Florian J Stadler

Abstract: A new sepn. principle was recently introduced into the anal. characterization of polyolefins by researchers from the German Institute for Polymers in Darmstadt. It was demonstrated that polyolefins can be selectively sepd. via high-performance liq. chromatog. on the basis of their adsorption/desorption behaviors at temps. as high as 160 DegC. A Hypercarb column packed with porous graphite gave the best results. The mobile phase consisted of a mixt. of 1-decanol and 1,2,4-trichlorobenzene. In this work, the same chromatog. system is applied to the sepn. of ethylene/alkene and ethylene/norbornene copolymers. It was found that the elution vols. of the samples correlate linearly with the av. chem. compn. of samples. The elution vol. is indirectly proportional to the concn. of branches in the ethylene/alkene copolymer. Branching shortens the length of continuous methylene sequences of the polymer backbone, thus decreasing the probability of orientation of a methylene sequence in a flat conformation on the graphite surface, which enables the most intensive van der Waals interactions between the methylene backbone and the carbon surface. An opposite trend in the elution order has been found for ethylene/norbornene copolymers. The elution vol. of the ethylene/norbornene copolymers increased with the concn. of norbornene. It indicates pronounced attractive interactions between graphite and the cyclic comonomer. Figure Overlay of chromatograms and dependence of the elution vol. on the av. chem. compn. of ethylene/1-butene copolymers.

Abstract: Intramol. phase sepn. is usually assocd. with block-copolymers, but the same phenomenon is also obtainable by random-copolymers. In this article, evidence of intramol. phase sepn. is reported for a linear octadecene-ethene copolymer, which shows an evolving 'yield point' at a long time and low frequency. This is attributed to a partial phase sepn. of the long short-chain branches. In creep recovery, this behavior is evident as increasing elastic steady-state creep recovery compliance Je 0. In contrast to 'normal' block-copolymers, this special polymer has an increase in phase sepn. with temp., which is caused by the chem. compn. and the short chain segments in the side chain domain, leading to a high surface fraction.

Abstract: Copolymer hydrogels were prepd. from an aq. micellar soln. of the nonionic surfactant monomer (surfmer) w-methoxy poly(ethylene oxide)40undecyl-alpha -methacrylate (PEO-R-MA-40) and acrylic acid (AA) in a one-step reaction using gamma -irradn. The hydrogels were transparent if the polymn. was carried out at pH >= 4, whereas turbid gels were obtained if the polymn. was carried out at lower pH. Exposure of the turbid gels to an aq. soln. of pH 11 led to swelling and clearing, whereas subsequent exposure to pH 1 had the reverse effect. Clear gels prepd. at pH 4 became turbid, if exposed to an aq. soln. of lower pH and became clear again if reswollen at higher pH. The pH at which clouding set in increased with the amt. of surfmer copolymd. in the gel. Pure poly(acrylic acid) (P-AA) hydrogels did not show any changes in transparency if the pH was varied. The presence of surfmer led to more pronounced shrinking and swelling, esp. if the gels were prepd. at pH 4. The mech. stability of P-AA and copolymer hydrogels was studied using elongational flow measurements. The presence of surfmer led to increased mech. stability of the hydrogels. The increase originates from copolymd. micellar aggregates acting as addnl., stable crosslinking units in the gel. The true stress at break of copolymer hydrogels prepd. at pH 2.4 (or 4) was 5.5 (or 3.4) times larger than for surfmer-free P-AA gels. Possible origins for the higher stability such as complex formation between P-AA and oxyethylene segments of copolymd. PEO-R-MA-40 are discussed.

Abstract: This article focuses on the characterization of a series of telechelic polybutadienes with acid end groups (PBd-COOH) neutralized with different alkali metal ions by elongational rheometry. Depending on the ion, the material is found to be strain-hardening or not. While the Li+ ions cause a strain hardening similar to that obsd. for low d. polyethylene, Na+ and K+ essentially do not lead to any strain hardening. Rb+ leads to a different type of strain hardening, like sparsely branched polymers. It is also found that the material behaves brittlely at strain rates e higher than the crossover frequency wc. Addnl., an esterified version of the material and the rubidium hydroxide neutralized PBd-COOH is characterized by Brillouin light scattering to assess the local chain dynamics, being essentially noninfluenced by the ion clusters. The dependence of the longitudinal sound velocity cl and hence the longitudinal modulus M from the phonon wave vector q and from the temp. T is compared for two different samples (with and without counterion). It is found that M is insensitive to the presence of the ionic clusters, and therefore, the local chain dynamics are essentially the same for the two model systems and do not play a role in the strain-hardening.

