Dietmar Mäder

NOVEL POLYPROPYLENE MATERIALS

Recent progress in transition metal catalyzed propylene polymerization based upon single-site catalysts and melt compounding of polypropylene is stimulating the development of novel polypropylene materials with unconventional property combinations such as improved low temperature toughness, low haze, elasticity, and improved toughness/stiffness balance. As a function of metallocene architectures, polypropylene microstructures can be varied over a very wide range in order to produce thermoplastic elastomers and highly flexible polymers as well as stiff engineering thermoplastics and fibers. Control of polypropylene molecular architectures, especially random placement of steric irregularities in the polypropylene main chain, and the addition of clarifiers represents the key to producing novel transparent polypropylenes. Metallocene-based ethene/1-olefin copolymers such as poly(ethylene-co-1-butene) are attractive blend components to afford either single-phase flexible or two-phase rigid blends with improved low temperature impact strength as a function of the 1-butene content. New families of polypropylene nanocomposites, containing nanowhiskers and anisotropic nanoparticles derived from organophilic layered silicates, exhibit effective matrix reinforcement at low filler content.

Short and long chain branching of polyethene prepared by means of ethene copolymerization with 1-eicosene using MAO activated Me2Si(Me4Cp)(NtBu)TiCl2

Ethene copolymers with 1-eicosene were prepared using the methylaluminoxane (MAO) activated dimethylsilanediyl (tetracyclopentadienyl) (ter-butylamido)- titanium dichloride (Me 2 Si(Me 4 Cp)(N t Bu)TiC1 2 , CBT) catalyst system in slurry polymerizations. The thermal behavior of the polymers was studied by differential scanning calorimetric (DSC) measurements in order to investigate the influence of long alkyl-branches on polyethene crystallinity, Upon increasing the incorporation of 1-eicosene from 0 to 50 wt.-%, the melting temperature decreased from 135°C to 35°C. The presence of a second peak in the DSC curves of ethene/1-eicosene copolymers with an incorporation of 1-eincosene exceeding 39 wt.-% was attributed to side chain crystallization. CBT is well known for introducing long chain branches (LCB) into polythene. Accordingly, the presence of additional long hain branches (with a chain length of more than 100 carbon atoms) was detected using rheological measurements. In oscillatory and creep tests, samples with low incorporation of 1-eicosene showed a behavior typical of long chain branched polymers. Poly (ethene-co-1-eicosene)s with high incorporation of 1-eicosene behaved like linear polymers, whereas ethene homopolymers contained less LCB. A long chain branching index (BI) was defined using terminal relaxation times. A correlation between BI and 1-eicosene content in the feed, as well as the number of long chain branches was established.

Melt modification of poly(styrene‐co‐maleic anhydride) with alcohols in the presence of 1,3‐oxazolines

Various copolyesteramides were prepared by melt compounding at 220 °C involving reaction of poly(styrene-co-maleic anhydride), SMA, with 6, 17, and 28 wt % maleic anhydride content, and 1-dodecanol, C12OH, in the presence of 2-undecyl-1,3-oxazoline, C11OXA. Copolymer architectures were examined by means of 1H NMR, FTIR, DSC, and TGA using model compounds prepared via solution reactions. While conversion of anhydride with alcohol was poor due to the thermodynamically favored anhydride ring formation, very high conversions were achieved when stoichiometric amounts of C11OXA were added. According to spectroscopic studies esteramide groups resulted from reaction of oxazoline with carboxylic acid intermediate. In the absence of alcohol, C11OXA reacted with anhydride to produce esterimides. Effective attachment of flexible n-alkyl side chains via simultaneous reaction of C12OH and C11OXA resulted in lower glass-transition temperatures of copolyesteramides.

Impact-modified poly(styrene-co-acrylonitrile) blends containing both oxazoline-functionalized poly(ethene-co-1-octene) elastomers and poly(styrene-co-maleic anhydride) as compatibilizer

Blends of a poly(styrene-co-acrylonitrile) (SAN) with poly(ethene-co-1-octene) rubber (EOR) were investigated. An improved toughness–stiffness balance was obtained when adding as a compatibilizer a blend consisting of oxazoline-functionalized EOR, prepared by grafting EOR with oxazoline-functional maleinate, and poly(styrene-co-maleic anhydride) (SMA), which is miscible with SAN. Enhanced interfacial adhesion was evidenced by the improved dispersion of the EOR in the SAN matrix and the reduced glass transition temperature of the dispersed EOR phase. Morphology studies using transmission electron microscopy revealed formation of an interphase between the matrix and the rubber particles.

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 .

Correlations Between Chain Branching, Morphology Development and Polymer Properties of Polyethenes

Molecular architectures of polyethenes, in particular short and long chain branching, were varied over a very wide range by means of either metallocene-catalyzed ethene/1-olefin copolymerization or Ni- and Pd-catalyzed migration/insertion-type ethene homopolymerization. While short chain branches affected melting, glass transition, and blend compatibility, long chain branching represented the key to improved melt processability. Both the number of short and long chain branches depended upon the ligand Substitution pattern of dimethylsilylene-bridged bisindenyl complexes. The degree of branching increased with Variation of the substitution in 4-position, i.e., 4-napthyl > 4-phenyl > benzannelation. Variation of the 1-butene content of ethene/1-butene (EB) copolymers gave control of morphology development and properties of isotactic polypropene (iPP) blends with EB. Highly flexible, single-phase as well as stiff and tough two-phase iPP/EB (70 wt.-%/30 wt.-%) blends were obtained. Rheological studies on ethene/1-eicosene model polyethene revealed the presence of a positive comonomer effect with respect to molar catalyst activity, molecular weight, and long-chain branching. A new family of thermoplastic elastomers based upon highly branched polyethene was prepared via Pd-catalyzed ethene copolymerization with 2,2,6,6-tetramethyl-piperidineoxy (TEMPO)-functionalized 1-olefin as macromonomers to produce macroinitiators for the initiation of the controlled free radical graft copolymerization of styrene onto highly branched polyethenes. The Variation of the polystyrene block length gave control on nanophase Separation of the resulting branched polyethene - graft - polystyrene.

