Ralph-Dieter Maier

Influence of stereoirregularities on the formation of the γ-phase in isotactic polypropene

Medium to high molar mass isotactic polypropenes with different amounts of stereoirregularities were characterised with respect to their crystallisation behaviour and for comparison a random copolymer of ethene and propene with 5.8 wt% ethene is used. The influence of stereoregularity and crystallisation temperature on the γ-content of the crystallised samples is studied by means of wide angle X-ray scattering, atomic force microscopy and light microscopy. The paper deals also with the temperature rising elution fractionation of an i-PP with large amounts of stereoirregularities and the influence of a nucleation agent on the γ-content. It is shown that effects which render the chainfolding in lamellae more difficult, enhance the formation of the γ-modification. The necessity of chainfolding in isotactic polypropene is discussed in terms of a model that is based on the number of chains that emerge from the lamellae surfaces of the α- and the γ-modification, respectively.

The influence of stereoregularity on the miscibility of poly (propylene)s

The melt miscibility of atactic poly(propylene) (a-PP) with isotactic (i-PP) and syndiotactic poly(propylene) (s-PP), respectively, is investigated by diffusion experiments ofi-PP/a-PP/i-PP or s-PP/a-PP/s-PP sandwich specimens using polarized light microscopy. It is shown that the system a-PP/i-PP is miscible in the melt, whereas for the system a-PP/s-PP no evidence for melt mixing is found. Pressure-volume-temperature (PVT) measurements of the three poly(propylene)s are carried out in order to determine the characteristic parameters of the Flory-Orwoll-Vrij equation-of-state theory. Theoretical predictions using the solubility parameter concept are in agreement with the observed miscibility behavior of the blends. Differences in the cohesive energy densities of a-PP and i-PP on the one side, and s-PP on the other side, are found to be responsible for the phase behavior of the mixtures of poly(propylene)s with different stereoregularity.

Influence of glass bead fillers on phase transitions of syndiotactic polypropene

Abstract The influence of glass beads on the phase transition of syndiotactic polypropene has been investigated. The glass transition at 4°C, detected by means of dynamic mechanical analysis, and multiple melt behaviour, detected by means of differential scanning calorimetry (DSC), does not depend upon the presence of glass bead fillers. However, dynamic mechanical analysis shows an unexpected phase transition at 55°C. This transition, which is not found for neat syndiotactic polypropene, can be also detected by DSC and pressure–volume–temperature (PVT) measurements. The signal detected by PVT appears at higher temperatures, due to higher pressure during measurement. Wide angle X-ray scattering (WAXS) measurements reveal that neat syndiotactic polypropene crystallizes in unit cell II, whereas glass bead-filled syndiotactic polypropene crystallizes in unit cells I and II. Glass bead-filled syndiotactic polypropene, heated up above 60°C, shows a WAXS pattern corresponding to unit cell II. From these results, it can be concluded, that glass beads can nucleate the formation of unit cell type I, which transforms into unit cell type II upon heating at 55°C.

The influence of metallocene-based LLDPE on polypropene compounds in the presence of SEBS and talcum

The influence of metallocene-based poly(ethene-co-1-butene) (linear low-density polyethylene; LLDPE) containing 10 wt.-% of 1-butene on the compounding of polypropene (PP) in the presence of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene (SEBS) and talcum was studied. With increasing LLDPE and SEBS volume fraction, the stiffness and yield stress of PP decrease, due to the low stiffness and tensile strength of the dispersed components. The low impact strength of PP/LLDPE blends, due to weak interfacial interactions, can be improved significantly by simultaneously blending with SEBS. This is due to the compatibilizer function of SEBS, as demonstrated by transmission electron microscopy. The stiffness of the terblends can be enhanced remarkably by addition of talcum, which also acts as nucleating agent for the PP crystallization. So, a new family of compounds was obtained, exhibiting an improved stiffness/toughness balance. Der Einflus von Poly(ethylen-co-1-buten) (lineares Polyethylen niedriger Dichte, LLDPE) mit 10 Gew.-% 1-Buten, das mittels Metallocen-Katalysatoren hergestellt wurde, auf die Compoundierung von Polypropylen (PP) in Anwesenheit von Polystyrol-block-Poly(ethylen-co-1-buten)-block-Polystyrol (SEBS) und Talkum wurde untersucht. Mit steigenden LLDPE- und SEBS-Volumengehalten nehmen Steifigkeit und Fliesspannung von PP aufgrund der geringen Steifigkeit und Festigkeit der dispergierten Komponenten ab. Die wegen geringer Grenzflachenwechselwirkungen niedrige Schlagzahigkeit von PP/LLDPE-Blends kann durch Zugabe von SEBS deutlich erhoht werden. Ursache hierfur ist die kompatibilisierende Wirkung von SEBS, wie transmissionselektronenmikroskopische Untersuchungen zeigen. Die durch den SEBS-Zusatz verursachten Steifigkeitverluste konnen durch Zusatz von Talkum, das gleichzeitig als Nukleierungsmittel fur PP wirkt, kompensiert werden. Die gefullten PP/LLDPE/SEBS-Terblends zeichnen sich gegenuber PP durch erhohte Schlagzahigkeit ohne Steifigkeitsverlust aus.

