Bimetallic Aluminum 5,6-Dihydro-7,7-dimethyl quinolin-8-olates as Pro-Initiators for the ROP of ε-CL; Probing the Nuclearity of the Active Initiator

Six examples of aluminum 5,6-dihydro-7,7-dimethylquinolin-8-olates, [{2-R1-7,7-Me2-8-R2C9H6N-8-O}AlR32]2 (R1 = R2 = H, R3 = Me C1; R1 = R2 = H, R3 = Et C2; R1 = R2 = H, R3 = i-Bu C3; R1 = Cl, R2 = H, R3 = Me C4; R1 = H, R2 = R3 = Me C5; R1 = Cl, R2 = R3 = Me C6), have been prepared by treating the corresponding pro-ligand (L1–L4) with either AlMe3, AlEt3 or Al(i-Bu)3. All complexes have been characterized by 1H and 13C NMR spectroscopy and in the case of C1 and C4 by single crystal X-ray diffraction; dimeric species are a feature of their molecular structures. In the presence of PhCH2OH (BnOH), C1–C6 displayed good control and efficiency for the ROP of ε-CL with almost 100% conversion achievable in 10 min at 90 °C; the chloro-substituted C4 and C6 notably exhibited the lowest activity of the series. However, in the absence of BnOH, C1 showed only low activity with 15% conversion achieved in 30 min forming a linear polymer capped with either a methyl or a L1 group. By contrast, when one or more equivalents of BnOH was employed in combination with C1, the resulting catalyst was not only more active but gave linear polymers capped with BnO end-groups. By using 1H and 27Al NMR spectroscopy to monitor solutions of C1, C1/BnOH and C1/BnOH/10 ε-CL over a range of temperatures, some support for a monomeric species being the active initiator at the operational temperature is presented.

Influence of less active initiator on the living performance of atom transfer radical polymerization and the structure of the synthesized grafted copolymer

By monitoring the grafting structure of P(VDF-CTFE)-g-PMMA synthesized from FeCl2/PPh3 and CuCl/BPy catalyzed ATRP process, the influence of less active initiator on the living performance and the evolution of growing polymer chains was disclosed.

Mono-, di- and tetra-zinc complexes derived from an amino-benzotriazole phenolate ligand containing a bulkier N-alkyl pendant arm: synthesis, structure and catalysis for ring-opening polymerization of cyclic esters

Tetranuclear alkoxide 3 with a saddle-shaped Zn4O4 conformation was an active initiator for living ROP of ε-caprolactone and β-butyrolactone.

CONSISTENCY OF DISTRIBUTED SYSTEM WITH ACTIVE INITIATOR PROCESS WITHOUT USELESS CHECKPOINTS

Checkpointing mechanism is the one of the best attractive approach for providing software fault tolerance in distributed message passing systems. This paper aims to implement a distributed checkpointing technique, which eliminates the drawbacks of the centralized approach like “domino effect”, “useless checkpoint” (checkpoints that do not contribute to global consistency), and “hidden and zigzag” dependencies. The proposed checkpointing protocol has a checkpoint initiator, but, coordination among the local checkpoints is done in a distributed fashion. This guaranty that no message would be lost in case of failure occurs, has been maintained in this work by exchange of information among the processes. However, there is no central checkpoint initiator, but each of the processes takes turn to act as an initiator. Processes take local checkpoints only after being notified by the initiator. The processes synchronize their activities of the current checkpointing interval before finally committing their checkpoints. Thus, the checkpointing pattern described in this paper takes only those checkpoints that will contribute to the consistent global snapshot thereby eliminating the number of useless checkpoints.

A convenient method to acquire third-order NLO materials by ATRP

A third-order nonlinear optical (NLO)-active initiator (NA3PH) was synthesized to prepare a NLO-active polystyrene (NA3PH-PSt) via atom transfer radical polymerization (ATRP). The polymerization initiated by NA3PH was studied and the third-order NLO properties of the obtained NA3PH-PSt were investigated by Z-scan technique in comparison with NA3PH. Results show that the endfunctionalized polystyrene possesses third-order nonlinear optical susceptibilities (10-11esu) close to NA3PH. In addition, NA3PH-PSt has good thermal stability and solubility, which holds potential for further application in NLO devices.

Complexes of stannic chloride and alkyl phenols and the influence of these complexes and of free phenol on the cationic polymerization of isobutene

The polymerization of isobutene in ethyl chloride solution at −78.5 °C has been studied using stannic chloride as catalyst and alkyl substituted phenols as cocatalysts. In preliminary experiments, the nature and extent of the complexing between phenols and stannic chloride was examined and it was shown that σ-complexing occurs between the oxygen of the phenol and the stannic chloride. Equilibrium constants were determined over the temperature range 30 to −50 °C and were used, together with hydrogen bonding data, to estimate the concentrations of complex and free phenol in the polymerization mixtures at −78.5 °C. The active initiator in the polymerization is probably the σ-complex but the free phenol acts as a chain terminating agent. This explains the ability of the cocatalyst to decrease the rate of polymerization under some experimental conditions. For isobutene concentrations up to 3 M and at constant dielectric constant the rate of polymerization and the molecular weight are proportional to the monomer concentration. A mechanism is proposed to account for the main features of the experimental results.