Influence of Copolymer Composition and Curing on Toughness of Isotactic Polypropene Blended Together with Metallocene-EPDM and Ethene/Propene/Vinylcyclohexane Terpolymers

Ethene/propene terpolymers containing either 1-vinylcylohexene-4 (VCHen) or vinylcyclohexane (VCHan) as termonomer component were prepared using MAO-activated rac-Me 2 Si(2-MeBenz[e]Ind 2 ZrCl 2 (MBI). Propene content was varied between 26 and 72 wt.-% with less than 1 mol-% termonomer incorporation. Blends containing 85 vol.-% isotactic polypropene (i-PP) and 15 vol.-% of the two EP terpolymer families were prepared by melt-compounding in a twin-screw kneader at 200°C to examine the role of sulfur-mediated crosslinking of the unsaturated EPDM terpolymer phase in comparison to the corresponding blends containing non-crosslinked saturated EP/VCHan terpolymers. The observed glass temperature (T g ) depression of the T g of EP(D)M phases with respect to the T g of the corresponding bulk EP(DM) was attributed to the presence of thermally induced stresses in both blend systems. Blends of i-PP with crosslinked EPDM showed smaller T g depression with respect to those of iPP/EPM blends containing non-crosslinked EP and EPM dispersed phases. Morphology differences were detected for i-PP/EPM and dynamically vulcanized i-PP/EPDM blends by means of atomic force microscopy (AFM). The crosslinked i-PP/EPDM blends exhibited significantly improved low temperature toughness as compared to the corresponding non-crosslinked i-PP/EPM blends. Curing of the EPDM elastomer phase in i-PP/EPDM (85 vol.-%15 vol.-%) blends afforded significantly improved toughness/stiffness balance and a wider toughness window with respect to the corresponding i-PP/EPM and i-PP/EP blends without sulfur-cured rubber phases.

Branched Polyethenes Prepared via Olefin Copolymerization and Migratory Insertion

Branched polyethenes with variable alkyl side chains were prepared via three routes: (1) metallocene-catalyzed copolymerization of ethene with propene, 1-octene, 1-eicosene, (2) simultaneous ethene polymerization and copolymerization of in-situ formed 1-alkenes resulting from ethene oligomerization, using a blend of Ni- and Ti-based catalysts (“hybrid catalysts”), and (3) Ni- and Pd-catalyzed ethene homopolymerization with branching occurring due to migratory insertion. The resulting families of materials included high density, low and ultralow density semierystalline polyethenes as well as highly flexible and elastomeric polyethenes. The degree of branching (DB), as measured by the number of branched C/1000 C, was correlated with comonomer incorporation, catalyst structure, polymerization conditions, polyethene melting temperature and melting enthalpy. Polyethenes prepared by ethene/1-olefin copolymerization were compared with branched ethene homopolymers. Linear low density polyethenes with DB<50, produced with Ni-catalysts, resembled poly(ethene-co-propene). Highly branched polyethene elastomers were applied as toughening agents and blend components of isotactic polypropene in order to improve polypropene’s impact resistance.

Interdiffusion measurements of modified poly(arylether sulfone)s using nuclear reaction analysis

The interdiffusion and miscibility behavior of three different types of modified poly(arylether sulfone)s with deuterated poly(arylether sulfone) is studied by depth profiling using the nuclear reaction D(3He, α)p. The diffusion coefficients are found to be in the range of 10−15 and 10−14 cm2/s at 195°C. A random copolymer of poly(arylether sulfone) containing 4,4-bis-(4′-hydroxyphenyl)valeric acid units is only partially miscible with deuterated poly(arylether sulfone) when the comonomer content is 8.8 mol %, whereas blends with comonomer contents of 1.7 and 4.5 mol % are miscible as indicated by complete interdiffusion. The transition from miscibility to immiscibility is caused by repulsive interactions of copolymer segments and can be explained in terms of a mean-field theory of random copolymer blends. Also, poly(arylether sulfone)s grafted with 0.4 wt % maleic anhydride or having pyromellitic anhydride endgroups are miscible with deuterated poly(arylether sulfone)s.

The interfacial reaction of modified poly (arylether sulfone)s and polyaramides

It is shown that a fracture test using an asymmetric double cantilever beam test geometry is a powerful tool to study the effect of interfacial reactions on the improvement of the interfacial fracture toughness (G c ) of immiscible polymer systems. The G c values between a partially aromatic polyamide (PA) and a poly(arylether sulfone) (PSU) can be increased significantly when reactive PSUs are used which are obtained by grafting with maleic anhydride by introducing pyromellitic anhydride endgroups or by introducing carboxylic acid groups via copolymerization. Optical and atomic force microscopy investigations of the fracture surfaces show different failure mechanisms for weak and strong interfaces. For weak interfaces it was possible to determine the crack opening geometry using interference microscopy. For significantly reinforced interfaces rib marking lines on the PSU fracture surface can be observed. X-ray photoelectron spectroscopy (XPS) measurements reveal that with increasing toughness of the interface more and more cohesive failure of the PA occurs. This results in an increasing amount of nitrogen detected on the PSU fracture surface and simultaneously no sulfur is detected on the PA fracture surface.