Paul Starck

Studies of the comonomer distributions in low density polyethylenes using temperature rising elution fractionation and stepwise crystallization by DSC

The comonomer distributions of commercial linear low density polyethylenes (LLDPE) and linear very low density polyethylenes (VLDPE) produced with traditional high activity Ziegler–Natta (Z–N) catalysts were characterized by temperature rising elution fractionation (TREF). In order to develop faster characterization methods the polymers were also characterized using a segregation fractionation technique (SFT) based on a stepwise crystallization by differential scanning calorimetry (DSC). Comparative studies of SFT and TREF demonstrated that SFT provides an alternative tool for the relative qualitative analysis of the chemical composition distribution (CCD) and the technique is useful to characterize the heterogeneity in comonomer unit distribution. Lamellar thickness distributions can be calculated from the DSC endo-therms by applying the Thomson–Gibbs equation. The SFT technique was also applied to commercial single-site (metaliocene) LLDPE and VLDPE polymers. In spite of their more homogeneous structure compared with the Z–N copolymers, which contain many active sites, these single site copolymers also gave thermograms resolved into several peaks.

Thermal properties of ethylene/long chain α-olefin copolymers produced by metallocenes

Metallocene type copolymers of ethylene with the α-olefins 1-octene, 1-tetradecene and 1-octadecene were characterized by dynamic scanning calorimeter (DSC) and by dynamic mechanical analysis (DMA). At a similar comonomer content above 3 mol%, the higher α-olefins gave lower melting points, crystallinities and densities than 1-octene. In DSC a separation technique sorting the crystalline sequence lengths of the polymer into groups was applied, and DSC index, DI, which gave a semiquantitative idea of the chemical homogeneity of the comonomer compositional distributions. By DMA the storage modulus as an indicator of stiffness and loss modulus and loss tangent as a measure of the effect of branching on the β relaxations were studied. The DMA measurements showed the loss modulus maximum to be a more sensitive value than the loss tangent maximum for the characterization of the comonomer distribution. The intensity of the β transition of 1-octadecene did not increase with increasing branching in contrast to the situation for 1-octene and 1-tetradecene copolymers.

Dynamic mechanical thermal analysis on Ziegler-Natta and metallocene type ethylene copolymers

Abstract Commercial linear low density polyethylenes (LLDPE) and linear very low density polyethylenes (VLDPE) produced with traditional high activity Ziegler-Natta (Z-N) and metallocene (single site) catalysts, respectively, have been characterized by dynamic mechanical thermal analysis (DMTA). The results demonstrated that particularly the study of the β relaxations from the tan δ and the loss modulus curves may give valuable information of differences in branching amounts and distributions of different types of polyethylenes. The intensity of the tan δ maximum peak increased with the incorporation of more comonomer (more amorphous species, more branching and lower density). The metallocene polymers, with the exception of the metallocene LLDPE studied, gave the highest tan δ intensity values which demonstrated the ease of incorporating higher comonomer amounts in the case of single site polymers. The studied metallocene LLDPE polymer showed a behaviour very close to that of low density polyethylenes (LDPE). For the metallocene polymers correlations between the tan δ maxima values and the melting points, densities and comonomer contents, respectively, were obtained. In many cases the study of the maxima of the loss modulus curves gave still more exact information of the smaller amounts of branching present in the polymer.

Co- and terpolymerizations of ethene and α-olefins with metallocenes

The suitability of the (n-butCp) 2 ZrCl 2 /methylaluminoxane (MAO) catalyst system for the copolymerization of ethene with propene, hexene, and hexadecene was studied and Ind 2 ZrCl 2 /MAO was tested as a catalyst for ethene/propene and ethene/hexene copolymerizations. The synergistic effect of longer α-olefin on propene incorporation in ethene/ propene/hexene and ethene/propene/hexadecene terpolymerizations was investigated with Et(Ind) 2 ZrCl 2 /MAO and (n-butCp) 2 ZrCl 2 /MAO catalyst systems. The molar masses, molar mass distributions, melting points, and densities of the products were measured. The incorporation of comonomer in the chain was further studied by segregation fractionation techniques (SFT), by differential scanning calorimetry (DSC), studying the β relaxations by dynamic mechanical analysis (DMA) and by studying the microstructure of some copolymers by 13 C-NMR. In this study (n-butCp) 2 ZrCl 2 and Ind 2 ZrCl 2 exhibited equal response in copolymerization of ethene and propene and both catalysts were more active towards propene than longer α-olefins. A nearly identical incorporation of propene in the chain was found for the two catalysts when a higher propene feed was used. A lower hexene feed gave a more homogeneous comonomer distribution curve than a higher hexene feed and also showed the presence of branching. In terpolymerizations catalyzed with (n-butCp) 2 ZrCl 2 , the hexadecene concentrations of the ethene/propene/hexadecene terpolymers were always very low, and only traces of hexene were detected in ethene/propene/hexene terpolymers. With hexene no clear synergistic effect on the propene incorporation in the terpolymer was detected and with hexadecene the effect of the longer a-olefin was even slightly negative. With an Et(Ind) 2 ZrCl 2 /MAO catalyst system both hexene and hexadecene were incorporated in the chain in the terpolymerizations.

