N-butyl N-carboxyanhydride (Bu-NCA) was polymerized in THF to produce poly(N-butyl glycine) using benzyl alcohol initiator and 1,1,3,3-tetramethylguanidine (TMG) organocatalyst. Poly(N-butyl glycine) (PNBG) with controlled polymer molecular weight (Mn= 2.9-20.5 kg/mol) and narrow size distribution (PDI=1.04-1.11) can be obtained by controlling the initial monomer to initiator ratio and conversion. The reaction exhibits characteristics of a living polymerization, as evidenced by the linear increase of Mn with conversion and the successful chain extension experiments. Kinetic studies revealed that the reaction is first-order dependent on the monomer concentration with a slow initiation (ki=0.019 M-1s-1) relative to the propagation (kp = 104 M-1s-1). MALDI-TOF MS and 1H NMR analysis confirmed that the polymer chains were terminated with benzyl alcohol end groups. Polymerization in other solvents such as toluene, DMF and CH2Cl2 or using other alcohol initiators such as EtOH and iPrOH yielded PBNGs whose molecular weights deviated to varying extents from the theoretical values based on single-site initiation. Alcohols with lower pKa appear to initiate the polymerization more efficiently than those with higher pKa, resulting in more controlled Mn in the former than the latter. The polymerization has been successfully extended towards the synthesis of block copolymers based on poly(ethylene glycol) and PNBG by using a PEG-OH initiator and TMG promoter.

1,1,3,3-Tetramethylguanidine promoted ring-opening polymerization of N-carboxyanhydrides using an alcohol initiator

247th National Meeting (2014)

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