Abstract
The 13C NMR microstructure of a polypropylene (PP) sample is a fundamental source of information on its properties, and also a ‘fingerprint’ of the catalytic species used to produce it. Likely due to a much greater technological importance, isotactic polymers (i-PP) have been more thoroughly investigated that syndiotactic ones (s-PP). In this paper, we report the first full assignment of regioirregular sequences in s-PP samples made with two well-known molecular catalysts, namely a Cs-symmetric (cyclopentadienyl)(fluorenyl) ansa-zirconocene and a fluxional bis(phenoxyimine)Ti species. The results shed more light on the mechanism of chain propagation at the two catalysts, and open the door to the investigation of more elusive cases like the formation of s-PP blocks in the presence of multi-sited heterogeneous Ziegler-Natta systems.
Highlights
The 13 C NMR microstructure of a polypropylene (PP) sample is a fundamental source of information on its properties, and a ‘fingerprint’ of the catalytic species used to produce it
NMR spectroscopy in solution is the technique of choice for the investigation of polyolefin microstructure [1]
This can be exploited in High Throughput Experimentation (HTE) applications [4,5], or aimed to the detection of rare microstructural features, such as chain ends, long chain branches, or regioirregular sequences
Summary
The 13 C NMR microstructure of a polypropylene (PP) sample is a fundamental source of information on its properties, and a ‘fingerprint’ of the catalytic species used to produce it. We report the first full assignment of regioirregular sequences in s-PP samples made with two well-known molecular catalysts, namely a Cs -symmetric (cyclopentadienyl)(fluorenyl) ansa-zirconocene and a fluxional bis(phenoxyimine)Ti species. NMR spectroscopy in solution is the technique of choice for the investigation of polyolefin microstructure [1]. This can be exploited in High Throughput Experimentation (HTE) applications [4,5], or aimed to the detection of rare (albeit influential) microstructural features, such as chain ends, long chain branches, or regioirregular sequences
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