused on the 1H NMR analysis of F127 in D2O. All spectra were recorded on samples dissolved in D2O contained in a 5 mm o.d. NMR tube, on a Varian Unity 500 MHz NMR Spectrometer equipped with a 5 mm inverse probe. Excitation pulse width was approximately 81 (10 ls), data acquisition time 4.096 s, relaxation delay time 6 s, pulse repeat time approximately 10 s. The residual HDO peak was used as a secondary reference as a function of temperature [13] to calibrate the chemical shifts. Although not ideal, this should remove the gross effects of temperature dependence of the chemical shift. As shown in Fig. 1, the chemical shifts of both PO70 and EO106 blocks appear to be temperature-dependent. There is a fine structure (bCH2 or cCH) at 20 C, and partial overlap with b‘CH2 units of EO106 block. The spectra at 40 and 60 C are similar; the resonances of 1H (aCH3, cCH and bCH2) of PO70 block decrease as temperature increases. At temperatures above the phase transition, [ 7 ] the signal is increased, due to an increased relaxation rate of the interacting PO70 blocks, with the decrease of segmental mobility (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2Fs11671-007-9038-8.pdf

Yong J. Yuan, Ka-Wai Choi, Herbert Wong. Self-organization of stack-up block copolymers into polymeric supramolecules, Nanoscale Research Letters, 2007, pp. 104, Volume 2, Issue 2, DOI: 10.1007/s11671-007-9038-8