M.Sc Thesis


M.Sc StudentGouli Oleg
SubjectIs There (Regio) Selectivity in Polymer Mechanochemical C-C
Bond Scission?
DepartmentDepartment of Polymer Engineering
Supervisor ASSOCIATE PROF. Charles E. Diesendruck
Full Thesis textFull thesis text - English Version


Abstract

Stable carbon-carbon bonds can be broken in a metathesis cracking process, however, this process is non-selective and very energy expensive. C-C bonds were also shown to be cleaved easily using mechanical stress in polymers (mechanochemistry); however, this is also not a selective process. This research aims at finding a way to manipulate the mechanical scission of a C-C bond in polymers and make it regioselective. First, more than 40 different structures were tested in silico using the Constrained Geometry simulates External Force (CoGEF) method. It was found that carbon substituents can reduce the required force for bond scission by up to 10%, while changing the bond angle leads to a reduction of up to 15%, and, finally, a C-C bond inside a cyclooctane structure showed a significant force reduction of up to 35%. In cyclic structures, cis and trans isomers showed breaking force reduction by up to 15%. The trans-cyclooctane structure, which offered the highest chance of presenting regioselective C-C bond scission, was tested experimentally using ultrasound-induced stressing of polymer solutions. Three different polyphthalaldehydes were prepared and their mechanochemical depolymerization kinetics compared. Two controls having regular unsubstituted C-C bonds, one at the center and the other at the edge, show similar depolymerization rates, indicating no selectivity in this case. However, the polyphthalaldehyde with a chain-centered cyclooctane shows reduced depolymerization rate and different mechanochemistry profile, indicating more selective C-C bond scission is obtained. This work emphasizes the challenges in accomplishing a regioselective C-C bond scission in polymers, but provides fundamental understanding on how different structural parameters can lead to such selectivity