A series of tertiary aminosquaramides as bifunctional organocatalysts in the ring-opening polymerization (ROP) of L-lactide (L-LA) were developed, allowing the activation of both the L-LA monomer and the alcohol group of the initiator/propagating species. Further, the impact of tertiary nitrogen substituents on catalytic activity in ROP of L-LA was explored. The tertiary aminosquaramide-an air-stable and moisture-stable catalyst-exhibited superior activity in contest with thiourea counterpart when both were equipped with a similar tertiary amine group. Kinetic and chain-extension experiments indicated that the formed poly(L-LA) is featured with narrow polydispersity and high end-group fidelity, hallmarks of a living polymerization process. The initiator efficiency was further executed at ease by preparation of an ABA triblock copolymer poly (L-LA)-b-poly (ethylene glycol)-b-poly (L-LA) in the presence of a dual-headed PEG macroinitiator. 1 H NMR titration experiments suggested a bifunctional catalytic mechanism, wherein both the L-LA monomer and the propagating hydroxyl group were activated en route to polymerization. The 1 H NMR, SEC, and MALDI-TOF MS measurements validated the quantitative incorporation of the initiator in the polymeric chains and enchainment over competitive transesterification reaction. Overall, the structure-activity relationships were surveyed to uncover aminosquaramide as a new bifunctional dual hydrogen-bond donor catalyst for living ROP of L-LA.Of the existing living polymerization techniques, organocatalytic ring-opening polymerization (ROP) 4 -invented by Hedrick and co-workers 5 -is featured by its ability to provide a variety of structurally well-defined polymers. These polymers are featured with remarkably low degree of polydispersity and excellent end-group fidelity, making this procedure particularly attractive for the preparation of advanced polymeric materials. 6 Also, the requisite absence of metal residue, and efficient catalyst removal from the final polymers for biomedical 7 and microelectronic 8 applications advocate the use of such sustainable approaches versus metalcatalyzed processes. Thus, a broad range of organocatalytic systems that function by different modes of activation (monomer, initiator, polymer growing chain) have been developed. 4Among various fascinating systems, the binary catalytic systems composed of a hydrogen bond donor (HBD), and a wide-ranging slate of hydrogen bond acceptors (HBA) represent the current state-of-the-art in organocatalytic ROP of cyclic esters. 9 These systems are believed to affect catalysis through hydrogen bond mediated activation of HBD upon monomer and of HBA upon alcohol, respectively. However, the catalytic activity of such systems could be attenuated because of the following drawbacks: (i) low Additional Supporting Information may be found in the online version of this article.

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In this paper we have studied an Ergodic Magnetic Limiter (EML) based chaotic magnetic field for transport control in the edge plasma of IR-T1 tokamak. The resonance created by the EML causes perturbation of the equilibrium field line in tokamak and as a result, the field lines are chaotic in the vicinity of the dimerized island chains. Transport barriers are formed in the chaotic field line and actually observe in tokamak with reverse magnetic shear. We used area-preserving non-twist (and twist) Poincaré maps to describe the formation of transport barriers, which are actually features of Hamiltonian systems. This transport barrier is useful in reducing radial diffusion of the field line and thus improving the plasma confinement.

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