Unperturbed dimensions of isotactic and atactic polypropylene at various temperatures

The dimensions of both atactic and isotactic polypropylene were determined at various temperatures in θ solvents with the following results:$\text{—(}\text{d ln}\text{r}{}_{\mathrm{o}}{}^2\text{/d}$T) = 1 · 8 (atactic polymer), and 3 (isotactic polymer). These results, compared with those obtained in our laboratory for polybutene-1 and poly-pentene-1, allow us to construct a general picture of the variation of the unperturbed dimensions of poly-α-olefins with temperature.     

Nuclear magnetic resonance investigation on isotactic,atactic and deuterated isotactic polypropylene

Ohne ZusammenfassungProf. Dr.Alfons Krause, Pozna (Polen), Grunwaldzka 6.     

Mesoscopic modeling of the polymerization,morphology, and crystallization of stereoblock and stereoregular polypropylenes

Thermoplastic elastomers require domains that act as physical crosslinks, and these can be either glassy regions or crystallites. For crystallites in a polymer such as polypropylene (PP), the challenge is to develop polymerizations that form the long stereoregular chain sequences required to produce crystallites large enough to act as stable temporary crosslinks but not so many of them that the material becomes a significantly crystalline thermoplastic rather than an elastomer. For PP, the requirement is for long isotactic sequences within predominantly elastomeric atactic chains, and catalysts required to achieve such an unusual stereoblock structure are now available. This provided encouragement for the simulations described herein that illustrate some relationships between polymerization mechanisms and distributions of isotactic sequences (particularly those long enough to crystallize). A Windle‐type Monte Carlo algorithm was then applied to arrays of the representative PP chains in searches for matches of crystallizable sequences. This approach provided estimates of degrees of crystallinity, melting points, interfacial free energies, standard free energies of fusion, and Young's moduli at small extensions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 840–853, 2002     

Miscibility of isotactic polypropylene with atactic polystyrene

The miscibility of isotactic polypropylene-atactic polystyrene blends using dilatometric, TOA, DAT and stress-strain methods were studied. It appears that the blends are heterogeneous, having two glass transition temperatures. However, some interactions between components are evident to change theTgs of their amorphous phases and theTm of isotactic polypropylene crystals. The results are discussed on the basis of the blends' thermal and tensile properties.     

Glass transition temperatures of several fluorine-containing polymers

The glass transition temperatures T_g of several fluorine-containing polymers were determined by use of the differential scanning calorimeter. Values between ?3 and 230°C were obtained. In polymers of α-olefins, T_g increases with the fluorine content of the backbone and the length of the n-perfluoroalkyl branch. In styrene polymers T_g also is higher if the backbone contains fluorine but nearly the same T_g's are found for polymers with phenyl and pentafluorophenyl groups. Saturated polymers of perfluoro-α,ω-dienes have lower T_g's than polyperfluoro-α-olefins. The T_g's of chloroperfluoropolymers are higher than those of perfluoropolymers. Polyperfluoropentadiene-1,3 has the lowest T_g of the polymers examined. Polyperfluoropentadiene-1,3 forms by 1,4-addition.     

Glass transition temperatures in binary polymer blends

Knowledge of the glass transition temperatures (T_gs) as function of composition reflects miscibility (or lack of it) and is decisive for virtually all properties of polymer‐based materials. In this article, we analyze single blend‐average and effective T_gs of miscible polymer blends in full concentration ranges. Shortcomings of the extant equations are discussed to support the need for an alternative. Focusing on the deviation from a linear relationship, defined as ΔT_g = T_g ? φ₁T_g,1 ? φ₂T_g,2 (where φ_i and T_g,i are, respectively, the weight fraction and the T_g of the i‐th component), a recently proposed equation for the blend T_g as a function of composition is tested extensively. This equation is simple; a quadratic polynomial centered around 2φ₁ ? 1 = 0 is defined to represent deviations from linearity, and up to three parameters are used. The number of parameters needed to describe the experimental data, along with their magnitude and sign, provide a measure of the system complexity. For most binary polymer systems tested, the results obtained with the new equation are better than those attained from existing T_g equations. The key parameter of the equation a₀ is related to parameters commonly used to represent intersegmental interactions and miscibility in binary polymer blends. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 80–95, 2008     

Synthesis of hydrophilic isotactic polypropylenes promoted by metallocene catalysts

