The new generation of catalytic systems for Controlled/"Living" Radical Polymerization (CLRP) of vinyl monomers should be non-toxic, inexpensive and provide fast polymerizations in environmentally friendly media. Herein, we report the successful ambient temperature ATRP of several vinyl monomers (MA, n-BA, MMA and DMAEMA) catalyzed by inorganic sulfites (Na S O and Na S O) and small amounts of a Cu(II)Br /Me TREN system in alcohol-water mixtures. The
Inorganic sulfites such as sodium dithionite (Na 2 S 2 O 4 ), sodium metabisulfite (Na 2 S 2 O 5 ), and sodium bisulfite (NaHSO 3 ) have been studied as reducing agents for atom transfer radical polymerization (ATRP). They act not only as very efficient reducing agents but also as supplemental activators for SARA (supplemental activator and reducing agent) ATRP of methyl acrylate in DMSO at ambient temperature. In combination with Cu(II)Br 2 /Me 6 TREN, they produced poly(methyl acrylate) with controlled molecular weight, low dispersity (M w /M n = 1.05), and well-defined chain-end functionality. Sulfites are eco-friendly, approved by FDA as food and beverage additives, and used commercially in many industrial processes.
Controlled/“living” radical polymerization
(CLRP) of vinyl chloride (VC) via the reversible addition–fragmentation
chain transfer (RAFT) process is reported for the first time. The
cyanomethyl methyl(phenyl)carbamodithioate (CMPCD) was found to be
an efficient RAFT agent enabling the CLRP polymerization of VC monomer
under certain experimental conditions. Two different radical initiators,
having very distinct half-life times at room temperature, were employed
in this study. The kinetic studies of RAFT polymerization of VC show
a linear increase of the molecular weight with the monomer conversion
and the lowest polydispersity (PDI) ever reported for poly(vinyl chloride)
(PVC) synthesized with CLRP method (PDI ∼ 1.4). The resulting
PVC was fully characterized using the matrix-assisted laser desorption
ionization time-of-flight mass spectrometry (MALDI-TOF-MS), 1H
nuclear magnetic resonance spectroscopy (1H NMR), and gel
permeation chromatography (GPC) techniques. The 1H NMR
and MALDI-TOF-MS analysis of PVC prepared via RAFT polymerization method
have shown the absence of structural defects and the presence of chain-end
functional groups. The “livingness” of the PVC was also
confirmed by a successful reinitiation experiment. The suitability
of the RAFT agent was also confirmed via high-level ab initio molecular orbital calculations.
A series of polyacrylonitrile-block-poly(butyl acrylate) (PAN-b-PBA) copolymers were prepared by supplemental activator reducing agent atom transfer radical polymerization (SARA ATRP). These copolymers were then used as precursors to pyrolytic nanostructured carbons with the PAN block serving as a nitrogen-rich carbon precursors and the PBA block acting as a sacrificial porogen. The study revealed that while the size of mesopores can be controlled by the size of the porogenic block, the connectivity of pores diminishes with the decrease of the overall molecular weight of the precursor. This partial loss of mesopore connectivity was attributed to the weaker phase segregation between the blocks of shorter lengths inferred from the shape of small-angle X-ray scattering profiles and from the crystallinity of polyacrylonitrile phase.
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