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Tire tread pattern is a crucial parameter to prevent hydroplaning. In this study, numerical modeling was used to investigate tire hydroplaning based on flow–structure interaction. The empirical model of hydroplaning speed published in the literature was used to validate the computational model. Analysis of water flow velocity and turbulent flow energy revealed that lateral grooves of the tire significantly influenced water drainage capacity. Based on the relationship between water flow vector and lateral groove shape, a combination of Kriging surrogate model and simulated annealing algorithm was used to optimize lateral groove design to minimize hydrodynamic lift force. Four geometry parameters of lateral grooves were selected as the design variables. Based on design of experiment principle, 12 simulation cases based on the optimal Latin hypercube design method were used to analyze the influence of design variables on hydrodynamic lift force. The surrogate model was optimized by the simulated annealing algorithm to optimize tire tread pattern. The results indicated that at the same water flow speed, the optimized lateral grooves can reduce hydrodynamic lift force by 14.05% and thus greatly improve safety performance of the tire. This study proves the validity and applicability of using numerical modeling for solving the complex design of tire tread pattern and optimization problem.

Propylene slurry polymerization with a MgCl2-supported Ziegler-Natta catalyst containing internal electron donor was conducted after different durations of pre-contact of the catalyst with triethylaluminum cocatalyst. The number of active centers ([C*]/[Ti]) was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and measuring sulfur content in the polymer. The pre-contact treatment caused selective deactivation of a part of active centers with low stereoselectivity and much lower activity in the initial stage of polymerization as compared with the polymerization run without the pre-contact stage. The active center concentration and polymerization activity decreased with prolonging of the pre-contact stage. The proportion of stereoselective active centers was increased by prolonging the pre-contact stage, so the isotacticity of produced polypropylene was enhanced. Release of active centers through catalyst particle fragmentation was significantly retarded, and the polymerization rate curve changed from decay type to induction type by the precontact treatment. In the induction period both non-stereoselective and stereoselective active centers were released and activated, resulting in gradual reduction of the polymer’s isotacticity in the first 5–10 min of polymerization. Selective deactivation of non-stereoselective active centers also took place in propylene polymerization using the catalyst without pre-contacting with the cocatalyst. In this case, the polymerization rate decayed with time after a short induction period of 2–5 min. Over reduction of the active center precursors with low stereoselectivity by triethylaluminum was considered as the reason for their deactivation during the pre-contact or the polymerization processes.

Propylene polymerization with two TiCl4/MgCl2 catalysts (Cat-1: Ti 0.1%; Cat-2: Ti 1.0%) showed different responses to (cyclo-C5H9)2Si(OCH3)2 (De) addition. Cat-1 was deactivated more than Cat-2 by De. Amount of three groups of active centers producing atactic, medium isotactic and isotactic polypropylene chains were all reduced by De addition, but those of Cat-1 were reduced more. Reactivity of the isospecific active centers (kpi) was enhanced by De, but kpi of Cat-2 was changed more sensitively than Cat-1. The lower stereoselectivity of Cat-1 than Cat-2 are attributable to weaker De adsorption on its surface Mg, and the more sparsely dispersed Ti species on Cat-1 is responsible for weak De adsorption.

A novel α-diimine nickel pre-catalyst Cat.1 with two electron-donating methyl substituents on the ligand backbone was synthesized and investigated for ethylene polymerization using methylaluminoxane as cocatalyst. Cat.1 exhibited higher polymerization activity and produced highly branched polyethylene with slightly higher molecular weight than that of the typical Brookhart catalyst (B-Cat) at elevated temperature. By tracing the changes of active center number in the polymerization process, Cat.1 was found to have higher ratio of activated nickel ([C∗]/[Ni]), longer catalyst lifetime and larger chain propagation rate constant (kp) as compared with B-Cat. The computational studies demonstrated the electron-donating methyl substituents can make a more electron-rich ligand to influence the catalytic properties of Cat.1. Stronger interactions between the electron-rich ligand and the nickel center should be the main reasons for longer catalyst lifetime and enhanced thermal stability of Cat.1. The production of polyethylene with higher molecular weight by Cat.1 can be explained by its larger kp value and more stable transition state for ethylene insertion than for chain transfer reaction due to the electron-donating ligand. Overall, the results of this work clearly support the importance of ligand electronic effects on the thermal stability and intrinsic reactivity of active centers in α-diimine Ni(II) catalysts.

