Reaction kinetics of polymer substituents: macromolecular steric hindrance effect in quaternization of poly(vinylpyridines)

Abstract

The retardation in the quaternization of poly(vinylpyridines) is of steric origin. Using very voluminous reagents, a steric effect also induces an important limitation to the extent of quaternization which is not included in theoretical treatments of neighboring group effects. A kinetic expression based on the classical second-order equation is proposed. It includes the rate constant feo for reaction of a pyridyl group and a macromolecular steric factor ß lowering the effective pyridine group concentration capable of reacting. ß characterizes the effect of the size and nature of the substituents on the accessibility of the pyridine groups. The expression describes very well the experimental kinetics published and associates to each alkylating agent a steric factor related to its bulkiness. Cessation of the reaction at a given temperature is predicted, in full agreement with experimental results. Possible reasons for such a limitation are discussed, and the change in the polymer conformation from a free-draining coil to a scarcely permeable globule is shown to account for the effect.

Mechanical relaxation times as indicators of stickiness in skim milk–maltodextrin solids systems

“…An increase in maltodextrin content also shifted a-relaxations to higher temperatures. The addition of high molecular weight compounds, such as maltodextrins, could increase stiffness (Frère and Gramain, 1992;Han and Nam, 2002;Sillick and Gregson, 2009) and, thus, reduce molecular mobility of lactose molecules due to a high degree of association as observed from the small magnitudes of modulus changes. This was consistent with our previous study (Silalai and Roos, 2010b) revealing the reduced molecular mobility of high protein-content skim milk solids systems.…”

“…A considerable change in modulus of the skim milk-maltodextrin solids systems with DE17 maltodextrin (10%, w/w) could be explained by effects of maltodextrin miscibility with lactose, its average molecular weight and lowmolecular-weight components. High DE maltodextrins contain high amounts of glucose molecules, which decreased viscosity due to plasticizing behavior of sugars and water resulting in an increase in overall molecular mobility of the systems (Frère and Gramain, 1992;Kalichevsky Fig. 3.…”

Reactions on polymers with amine groups. III. Description of the addition reaction of pyridine and imidazole compounds with ?,?-unsaturated monocarboxylic acids

“…These determinations give line Da in Figure 2 when assented to the procedure discussed for relation ( 15) and line Ea when assented to relation ( 2 3 ) . The slope of Ea gives k, = 5.2 X lop3 mol-2L2min-1, which is practically equal with k, = 5.1 X mol-2L2min-' obtained from the slope of Da.…”

“…t)) plots for the reaction between 4MP and AA with r = 1.87 (Ca, Da, and Ea) and r = 1.18 (Cb and Db), the other conditions being given in Table 111. The plots C and D were obtained with relation (15); the curves in C result from K, = 0 while lines D correspond to the K , values that give the most linear dependencies (see Table 111). The plot Ea was obtained with relation (23); therefore, considering r = 1.87 close to r = 2.…”

“…Considering the left member of relation ( 15) as a function F ( x * ( t ) ) , the value of equilibrium constant K, would be the one so that the plot F vs t fits best a straight line starting from origin, and the value of rate constant k, is determined from the slope of that line.…”