Abstract: A hierarchal self-assembly of a diblock copolymer polystyrene-block-polytert-Bu acrylate (PS-b-PtBA) end-functionalized with a terpyridine is proposed. The first level of self-organization consists in the formation of micelles in a selective solvent of PtBA. The micelles are thus made of a PS core and PtBA coronal chains with the terpyridine at their extremity. The second level is obtained by the addn. of various metals (Ni2+, Fe2+ and Zn2+) to the micelles to induce the formation of a supramol. gel, with an exciting stimuli responsive behavior.

Abstract: In this article, the effect of an incomplete frequency range on relaxation spectra calcd. with the new spline-based method presented before is discussed. The range, in which the spectrum can be detd., is limited by the range of the input data, but not directly by the inverse frequency. The actual limits depend on the range of input data. Depending on the shape of the spectrum the relaxation spectrum can be detd. from the input data in a range up to three decades larger than the input data. This can be explained by the influence of the modes outside the inverse frequency range. For this purpose, a new concept, the relevance factor anal., was introduced, which allows for a detn. of the limits of spectrum calcn. The characteristic relaxation times are discussed in comparison for to the calcn. of J0e and h0 from the spectrum.

Abstract: Syndiotactic polypropene was synthesized using a metallocene catalyst system and traces of VC. The use of VC was found to decrease the molar mass Mw of the samples distinctly and linearly, while retaining the molar mass distribution, the crystallinity, and the syndiotacticity. The VC, however, initiates the formation of long-chain branches, which were detected by GPC-MALLS and rheol. Besides their effect on the viscosity and modulus functions, a thermorheol. complexity can be obsd. Also the flow activation energy Ea was found to be increased. The modified samples did not obey the h0 Mw relation for linear sPP, indicating the presence of LCBs.

Abstract: This paper deals with the characterization of a broad range of linear polyethylenes (PE) by means of thermorheol. It is demonstrated, in which way the thermorheol. behavior can be related to the comonomer type and content of copolymers. In the first part of this paper, well-established anal. and rheol. methods are applied to distinguish linear and branched samples. The resoln. limit of these methods is demonstrated by the investigation of a blend from a linear-low d. PE (LLDPE) and a branched low d. PE (LDPE). Special attention is paid to nuclear-magnetic resonance (NMR) spectroscopy in order to reliably det. the comonomer type and content of the samples chosen. The main focus of this paper lies on thermorheol. investigations and correlations with the mol. structure. The comparatively high sensitivity of such investigations is highlighted: even small amts. of long-chain branches (LCB) are revealed. The activation energy (Ea) of linear samples increases with growing comonomer length and content, resp. As such, thermorheol. is demonstrated to be an interesting rheol. "tool" to get an insight into branching structures. Moreover, the exptl. effort is relatively small as solely usual dynamic-mech. expts. at different temps. are required.

Abstract: This reports describe the improved method to obtain direct rheol. evidence of monomer d. reequilibration for entangled polymer melts.

Abstract: We propose a method of obtaining all three key "tube" model parameters, namely, the plateau modulus GN0, the entanglement mol. wt., Me, and the frictional equilibration time te, from the mol. wt. per backbone bond of ethene/alpha -olefin copolymers with longer comonomers, ranging from C4 (butylene) to C26 (hexacosene). GN0 is obtained from a correlation by Fetters et al. and Me is obtained from this using the std. tube-model formula, Me=(4/5)(rRT/GN0). The equilibration time te is obtained from a remarkable finding by Stadler and Munstedt that, at fixed wt.-av. mol. wt., the zero-shear viscosity of linear ethene/alpha -olefin copolymers is independent of comonomer type and content over a wide range of alpha -olefin comonomers. From this observation, and from the values of GN0 and Me, we use the tube theory to construct a method for obtaining te from the comonomer type and content. We show that these a priori values of the tube model parameters, when used in two publicly available models ("hierarchical model" and "branch-on-branch" model) for predicting linear rheol., yield accurate predictions for a wide range of polydisperse copolymers. These results show that a priori predictions of linear rheol. of complex com. polyolefin copolymers are now possible. (c) 2010 American Institute of Physics.

