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The reactivity‐selectivity principle in polymerization. The case of polymerization of ϵ‐caprolactone
Author(s) -
Penczek Stanislaw,
Duda Andrzej,
Slomkowski Stanislaw
Publication year - 1992
Publication title -
makromolekulare chemie. macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 0258-0322
DOI - 10.1002/masy.19920540106
Subject(s) - chemistry , selectivity , reactivity (psychology) , reagent , polymerization , dimer , reaction rate constant , medicinal chemistry , solvent , stereochemistry , kinetics , organic chemistry , polymer , catalysis , medicine , alternative medicine , physics , pathology , quantum mechanics
Anionic and pseudoanionic polymerizations of ϵ‐caprolactone (CL) have been compared in terms of the principle relating reactivity with selectivity (reactivity‐selectivity principle, RSP). RSP can be formulated as follows: there are two reagents X and Y; reagent X reacts faster with substrates A and B than reagent Y does (i.e. k xa >k ya and k xb >k yb , where k xa , k ya , k xb and k yb are the respective rate constants); moreover, reactions with A are faster than reactions with B (i.e. k xa >k xb and k ya >k yb ); finally, if RSP is operative the inequality k ya /k yb >k xa /k xb holds. Comparison of the anionic and pseudoanionic polymerizations of CL reveals that this system conforms to the RSP. Propagation on the …‐O − Na + ion pairs proceeds much faster than on the … − OAIR 2 covalent species (k p ∓ = 1,7 l/mol · s vs k p c = 3,0 · 10 −2 l/mol · s, THF solvent, 20°C). Propagation is accompanied by transesterification and cyclization. Formation of the cyclic dimer (with the rate constant k b (2)) was taken as a measure of an extent of these “side” reactions. Following selectivity coefficients ß = k p /k b (2) have been measured (in l/mol): 1, 55 · 10 3 (… − O − Na + ), 4, 6 · 10 4 (…‐OAl(C 2 H 5 ) 2 ), and 7,7 · 10 4 (… − OAl(i‐C 4 H 9 ) 2 ). Thus, k p c /k b c (2)>k p ∓ /k b ∓(2). Therefore formation of the linear, high molar mass polymer is more pronounced in the system with the less reactive active centers.