New molecular and supermolecular polymer architecturesvia transition metal catalyzed alkene polymerization

Superstructure formation during crystallization has been examined as a function of isotactic poly(propene) and poly(ethene) molecular architectures, tailored by means of metallocene catalyzed propene polymerization, metallocene catalyzed ethene/alk-1-ene copolymerization, and nickel-catalyzed migratory insertion polymerization of ethene to afford methyl-branched poly(ethene) without using comonomers. The role of steric irregularities in the chain resulting from false insertion in stereoselective polymerization or from short chain branching, respectively, was investigated. Randomly distributed regio- and stereo-regularities in isotactic poly(propene) chains and variation of crystallization temperature were the key to controlled poly(propene) crystallization and predominant formation of the γ-modification. Poly(propene) melting temperature increased with increasing isotactic segment length between stereo- and regio-irregularities. Superstructures of isotactic γ-poly(propene) were analyzed by means of light and atomic force microscopy. Both types of short-chain branched poly(ethene)s, prepared by ethene/oct-1-ene copolymerization and migratory insertion homopolymerization, showed similar dependence of melting temperature on the degree of branching, calculated as the number of branching carbon atoms per 1000 carbon atoms. Phase transitions were monitored by means of wide angle X-ray scattering and pressure–volume–temperature measurements. Atomic force microscopy was applied to image both lamella- and fringed micelle-type superstructures as a function of the degree of branching.

Microstructure and pressure—volume—temperature properties of ethene/1-octene random copolymers

Copolymers of ethene and 1-octene were synthesized covering the entire composition range by means of the methylalumoxane activated rac-Me 2 Si(2-MeBenz[e]Ind) 2 ZrCl 2 catalyst. 13 C-NMR spcctroscopy revealed first-order Markov statistics to be reasonably suited for the description of the copolymer sequence distribution. Characteristic parameters of ethene/1-octene copolymers were obtained by evaluation of pressure-volume-temperature data using the Flory-Orwoll-Vrij equation-of-state theory. The characteristic pressure could not be correlated with 1-octene comonomer incorporation when assuming validity of the mixing rules known for homopolymer blends, whereas the characteristic specific volume and characteristic temperature are independent of copolymer composition within experimental errors. A possible explanation is presented for why the attempts to predict the characteristic pressure of ethene/1-octene copolymers from the corresponding homopolymer parameters fail using Florys mixing rules.

Thermodynamics of polymer blends of poly(isobutylene) and poly(dimethylsilylenemethylene)

The phase behavior of blends of poly(isobutylene) (PIB) having different molecular weights and its carbosilane analog poly(dimethylsilylenemethylene) (PDMSM) is studied by optical microscopy, differential scanning calorimetry (DSC) and pressure-volume-temperature (PVT) measurements. DSC and microscopy measurements reveal that PDMSM with M w = 721000 g/mol is miscible at all blend ratios with a PIB of M w = 1500 g/mol, and immiscible at virtually all blend ratios and temperatures with PIBs of higher molecular weight. PVT measurements of the neat blend components are evaluated in terms of the Flory-Orwool-Vrij equation-of-state and Patterson theory. Free volume and interactional contributions to the overall X parameter are of comparable size, but have opposing trends in temperature dependence. This leads to a X(T) function that does not obey the proportionality between X and 1/T observed for systems with dominating repulsive enthalpic interactions. The miscibility as a function of blend ratio and molecular weight is successfully described by the Patterson theory with the parameter X 12 = 0.4 J/cm 3 .