Polymerization of ε-caprolactone initiated by Nd(BH4)3(THF)3:: Synthesis of hydroxytelechelic poly(ε-caprolactone)

The ring-opening polymerization of is an element of-caprolactone initiated by Nd(BH4)(3)(THF)(3), 1a, has been investigated, The polymerization occurs rapidly ( <5 min) and quantitatively at room temperature to give, in high yields, polymers which exhibit controlled molecular weights and relatively low polydispersities. Initially, 3 mol of is an element of-caprolactone may coordinate the neodymium center to form the Nd(BH4)(3)(is an element of-caprolactone)(3) complex, 1b. Then, is an element of-caprolactone inserts into the metal-borohydride hydrogen bond of 1a or 1b to give the intermediate [(BH4)(2)Nd[O(CH2)(5)C(O)(HBH3)]], [i], in which each (HBH3) unit immediately interacts with the a-carbonyl group to form the corresponding neodymium(trisalkoxide) derivative [Nd[O(CH2)(5)CH2(OBH2)](3)], 2a. Polymerization of is an element of-caprolactone by 2a then proceeds via a pseudoanionic mechanism through the alkoxide attack at the monomer resulting in the oxygen-acyl bond cleavage. Further treatment of the resulting product with benzyl alcohol gives alpha,omega-telechelic poly(is an element of-caprolactone) diols, HO(CH2)(5)C(O){O(CH2)(5)C(O)}(n)O(CH2)(6)OH. The proposed mechanism is supported by H-1 and C-13 NMR, SEC, and MALDI-TOF analyses of the polymers.