Abstract: A detailed kinetic modeling study of the atom transfer radical polymn. (ATRP) of isobornyl acrylate (iBoA) is presented. This study combines a detailed reaction scheme with a systematic approach to account for diffusional limitations. Calcd. values for diffusion coeffs. and the Williams-Landel-Ferry parameters for poly(iBoA) are based on rheol. measurements. A good agreement with exptl. data is obtained for the polymn. rate, av. chain length, and polydispersity index in conditions ranging from 323 to 348 K for targeted chain lengths varying from 50 to 100 and initial activator/deactivator concns. between 10-50/0-2.5 mol m-3. In these conditions, beta C-scission reactions are insignificant and backbiting reactions result in a slight decrease of the polymn. rate and level of control at high conversions only. Termination is subject to diffusional limitations during the whole ATRP, while diffusional limitations on deactivation cannot be neglected at higher conversion. Diffusional limitations are shown to be codetd. by the evolution of the chain length distribution of both the end-chain and mid-chain macromol. species.

Abstract: Copolymer hydrogels were prepd. upon gamma -ray-induced polymn. of aq. micellar solns. contg. N-isopropylacrylamide (NiPAAm) and the surfactant monomer (surfmer) w-methoxy poly(ethylene oxide)40undecyl-alpha -methacrylate (PEO-R-MA-40). Stable, transparent, and thermosensitive hydrogels were obtained in a one-step process. Dose vs. conversion measurements showed a complete conversion of comonomer solns. to hydrogels. The size of the surfmer micelles prior and subsequent to polymn. was studied using SAXS measurements. Presence of NiPAAm in the aq. phase did not influence the size of the PEO-R-MA-40 micelles. During the polymn. process the particle diam. decreased from 7.0 to 5.6 nm probably due to crosslinking in the shell of the micelles. The thermosensitive behavior of the copolymer gels was investigated. The lower crit. soln. temp. (LCST) of the surfmer-contg. gels was higher than for pure poly-NiPAAm (P-NiPAAm) gels, the increase being a direct function of the surfmer concn. For hydrogels contg. small amts. of surfmer, the shrinking at temps. above the LCST was increased, and the swelling behavior at temps. below the LCST was slightly increased. The mech. stability of the copolymer hydrogels was studied using elongational deformation measurements. Presence of surfmer increased the mech. stability of the hydrogels, the true stress at break being clearly higher for the copolymer gels compared with pure P-NiPAAm gels. A hydrogel contg. only 1% (wt./wt.) of surfmer can be elongated up to a true stress being nearly twice as large as for the pure P-NiPAAm gel. This can be explained by the presence of copolymd. micellar aggregates acting as new, stable crosslinking units. A structure model correlating the mech. properties with a possible network structure is presented.

Abstract: A novel strategy to link block copolymer micelles via metal-ligand interactions, leading to hierarchical supramol. networks is presented. The mech. properties of the obtained materials can be tuned easily by the choice of the metal ions used. The strong networks exhibit a chem. and mech. stimuli responsive behavior, with almost instantaneous recovery in the latter case.

Abstract: A new method is presented for the detn. of highly precise continuous relaxation spectra. The method is based on the use of piecewise cubic Hermite splines, which are fairly easy to tabulate by using their knots. The Hermite splines method allows a continuous description of the spectrum by a series of polynomial functions. The numerical instabilities of the spectrum calcn. are minimized by limiting the slope of the spectrum to phys. meaningful values. The reproducibility of the spectrum calcn. is within an error margin of about +-10% in the phys. relevant relaxation time range. This method is able to retrieve the spectrum based on data calcd. from a benchmark with high accuracy and precision.

