Controlled ring‐opening polymerization of l‐lactide and ε‐caprolactone catalyzed by aluminum‐based Lewis pairs or Lewis acid alone

Abstract

Ring‐opening polymerization of cyclic esters was studied using catalysts composed of bulky Lewis acids (LA) and Lewis bases (LB). Controlled polymerization of l‐lactide (l‐Lac) was proceeded by Al(C6F5)3·THF in combination with trimesitylphosphine (Mes3P) or triphenylphosphine (Ph3P) using BnOH as an initiator to produce poly(l‐Lac) with narrow molecular weight distribution (MWD; Mw/Mn = 1.1). Both the LA and the LB were indispensable to promote the polymerization. The molecular weights of the resulting poly(l‐Lac)s were controlled by the feed monomer to initiator ratio. ε‐Caprolactone (CL) was rapidly polymerized by Al(C6F5)3·THF with or without Mes3P, although the resulting polymer had rather broad MWD (Mw/Mn = 1.7). The CL polymerization by Al(C6F5)3·THF alone at r.t. gave poly(CL) with relatively narrow MWD (Mw/Mn = 1.2). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 297–303

Structures and Stability of Complexes of E(C6F5)3 (E = B, Al, Ga, In) with Acetonitrile

“…TMS and CFCl 3 were used as external standards. The resonance frequency in 1 H NMR is 400 MHz, 13 C{H} NMR is 100.6 MHz, 19 F{H} NMR is 376.5 MHz. Chemical shifts are given in ppm.…”

“…The distortion of EC 3 moiety from planarity (sum of the C-E-C angles 360°) is insignificant for trigonal bipyramidal complexes 2 and 4 [359.9(2)°and 359.9(1)°], and Ellipsoids are at 50 % probability level. Selected bond lengths /Å and valence angles /°: for 1 B1-N1 1.6113 (18), B1-C1 1.6356 (19), B1-C7 1.633(2), B1-C13 1.637(2), N1-C19 1.1355 (18), N1-B1-C1 105.61(10), N1-B1-C7 104.15 (10), N1-B1-C13 103.18 (10), C1-B1-C13 115.38 (11), C7-B1-C13 115.33 (11), C1-B1-C7 111.60 (11); for 2 Al1-N1 2.082(2), Al1-N2 2.090(2), Al1-C1 2.008(2), Al1-C7 2.018(2), Al1-C13 2.016(2), N1-C19 1.138(4), N2-C21 1.138(4), N2S-C3S 1.133(4), Al1B-N1B 2.097(2), Al1B-N2B 2.083(2), Al1B-C1B 2.009(2), Al1B-C7B 2.004(2), Al1B-C13B 2.015(2), N1B-C142 1.142(4), N2B-C73 1.143(4), N1-Al1-N2 174.80(9), N1-Al1-C1 91.86(10), N1-Al1-C7 88.45 (10), N1-Al1-C13 93.2(1), N2-Al1-C7 86.39 (9), N2-Al1-C1 91.33 (9), C1-Al1-C7 120.78(10), C1-Al1-C13 114.44 (10), C7-Al1-C13 124.67 (10), N1B-Al1B-N2B 175.48 (9), N1B-Al1B-C1B 90.36 (9), N1B-Al1B-C7B 90.03(10), N1B-Al1B-C13B 86.64(10), N2B-Al1B-C7B 92.33 (10), N2B-Al1B-C1B 92.12(10), C1B-Al1B-C7B 115.36 (10), C1B-Al1B-C13B 121.89(10), C7B-Al1B-C13B 122.65 (10); for 3: Ga1-N1 2.0467 (19), Ga1-C1 1.981(2), Ga1-C7 1.985(2), Ga1-C13 1.981(2), N1-C19 1.122(3), N1-Ga1-C1 101.91 (8), N1-Ga1-C7 100.61 (8), N1-Ga1-C13 99.95 (8), C1-Ga1-C7 112.19 (9), C1-Ga1-C13 118.52(9), C7-Ga1-C13 118.97(9); for 4: In1-N1 2.4557(15), In1-C1 2.1677(16), In1-C7 2.160(2), N1-C11 1.135(2), N1-In1-N1' 179.76 7 Valence E-N-C angles deviate from the perfect 180°found by computational studies for C 3 symmetric gaseous complexes of 1:1 and 1:2 composition. Experimental values are 177.0(1), 167.5(2)-171.1(2), 173.6(2), and 171.9(1) for 1, 2, 3, and 4 respectively.…”

“…A valve with a sample of volatile components was opened under argon in an InertLab 2GB glove box. The sample was analyzed by 1 H, 19 F {H} NMR in CDCl 3 . Analysis of the gas phase reveals formation of pentafluorobenzene.…”

Lewis Pair Catalysts in the Polymerization of Lactide and Related Cyclic Esters

“…Al(C 6 F 5 ) 3 ∙THF in combination with trimesitylphosphine (Mes 3 P) or triphenylphosphine (Ph 3 P) also was utilized as catalysts to achieve a controlled polymerization of l -lactide at 100 °C by using BnOH as an initiator to produce poly( l -lactide) with narrow molecular weight distribution ( Đ = 1.1), reported by Nakayama et al ( Scheme 9 ) [ 25 ]. Both the Lewis acid and the Lewis base ( LB ) were indispensable to promote the polymerization.…”

Neodymium‐based catalysts bearing phosphate ligands for ring‐opening polymerization of ɛ‐caprolactone

“…Aliphatic polyesters are used in tissue engineering and drug delivery applications as biocompatible and biodegradable polymers . These polymers are typically produced by ring‐opening polymerization (ROP) of cyclic esters such as caprolactones and lactides . The use of a living polymerization method has many advantages such as well‐defined molecular weights, narrow molecular weight distribution, and ability to synthesize block copolymers.…”