Siripon Anantawaraskul

Effect of molecular weight and average comonomer content on the crystallization analysis fractionation (Crystaf) of ethylene α-olefin copolymers

The effect of molecular weight and average comonomer content on the crystallization analysis fractionation (Crystaf) of ethylene/1-hexene copolymers was investigated experimentally and modeled via stochastic simulations. Molecular weight and comonomer content are the main structural parameters that affect the crystallizability of polymer molecules from dilute solutions. Sets of samples with varying molecular weight and comonomer content were prepared to study each effect separately. Although both structural parameters significantly affect the shape of Crystaf profiles, comonomer content is the main determining factor for Crystaf peak location for most molecular weights of interest. The results of the stochastic simulations show good qualitative agreement with the experimental data, but also indicate some clear limitations that might be related to the kinetics of crystallization effects during Crystaf analysis.

Distribution of the longest ethylene sequence in ethylene/α-olefin copolymers synthesized with single-site-type catalysts

We present an analytical solution for Monte Carlo simulations of the microstructure of ethylene/α-olefin copolymerss synthesized using single-site catalysts. The bivariate distribution and the longest ethylene sequence (LES) distribution in number and weight are derived for this system. All the results were compared with Monte Carlo simulations and the validity of the LES distribution is verified. We expect these results to be a first step towards the modeling of the fractionation processes in temperature-rising elution fractionation (TREF) and crystallization analysis fractionation (CR YST AF) and the understanding of structure-properties relationships of these copolymers.

SIMULATION OF CRYSTALLIZATION KINETICS AND MORPHOLOGICAL DEVELOPMENT DURING ISOTHERMAL CRYSTALLIZATION OF POLYMERS: EFFECT OF NUMBER OF NUCLEI AND GROWTH RATE

The effect of number of nuclei and growth rate on crystallization kinetics and detailed morphological development during isothermal crystallization of a polymer was investigated using a stochastic simulation. The results show that number of nuclei significantly affects both crystallization kinetics and polymer morphology. An increase in the number of nuclei hastens the crystallization process by speeding up the impingement phenomenon and increasing the levels of impingement. Growth rate has a stronger impact on crystallization kinetics, but it only helps speed up the impingement phenomenon without increasing the level of impingement. Although growth rate influences an average spherulite size and distribution of spherulite size during crystallization, it has no effect on final morphology. The quantitative understanding of morphological development obtained from this work will be a key element for constructing quantitative morphology-property relationships.

Ethylene homo- and copolymerization chain-transfers: A perspective from supported ( n BuCp) 2 ZrCl 2 catalyst active centre distribution

AbstractPolymerization chain termination reactions and unsaturation of the polymer backbone end are related. Therefore, in this study, the parameters resulting from the modelling of the active centre distribution of the supported catalyst—silica/MAO/(nBuCp)2ZrCl2—were applied to evaluate the active-centre-dependent ethylene homo- and copolymerization rates, as well as the corresponding chain termination rates. This approach, from a microkinetic mechanistic viewpoint, elucidates better the 1-hexene-induced positive comonomer effect and chain transfer phenomenon. The kinetic expressions, developed on the basis of the proposed polymerization mechanisms, illustrate how the active site type-dependent chain transfer phenomenon is influenced by the different apparent termination rate constants and momoner concentrations. The active centre-specific molecular weight Mni (for the above homo- and copolymer), as a function of chain transfer probability, pCTi

Fractionation of Semicrystalline Polymers by Crystallization Analysis Fractionationand Temperature Rising Elution Fractionation

p_{CT_{i}}

Crystallization analysis fractionation

, varied as follows: logpCTi=logmwru−logMni

Effect of operation parameters on temperature rising elution fractionation and crystallization analysis fractionation

log\left ({p_{CT_{i}} } \right )=log\left ({mw_{ru}} \right )-log\left ({M_{ni}} \right )

Cocrystallization of blends of ethylene/1-olefin copolymers: An investigation with crystallization analysis fractionation (Crystaf)

, where mwru is the molecular weight of the repeat unit. The physical significance of this finding has been explained. The homo- and copolymer backbones showed all the three chain end unsaturations (vinyl, vinylidene, and trans-vinylene). The postulated polymerization mechanisms reveal the underlying polymer chemistry. The results of the present study will contribute to develop in future supported metallocene catalysts that will be useful to synthesize polyethylene precursors having varying chain end unsaturations, which can be eventually used to prepare functional polyethylenes. Graphical AbstractThe active-centre-dependent ethylene homo- and copolymerization rates and the corresponding chain termination rates support the 1-hexene-induced positive comonomer effect and chain transfer phenomenon from a microkinetic mechanistic viewpoint. The chain transfer probability pCTi

Mathematical modeling of crystallization analysis fractionation of ethylene/1‐hexene copolymers

p_{CT_{i}}

Mathematical modeling of crystallization analysis fractionation (crystaf) of polyethylene

decreased with increasing active centre-specific molecular weight Mni