Synthesis of Discrete Mass Poly(butylene glutarate) Oligomers

A series of discrete mass oligomers of the perfectly alternating copolymer poly(butylene glutarate) containing 2, 4, 8, 16, 32, and 64 structural units have been synthesized from glutaric anhydride and butanediol using an iterative divergent−convergent strategy. These materials were designed to serve as models for more complex polymer distributions. Orthogonal protection of difunctional starting material using 9-fluorenylmethoxycarbonyl chloride and p-methoxybenyl alcohol allowed control of chain growth during coupling with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride and (N,N-dimethylamino)pyridine. Condensation products were monofunctionalized by removal of one protecting group using mild acidic or basic conditions that preserved the orthogonal protecting group. The fully unprotected target products were isolated in highly pure form and, with the exception of the 64-mer, in high yield (>70%). The synthetic oligomers were characterized using 1H NMR, HPLC, GPC, EI-MS, CI-MS, LSI-MS, and MALDI-TOF-MS to confirm structure, molecular weight, and purity.