Alkenylsilanes of varying chain lengths are investigated as simultaneous chain transfer agents + comonomers in organotitanium-mediated olefin polymerization processes. Ethylene + alkenylsilane polymerizations were carried out with activated Me2Si(Me4C5)(NtBu)TiMe2 and (-CH2CH2-3,3'){(5-indenyl )[1-Me2Si(tBuN)]}2Ti2Me4 precatalysts. Alkenylsilane incorporation levels follow the trend C8H15SiH3 < C6H11SiH3 ≈ C4H7SiH3 < C3H5SiH3. Long-chain branching levels versus total branch content follow the trend C3H5SiH3 < C4H7SiH3 ≈ C6H11SiH3 ≈ C8H15SiH3. Ti nuclearity influences silanolytic chain transfer processes, with binuclear systems exhibiting sublinear relationships between Mn and [alkenylsilane]-1 for allylsilane and 3-butenylsilane, and superlinear relationships between Mn and [alkenylsilane]-1 for 5-hexenylsilane and 7-octenylsilane. For mononuclear Ti systems, alkenylsilanes up to C6 demonstrate linear relationships between Mn and [alkenylsilane]-1, consistent with a silanolytic chain termination mechanism. Organosilane reagents are introduced into organotitanium-mediated styrene polymerizations to produce atactic polystyrene. The resulting polymers were characterized by 1H and 13C NMR, GPC, and DSC. High activities (up to 106 g polymer/ (mol Ti ● h)) and narrow polydispersities are observed in the polymerization process. Previously recognized CGCTiMe2 systems having marginal styrene homopolymerization activity are shown to be up to 3 orders of magnitude more active upon addition of organosilane. Control experiments indicate that the SiH moiety is significant in the organotitanium-mediated styrene polymerization process. Amines of varying Brønsted acidity and steric encumberance are investigated as chain-transfer agents in organolanthanide-mediated olefin polymerization processes. Ethylene homopolymerizations are carried out with activated Cp'2LnCH(Si(CH3)3)2 (Cp' = 5-Me5C5); Ln = La, Sm, Y, Lu precatalysts in the presence of primary and secondary amines. Amine chain transfer efficiency follows the trend C6H5NH2 ≈ C3H7NH2 << (Si(CH3)3)2NH ≈ secBu2NH < N-tBu(Si(CH3)3)NH ≈ iPr2NH < (C6H11)2NH to yield polyethylenes of the structure H(CH2CH2)nNRR'. Under the conditions investigated, primary amines are the most stable towards Cp'2La-mediated polymerizations, affording no detectable insertion products, while secondary amines produce mono-ethylene insertion products, amine-capped oligoethylenes, and high molecular weight amine-terminated polyethylenes. Here, protonolysis appears to be the dominant chain-transfer pathway. Organotitanium-mediated ethylene and propylene polymerizations in the presence of secondary amines result in modest polymerization rates with activities of 104 g polymer/(mol of Ti atm ethylene h)

Last modified

• 08/01/2018

Creator

• Smruti Amin

DOI

• https://doi.org/10.21985/N2B14G

Subject

• Chemistry

Keyword

• Chemistry

Date created

• 2007-08-29

Resource type

• Dissertation

Rights statement

• In Copyright