Abstract: We investigate the time-dependent linear viscoelastic behavior of amine and alk. metal-neutralized carboxy-telechelic 1,4-polybutadiene, and compare it with the acid precursor as well as an ester end-modified version. The ionic groups form aggregates with a aggregate spacing period around 85 .ANG., contg. about 90 chain-ends. Rheol. tests highlight the existence of a strongly time-dependent terminal relaxation and an intermediate frequency relaxation, which can be assimilated to a glass transition of the ionic aggregates and their immediate environment. The terminal relaxation time after neutralization with alkali metal increases by up to 7 decades. Contrary to previously published results, this time is found to be a strongly increasing function of metal at. mass for the equilibrated structures. The discrepancy can be rationalized by analyzing the annealing time dependence of the phenomena. Earlier studies did not report on truly equilibrated systems. While the main phase glass transition is hardly affected by neutralization, the temporary network formed by the ionic assocns. shows a very high and ion-dependent temp. sensitivity. Moreover, a failure of the time-temp. superposition principle is found at intermediate temps. or frequencies, because the terminal and intermediate frequency relaxations do not follow the same temp. dependence.

Abstract: Low-d. polyethylenes (LDPE) were synthesized in a lab.-scale autoclave under high pressure. These samples were found to possess a high molar mass tail, resulting in a distinctly bimodal molar mass distribution and a lower concn. of long-chain branching than typical of com. LDPEs. Rheol. expts. in elongation showed that these samples exhibit a very pronounced strain hardening, which could be favorable for distinct processing operations. Although the samples have a rather high molar mass (Mw = 2-4 * 106 g/mol), their zero shear-rate viscosities h0 and their shear thinning behavior are still in a range, where thermoplastic processing is possible. A qual. understanding of the exptl. results is tried by the model of the Cayley tree.

Abstract: The viscosity functions of long-chain branched metallocene-catalyzed ethene homopolymers and copolymers (LCB-mPE) were described by an extended Carreau-Yasuda model. The two characteristic relaxation times, l1 and l2, and the slope of the viscosity function between these two characteristic relaxation times can be correlated to the zero shear-rate viscosity, h0, and the molar mass .hivin.MW. The characteristic relaxation times, l1 and l2 (describing the main curvatures of the viscosity function) exhibit a power law dependency on the molar mass, .hivin.MW. The parameterization of the viscosity function can be used for a mol. characterization and flow simulations of various kinds.

Abstract: In this contribution, we show that the addn. of metal ions to micelles formed by 3;-PtBA-b-PS copolymers in ethanol, and consisting of a PS core and PtBA coronal chains with terpyridine ligands at their extremity, allows to tune their hydrodynamic radius by changing the conformation of the coronal chains, to add a third layer in the micellar structure by complexing a terpyridine-functionalized third block onto the initial micelles, and finally to create hierarchical self-assembly of micelles into gels by promoting inter-micellar connections through metal-ligand complexation. We believe that this new approach significantly broaden the scope of utilization of metal-ligands complexes in self-assembled micellar systems.

Abstract: Ethene-/alpha -olefin copolymers having a wide range of comonomer contents and comonomers between 4 and 26 carbon atoms in length were characterized by wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS). The data was evaluated with respect to the crystallite size. The half-width of the main crystallite peaks was transformed into the crystallite size s110 and s200 using the Scherrer equation. It was found to decrease with increasing comonomer content. The crystal lamella thickness was detd. from the long period and the crystallinity of the samples. The crystal lamella thickness was found to decrease with decreasing crystallinity following a 3rd order polynomial. This means that the introduction of SCBs leads to a decrease of the crystallite size. A higher Mw leads to an increase of the lamella size in comparison to lower mol. samples with the same crystallinity. The lamella thickness is limited by the av. distance between two short-chain branches which is dependent on the comonomer content.

