The radical polymerization of N,N-dimethylacrylamide (DMAAm) has been investigated in the presence of several alkali metal salts, including lithium bis(trifluoromethanesulfonyl)imide (LiNTf 2 ). The addition of an alkali metal salt led to a significant increase in the yield and molecular weight of the resulting polymer.NMR analysis of mixtures of DMAAm and LiNTf 2 suggested that DMAAm was being activated by the coordination of Li + to its CvO group. Electron spin resonance analysis of the DMAAm polymerization in the presence of LiNTf 2 suggested that the propagating radical was being stabilized by Li + through a single-electron lithium bond, because a signal for the propagating radical of the acrylamide derivatives was observed for the first time in solution when LiNTf 2 was added. Based on these results, we have proposed a mechanism for this polymerization, where the propagation steps occur between a lithium ionstabilized propagating radical and a lithium ion-activated incoming monomer. Furthermore, polymers with a wide range of stereoregularities, such as isotactic, syndiotactic and heterotactic systems, were successfully prepared using this method by carefully selecting the appropriate combination of solvent and alkali metal salt. † Electronic supplementary information (ESI) available: Dependence of polymer yield on the added amount of LiNTf 2 in toluene, additional 1 H NMR spectra of the main-chain methylene groups of the poly(DMAAm)s prepared in this study and changes in the chemical shifts of DMAAm in the presence of MNTf 2 . See View Article Online a [Monomer] 0 = 1.0 mol L −1 , [MAIB] 0 = 1.0 × 10 −2 mol L −1 , [alkali metal salts] 0 = 1.0 mol L −1 . b Determined from 1 H NMR signals. c Determined by SEC (PMMA standards). d Alkali metal salt was not completely dissolved. e Polymer precipitated during polymerization reaction. Polymer Chemistry PaperThis journal is

We examined ring-opening polymerizations (ROPs) of ε-caprolactone in toluene at 25−60 °C catalyzed by scandium perfluoroalkanesulfonates and perfluoroalkanesulfonimides. Using these scandium catalysts, which have strong electron-withdrawing ligands, the ROPs proceeded quickly. Under identical conditions, polymerizations were completed more rapidly for reactions catalyzed by scandium trifluoromethanesulfonimide [Sc(NTf2)3] and scandium nonafluorobutanesulfonimide [Sc(NNf2)3] than for those catalyzed by scandium trifluoromethanesulfonate [Sc(OTf)3]. It was possible to synthesize poly(ε-caprolactone)s (M n = 2.6 × 103−9.8 × 103) with low polydispersities (M w/M n = 1.12−1.40). After polymerization, the catalysts were easily recovered by simple filtration or by extraction with H2O and could be reused. Other rare-earth nonafluorobutanesulfonimides [M(NNf2)3; M = Tm, Sm, and Nd] were also tested. Samarium nonafluorobutanesulfonimide [Sm(NNf2)3], as well as Sc(NNf2)3, catalyzed living polymerizations of ε-caprolactone. The reaction kinetics and activation thermodynamics of certain scandium catalysts and Sm(NNf2)3 were investigated. Increasing the perfluoroalkane chain length decreased the values of both the activation energy and the activation enthalpy. The ranked values of the activation free energies parallel those of the times required for completion of the polymerizations. 13C NMR spectroscopy was used to characterize the relative Lewis acidities of certain catalysts. Our findings indicate that Sc(NNf2)3, which accelerated the ROP than Sc(OTf)3 or Sc(NTf2)3, is an excellent catalyst for the ROP of ε-caprolactone.

