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 # GM103430 from NIGMS, NIH. GPC separates products by hydrodynamic volume, determining weight and polydispersity