Udo M. Wahner

Investigation of the Melting and Crystallization Behavior of Random Propene/α-Olefin Copolymers by DSC and CRYSTAF

The melting and crystallization behavior of random propene/higher linear α-olefin copolymers synthesized with the catalyst system (CH3)2Si(2-methylbenz-[e]indenyl)2ZrCl2/MAO were investigated. According to Florys theory, the melting point depression is linearly related to the amount of comonomer incorporated irrespective of the nature thereof. The crystallization temperature decreased as well linearly with increasing comonomer content, but was independent of the comonomer type. The comonomer amount had an equally depressant effect on the melting temperature and on the crystallization temperature regardless of whether the crystallization occurred from melt or from dilute solution.

The copolymerization of Propylene with higher, linear α-olefins

Propylene was copolymerized with the linear α-olefins 1-octene, 1-decene, 1-tetradecene, and 1-octadecene. The metallocene catalyst Me2Si(2-MeBenz[e]Ind)2ZrCl2, in conjunction with methylalumoxane as a cocatalyst, was used to synthesize the copolymers. The copolymers were characterized by 13C and 1H NMR with a solvent mixture of 1,2,4-trichlorobenzene (TCB) and benzene-d6 (9/1) at 100 °C. Thermal analyses were carried out to determine the melting and crystallization temperatures, whereas the molecular weights and molecular weight distributions were determined by gel permeation chromatography with TCB at 140 °C. Glass-transition temperatures were determined with dynamic mechanical analysis. Relationships among the comonomer type and amount of incorporation and the melting/crystallization temperatures, glass-transition temperature, crystallinity, and molecular weight were established. Moreover, up to 3.5% of the comonomer was incorporated, and there was a decrease in the molecular weight with increased comonomer content. Also, the melting and crystallization temperatures decreased as the comonomer content increased, but this relationship was independent of the comonomer type. In contrast, the values for the glass-transition temperature also decreased with increased comonomer content, but the extent of the decrease was dependent on the comonomer type.

Analysis of polyolefin blends by crystallization analysis fractionation

Crystallization analysis fractionation (CRYSTAF) is a new technique for the analysis of the composition of polyolefin blends. CRYSTAF fractionates blend components of different crystallizability by slow cooling of a polymer solution. During the crystallization step the concentration of the polymer solution is monitored as a function of temperature. Different from DSC, blends of HDPE, LDPE and PP are separated into the components and quantitative information can be obtained directly from the crystallization curves. Even very low amounts of one component in PE/PP and HDPE/LDPE blends can be quantified with good accuracy. The applicability of the technique for the analysis of Ziegler-Natta, and metallocene-catalyzed polyolefins is demonstrated and the analysis of waste plastics fractions is discussed.

Polymerization of higher linear α-olefins with (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2

Poly-α-olefins ranging from poly-1-pentene to poly-1-octadecene with narrow polydispersities were synthesized with (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2 and methylaluminoxane at polymerization temperatures (Tp s) ranging from −15 to 180 °C and were characterized by gel permeation chromatography, NMR spectroscopy, and differential scanning calorimetry. The molar masses of the homopolymers obtained with (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2 were notably higher than those of poly-α-olefins synthesized with other zirconium-based metallocenes under similar conditions. The temperature dependence of the molar mass distribution of the poly-α-olefins can be described by a common exponential decay function regardless of the investigated monomer. At Tp s ranging from 20 to 100 °C, moderate isotacticity prevailed, but outside this temperature range, the polymers were less stereoregular.

Analysis of polyolefin blends by CRYSTAF

Crystallization analysis fractionation (CRYSTAF) has been introduced for the analysis of the composition of polyolefin blends and the chemical composition distribution of polyolefins. Blends of syndiotactic and isotactic polypropylene (sPP and iPP) and of sPP/High density polyethylene (HDPE) have been fractionated by CRYSTAF and the results been compared to those from DSC. While the blends of sPP and HDPE cannot be separated by DSC a quantitative determination of both components is possible by CRYSTAF over the whole range with the detection limit being 1% on both ends. Furthermore it is demonstrated that the separation of ternary blends of sPP, iPP and HDPE is possible by CRYSTAF.

Oligomerisation of 1-pentene with metallocene catalysts

The homo-oligomerisation of 1-pentene in the presence of various bridged and non-bridged metallocenes and methylaluminoxane (MAO) at room temperature and at 60°C, respectively, has been studied. The use of the bridged catalysts rac-[C2H4(Ind)2]ZrCl2 (1) and [(CH3)2Si(Ind)2]ZrCl2 (2) leads to the formation of isotactic poly(1-pentene). The use of Cp2ZrCl2 (3), Cp2HfCl2 (4) and [(CH3)5C5]2ZrCl2 (5) leads to the formation of atactic poly(1-pentene). The stereoregularity of the isotactic poly(1-pentene) obtained with 1 was higher than that of the poly(1-pentene) synthesised with 2. The degree of polymerisation was highly dependent on the metallocene catalyst. Oligomers ranging from the dimer of 1-pentene to poly(1-pentene) with a number-average molar mass Mn = 5100 g mol–1 were formed. The 1H NMR spectra of the samples were analysed with regard to functional groups and these were attributed to different chain termination processes. A MALDI-TOF spectrum of low-molar-mass poly(1-pentene) could be recorded using dithranol as matrix and adding silver trifluoroacetate to promote ion formation. Die Homooligomerisation von 1-Penten wurde bei Raumtemperatur bzw. bei 60°C mit verbruckten und unverbruckten Metallocenen und Methylaluminoxan (MAO) untersucht. Die verbruckten Katalysatoren rac-[C2H4(Ind)2]ZrCl2 (1) und [(CH3)2Si(Ind)2]ZrCl2 (2) fuhrten zu isotaktischem Poly-1-penten, wogegen Cp2ZrCl2 (3),Cp2HfCl2 (4) und [(CH3)5C5]2ZrCl2 (5) ataktisches Poly-1-penten lieferten. Die Stereoregularitat des mit 1 hergestellten isotaktischen Poly-1-pentens war groser als die des mit 2 erhaltenen Poly-1-pentens. Der Polymerisationsgrad zeigte eine starke Abhangigkeit vom verwendeten Metallocen-Katalysator. So konnte die Bildung von Pentendimeren bis hin zu Poly-1-penten mit einer zahlenmittleren Molmasse Mn von 5100 g mol–1 beobachtet werden. Die 1H NMR-Spektren wurden bezuglich funktioneller Gruppen analysiert und diese unterschiedlichen Kettenabbruchreaktionen zugeordnet. Ein MALDI-TOF-Spektrum von niedermolekularem Poly-1-penten konnte mit Dithranol als Matrix mit Zugabe von Silbertrifluoracetat erhalten werden.