Abstract: Ethene/alpha -olefin copolymers having a wide range of comonomer contents with comonomers between 4 and 26 C atoms in length were characterized by wide angle x-ray scattering (WAXS). The crystallinities matched fairly well with the crystallinities from DSC and volumetric measurements. An increase of the crystal lattice size was found with increasing comonomer content and comonomer length. Both are attributed to the formation of defects around these short-chain branches in the crystal lattice, which widen it. Increasing the cooling time will lead to a more densely packed crystal structure, if the quenched structure is distorted, i.e. if the sample contains comonomer. A higher molar mass Mw widens the av. space between chains in the amorphous phase as well as the addn. of comonomer. The latter finding is explained by the increasing no. of chain ends introduced by the comonomer which increases the free vol. in the sample because of the worse amorphous packing of the chain ends.

Abstract: The adsorption of amphiphilic RuII complex Z = 907 onto the surface of ZnO nanospheres and nanorods causes the gelation of org. solvents, such as THF and acetone. The gels are thermally stable at very low concn. (nanoparticle vol. fraction j = 0.009) but mech. fragile, with the behavior being dependent on the nature of the solvent, nanoparticle concn., and the Z = 907/ZnO mole/wt. ratio. Rheol. expts. confirmed that the solid component built up a network to give a viscoelastic gel-phase material with a weak value of storage modulus G'. However, TEM and SEM expts. did not give evidence that nanoparticle long-range ordering occurred under the exptl. conditions studied. Also, time-dependent SAXS measurements pointed to a decrease in the nanoparticle aggregate size upon gelation. All together, the data obtained might be rationalized in terms of the aggregate-to-aggregate transition in soln., with the primitive large aggregates giving rise to smaller ones upon reaction with Z = 907. The resulting smaller hybrid aggregates could be the active species that act as self-assembling components in the gelation process. Given the interesting electronic and photonic properties of Zn oxide nanoparticles, such hybrid org.-inorg. gels could open new directions in materials science, low-cost electronics, and photovoltaics.

Abstract: The linear steady-state shear compliances Je of two linear short-chain branched metallocene-catalyzed polyethylenes (mLLDPE), two long-chain branched metallocene-catalyzed polyethylenes (LCB-mLLDPE), and two classical low d. polyethylenes (LDPE) were detd. in creep-recovery tests in shear between 130 and 190 DegC. In order to investigate the dependence of Je on the mol. structure the polyethylenes were characterized by high-temp. size-exclusion chromatog. coupled with a multiangle laser light scattering device (SEC-MALLS). For the linear mLLDPE the lowest Je independent of temp. were obsd. For the LCB-mLLDPE having similar polydispersities as the linear mLLDPE not only an increase of Je by about 1 order of magnitude compared to the linear mLLDPE but also a significant decrease in Je with increasing temp. was found. For the LDPE possessing long-chain branches as well as higher polydispersities, the highest Je values were detected, which were also temp. dependent. For the LDPE, the decrease of Je with increasing temp. is less pronounced than for the LCB-mLLDPE. However, for both material types the temp. dependence of Je is much stronger than expected from the rubber elastic theory.

Abstract: In this contribution, we show that the addn. of metal ions to micelles formed by 3;-PtBA-b-PS copolymers in ethanol, and consisting of a PS core and PtBA coronal chains with terpyridine ligands at their extremity, allows to tune their hydrodynamic radius by changing the conformation of the coronal chains, to add a third layer in the micellar structure by complexing a terpyridine-functionalized third block onto the initial micelles, and finally to create hierarchical self-assembly of micelles into gels by promoting inter-micellar connections through metal-ligand complexation. We believe that this new approach significantly broaden the scope of utilization of metal-ligands complexes in self-assembled micellar systems.

Abstract: Spectra are material functions, whose different integral transforms yield the measurable rheol. quantities in the linear viscoelastic regime. Therefore, their knowledge is of high fundamental interest. However, the calcn. of spectra from exptl. data is an ill-posed problem. Thus, it is hampered by the problem that a too low d. of relaxation modes does not lead to a good description of the input data, while a higher one usually causes a wavy spectrum which cannot be interpreted. To overcome this problem, an addnl. criterion assuming only gradual changes in the spectrum is introduced allowing for an increase in mode d. without an enhanced waviness of the spectrum. This is novel in comparison to previously published spectra algorithms and com. software packages.