In this paper, the synthesis of isotactic polypropylenes (i‐PP) modified with ? OH groups in sides (iPP‐OH), by combination of polyinsertion ansa‐metallocene catalysis and ring opening of propene oxide (PO), is described. i‐PP sequences interrupted by isolated ethylene/p‐methylstyrene units forms the backbone. This enchainment is obtained by controlled copolymerization of propene with ethylene and p‐methylstyrene comonomers in the presence of rac‐ethylenebis(1‐indenyl)zirconiumdichloride/methylalumoxane system. The metallation reaction of the p‐methyl group with sec‐BuLi generates an anionic center that can be reacted with PO. The iPP‐OH is the result of the monoaddition reaction of PO followed by hydrolysis with acidified methanol. By changing experimental conditions in the backbone synthesis, a tuned number of the functionalizable sites as well as polypropylene sequence lengths can be obtained. As a consequence, iPP samples with a different number of ? OH groups for the backbone can be synthesized after the PO monoaddition reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7008–7013, 2006     

Glass transition temperatures of polymer materials,measured by thermomechanical analysis

The linear expansions of two materials have been measured, a double-base propellant and a carboxyl-terminated polybutadiene. The glass transition temperature,T _g and expansion coefficients below and aboveT _g have been calculated. The influence of the heating and cooling rates and sample thickness has been investigated. The results show that the value ofT _g is dependent on the rates of heating and cooling but not on the sample thickness. Extrapolating to zero rate gives the sameT _g for both heating and cooling. The expansion coefficients are not influenced by the rates of heating and cooling or by the sample thickness.

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Zusammenfassung Die lineare Ausdehnung wurde an zwei Stoffen, einem doppelbasischen Triebstoff und einem Polybutadien mit Carboxyl-Endung gemessen. Die Glas-Übergangs-temperaturT _g und die Ausdehnungskoeffizienten unterhalb und oberhalb vonT _g wurden berechnet. Der Einfluss der Aufheiz- und Abkülhgeschwindigkeiten und die Stärke der Probe wurden geprüft. Die Ergebnisse zeigen, daß der Wert vonT _g der von Aufheiz- und Abkühlgeschwindigkeit, nicht aber von der Probenstärke abhängt. Die Extrapolierung auf die Geschwindigkeit 0 ergibt denselbenT _g -Wert bei Aufheizung und Kühlung. Die Ausdehnungskoeffizienten werden durch die Aufheiz- und Abkühlgeschwindigkeit oder durch die Probenstärke nicht beeinflusst.

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Résumé On a mesuré la dilatation linéaire de deux matériaux, un agent de propulsion à base double et un polybutadiène avec un carboxyle comme groupe terminal. On a calculé la températureT _g de la transition vitreuse ainsi que les coefficients de dilatation au-dessous et au-dessus deT _g . L'influence des vitesses de chauffage et de refroidissement ainsi que l'épaisseur de l'échantillon ont été étudiées. Les résultats montrent que la valeur deT _g dépend des vitesses de chauffage et de refroidissement, mais pas de l'épaisseur de l'échantillon. L'extrapolation à la vitesse zéro donne la même valeur de la températureT _g lors du chauffage et du refoidissement. Les coefficients de dilatation ne sont influencés ni par les vitesses de chauffage ou de refroidissement ni par l'épaisseur de l'échantillon.

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. T_{g g}. , . , _g , . _g , . , .

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This is the last paper belonging to the Fifth Scandinavian Symposium on Thermal Analysis.     

Catalytic synthesis of styryl‐capped isotactic polypropylenes

Bis‐styrenic molecules, 1,4‐divinylbenzene (DVB) and 1,2‐bis(4‐vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H₂) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)zirconium dichloride, I ) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl‐capped isotactic polypropylenes (i‐PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H₂ or BVPE/H₂ caused a copolymerization‐like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H₂ or BVPE/H₂, which gave the styryl‐terminated polymer chain alongside a metal‐hydride active species. It was confirmed that the chain reinsertion occurred in a regio‐irregular 1,2‐fashion, which contrasted with a normal 2,1‐insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal‐hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl‐terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non‐conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709–3713, 2010     

Glass transition temperatures of polyurethane-urea elastomers based on N,N′-ethylenethiourea and N,N′-ethyleneurea as chain extenders

Glass transition temperatures of polyurethane-urea elastomers (PU) based on two urea derivatives, have been investigated with differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) methods. The DMTA measurements have been proved as more useful to determine an optimal annealing time and to controlling polyurethane-urea synthesis then the DSC analysis.

