A response of a silicone polymer fragment to external stresses is considered in terms of a mechanochemical reaction. The quantum-chemical realization of the approach is based on a coordinate-of-reaction concept for which purpose a mechanochemical internal coordinate (MIC) specifying a deformational mode is introduced. The related force of response is calculated as the total-energy gradient along the MIC, while the atomic configuration is optimised over all other coordinates under the MIC constant-pitch elongation. The approach is applied to a set of linear silicone oligomers Sin with n = 4, 5, and 10, subjected to uniaxial tension followed by the rupture of the molecule and a post-fracture relaxation. Peculiarities of the mechanical behavior of the oligomer are analyzed as well as the oligomer strength and the related Young's moduli. A cooperative radical-driven mechanism of silicone polymer fracture is suggested. © 2008 VCH Verlagsgesellschaft mbH. All rights reserved..