1. Rate Acceleration of Organocatalytic Ring-Opening Polymerization Through the Application of Bis- and Tris- (Thio)Urea H- Bond Donors
Samuel S. Spink, Oleg I. Kazakov, Elizabeth T. Kiesewetter, Matthew K. Kiesewetter
Department of Chemistry, University of Rhode Island, Kingston, RI 02881
Abstract
Rate Accelerated ROP of VL and CL
‘Living’ Characteristics of ROP
My development of systems for the ROP of cyclic ester monomers, namely δ-valerolactone and ε-caprolactone, involving various H-bond donating bis- and tris- (thio)urea cocatalysts has yielded significant reaction rate enhancement in comparison with that of the monomeric analogue. Polymerizations catalyzed by
the tris-urea cocatalyst exhibited reaction rates up to 100 times those of ROPs
employing the previously
disclosed mono-thiourea.
Despite this significant rate
enhancement, these
polymerizations retain the
characteristics of ‘living’
polymerizations: low
polydispersity, predictable
molecular weight, and linear
evolution of molecular weight
with conversion. A mechanism
for the rate acceleration with
both bis- and tris- catalysts is proposed.
Table 1. Comparison of mono-, bis-, and tris- (thio)urea and MTBD Cocatalyzed ROPs of valerolactone and caprolactone.a
Figure 2. GPC traces of the polymer resulting from the 3-O/MTBD cocatalyzed ROP and subsequent chain extension of CL.
entry
Monomer
H-bond donor
(mol%)
[M]o/[I]o
conv.b
(%)
time (min)
Mnc (g/mol)
Mw/Mnc 1 VL
1-S (5) 50 94
110
8,300
1.06 2
2-S (2.5) 90 80
6,800
1.07 3
3-S (1.67)
230
7,600 4
1-O (5) 70
6,100
1.08 5
2-OS (2.5) 88
8,100 6
2-O (2.5)d 34
8,000 7
3-O (1.67) 89
7,500 8
100
15,000
1.04 9
200 92 10
28,600
1.02
500 16
41,500 11 CL
45 hr
7,200
1.09 12
10 hr
1.11 13 55
42 hr 14 97 26
7,900
1.05 15 57
18,500
116
30,700
1.03 17 93
166
58,600
Cyclic Ester Monomers and H-bonding Cocatalysts for ROP
Proposed Mechanisms for 2-X/MTBD and 3-O/MTBD cocatalyzed ROP
a) Reaction conditions: VL or CL (1.0 mmol, 1.0 eqiv., 2M), urea or thiourea (given mol%), MTBD (mol% matched to H-bond donor). b) Monomer conversion monitored by 1H NMR. c) Mn and Mw/Mn were determined by GPC (CH2Cl2) vs polystyrene standards. d) 2-O (2.5 mol%) and MTBD (5 mol%) cocatalysts.
Methods
Polymerization reactions are performed in the glove box
Monomer to polymer conversion is tracked via NMR. Depicted above is a sample 1H NMR Spectrum showing polymer (left) and monomer (right)
Depicted below is a sample GPC spectrum showing a polymer peak.
Acknowledgments
University of Rhode Island; RI-INBRE from the NIH under grant number 2P20GM103430; SURF Fellowship for S.S.; donors of the ACS Petroleum Research Fund. Printing services provided by the RI-INBRE Centralized Research Core Facility supported by Grant # GM from NIGMS, NIH.
GPC separates products by hydrodynamic volume, determining weight and polydispersity