Self-controlled synthesis of hyperbranched poly(ether ketone)s from A(3)+B-2 approach via different solubilities of monomers in the reaction medium

Hyperbranched poly(ether ketone)s (PEK's) were synthesized via A 3 + B2 polymerization approach without forming cross-linked products, because the polymer-forming process based on Friedel-Crafts reaction was kinetically controlled by the solubility difference of monomers in the viscous hydrophilic reaction medium, poly(phosphoric acid) (PPA)/phosphorus pentoxide (P2O5). The hydrophilic trimesic acid as an A3 monomer is soluble in the reaction medium, while hydrophobic diphenyl ether and 1,4-diphenoxybenzene as B2 monomers are marginally soluble. It is hypothesized that the gelation was avoided because of the following two factors: (i) self-regulated feeding of the arylether monomers into the system driven by their poor solubility and phase separation from PPA/P2O5 medium; (ii) reaction-medium- induced isolation of growing macromolecules promoted by the high bulk viscosity. Both polymerization experiments based on equimolar or equifunctional stoichiometry (A3: B2) resulted in completely soluble hyperbranched PEK's in polar aprotic solvents when these polymers contained a little amount of solvent residues and only in strong acids if they were rigorously dried. The structural analysis by using MALDI-TOF mass spectroscopy in the low molar mass region provided further confirmation that there was no trace of networks; various sizes of cyclics were detected instead.close262

In-situ grafting of hyperbranched poly(ether ketone)s onto multiwalled carbon nanotubes via the A(3)+B-2 approach

Trimesic acid and phenyl ether were in-situ polymerized as A3 and B2 monomers, respectively, in the presence of a fixed amount (10 wt %) of multiwalled carbon nanotube (MWNT) to afford hyperbranched poly(ether ketone)s (PEK's)/MWNT nanocomposites. The feed ratios of A3 and B2 monomers vary from 3:2 to 1:2 in the A3 + B2 polycondensations. The polymerization was carried out in a mildly acidic medium, i.e., poly-(phosphoric acid) or PPA, with an optimized amount of phosphorus pentoxide (P2O5) added. The overall evidence based on the data of elemental analysis (EA), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) implicates that hyperbranched PEK's were attached to the surface of MWNT to form hyperbranched PEK-g-MWNT nanocomposites. Furthermore, MWNT remained structurally intact under the polymerization and workup conditions. Evidently driven by the molecular architecture of globular hyperbranched polymers, the morphology of the nanocomposites resembles "mushroom-like clusters on MWNT stalks". The hyperbranched PEK-g-MWNT nanocomposites were soluble in polar aprotic solvents stemming from numerous carboxylic acids on their surfaces. When some of samples were dispersed in 1 M LiOH aqueous solutions, they formed very stable suspensions. The resulting lithiated nanocomposites are being investigated in the applications such as ion conductivity and energy capacitance.close343