Alkyl Aluminum (alkyl + aluminum)

Distribution by Scientific Domains

Selected Abstracts

Kinetics Approximation Considering Different Reactivities of the Structural Units Formed by the Anionic Copolymerization of 1,3-Butadiene and Styrene Using Al/Li/Ba as Initiator

José. A. Tenorio López
Abstract The copolymerization reaction of butadiene and styrene copolymers prepared by anionic living polymerization using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxide is studied using a kinetic model that considers the reactivity of active sites to be different; this assumption is justified by the varying geometric configurations. With the first-order Markov model, the expressions for the fraction of active sites and dyad distribution are obtained. The rate constants are determined by fitting to the conversion and Bernoulli dyad data using the nonlinear least squares method. The conversion and dyad sequence distribution are correctly predicted, and the experimental results indicate that the microstructure and sequence distribution do not change with the conversion and temperature. [source]

Polyethylene-Palygorskite nanocomposite prepared via in situ coordinated polymerization

Junfeng Rong
A polyethylene/palygorskite nano-composite (IPC composite) was prepared via an in-situ coordinated polymerization method, using TiCl4 supported on palygorskite fibers as catalyst and alkyl aluminum as co-catalyst. These composites were compared with those prepared by melt blending (MBC composites). It was found that in the IPC composites, nano-size fibers of palygorskite were uniformly dispersed in the polyethylene matrix. In contrast, in the MBC composites, the palygorskite was dispersed as large clusters of fibers. Regarding the mechanical properties of the IPCs, the tensile modulus increased and the elongation at break decreased with increasing fiber content, while the tensile strength passed through a maximum. The tensile strength and elongation at break were much smaller for the MBC composites. The final degree of crystallinity of the IPC composites decreased with increasing palygorskite content. Regarding the kinetics of crystallization, the ratio between the degree of crystallinity at a given time and the final one was a universal function of time. It was found that large amouns of gel were present in the IPC composites and much smaller amountes in the MBC composites. [source]

Microstructure-thermal property relationship of high trans -1,4-poly(butadiene) produced by anionic polymerization of 1,3-butadiene using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxide

Juan J. Benvenuta-Tapia
This article deals with the characterization of high trans -1,4-poly(butadiene) (TPBD) prepared by means of an anionic polymerization using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxide. By controlling both initiator composition and polymerization temperature, a set of TPBD was prepared with well-known number of 1,4-trans units, molecular weight distribution, and average molecular weight. Analyses by differential scanning calorimetry and diffraction of wide-angle X-rays showed a direct relationship between the microstructure of the polymer and its thermal properties. By increasing the number of 1,4-trans units (70,90%), the crystallinity of the polymer was increased (10,30%); polymers with less than 65% of 1,4-trans units were amorphous, whereas TPBD with a number of 1,4-trans units greater than 80% were polymorphous and presented two endothermic transitions. Summing up, the results presented in this article indicate that cyclohexane solutions of alkyl aluminum, n -butyl lithium, and barium alkoxide allow produce polybutadienes with enough amount of 1,4-trans units to display a regular microstructure that makes them susceptible to experience-induced crystallization, likewise at a reaction rate similar to that observed for the commercial production of poly(butadiene) with n -butyl lithium. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source]