Abstract: Several linear ethene/alpha -olefin copolymers with butene, hexene, octene, dodecene, octadecene, and hexacosene as comonomers were characterized in linear-viscoelastic shear flow. Creep and creep recovery measurements were used to obtain the zero shear-rate viscosity h0 and the steady-state elastic recovery compliance Je0. The correlation between the zero shear-rate viscosity and the wt. av. molar mass h0(Mw) established for metallocene catalyzed high d. polyethylene (mHDPE) was found to be obeyed by all samples contg. comonomer contents up to 29 wt%. For the linear steady-state elastic compliance Je0 an increase with growing molar mass Mw or comonomer content wc was obsd. (c) 2008 American Institute of Physics.

Abstract:

Abstract: Apolar polymers with hydrogen-bonding or ionic end-groups have a natural tendency to form temporary networks and are as such interesting systems to study the interplay between topol. interactions, i.e. entanglements, and reversible supramol. linkages. While some rheol. and structural characterization of such systems has been published in the past, no systematic study on the resp. influences of topol. vs. supramol. interactions has been reported. In this work, we focus on the linear and non linear rheol. characterization of telechelic polybutadienes (PBd) with carboxylic end groups neutralized with various inorg. and org. bases. A difunctional carboxylic acid terminated PBd shows only very weak associative behavior with a slightly increased temp. dependence by comparison with the neat polymer. The neutralization of the acid end-groups, however, leads to the formation of a reversible network, whose bonding strength and characteristic relaxation time depend very much on the nature of the ion, and to a much higher temp. dependence. An increase of the relaxation time by several orders of magnitude is obsd. together with a dramatic change of the plateau modulus by comparison with the ref. polymer. (c) 2008 American Institute of Physics.

Abstract: This paper deals with the nonlinear shear behavior of linear and long-chain branched polyethylenes (PE) and polypropylenes (PP) as detd. at high step strains. For linear polyethylenes, the comonomer content, molar mass, and molar mass distribution were confirmed to have no influence on the damping function, while a clear difference between linear PP and PE was obvious. Long-chain branched metallocene catalyzed polyethylene (mPE) as well as irradiated long-chain branched PP samples showed a weaker strain dependence compared to their linear counterparts depending on the amt. of branching. With an increasing no. of long-chain branches, this trend becomes more pronounced. Most of the damping functions measured can well be described by a function similar to the Carreau-Yasuda equation. The relation of the three parameters of this equation with the mol. structure of the samples is discussed.

Abstract: Creep and creep recovery measurements of several mLLDPEs were used to investigate the time dependence and to det. both the zero shear-rate viscosity h0 and the steady-state elastic recovery compliance Je0. The well-known correlation between the zero shear-rate viscosity h0 and the molar mass Mw was found to be obeyed by all samples contg. comonomer contents up to 29 wt.-%, too. This is somewhat surprising, as such a high comonomer content means that more than 25 wt.-% of the molar mass are not in the main chain and thus the no. of entanglements should be significantly reduced. For the linear steady-state elastic compliance Je0 an increase with growing molar mass Mw (for const. molar mass distribution) was obsd. independent of the kind and content of the comonomer. The reasons for this molar mass dependence of Je0 are not clear, as Je0 independent of Mw was found for linear monodisperse polymers, but might be attributed to intrachain phase sepn. However, to our knowledge this is one of the first studies so far for polydisperse polyethylenes with const. MMD. (c) 2008 American Institute of Physics.

Abstract: To analyze the thermorheol. behavior of various polyethylenes, the relaxation spectra were shifted. Not only linear and short-chain branched PE but also the classical high-pressure LDPE were found to be thermorheol. simple, i.e., the activation energy Ea is independent of the relaxation strength or the relaxation time, resp. However, for the long-chain branched metallocene catalyzed polyethylenes (LCB-mPE) investigated a significant dependence of the activation energy Ea on the relaxation time is detected. At shorter relaxation times Ea is very close to that of linear PE, but it increases with longer times. The lower Ea values are assumed to be due to linear mols. and the higher ones to different species of long-chain branched mols. These findings offer the possibility to use the anal. of the thermorheol. complexity to get an insight into the branching structure of polyethylenes. For the LCB-mPE investigated, it can be concluded that they are a mixt. of linear and long-chain branched chains.

