la8b01580_si_001.docx (3.26 MB)
Cleavage of Organosiloxanes with Dimethyl Carbonate: A Mild Approach To Graft-to-Surface Modification
journal contribution
posted on 2018-07-25, 00:00 authored by Iryna Protsak, Ian M. Henderson, Valentyn Tertykh, Wen Dong, Zi-Chun LeIn this work, we
explore the depolymerization of poly(dimethylsiloxane)
(PDMS-100) and poly(methylphenylsiloxane) (PMPS) using dimethyl carbonate
(DMC) and develop a surface functionalization method by utilizing
the DMC-imparted active methoxy end groups of the partially depolymerized
polysiloxanes. The efficiency of dimethyl carbonate as a reagent for
organosiloxane cleavage was confirmed by means of 1H NMR
spectroscopy, size-exclusion chromatography, and viscosity measurements.
The reaction of fumed silica with organosiloxanes (PMPS, PDMS-50)
in the presence of DMC was investigated using the ζ-potential, 29Si and 13C solid-state NMR spectroscopy, IR spectroscopy,
CHN analysis, contact angle goniometry, thermogravimetric analysis,
scanning and transmission electron microscopy (TEM), and rheology.
It was found that the interaction of PMPS/DMC with an SiO2 surface produced hydrophobic and thermally stable moieties (up to
550 °C) with a densely packed (average 2.2 groups/nm2) alkylsiloxane network for SiO2/PMPS + DMC in comparison
with SiO2/PMPS (average 1.4 groups/nm2). Surface
functionalization was successfully attained at a relatively moderate
temperature of 200 °C. Scanning electron microscopy data show
that the average size of aggregates of PMPS/DMC-modified silica nanoparticles
is smaller than that of the initial silica and silica modified with
neat PMPS. TEM images reveal uniform distribution of the PMPS/DMC
mixture across the SiO2 surface. Rheology studies show
thixotropic behavior in industrial oil (I-40A), a fully reversible
nanostructure and shorter structure recovery time for fumed silica
modified in the presence of DMC.