Abstract
A one-pot synthesis of block copolymer with regioregular poly(monothiocarbonate) block is described via metal-free catalysis. Lewis bases such as guanidine, quaternary onium salts, and Lewis acid triethyl borane (TEB) were equivalently combined and used as the catalysts. By using polyethylene glycol (PEG) as the macromolecular chain transfer agent (CTA), narrow polydispersity block copolymers were obtained from the copolymerization of carbonyl sulfide (COS) and propylene oxide (PO). The block copolymers had a poly(monothiocarbonate) block with perfect alternating degree and regioregularity. Unexpectedly, the addition of CTA to COS/PO copolymerization system could dramatically improve the turnover frequency (TOF) of PO (up to 240 h−1), higher than that of the copolymerization without CTA. In addition, the conversion of CTA could be up to 100% in most cases, as revealed by 1H NMR spectra. Of consequence, the number-average molecular weights (Mns) of the resultant block copolymers could be regulated by varying the feed ratio of CTA to PO. Oxygen-sulfur exchange reaction (O/S ER), which can generate randomly distributed thiocarbonate and carbonate units, was effectively suppressed in all of the cases in the presence of CTA, even at 80 °C. This work presents a versatile method for synthesizing sulfur-containing block copolymers through a metal-free route, providing an array of new block copolymers.
Highlights
Driven by the pressure of petroleum depletion, research on the utilization of renewable biomass-derived [1,2,3] and one-carbon (C1) building blocks [4,5,6,7,8] for making polymers has drawn much attention in the past few decades
The carbonyl sulfide (COS)/propylene oxide (PO) copolymerization was successfully catalyzed by the triethyl borane (TEB)/dodecyltrimethylammonium bromide (DTMeAB) pair in the presence of MPEG750 (M750) and PEG2000 (P2000) as chain transfer agent (CTA) in a variety of Lewis acid (LA)/Lewis bases (LBs)/CTA/PO
We further investigated the impact of the reaction temperature on the synthesis of the block copolymers, since previous reports [10,35] disclosed that the Oxygen-sulfur exchange reaction (O/S ER) was very sensitive to the reaction temperatures, whatever organic or metal catalysts were used
Summary
Driven by the pressure of petroleum depletion, research on the utilization of renewable biomass-derived [1,2,3] and one-carbon (C1) building blocks [4,5,6,7,8] for making polymers has drawn much attention in the past few decades. As a sulfur-containing analog of carbon dioxide (CO2 ), carbonyl sulfide (COS) is widely derived from the burning of fossil fuels, coal gas, and many chemical processes, and causes sulfur aerosols, fog, haze, acid rain, and damage of the ozonosphere via a series of photochemical reactions [9,10]. Similar to CO2 [11,12,13,14,15], COS can be used as a basic synthon for preparing sulfur-containing compounds and polymers. The copolymerization of COS with various epoxides (and oxetane) provided a series of functional poly(monothiocarbonate)s [17,18,19,20,21,22]. Reports on constructing block copolymers containing poly(monothiocarbonate) block are rare [20,23]. Ren and coworkers [20]
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