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Stereoselective Copolymerization of Styrene with para-Substituted Styrenes Catalyzed by Half-Titanocenes: An Experimental and Computational Study
journal contribution
posted on 2020-03-17, 15:33 authored by Chiara Costabile, Annaluisa Mariconda, Marco Sirignano, Pasquale LongoCopolymerization
of styrene (S) with p-methylstyrene
(PMS) and p-chlorostyrene (PCS), catalyzed by half-titanocenes
(CpCH2CH2O)TiCl2 (1)
and (CpCH2CH2OCH3)TiCl3 (2) activated by methylaluminoxane (MAO), was investigated
from both experimental and computational points of view. The reactivity
ratios and syndioselectivity of the reaction are affected by the styrene
derivative and the catalytic system, leading to the formation of block
or random copolymers. Using both catalytic systems, styrene, p-methylstyrene, and p-chlorostyrene show
the same reactivity trend (PMS > S > PCS) already reported in
the
presence of the CpTiCl3/MAO catalyst and in the syndiotactic
and isotactic polymerization of styrene derivatives with other Ti-based
catalysts. According to density functional theory (DFT) calculations,
extended also to the CpTiCl3/MAO catalyst, the reactivity
of the employed comonomers is mainly due to the different electron-donating
character of monomer para-substituents. As for stereoselectivity,
(1) and (2) lead to syndiotactic copolymer
sequences with PMS and S, whereas a loss of selectivity is observed
in the poly-p-chlorostyrene homosequences of PCS/S
copolymers. According to DFT studies, this lack of selectivity can
be attributed to the presence of a σ terminal growing chain
in the insertion transition states when PCS is involved in the polymerization.
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Keywords
syndiotactic copolymer sequencesstyrene derivativesComputational Study Copolymerizationreactivity ratiosMAOOCHPCSchlorostyrene showselectivityTi-based catalystsinsertion transition statescopolymerselectron-donating charactermonomer para-substituentsreactivity trendpara-Substituted Styrenes CatalyzedStereoselective CopolymerizationCpCHpresenceCpTiClisotactic polymerizationPMSchlorostyrene homosequencesCHDFT studiesmethylstyreneσ terminal
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