Cyclic and multicyclic polymers by thermodynamically controlled polycondensations—theory and experiments

Thermodynamically controlled polycondensations (TCPs) are defined as stage-growth polymerizations involving condensation step with rapid equilibration including “back-biting degradation”. It is theoretically demonstrated that the molar concentration of linear chains responsible for their cyclization tendency dramatically decreases with higher conversions, so that a clean TCP yields 100% cycles at 100% conversion. Therefore, a TCP with 100% conversion yields the same reaction product as are equilibration of monomeric or oligomeric heterocycles (in this connection a new definition of conversion is presented). In contrast, the classical theory of TCPs elaborated by Stockmayer and Flory postulates 2.5–3.0 weight% of cycles in combination with one giant linear chain (97.0–97.5 weight%) as the endproduct of 100% conversion. Furthermore, it is demonstrated that the new theory of TCPs also applies to “a2 + b n ” polycondensations. When the equilibrium favors smaller cycles, spirocycles and low molar mass multicycles are thermodynamically favored over macrocyclic networks. Experimental results discussed in this work concern nylon-6 and nylon −7/−6,8, poly(1,3-dioxolane), tin containing polyethers, and multicyclic polyethers derived from germanium, tin, titanium and zirconium alkoxides.