The recently discovered twin polymerization offers a remarkable access to new versatile hybrid materials. In order to develop an advanced model system to understand the reaction mechanism in detail we present an exemplary quantum chemical study on the role of the counter anion in the acid (trifluoroacetatic acid) catalyzed twin polymerization of 2,2'-spirobi[4H-1,3,2-benzodioxasiline]. Using three different model systems the reaction mechanism is investigated with respect to the influence of the anion (trifluoroacetate) in the reaction system. The extended model system with two monomers and two acid molecules exhibits lowest activation barriers for the first step of the organic network formation. The formation of the electrophile and the electrophilic substitution are supported by the present counter anion. The reaction mechanism of this initiating process is also influenced by sterical effects, since the size of the acid molecule is quite comparable to the size of other molecular structure units. The obtained sophisticated data base on the reaction mechanism and the energetics provides an important basis for structure formation modeling in future. (C) 2015 Elsevier Ltd. All rights reserved.