Polymerization
of methyl acrylate under ultraviolet (UV) irradiation
in the presence of S-1-dodecyl-S′-(α,α′-dimethyl-α″-acetic
acid) trithiocarbonate (DDMAT) was investigated by in situ 1H nuclear magnetic resonance spectroscopy. Effects of light intensity,
wavelength, and concentration of DDMAT on the polymerization behaviors
were studied in detail. The experimental results demonstrate that
the “living” features of the photopolymerization are
related to the concentration of DDMAT. “Living”/controlled
radical polymerization was successfully achieved with a high concentration
of DDMAT. However, with a low concentration of DDMAT, the polymerization
proceeded in an uncontrolled manner and produced polymers with high
molecular weights and broad polydispersities. Photochemical behavior
of DDMAT was studied in detail, and the results showed that the photolysis
of DDMAT was reversible at high concentration, whereas contrarily,
DDMAT decomposed irreversibly at low concentration. A possible mechanism
was proposed for the reversible photolysis of DDMAT at high concentration,
which may involve both reversible termination and reversible addition–fragmentation
chain transfer approaches.
Homogeneous dispersion and functionalization of pristine multiwalled carbon nanotubes (MWNTs) in various organic solvents was achieved by a simple ultrasonic process in the presence of an azide copolymer, poly(4-azidophenyl methacrylate-co-methyl acrylate)(P(APM-co-MA)). The copolymes were noncovalently attached to the surface of the MWNTs via pi-pi interactions to form MWNT-P(APM-co-MA) composites. The composites were characterized by transmission electron microscopy, thermogravimetric analysis, Raman spectra and UV-vis spectra. The solution dispersion of the MWNT-P(APM-co-MA) composites were used to prepare superhydrophobic cotton fabric by a facile dip-coating approach. MWNTs were covalently attached to the surface of the cotton fabric through the chemical reactions between the azide groups of P(APM-co-MA) with both MWNTs and cotton fibers. The reactions are based on UV-activated nitrene chemistry. Owing to the nanoscale roughness introduced by the attachment of MWNTs, the cotton fabric surface was transformed from hydrophilic to superhydrophobic with an apparent water contact angle of 154 degrees . Since MWNTs were covalently attached on the surface of the cotton fabric, the superhydrophobicity possesses high stability and chemical durability.
A new vinyl aryl azide monomer, 4-azidophenyl methacrylate (APM), has been synthesized and characterized by (1) H NMR and FT-IR spectroscopy. The thermal stability of APM has been investigated by temperature-dependent FT-IR spectroscopy and (1) H NMR, and the monomer has been demonstrated to be quite stable at ambient temperature. Reversible addition-fragmentation chain transfer (RAFT) homopolymerization and copolymerizations of APM with methyl acrylate, methyl methacrylate, and styrene have been carried out at room temperature using a redox initiator, benzoyl peroxide (BPO)/N,N-dimethylaniline (DMA). The results show that the polymerizations bear all the characteristics of controlled/living free-radical polymerizations. Moreover, the cycloaddition of azido group to carbon-carbon double bond can be avoided in the polymerization process at room temperature.
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