Synthesis and properties of poly-1-olefins

The oligomerization and polymerization of 1-pentene using Cp 2 ZrCl 2 , Cp 2 HfCl 2 , [(CH 3 ) 5 C 5 ] 2 ZrCl 2 , rac-[C 2 H 4 (Ind) 2 ]ZrCl 2 , [(CH 3 ) 2 Si-(Ind) 2 ]ZrCl 2 , (CH 3 ) 2 Si(2-methylbenz[e]indenyl) 2 ZrCl 2 , Cp 2 ZrCl-{O(Me)CW(CO) 5 }, Cp 2 ZrCl(OMe) and methylaluminoxane (MAO) has been studied. The degree of polymerization was highly dependent on the metallocene catalyst. Oligomers ranging from the dimer of 1-pentene to polymers of poly-1-pentene with a molar mass M w = 149000 g/mol were formed. Cp 2 ZrCl{O(Me)CW(CO) 5 } is a new highly active catalyst for the oligomerization of 1-pentene to low molecular weight products. The activity decreases in the order Cp 2 ZrCl{O(Me)CW(CO) 5 } > Cp 2 ZrCl 2 > Cp 2 ZrCl(OMe). Furthermore, poly-1-olefins ranging from poly-1-pentene to poly-1-octadecene were synthesized with (CH 3 ) 2 Si(2-methylbenz[e]indenyl) 2 ZrCl 2 and methylaluminoxane (MAO) at different temperatures. The temperature dependence of the molar mass can be described by a common exponential decay function irrespective of the investigated monomer.

Homopolymerization of higher 1-olefins with metallocene/MAO catalysts

Linear 1-olefins from 1-pentene to 1-octadecene are polymerized by non-stereospecific Cp 2 HfCl 2 (1), syndiospecific Me 2 C(Cp)(9-fluorenyl)ZrCl 2 (2) and isospecific Et(Ind) 2 ZrCl 2 (3) catalysts in the presence of MAO. The molecular weight of the resulting polymers (GPC) is highly dependent on the nature of the catalyst, but more or less independent of the monomer chain length. The stereoregularity of the poly(1-olefins) obtained with 2 and 3 as determined by NMR spectroscopy decreases linearly with increasing monomer chain length. A decrease in isotacticity occurs for the poly(1-olefins) synthesized with 3 when increasing the catalyst concentration. Vinylidene, 1,2-disubstituted and 1,1,2-trisubstituted double bonds attributed to different chain termination mechanisms are generated during the polymerization processes.

Monitoring the chemical heterogeneity of metallocenecatalysed copolymers of ethylene and higher 1-olefins using CRYSTAF and SEC-FTIR

Abstract Copolymers of ethylene with 1-decene, 1-tetradecene and 1-octadecene were prepared using the catalyst system racEt[Ind]2ZrCl2/MAO and were analysed with regard to chemical heterogeneity using crystallisation analysis fractionation (CRYSTAF), differential scanning calorimetry (DSC) and size exclusion chromatography coupled to FTIR (SEC-FTIR). The melting and crystallisation temperatures from DSC decrease linearly with increasing amount of comonomer, independently of the nature thereof. The decrease in crystallisation temperature from CRYSTAF of copolymers with higher 1-olefin content indicates a small dependence on the length of the side chain. The chemical heterogeneity of the copolymers as analysed by DSC and CRYSTAF broadens with increasing comonomer concentration.

Synthesis and characterisation of propene / higher 1-olefin copolymers with the catalyst system (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2/MAO

Abstract The melting and crystallization behaviour of random copolymers of propene with 1-butene, 1-pentene and 1-hexene synthesized with the catalyst system (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2/methylaluminoxane (MAO) were investigated by differential scanning calorimetry and crystallization analysis fractionation (CRYSTAF). The melting and crystallization temperatures decreased linearly with increasing comonomer content. The depressions of the melting and crystallization temperatures are strongly dependent on the nature of the monomer and are more pronounced for copolymers of propene with 1-hexene than with 1-butene. In comparison to 1-hexene and 1-butene, the incorporation of 1-pentene leads to an intermediate behaviour. This is in contrast to the behaviour of copolymers of propene with longer chain 1-olefins, where the melting and crystallization temperatures are independent of the comonomer type. The depressant effects of the amount of comonomer incorporated on the melting and the crystallization temperatures are equal.