The kinetics of ethylene and propylene polymerization catalyzed by homogeneous metallocene were investigated using 2-thiophenecarbonyl chloride followed by quenched-flow methods. The studied metallocene catalysts are: rac-Me₂Si(2-Me-4-Ph-Ind)₂ZrCl₂ (Mt-I), rac-Et(Ind)₂ZrCl₂ (Mt-II) activated with ([Me₂NPh][B(C₆F₅)₄] (Borate-I), [Ph₃C][B(C₆F₅)₄] (Borate-II), and were co-catalyzed with different molar ratios of alkylaluminum such as triethylaluminium (TEA) and triisobutylaluminium (TIBA). The change in molecular weight, molecular weight distribution, microstructure and thermal properties of the synthesized polymer are discussed in detail. Interestingly, both Mt-I and Mt-II showed high activity in polyethylene with productivities between 3.17 × 10⁶ g/mol_Mt·h to 5.06 × 10⁶ g/mol_Mt·h, activities were very close to each other with 100% TIBA, but Mt-II/borate-II became more active when TEA was more than 50% in cocatalyst. Similarly, Polypropylene showed the highest activity of 11.07 10⁶ g /mol_Mt·h with Mt-I/Borate-I/TIBA. The effects of alkylaluminum on PE molecular weight were much more complicated; MWD curve changed from mono-modal in Mt-I/borate-I/TIBA to bimodal type when TIBA was replaced by different amounts of TEA. In PE, the active center fractions [C*]/[Zr] of Mt-I/borate were higher than that of Mt-II/borate and average chain propagation rate constant (k_p) value slightly decreased with the increase of TEA/TIBA ratio, but the Mt-II/borate systems showed higher k_p 1007 k_p (L/mol·s). In PP, the Mt-I/borate presented much higher [C*]/[Zr] and k_p value than the Mt-II. This work also extend to investigate the mechanistic features of zirconocenes catalyzed olefin polymerizations that addressed the largely unknown issues in zirconocenes in the distribution of the catalyst, between species involved in polymer chain growth and dormant state. In both metallocene systems, chain transfer with alkylaluminum is the dominant way of chain termination. To understand the mechanism of cocatalyst effects on PE M_w and (MWD), the unsaturated chain ends formed via β-H transfer have been investigated by ¹H NMR analysis.

N-Nitrosamines (NAs) are potent carcinogens and have been found in food products. Herein we report a simple tandem liquid-phase extraction (TLPE) method coupled with high-performance liquid chromatography (HPLC) for the determination of trace N-nitrosamines (NAs) in food products. The TLPE method is based upon the tandem implementation of pressurized hot water extraction (PHWE) and dispersive liquid–liquid microextraction (DLLME). The target analytes were first extracted with pressurized hot water, and then concentrated into an organic phase (n-octanol) in the DLLME procedure. The TLPE-HPLC system allowed the analytes to be extracted, concentrated and analyzed in a single step with minimal manipulation of the sample preparation, with an overall analysis time of 25 min. The optimized method showed good linearity (r² ≥ 0.981) and satisfactory recoveries (74–117%) with good repeatability of the extractions (RSDs below 12.8%, n = 5). The limits of detection (LODs) for all nitrosamines in salted duck eggs were in the range of 0.08–0.55 μg kg⁻¹.