reactions and found that they can be used in the synthesis of diarylated compounds.Zolotukhin and co-workers [3][4][5][6][7][8][9] develo ped a superacid catalyzed polyhydroxyalkylation novel synthetic route (see Figure 2), which can be classified as an unusual A 2 + B 2 step-growth poly merization since ultrahigh molecular weights and molar mass dispersities (Ð) less or higher than two are possible, at nonstoichiometric conditions. The dramatic acceleration in polymerization rate observed in superacid catalyzed poly hydroxyalkylations with a small excess of the carbonyl compound is known as the "nonstoichiometric effect." [6] Superacid catalyzed polyhydroxyalkylations have the following advantages: [6] (i) the reaction proceeds at room temperature and atmospheric pressure, (ii) structural variety and commercial availability of monomers, (iii) high conversion yields, (iv) high regioselectivities, (v) acceptable reaction times, (vi) great versatility in polymer architectures, (vii) functional groups that allow polymer chemical modification reactions, (viii) easy polymer purification, (ix) good physical, chemical, and thermal properties of the produced polymers, and (x) high polymer molecular weights.

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during the early stages of polymerization, when monomers such as 6-aminehexanoic acid, which can lead to ε-caprolactam, a seven-member ring, [1] or monomers with higher member rings, such as those containing Si, P, or heavier elements from the periodic table are used. [2-5] We recently modeled the superacid catalyzed polymerization of isatin and biphenyl or terphenyl, [6] which are examples of superacid catalyzed poly hydroxyalkylation. This polymerization route, developed in one of our laboratories, [7-13] allows to produce ultra-high molecular weight polymer molecules by non-stoichiometric A 2 + B 2 step-growth polymerizations (r < 1, where r is stoichiometric imbalance ratio). It is usually assumed that cyclization is negligible (k c = 0) in superacid catalyzed polyhydroxyalkylations, which allows to reach ultra-high molecular weights (M n > 1.0 × 10 6). However, recent experimental data related to irreversible step-growth polymerizations suggest that cyclization may not be negligible in such systems. [14] Jacobson and Stockmayer (JS) addressed the case of cyclization in reversible step-growth polymerizations, establishing a relationship between equilibrium and kinetic rate constants for the cyclization reaction. In their theory, they assumed that enthalpic interactions between linear and cyclic polymer molecules are negligible, and that linear chains are flexible, following Gaussian behavior. They also assumed that the rates of cycle formation and opening are independent of cycle size. [15] The concentration of cyclic polymer molecules in thermodynamically controlled (reversible) step-growth polymerizations is usually low and it can usually be neglected. In the case of irreversible step-growth polymerizations, significantly large concentrations of cyclic polymer molecules have been detected using "matrix-assisted laser desorption/ionization-time-offlight" MALDI-TOF mass spectroscopy for a wide range of experimental systems. [16-33] 1.2. Kinetically Controlled Step-Growth Polymerizations at Medium to High Concentrations Kinetically controlled step-growth polymerizations (KCPs) proceed in the absence of equilibrium reactions and the A mathematical model for the kinetics and chain length development in A 2 + B 2 step-growth polymerization with competition between cyclization and linear chain growth is presented. The model requires two kinetic rate constants, one for the several reactions producing linear polymer molecules (k), and another one for chain length dependent cyclization (k c). The model describes well the qualitative behavior of the system, including the effects of initial monomer concentration and ratio of limiting to excess functional groups on degree of cyclization. The model is validated using two polymerization systems, a conventional A 2 + B 2 polymerization of hexamethylene diisocyanate (HDI) and poly(ethylene glycol) (PEG200), as well as the superacid catalyzed polyhydroxyalkylation of modified isatin and biphenyl. Four different kinetic rate constants for the four reactions producing linear p...

An experimental study on the superacid-catalyzed polyhydroxyalkylation of biphenyl (A2 monomer) and 1-propyl isatin (B2 monomer) at non-stoichiometric conditions is presented. The produced high-performance polymers were characterized by gel permeation chromatography matrix-assisted laser-desorption/ionization-time-of-flight (MALDI-TOF), nuclear magnetic resonance and diffusion-ordered spectroscopy (DOSY). High molecular weights (Mw > 150,000 Da) and ultra-high molecular weights (Mw ∼ 900,000 Da) are obtained when B2 is used in excess, which agrees with the behavior observed at non-stoichiometric conditions for other superacid catalyzed polyhydroxyalkylations, contrary to the case when A2 is used in excess, where a reduction in molecular weight is obtained, as reported in a previous study from our group. A, B, and M types of linear polymer molecules, as well as C-type cycles, were observed from the MALDI-TOF data.