Abstract: Large amplitude oscillatory shear (LAOS) has gained strong interest for the characterization of complex fluids. A unique advantage of the method is the independent control of strain and strain rate-unlike their coupling in capillary flow. However, the anal. of LAOS data has remained extremely empirical, in most cases, with no attempt being made to link the results to mol. dynamics. We found that the absence of secondary loops in the stress vs. shear-rate Lissajou curves can be considered as a sensitive fingerprint of the presence of long-chain branching. This is one of the strong links between mol. architecture and the LAOS-response. With this method, it is, for example, possible to discriminate clearly between linear and star-branched polymers. Another interesting insight into long-chain branching is provided by the nonlinearity of the complex modulus G'(<s,fx0) & G"(<s,fx0) as a function of strain and oscillation frequency. The nonlinearity decreases with increasing proximity to the terminal regime and thus the nonlinear regime is less pronounced than in the plateau region.

Abstract: The steady-state recoverable shear compliance, Je0, of com. linear and long-chain-branched metallocene LLDPE and LDPE was measured at temps. between 130 DegC and 190 DegC. For the linear material and the LDPE contg. tree-like branches no distinct temp. dependence of Je0 was found. However, a decrease in Je0 with increasing temp. was obsd. for the long-chain branched LLDPE (star-like branching topog.). This temp. dependence of Je0 can be explained by the anal. of the temp. dependent shape of the relaxation spectra calcd. For the linear-mLLDPE the shape of the spectra is the same for all temps. leading to thermorheol. simplicity and a const. Je0. The spectra of the LDPE are identical in shape in the terminal regime but differ at high relaxation strengths. Thus, a const. Je0 results but also a slight thermorheol. complexity in the rubbery plateau. The long-chain branched mLLDPE clearly reveals different temp. dependencies within various parts of the spectra. By this finding the temp. dependence of Je0 can be explained. (c) 2008 American Institute of Physics.

Abstract: This contribution describes the influence of short-chain branching on the temp. dependence of rheol. properties of polyethylene (PE) melts in shear. The materials investigated are linear and short-chain branched, metallocene-catalyzed PE of narrow mol. mass distribution. The linear viscoelastic properties are detd. by dynamic-mech. anal. Short-chain branching leads to an increase of the flow activation energy. The activation energy was found to increase linearly with rising wt. comonomer content.

Abstract: For processing operations with a pronounced elongational component, it was found that the uniformity of extruded items is improved by the presence of strain hardening usually measured in uniaxial elongation. Many processing operations such as foaming, film blowing, and blow molding are dominated by biaxial deformations, however, and therefore, the question arises how strain hardening in uniaxial and biaxial deformation compares. Besides a linear and long-chain branched polypropylene (PP), one classical LDPE, an HDPE pipe extrusion grade with a bimodal MMD, and a long-chain branched metallocene polyethylene (LCB-mPE) were also characterized. For the measurements in uniaxial elongation the Muenstedt tensile rheometer (MTR) and the ARES-EVF were used, while the lubricated flow method was applied for equibiaxial deformation. It was found that the strain hardening in uniaxial elongation is more pronounced. The dependence of strain hardening on strain rate is qual. the same in both modes. In the range of strain rates, the chosen long-chain branched LDPE and PP exhibit a strain hardening, which is approx. independent of the elongational rates applied, whereas for the HDPE it becomes smaller with increasing rate.

Abstract: The synthesis of ethene/propene macromers with a high amt. of sterically unhindered vinyl groups is described. These macromers are incorporated as long-chain branches into polyethylene (PE). The remaining low mol. fractions were removed by Soxhlet extn. Up to 60 wt.-% macromer was included, which leads to comb-like mol. topogs. that distinctly affect the rheol. behavior. The thermal activation energy increased significantly and the zero shear-rate viscosity enhancement factor h0/hlin0 was also changed noticeably.