We investigated the radical polymerization of N-n-propylmethacrylamide (NNPMAAm) in the presence of alkali metal bis(trifluoromethanesulfonyl)imides (MNTf 2 ), in particular LiNTf 2 . The addition of MNTf 2 led to a significant improvement in the yield and molecular weight of the resulting poly(NNPMAAm)s. Furthermore, the solvent employed influenced stereospecificity in the presence of LiNTf 2 . The stoichiometry of the NNPMAAm-Li + complex appeared to be critical for determining the stereospecificity in the NNPMAAm polymerization. The 1 : 1-complexed monomer in protic polar solvents provided syndiotacticrich polymers, whereas the 2 : 1-complexed monomer in aprotic solvents gave heterotactic-rich polymers. Stereochemical analyses revealed that m-addition by an r-ended radical was the key step in the induction of heterotactic specificity in the aprotic solvents. Spectroscopic analyses suggested that the Li + cation played a dual role in the polymerization process, with Li + stabilizing the propagating radical species and also activating the incoming monomer. Kinetic studies with the aid of electron spin resonance spectroscopy revealed that the addition of LiNTf 2 caused a significant increase in the k p value and a decrease in the k t value. The stereoregularity of poly(NNPMAAm)s was found to influence the phase transition behavior of their aqueous solutions. In a series of syndiotactic-rich polymers, the phase-transition temperature decreased gradually with increase in the rr triad content. Furthermore, heterotactic-rich poly-(NNPMAAm) exhibited high hysteresis, which increased in magnitude with increasing mr triad content. † Electronic supplementary information (ESI) available: 13 C NMR spectra of the CvO group of NNPMAAm in the presence of MNTf 2 , changes in the chemical shifts of 1 H NMR spectra of the vinylidene group of NNPMAAm in the presence of LiNTf 2 , relationship between the radical concentration and time, additional ESR spectra and relationship between the ΔT c and n r values. See

We examined ring-opening polymerizations (ROPs) of e-caprolactone in toluene at 25-50 C catalyzed by perfluoroalkanesulfonates and perfluoroalkanesulfonimides as organic catalysts. The ROPs proceeded quickly using these super Brö nsted acids as catalysts. We synthesized poly(e-caprolactone)s (M n ¼ 4.8 Â 10 3-13.5 Â 10 3) with low polydispersity (M w /M n ¼ 1.10-1.48). These strong Brö nsted acids catalyzed living polymerizations of e-caprolactone. After polymerization, Nf 2 NH was recovered and reused. To survey solvents, CHCl 3 and tetrahydrofuran (THF) were used instead of toluene as solvents for polymerization. When THF was used as a solvent, not only e-caprolactone, but also THF was polymerized and incorporated into the polymer chain (incorporated THF ratio; 6-10%). We investigated the reaction kinetics and activation thermodynamics of the organic catalysts. The activation energy and the activation enthalpy values for the ROPs of e-caprolactone using the catalyst having electron-withdrawing ligand were smaller, but the activation entropy value is more negative. Moreover, the ranked values of the activation enthalpy for the reaction well parallel the polarity of solvents. The ranked values of the activation free energies well parallel those of the times required for polymerization completion. Our findings indicate that the super Brö nsted acids are excellent catalysts for rapid ROP of e-caprolactone: they are more active than N, N-dimethylaminopyridine (DMAP) or stannous (II) 2-ethylhexanoate [Sn(Oct) 2 ]. V

To synthesize polyesters and periodic copolymers catalyzed by nonafluorobutanesulfonimide (Nf2NH), we performed ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran (THF) at 50–120 °C. At high temperature (100–120 °C), the cyclic anhydrides, such as succinic anhydride (SAn), glutaric anhydride (GAn), phthalic anhydride (PAn), maleic anhydride (MAn), and citraconic anhydride (CAn), copolymerized with THF via ring‐opening to produce polyesters (Mn = 0.8–6.8 × 103, Mn/Mw = 2.03–3.51). Ether units were temporarily formed during this copolymerization and subsequently, the ether units were transformed into esters by chain transfer reaction, thus giving the corresponding polyester. On the other hand, at low temperature (25–50 °C), ring‐opening copolymerizations of the cyclic anhydrides with THF produced poly(ester‐ether) (Mn = 3.4–12.1 × 103, Mw/Mn = 1.44–2.10). NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra revealed that when toluene (4 M) was used as a solvent, GAn reacted with THF (unit ratio: 1:2) to produce periodic copolymers (Mn = 5.9 × 103, Mw/Mn = 2.10). We have also performed model reactions to delineate the mechanism by which periodic copolymers containing both ester and ether units were transformed into polyesters by raising the reaction temperature to 120 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012