Metal‐Free Activation in the Anionic Ring‐Opening Polymerization of Cyclopropane Derivatives

Abstract

The successful activation observed when using Bu(t) P(4) phosphazene base and thiophenol or bisthiols for the anionic ring opening polymerization (ROP) of di-n-propyl cyclopropane-1,1-dicarboxylate is described. Well-defined monofunctional or difunctional polymers with a very narrow molecular weight distribution were obtained through a living process. Quantitative end-capping of the propagating malonate carbanion was accessible by using either an electrophilic reagent such as allyl bromide or a strong acid such as HCl. Kinetics studies demonstrated a much higher reactivity compared to the conventional route using alkali metal thiophenolates.

Phosphazene/triisobutylaluminum-promoted anionic ring-opening polymerization of 1,2-epoxybutane initiated by secondary carbamates

“…After polymer purification, the triplet and quadruplet associated with the carbamate CH3CH2-group are still observed at 1.25 and 4.11 ppm. This assignment is confirmed by a COSY NMR spectrum ( Figure S14) and HSQC NMR experiment ( Figure S15) that indicated correlations between the CH3CH2-proton signals and peaks at 14.85 and 61.27 ppm on the 13 C NMR spectrum compatible with the CH3CH2O-group of a carbamate. Further evidence regarding the presence of the carbamate initiator was obtained from the signal of the N-methyl protons at 2.95 ppm.…”

“…No polymer chains with an unsaturated end-group resulting from transfer reaction to 1,2-epoxybutane have been detected by mass or NMR spectroscopy. It has to be noted that 13 C NMR spectrum which confirms the absence of carbamate chain end ( Figure S2). In addition, signals at 15.32 and 66.80 ppm correspond to CH3 and CH2 groups resulting from ethanolate initiation.…”

“…1 These "superbases" are able to deprotonate low acidic molecules, generating extremely reactive anions which can be used as initiator for anionic polymerizations: e.g. monofunctional alcohols 2 (methanol, 3 solketal, 4 4-phenyl-2-butanol, 2-methyl-1-phenyl-2-propanol 5 , 3-phenyl-1-propanol, 6,7 terpene, 8 (p-cresol,) 9 ); polyfunctional alcohol (glycerol, 10 ethylene glycol, 3 tris(hydroxymethyl)propane, 6 1,2,4,5-benzenetetramethanol 11 ); phenol; 12 thiols (Thiophenol, 13 furfuryl mercaptan 14 ); CH-acidic compounds like di-alkyl malonate, 12 ethyl acetate 3 or α-methylbenzyl cyanide; 9 NHacidic compounds like carbazole; 12 carboxylic acids (MeO-PEG-COOH, 15 1-pyreneacetic acid 16 ). For the most part, these precursors have been small molecules but polymer chain-ends (poly(propylene glycol), 4 PEO 7 ) or polymer side-groups (starch 17 ) have also been considered.…”

Design of Optimized Reaction Conditions for the Efficient Living Anionic Polymerization of Cyclopropane‐1,1‐Dicarboxylates

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] The ringopening polymeri zation of cyclopropanes was not a new concept at the time we started investigating the issue, but previous attempts had always led to oligomers, with broad to very broad molecular weight dis tributions. [14] For the first time, with the advent of our activated monomer approach, efficient procedures to polymerize livingly threemembered ring carbon monomers became available, yielding carbonchain polymers substituted on every third atom alongside the backbone (see Scheme 1A for an example).…”

“…One set involves simple alkali ions, [1][2][3][4] while the other one implicates the large tBuP 4 H + phosphazenium cation derived from the protonation of tBuP 4 superbase (see Scheme 3 for a mechanism). [6,7] Both systems have their pros and cons. The first one is much cheaper, involves relatively straightforward workup processes, but the polymerization is slow, has to be carried out at high tempera tures (typically over 100 °C), which are not necessarily compat ible with some functional groups on the ester, and is practi cally limited to degrees of polymerization of 20-30.…”