Abstract: Linear and long-chain branched HDPE with a molar mass .hivin.Mw between 1700 and 1,150,000 g.mol-1 were synthesized using metallocene catalyst systems. Depending on the polymn. parameters the molar mass distribution reached values ranging from 2 to 12. The resins were characterized with various anal. methods. The branch detection took place via two independent methods, melt rheol. and SEC-MALLS. New relationships between catalyst structure, polymn. conditions, and the branching content of polyethylenes were established. Besides the branched materials strictly linear polymers are presented; for those no long-chain branches were detected either by light scattering or by rheol. The viscosity function was obsd. to be strongly influenced by the molar mass distribution and the degree of long-chain branching. The molar mass distribution was affected by the catalyst type and the polymn. conditions. A dependence of the m.p. and the melting enthalpy on the molar mass was obsd.

Abstract: One polyethylene and nine ethene/alpha -olefin copolymers differing in amt. (0.4-2.9 mol%) and molar mass of the comonomer were characterized by NMR, SEC-MALLS, and rheol. Samples were polymd. using a [Ph2C(2,7-di-t-BuFlu)(Cp)]ZrCl2/MAO catalyst, with octene, octadecene, and hexacosene as comonomers, resulting in polymers of Mw ~ 190 kg/mol. The comonomer content was detd. by melt-state NMR. For the homopolymer 0.37 and 0.30 LCB (long-chain branching)/mol. were found by NMR and SEC-MALLS, resp. Rheol. quantities, such as the zero shear rate viscosity (h0), increased with LCB as compared to linear samples of the same Mw. The shape of the viscosity function and the linear steady-state elastic compliance (J0e) showed a dependence on comonomer content and length. These findings are used to elucidate the various long-chain branching architectures. The highest comonomer content samples behaved like typical linear polymers in rheol. expts., while those with less comonomer contents were found to be long-chain branched. Besides the comonomer content, the type of comonomer has an influence on the branching structure.

Abstract: Long-chain branched polyethylenes are still of great interest today. In some cases their characterization is not an easy task with classical analytic methods (GPC-MALLS and NMR) because of the limited sensitivity at low concns. of long-chain branches. Rheol. methods make a valuable contribution to the characterization due to their high sensitivity with respect to long-chain branches. Using rheol. it was possible to get an insight into the influence of different comonomers and comonomer concns. on the long-chain branch incorporation in LLDPE. A variation of polymn. parameters such as polymn. pressure was found to influence the rheol. behavior. From these findings some conclusions with respect to the mol. structure could be drawn.

Abstract: Linear high-d. polyethylenes with molar masses Mw between 240 and 1,000,000 g/mol, obtained by metallocene catalysts, were characterized in shear using oscillatory and creep tests. The polydispersities of the molar mass distributions (MMDs) lay between 1 and 16. The resulting zero shear-rate viscosities h0 covered a range from 2.5 * 10-3 to around 108 Pas. Above a crit. molar mass of Mc ~ 2,900 g/mol, the exptl. results can be described by the relation h0 .apprx. M, independently of the MMD. The oscillatory data were fitted with a Carreau-Yasuda equation. The resulting parameters were correlated to mol. structure. The parameter a, being a quantity for the width of the transition between the Newtonian and the non-Newtonian regime, showed a dependence on the molar mass Mw but not on Mw/Mn. The parameter l of the Carreau-Yasuda equation was the reciprocal crossover frequency for all samples with a log-Gaussian MMD. l depends on the molar mass Mw and also on Mw/Mn.

Abstract: Polyethylenes and polyethylene/alpha -olefin-copolymers covering a range in crystallinity between 12 and 85% were studied by dynamic-mech. measurements between -145 Deg and their m.p. From the temp. and frequency dependence of the complex modulus alpha '-, alpha -, beta - and gamma -relaxations were analyzed. The alpha '-relaxation was found in all HDPE, LDPE, and LLDPE samples but not in plastomer and elastomer samples. The activation energy (30-140 kJ/mol) of this relaxation decreased with increasing crystallinity. The alpha '-transition temp. at a fixed frequency rises with increasing degree of crystallinity and tends to reach the m.p. when approaching the fully cryst. state. Thus, the alpha '-relaxation originates from the interface between crystal lamellae and amorphous interlamellar regions. By extrapolation of the storage modulus to the amorphous state, the entanglement mol. wt. was calcd. as 2300 g/mol for a completely amorphous polyethylene/alpha -olefin-copolymer.