The microstructure of propene/1‐pentene copolymers prepared with the metallocene catalysts rac‐Et(Ind)2ZrCl2 and rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 was studied by 13C NMR spectroscopy. Both catalysts lead to the formation of random copolymers although rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 favors a somewhat higher incorporation of 1‐pentene than rac‐Et(Ind)2ZrCl2. Surprisingly, the presence of 1‐pentene has a significant influence on the stereoregularity of the copolymers formed with rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2. Propene/1‐pentene copolymers produced with rac‐Et(Ind)2ZrCl2 retained the isotacticity of polypropene and featured only the stereoerror pentads mmmr, mmrr and mrrm typical for enantiomorphic site control. However, propene/1‐pentene copolymers obtained with rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 are characterized by a gradual loss of tacticity which is concurrent with an increase in the amount of all irregular pentads. It is proposed that the presence of 1‐pentene can lead to a reversible loss of stereocontrol over a whole sequence of inserted monomer units. Subsequently, more or less atactic blocks are formed besides isotactic blocks.Percentage of 1‐pentene in the copolymer as function of the feed composition for 1‐pentene/propene copolymers prepared with EI and MBI.magnified imagePercentage of 1‐pentene in the copolymer as function of the feed composition for 1‐pentene/propene copolymers prepared with EI and MBI.

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The catalyst system i‐Pr(Cp)(9‐Flu)ZrCl2/methylaluminoxane was used for the synthesis of random syndiotactic copolymers of propylene with 1‐hexene, 1‐dodecene, and 1‐octadecene as comonomers. An investigation of the microstructure by 13C NMR spectroscopy revealed that the stereoregularity of the copolymers decreased because of an increase in skipped insertions in the presence of the higher 1‐olefin. The melting temperature of the copolymers, as measured by differential scanning calorimetry (DSC), decreased linearly with increasing comonomer content independently of the comonomer nature. During the DSC heating cycle, an exothermic peak indicating a crystallization process was observed. The decrease in the crystallization temperature with higher 1‐olefin content, measured by crystallization analysis fractionation, indicated a small but significant dependence on the nature of the comonomer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 128–140, 2002

Copolymers of propene and higher 1‐olefins (1‐butene, 1‐pentene, 1‐hexene, 1‐heptene, 1‐octene, and 4‐methyl‐1‐pentene (4M1P)), prepared with rac‐Et(Ind)2ZrCl2 (EI) and rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 (MBI), were comprehensively analyzed by 13C NMR spectroscopy. These catalysts known to produce isotactic polypropene lead to two vastly different families of copolymers under the chosen experimental conditions. All copolymers produced with EI possessed comparable isotacticities as well as similar stereosequences. Furthermore, these copolymers did not significantly differ from those of the reference propene homopolymer. However, the copolymers produced with MBI significantly differed both from the reference propene homopolymer and among themselves. In fact, in contrast to the corresponding highly isotactic homopolymer, the whole series of copolymers was characterized by rather low isotacticities. The degree of tacticity was strongly influenced by the comonomer type. A detailed 13C NMR analysis revealed that these copolymers are constituted by highly isotactic sequences and by atactic sequences of various lengths. It is proposed that the formation of atactic sequences is triggered by the insertion of a comonomer. It seems likely that MBI can shift from a stereoselective to a non‐stereoselective state due to an interaction with higher linear or branched comonomer.13C NMR spectra of propene/1‐pentene (a) and propene/4‐methyl‐1‐pentene (b) prepared with MBI.magnified image13C NMR spectra of propene/1‐pentene (a) and propene/4‐methyl‐1‐pentene (b) prepared with MBI.