Characterization of Comonomer Distributions in Ethylene/Diene Copolymers by 13C-NMR, and Using the Segregation Fractionation Technique by DSC and DMTA

Ethylene and linear, nonconjugated dienes were copolymerized with the catalyst system Cp2ZrCl2/methylaluminoxane (MAO). The comonomer incorporation and the relationships between structure and properties were evaluated by NMR and by thermal techniques, especially the segregation fractionation technique (SFT) using DSC and dynamic mechanical thermal analysis (DMTA). The ethylene-1,5-hexadiene (HD) copolymers showed different behavior than the others and it was possible to incorporate as much as 7 mol % of the hexadiene comonomer into soluble polymer compared with only 2.4 mol % of the 1,7-octadiene (OD) and 7-methyl-1,6-octadiene (MOD). The melting endotherms of the HD copolymers obtained after segregation fractionation were very much like corresponding endotherms of high-density polyethylene (HDPE) and a population with nearly one lamellar thickness was postulated. This is in agreement with cyclic structure formation and absence of branching with crosslinking for these copolymers. The OD and MOD copolymers, on the other side, showed endotherms with several peaks indicating a distribution of the comonomers along the chain. Lamellar thickness distributions were calculated from the melting endotherms by using the Gibbs–Thomson equation. The DMTA measurements confirmed the absence of branches in the HD copolymers and the presence of branches in the OD and the MOD copolymers.

Influence of the polymerization conditions on the rigidity of phenylnorbornene-ethylene copolymers made using ethylene bis (indenyl) zirconium dichloride and MAO

When characterized with DMA it was found that Phenylnorbornene-ethyl-ene copolymers with equivalent comonomer concentrations had very different storage moduli in the glassy state as well as glass transition temperatures. NMR analysis of the copolymers revealed that they had different ratios of Exo- and Endo-diastereomers even if the same comonomer composition had been used. The Exo/Endo-ratio in the polymer was surprisingly higher than in the monomer and increased with higher incorporations of the comonomer. Copolymers with higher Exo/Endo-ratios also had a tendency for lower storage moduli in the glassy state and higher tan δ peaks. These properties are valuable because more flexible and impact-resistant copolymers are obtained.

Studies on metallocene catalyzed copolymers of ethylene with 10- undecen- 1- ol

Ethylene was copolymerized with 10-undecen-1- ol in the presence of four different metallocene catalyst systems. The copolymers were characterized by differential scanning calorimeter (DSC) and by dynamic mechanical analysis (DMA). It was demonstrated that properties of the catalysts used affected the crystallization behaviour of the copolymers because the catalysts exhibited differences in conversions of the polar comonomer. The step crystallization technique using DSC provided useful information about the differences in comonomer incorporation in the chain. The formation of multiple peaks, based on differences in ethylene sequence length, is much weaker for the copolymers produced with a non- bridged metallocene, than for polymers produced with bridged catalysts. A study of the crystallization rates in nonisothermal experiments exhibited a small decrease in crystallization temperatures with increasing branching. The Hoffman-Weeks extrapolation of melting point vs crystallization temperature gave reasonable results for silylene-bridged copolymers. In DMA, study was made of the storage modulus as an indicator of stiffness and loss tangent as a measure of the effect of branching on the β-relaxations. The DMA measurements indicated a slight increase in the flexural modulus, or stiffness values, of the copolymers relative to the corresponding homopolymers. The damping curves did not show any peaks in the β-relaxation range, which indicates that the amount of short branching in the copolymers is negligible.

Comparison of the weather resistance of different thermoplastic elastomers

Abstract The weather resistance of different thermoplastic elastomer (TPE) blends was compared by measuring changes in hardness, tensile modulus, tensile strength and elongation at break. The hardness and tensile modulus of all polymers increased to some extent during the exposure period. This behaviour was expected to be caused by desorption of oils. The partly crosslinked PP/EPDM-polymers showed the strongest decrease in the elongation at break values but the tensile strength of all blends decreased due to the weathering. Dynamic mechanical properties such as storage modulus, loss modulus and damping properties were studied over a wide range of temperatures. The differences in stiffness existing between the polymers and due to the exposure duration were consistent with the differences in hardness and tensile modulus, especially for the soft blends. Smaller changes in the elastic behaviour of the blends below and above the glass transition temperature Tg were also noticed.

Study of polyester-based coil coatings by using thermal analysis methods

The curing of polyester-based clearcoats has been studied by using thermal analysis methods. Polyester resins are used as raw materials for coil coatings. The aim of this work was to study the viscoelastic properties of coil coatings. Differential scanning calorimetry (DSC) was found to be useful in curing studies of lacquers, for example, to predict conversion as a function of cure time or cure temperature. Dynamic mechanical analysis (DMA) was used to determine the gel times of some clearcoats. The DSC measurements were done with different apparatus and software programs. This study concentrates on the use of these modern techniques to predict the curing and correlation of the results.