Kinetic Analysis of "Living" Polymerization Processes Exhibiting Slow Equilibria. 2. Molecular Weight Distribution for Degenerative Transfer (Direct Activity Exchange between Active and "Dormant" Species) at Constant Monomer Concentration

Abstract

The MWD function and moments are derived for a "living" polymerization process which proceeds via active and "dormant" species and where the activity is directly exchanged between these chain ends in a bimolecular reaction ("degenerative transfer"). Such a mechanism is believed to be applicable to many "living" polymerizations (e.g., anionic, group transfer, cationic, and radical). For constant monomer concentration (slow addition of monomer or low conversion), the polydispersity index, PJPn, depends on the ratio of molar concentrations of monomer and initiator, = M/Io, the degree of polymerization, Pn, and the ratio of rate constants of exchange and propagation, ß = keJkv. In a limiting case (ß > 1 and Pn » 1), Pw/Pn ~1 + 2 /(ß ). The molecular weight distributions are always narrower than those obtained for a batch process, where monomer concentration decreases during polymerization.

Chain Transfer in Degenerative RAFT Polymerization Revisited: A Comparative Study of Literature Methods

“…[30][31][32] Alternatively, values for C tr have also been determined based on approximate analytical correlations for the polymer dispersity ( Ð ) profi le. For example, under the stringent model assumptions that conventional radical initiation occurs instantaneously and termination is irrelevant, Muller et al [ 22,23 ] derived a set of analytical expressions for the average polymer properties as function of x. Based on the work of Muller et al, [ 22 , 23 ] Goto and Fukuda [ 25,33 ] proposed various methods to determine C tr .…”

“…[ 4,[23][24][25] However, as these analytical methods are typically based on expressions for the dispersity of the dormant polymers, they only hold for a well-controlled RAFT polymerization, in which the observed polymer dispersity can thus be approximated by one of the dormant polymer. Furthermore, as highlighted before, the derivation of these equations is based on several assumptions which limit the application scope (cf.…”

“…Table 1 ), including those from approximate analytical correlations for the polymer dispersity ( Ð ) profi le. [ 4,[23][24][25] In the present work, the different direct experimental methods to determine the RAFT exchange reactivities ( C tr,0 , C −tr,0 , and C tr ) are briefl y discussed, focusing on their model assumptions. Next, the accuracy of the most important methods which are based on an analytical expression is assessed for a wide range of representative conditions, focusing on their inherent limitations in the absence of experimental error.…”

RAFT Miniemulsion Polymerization Kinetics, 1 – Polymerization Rate

“…[1][2][3] The CLRP techniques includes stable-radicalmediated polymerization (SFRP), [4][5][6] which includes nitroxide-mediated polymerization (NMP), atom-transfer radical polymerization (ATRP), [7][8][9] reversible additionfragmentation chain transfer (RAFT) polymerization [10,11] and degenerative transfer (DT) polymerization. [12,13] In comparison with conventional types of free radical polymerization, the essential difference of CLRP resides in the reversible reaction, shown each for SFRP, ATRP, RAFT, and DT in Scheme 1. The CLRPs have also been applied to the dispersed systems.…”

The influence of intermediate radical termination and fragmentation on controlled polymer synthesis via RAFT polymerization

“…The number (M n ) and weight (M w ) average molecular weights can be estimated from the equation [27] for degenerative chain transfer:…”