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Zusammenfassung Mittels DSC und DMTA wurden die Glasumwandlungspunkte von Polyurethan-Harnstoff Elastomeren (PU) auf der Basis zweier Harnstoffderivate untersucht. DMTA-Messungen erwiesen sich als nutzbringender zur Bestimmung einer optimalen Temperungsdauer und zur überwachung der Polyurethan-Harnstoff-Synthese als die DSC-Analyse.

     

Thermal degradation of gamma irradiated isotactic and atactic polymethyl methacrylate

Thermal behaviour of gamma irradiated free radical and isotactic polymethyl methacrylate has been studied at 256°.     

Crystallization kinetics of isotactic polypropylene blended with atactic polystyrene

Crystallization kinetic parameters, such as spherulitic growth rates, nucleation densities, and Avrami-exponents, have been determined by optical microscopy for isotactic polypropylene blended with atactic polystyrene. It is found that the crystallization of iPP is strongly influenced by the presence of polystyrene. With increasing PS concentration in the blend, the nucleation densities decrease, while the spherulitic growth rates as well as the positions of thermal peaks, measured by DSC, remain independent of sample composition. Due to the formation of interfaces as a consequence of increasing dispersion of polystyrene the nucleation changes from preferentially thermal to athermal.     

Blends of isotactic polypropylenes and a plastomer: crystallization and viscoelastic behavior

Blends covering the entire range of compositions of a metallocenic ethylene-1-octene, CEO, copolymer and two conventional isotactic polypropylenes, iPP, of different molecular weights have been prepared, analyzing the effect of composition and molecular weight on the crystallization (studied by DSC and X-ray diffraction) and viscoelastic behavior (DMTA). It was found that those blends rich in the iPP component show a behavior practically coincident with the weighted addition of the two components. On the contrary, significant deviations were found for the blends where the CEO copolymer is the major component. These deviations are considerably more important in the case of the blends with the iPP of higher molecular weight. Moreover, both components are not miscible, exhibiting the glass transitions of the two neat components. The area under the loss tangent curves provides a preliminary information about how the toughness is enhanced using this type of impact modifier, though it provokes a significant reduction of stiffness.     

Glass transition temperatures of copolymers of ethyl acrylate and vinylidene chloride

Glass transition temperatures of poly(ethyl acrylate-vinylidene chloride) and reactivity ratios for the copolymerization of the parent monomers are reported. All the copolymers have glass transition temperatures higher than those of polyethylacrylate or polyvinylidene chloride: the copolymer containing equal molar quantities of each monomer has the highest. The data are accounted for in terms of the fractions of AA. AB and BB diads contained in the copolymers.     

Pretilt angle for BTDA,PMDA and CPDA series polyimides with various side chain lengths

Polyamic acid precursors were prepared by mixing dianhydride of 3,3',4,4'-benzophenone-tetracarboxylic dianhydride (BTDA), 1,2,3,4-benzene-tetracarboxylic dianhydride (pyrromellitic dianhydride PMDA), cis-1,2,3,4-cyclopentane-tetracarboxylic dianhydride (CPDA), the diamine (alkyl 3,5-diaminobenzoate) with side chain, and 4,4'-oxydianiline (ODA) without side chain. Copolyimide films with various side chain lengths were prepared by thermal imidization of polyamic acid precursors. The roughness of rubbed polyimide surface increased with increase in the side chain length. The pretilt angle for the BTDA and PMDA series polyimide (PI) increased exponentially with increase in side chain length. Various pretilt angles were obtained on the synthesized polyimides. In the case of CPDA series PI, the pretilt angle was nearly constant at 0 until the alkyl side chain length reached 12 (C12) and then increased markedly at C18. Models of pretilt angle generation were tested.     

A small-angle x-ray scattering study of blends of isotactic and atactic polystyrene

Small-angle x-ray scattering (SAXS) from blends of isotactic and atactic polystyrene has been studied. Results have been interpreted and compared using the Tsvankin, Vonk, and Hosemann techniques. The studies suggest that segregation of the atactic component occurs during crystallization within the growing spherulite of the isotactic component. However, since the interlamellar distance does not increase with atactic content, segregation is believed to occur with the formation of domains larger than interlamellar but smaller than spherulite size.