The living anionic polymerization of isocyanates carried out using conventional initiators is associated with side reactions due to rapid initiation rates as well as back-biting by the growing chain, resulting in a lack of control on the molecular weight (MW) and molecular weight distribution (MWD) of the polymers. Successful control over the reaction was possible by using additives that could prevent back-biting. We find an initiator in sodium benzanilide (Na-BA), which has a slow initiation rate combined with additive function, so that use of an external additive is eliminated. The initiator has resulted in polymers with high yields and an unprecedented control over the MW and MWD. It is possible to introduce a number of functionalities at the termini of the polymer by using Na-BA derivatives as well as suitable terminating agents, leading to macromonomer, reactive and chiral polymers, and chiral macromonomer in approximately 100% yields. In the process, the finding has expanded the scope of polyisocyanates in diverse applications.

Introduction.Polyisocyanates are stiff polymers due to the amide bonds in the polymer main chain, and the polyisocyanate chains are twisted into helical conformations because of steric constraints. 1 Due to these structural properties, polyisocyanates have been studied in many applications such as chiral recognition materials, optical switches, and liquid crystal materials. 2 Since Shashoua and co-workers first reported the polymerization of isocyanates with sodium cyanide in dimethylformamide in 1959, 3 many researchers have studied the synthesis of polyisocyanates. 4 However, living polymerizations of isocyanates were difficult because of depolymerization by the formation of trimer. Despite this difficulty, Novak and co-workers synthesized poly-(n-hexyl isocyanate) using organotitanium initiators without trimer formation, even though it is a coordination polymerization. 5 Recently, Lee and co-workers succeeded in the synthesis of well-defined poly(3-(triethoxysilyl)propyl isocyanate)) using sodium naphthalene (Na-Naph) and 15-crown-5 (15C5) in THF at -98 °C under high vacuum. 6 The system successfully protected the backbiting of the anionic chain ends using a big countercation, the complex of Na-Naph-15C5. However, that is still unstable due to the greater distance between the active ends and the big ligand in polar solvent.In this study, poly(n-hexyl isocyanate) (PHIC) was synthesized via anionic polymerization as a function of reaction time at -98 °C in THF. We attempted to prevent the formation of trimers by utilizing sodium tetraphenylborate (NaBPh 4 ) as a common ion salt, which stabilizes the active anion by excess counter sodium cations. 7 A postpolymerization was carried out to confirm the living character of the active anionic chain ends of PHIC.Experimental Section. a. Materials. n-Hexyl isocyanate (HIC, Aldrich Chemical Co. Inc., 97%) was dried over CaH 2 for 24 h and distilled under reduced pressure. The resulting monomer was distilled once more from CaH 2 under vacuum. Tetrahydrofuran (THF, Fisher Scientific Co., GR grade) was distilled under N 2 after refluxing over Na for 4 h and stored as Na-Naph solution under vacuum at -30 °C.b. Anionic Polymerization. All polymerizations were carried out under high vacuum in a glass apparatus equipped with break-seals. In a typical polymerization procedure, the initiator solution, Na-Naph (0.10 mmol) in THF, was transferred into the reaction flask through the break-seal followed by 10-fold excess NaBPh 4 (0.97 mmol) in THF to the initiator. The

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Poly(n-hexyl isocyanate) was synthesized by anionic polymerization using various oxy-initiators, including sodium phenoxide (Na-PO), sodium benzhydroxide (Na-BH), and sodium methoxyphenylethoxide (Na-MPE). We optimized polymerization conditions. To confirm the living natures of the polymerization, we carried out various polymerizations changing mole ratio between monomers and initiators and a postpolymerization by sequential monomer addition method. Our results indicated that the anionic polymerization of n-hexyl isocyanate was not controlled using Na-PO and Na-MPE. However, Na-BH as an initiator is favorable for the living anionic polymerization of n-hexyl isocyanate because it has a dual function in the initiation and in the efficient prevetion of trimerization by reducing the reactivity at the growth chain ends. Polymers were thus synthesized with predictable molecular weights (MW), narrow molecular weight distributions (MWD), and high yields.

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