Table 1 COS/PO copolymerization catalyzed by TU-1/organic base pairs at 25 °C

Entry^a	LB	[PO]: [LB]: [TU-1]: [I]	TOF (h^–1)^b	Copolymer selectivity^c	Alternating degree (%)^c	T–H diad content (%)^d	O/S ER product^d	M_n (kg/mol)^e	PDI^e
1	DBU	250:1:0:0	4	93/7	100	>99	N.F.	38.3	1.35
2	P4	1000:1:0:0	23	60/40	92/8	>99	N.F.	29.4	1.58
3	P2	250:1:0:0	4	98/2	100	>99	N.F.	45.1	1.14
4	P1	250:1:0:0	1	>99	100	>99	N.F.	9.0	1.05
5	MTBD	250:1:0:0	3	96/4	100	>99	N.F.	46.0	1.20
6	DBU	2000:1:0:1	10	92/8	100	>99	N.F.	13.9	1.20
7	P4	2000:1:0:1	55	99/1	100	>99	N.F.	42.5	1.23
8	P2	2000:1:0:1	29	99/1	100	>99	N.F.	35.6	1.15
9	P4	2000:1:1:0	41	97/3	100	>99	N.F.	31.3	1.16
10	P2	1000:1:1:0	24	>99	100	>99	N.F.	34.3	1.16
11	DBU	250:1:1:0	7	93/7	100	>99	N.F.	30.2	1.13
12	MTBD	250:1:1:0	4	95/5	100	>99	N.F.	36.1	1.16
13^f	MTBD	1000:1:1:0	10	98/2	100	>99	N.F.	98.4	1.14
14	P4	4000:1:1:1	75	>99	100	>99	N.F.	21.3	1.21
15	P4	4000:1:5:5	112	98/2	100	>99	N.F.	9.9	1.13
16	P2	2000:1:1:1	35	>99	100	>99	N.F.	19.3	1.13
17	DBU	2000:1:1:1	22	94/6	100	>99	N.F.	11.3	1.19
18	MTBD	2000:1:1:1	17	97/3	100	>99	N.F.	12.0	1.23

The copolymerization results under other conditions (including controls), representative NMR spectra and corresponding calculations are in Supplementary Figs. 2–11 and 35, and the Methods
^aReactions were run at 25 °C in neat PO (1.0 ml; COS: PO = 1.2: 1) in a 10 ml autoclave, 24 h
^bTurnover of frequency (TOF), (Mol epoxide consumed)/(mol LB h), PO conversion was determined by ¹H NMR spectroscopy
^cDetermined by ¹H NMR spectroscopy. The copolymer selectivity is the molar ratio of the copolymer/cyclic product; The alternating degree is the molar percentage of the monothiocarbonate unit in the polymer chain
^dDetermined by ¹³C NMR spectroscopy. O/S ER = oxygen-sulfur exchange reaction. N.F. = not found (dithiocarbonate and carbonate units)
^eDetermined by gel permeation chromatography in THF, calibrated with polystyrene standards
^f72 h

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