Regio- and Stereospecific Cyclopolymerization of Bis(2-propenyl)diorganosilanes and the Two-State Stereoengineering of 3,5- cis, isotactic Poly(3,5-methylene-1-silacyclohexane)s

Kaitlyn E Crawford; Lawrence R Sita

doi:10.1021/mz500126r

Regio- and Stereospecific Cyclopolymerization of Bis(2-propenyl)diorganosilanes and the Two-State Stereoengineering of 3,5- cis, isotactic Poly(3,5-methylene-1-silacyclohexane)s

ACS Macro Lett. 2014 Jun 17;3(6):506-509. doi: 10.1021/mz500126r. Epub 2014 May 13.

Authors

Kaitlyn E Crawford¹, Lawrence R Sita¹

Affiliation

¹ Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States.

PMID: 35590716
DOI: 10.1021/mz500126r

Abstract

Transition-metal-mediated coordination cyclopolymerization of bis(2-propenyl)dimethylsilane (1a) using the C₁-symmetric, group 4 metal preinitiator, (η⁵-C₅Me₅)Zr(Me)₂[N(Et)C(Me)N(^tBu)] (I), in combination with 1 equiv of the borate coinitiator, [PhNHMe₂][B(C₆F₅)₄] (II), proceeds in a regio- and stereospecific manner to provide highly stereoregular 3,5-cis,isotactic poly(3,5-methylene-1,1-dimethyl-1-silacyclohexane) (2a). Successful stereoengineering of 2a to eliminate undesirable crystallinity while preserving a high T_g value of >120 °C was subsequently accomplished by employing a "two-state" propagation system that uniquely produces an isotactic stereoblock microstructure of decreasing stereoblock length with decreasing percent level of "activation" of I with II. The controlled character of cyclopolymerization of 1a using the less sterically encumbered preinitiator, (η⁵-C₅Me₅)Hf(Me)₂[N(Et)C(Me)N(Et)] (III), and 1 equiv of II was used to prepare well-defined poly(1-hexene)-b-poly(3,5-methylene-1-silacyclohexane) block copolymers through sequential monomer additions.