Ethylene-propylene (EP) copolymerizations was carried out with two ansa-metallocene: rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (Mt-I) and rac-Et(Ind)2ZrCl2 (Mt-II) combined with borates activators like ([Me2NPh][B(C6F5)4] (Borate-I), [Ph3C][B(C6F5)4] (Borate-II). Different structures of alkylaluminum( triethylaluminium (TEA), triisobutylaluminium (TIBA) and TEA/TIBA mixture of 25/75, 50/50, 75/25 mol ratios were used as cocatalysts. The choice of ligand structure and, more importantly, the nature of the cocatalyst significantly impact these systems' activity and the polymeric materials' properties. Borate-II has been shown as giving higher activities than Borate-I with both ansa-metallocene, attending 5.6 × 106 g/mol Zr*h. Mt-I gives higher activities and molecular weight but produced copolymers with low ethylene content, melting points, and crystallinity than Mt-II. The activities were very close to each other with 100% TIBA. Still, Mt-I became more active than Mt-II when TEA was more than 25% in the cocatalyst system. The effects of alkylaluminiums catalysts cocatalyst on EP copolymer molecular weight (Mw) and molecular weight distribution (MWD) were much more complicated. The MWD curve changed from broad to narrow with Mt-I when TIBA was replaced by a different mole ratio of TEA/TIBA ratio. The technique used for the assessment of active centers [C*]/[Zr] fraction in the ansa-metallocene catalyst was quenched label by using 2-thiophenecarbonyl chloride (TPCC) to determine the effects of alkylaluminiums catalysts structure on the propagation rate constants (kP) of EP copolymers. The [C*]/[Zr] value of Mt-I/Borate-I/TIBA is lower than those of the Mt-I/Borate-I/TEA and Mt-I/Borate-I/TEA/TIBA system. The main differences appear between catalysts containing pure TIBA and those containing TEA, possibly due to the faster rate of chain transfer with Al—Et than with bulky Al—iBu. Adding TEA in metallocene/borate/alkylaluminiums catalysts catalysts can be applied as an effective method to regulate the molecular weight of EP copolymer with a high degree of activity

Ethylene-1-hexene copolymerization was catalyzed by TiCl4/diester/MgCl2 type Z-N catalyst activated by triethylaluminium (TEA), triisobutylaluminium (TIBA) or TEA/TIBA mixtures. Copolymerization activity decreased with increase of TIBA content in the cocatalyst. Each copolymer sample was fractionated into boiling n-heptane soluble and insoluble fractions. 1-Hexene content of the soluble fraction was 2 ∼ 6 times larger than that of the insoluble fraction. With introduction of TIBA in the cocatalyst, chemical composition distribution of the copolymer was broadened, attributable to increase of 1-hexene in the soluble fraction. Total number of active centers markedly decreased with increasing TIBA in cocatalyst, and active center number in the soluble fraction decreased more than that in the insoluble fraction. Rate constant of ethylene insertion (kpE) in the soluble fraction was much smaller than that of the insoluble fraction. Rate constant of 1-hexene insertion (kpH) of the soluble fraction became far larger than that of the insoluble fraction when TEA/TIBA ratio was lower than 80/20. In the presence of TIBA, only a part of active center precursors with stronger ability of incorporating 1-hexene were effectively activated in the soluble fraction. For the active centers in insoluble fraction, cocatalyst structure exerted more complicated effects on their activation. Active center models were proposed to explain the observed cocatalyst effects.

Two MgCl2-supported Ziegler-Natta model catalysts were prepared by contacting activated MgCl2 with deficient or excess amount of TiCl4. Ethylene/1-hexene copolymerization with the catalysts was conducted under different 1-hexene feed, and active center concentration of the reaction system was determined by quench-labeling method using thiophene-2-carbonyl chloride as the quencher. The catalytic activity was only moderately enhanced (increment

Two MgCl2-supported Ziegler–Natta catalysts were prepared by loading TiCl4 onto activated δ-MgCl2 supports, which contained 0.1 wt% (Cat-1) and 1.0 wt% (Cat-2) of titanium (Ti), respectively. Cat-1 has a slightly larger specific surface area (88.1 m2/g) and nearly the same pore volume (0.45 cm3/g) as the δ-MgCl2 support, but the catalyst with 1.0% Ti (Cat-2) has smaller specific surface area (66.3 m2/g) and pore volume (0.40 cm3/g). The kinetics and active center distribution of ethylene polymerization with the catalysts were compared. Cat-1 showed much higher activity per gram of titanium than Cat-2, which can be attributed mainly to the much higher [C∗]/[Ti] value of Cat-1 (60%) than of Cat-2 (12%). In both polymerization systems, the [C∗]/[Ti] value increased with time, but the Cat-2 system showed a much larger [C∗]/[Ti] increase than the Cat-1 system. Active center distribution of the catalysts disclosed by deconvolution of the molecular weight distribution into multiple Flory components was evidently different in the initial stage (0–200 s). The Cat-1 system produced more polymer with low molecular weight than the Cat-2 system, and the Flory components of low molecular weight decayed faster than those with high molecular weight. Influence of Ti content on number and structure of active centers formed on clustered Ti species is discussed with reconsideration of the current models of catalyst structure.

