Small
quantities of regio-defects in a regio-/stereoregular polymer
weaken its tacticity and properties. This work clarified the origin
of the regio-defect in the process of synthesizing poly(monothiocarbonate)
through the copolymerization of propylene oxide (PO) and carbonyl
sulfide (COS) catalyzed by a (salen)CrCl complex accompanied by bis(triphenylphosphoranylidene)ammonium
chloride ([PPN]Cl). Quantitative characterization results from the
MALDI-TOF-MS and 1H (13C) NMR spectroscopy suggested
that the chain transfer reaction resulted in the regio-defect in the
final copolymer, i.e., tail-to-tail (T–T) diad and dithiocarbonate
(DTC) unit. The chain transferring to water in the reaction system
led to the production of a (salen)Cr–OH intermediate, which
initiated the copolymerization via either attacking PO first to result
in formation of a T–T diad or first activating COS to produce
mercapto (−SH) end-capped dormant chains via decarboxylation,
thus generating a DTC unit in the final product through another chain
transfer reaction and regrowth of the chain. The content of regio-defect
in the final copolymer was directly related to the water content in
the system. It is essential to reduce the regio-defect for an immortal COS/PO copolymerization reaction by eliminating
trace amounts of water. We also demonstrated the application of α-OH,
ω-OH poly(propylene monothiocarbonate) for synthesizing
a well-defined ABA triblock copolymer, polystyrene-block-poly(propylene monothiocarbonate)-block-polystyrene
(PS-b-PPMTC-b-PS), with a M
n of 10 800 g/mol and a PDI of 1.08 via
an atom transfer radical polymerization (ATRP) method.