The number of active centers in α-diimine nickel-catalyzed olefin homogeneous polymerization system is rarely studied before. A systemic study on quenching method with 2-thiophenecarbonyl chloride (TPCC) in homogeneous catalytic system is presented. Ethylene and propylene polymerizations catalyzed with homogeneous α-diimine nickel catalysts (ArN=C(An)–C(An)=NAr)NiBr2 (cat.1, Ar=2,6-C6H3(i-Pr)2) and (ArN=C(C12H8)C=NAr)NiBr2 (cat.2, Ar=2,6-C6H3(i-Pr)2, C12H8=acenaphthene-1,8-diyl) were quenched by TPCC. The potential side reaction between TPCC and alkyl aluminum-terminated polymer chain caused by chain transfer to cocatalyst under different quenching conditions was investigated. Samples were obtained with different TPCC/AlMAO molar ratios and had similar sulfur contents; a confirmation that the excess TPCC in the system did not cause obvious side reactions which could lead to place more thiophene groups to the polymer chains. Moreover, when the quenching time was in the range of 3–20 min, the sulfur contents remained stable and the value of Npol (number of moles of polymer chains) was not obviously changed, supporting that sufficient quenching reaction had already accomplished within the first 3 min. We claimed that the side reaction could be ignored under controllable conditions. TPCC was confirmed to be an effective quenching agent in homogeneous catalytic system. The quenching method with TPCC was also established.

Concomitant double crystallization processes widely occur in semicrystalline polymers and their blends because of structural and morphological heterogeneity. In this work, a generalized kinetics model was established for the isothermal crystallization in the presence of concomitant double crystallization processes, based on the Avrami theory for single crystallization process. The different situations of the double crystallization processes, including independent, competitive, and composite types, are considered in the model by introducing the concept of “domains”. This model was applied to crystallization of triblock terpolymer with morphological defects, polymorphic poly(vinylidene fluoride)/nanoclay nanocomposite, isotactic polypropylene with a broad isotacticity distribution, and poly(ethylene terephthalate) ultrathin film. It is found that, besides the information on crystallization kinetics, other information such as morphological defect, nucleation density, cocrystallization, and structure of ultra...

Ethylene and propylene polymerizations catalyzed with two ansa-zirconocenes (rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (M-I) and rac-Et(Ind)2ZrCl2 (Mt-II)) activated by (Ph3C)B(C6F5)4/triisobutylaluminum were respectively conducted under the same conditions for different duration ranging from 0.5 to 30 min, and quenched with 2-thiophenecarbonyl chloride for determining the active center fraction ([C∗]/[Zr]). Variations of polymerization rate, molecular weight, isotacticity and thermal properties with time were also studied. The [C∗]/[Zr] fraction gradually increased with time in the first 20 min and then reached steady stage in all polymerization systems. [C∗]/[Zr] value in the steady stage of Mt-II catalyzed ethylene polymerization was significantly higher than that of propylene polymerization, similar to the phenomena previously observed in ethylene and propylene polymerizations catalyzed with Mt-II/methylaluminoxane. When M-I/borate was used as the catalyst, both ethylene and propylene polymerization showed higher steady stage [C∗]/[Zr] levels than those of the Mt-II/borate systems, and the influence of zirconocene structure on [C∗]/[Zr] of propylene polymerization was much stronger than that of ethylene polymerization. Change in zirconocene structure also significantly influenced apparent chain propagation rate constant (kp) and its time-dependent variations. By taking into consideration the time-dependent changes of [C∗]/[Zr], polymer’s molecular weight distribution and chain structure, presence of multiple active centers in the polymerization system and late activation of the centers with lower intrinsic reactivity are proposed to be the main reasons for steep decay of kp with time. Structure-performance relationships of the ansa-zirconocene catalysts have also been discussed based on the results of kinetic study.

Propagation chains with 1,2 and 2,1 last-inserted monomer unit in 1-hexene polymerization with MgCl2-supported Ziegler-Natta catalysts were quench-labeled by thiophene-2-carbonyl chloride, and the two kinds of 2-thenoyl-labeled chain ends were determined by 1H NMR analysis. The number of labeled chains was noticeably smaller than the number of dead chains formed by chain transfer with alkylaluminum cocatalyst, and grew with time more slowly than the latter, showing that side reactions between the quencher and Al-polymeryl moieties are negligible. The active sites with 2,1 last-inserted monomer were halted in dormant state, which lead to their gradual accumulation in the 30 s polymerization process. The catalyst containing phthalate type internal donor has higher percentage of dormant sites as compared with the catalyst containing diol ester. The combination of acyl chloride quench-labeling and 1H NMR analysis forms a reliable and easily accessible method of tracing and characterizing active sites in transition metal catalyzed olefin polymerization.