Interpretation of Reversible Addition−Fragmentation Chain-Transfer Polymerization Mechanism by MALDI-TOF-MS

Abstract

Several polystyrene polymers were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization of styrene, using two different RAFT agent-initiator systems, and then further characterized by NMR and SEC as well as MALDI-TOF-MS techniques. The data indicate that most of the polymer chains are terminated by the active groups (Ph-C(=S)-S-) derived from RAFT agents, and few of the polymer chains bear initiator fragments at one end. Most importantly, the structures arising from the intermediate RAFT radicals and their cross-termination adducts were detected. Also, the MALDI-TOF-MS analysis shows that the combination termination between two macromolecular radicals is minor, and the amount of dead chains is quite low. Thus, narrow molecular weight distribution is obtained. This analysis confirms the operation of the Rizzardo mechanism including the Monteiro intermediate radical termination model for the RAFT polymerization.

Living Radical Polymerization by the RAFT Process - A Second Update

“…Mass spectrometry has been used to provide evidence to support the occurrence of intermediate radical termination during RAFT polymerization of acrylates, [44] styrene (St), [45,46] and N-acryloylmorpholine (NAM) [47] with dithiobenzoate RAFT agents. A recent paper [48] purports to suggest a possible compromise between the 'slow fragmentation' and 'intermediate radical termination' models for retardation in RAFT polymerization with dithiobenzoate RAFT agents.…”

“…NIPAM [229] 68* [230] S S St [230] (Continued) [45] St [45] S S N N 70 [45,231] St [45,231] NIPAM [231,232] S S N ϩ N 71 [233] St [233] N S S 72 [234] St [234] MA [234] St-b-MA [234] 73 [235] S S tBA [235] tBA-b-338 [235] S S 74 [236] St [236] (Continued) [237] St [237] S CO 2 H S…”

“…The use of the corresponding trithiocarbonates 118-125 has also been promoted in this context. [27] Secondary aromatic dithioesters with R = -CHPh(CN) (42) and -CHPh(CO 2 R) (43)(44)(45)(46)(47)(48) and analogous trithiocarbonates 144, 145, and 146-148, respectively, have been shown to have utility in controlling 'R'-connected 79* [227] S S S S NIPAM [240] S S S S 80* [86,241,242] BMA [243] DMAEMA [240][241][242][243] AA [241] BA [243] St [241,243] DMAEMA-b-BMA [243] DMAEMA-b-BA [243] DMAEMA-b-St [243] St-b-HEMA/DMAEMA [86] 81 [244] CN S S…”

“…[46] A MALDI-TOF mass spectrometry study of PSt with dithiobenzoate RAFT agents 69 and 70 has claimed to provide evidence of intermediate radical termination. [45] The application of ESI mass spectrometry to PSt with labile chain ends is facilitated by use of silver(i) tetrafluoroborate salt. The method was applied in identifying products and mapping reaction pathways in forming PSt with 92, [254] PMA with 92, [252] and PAA and PNIPAM with 103, [269] and in forming star polymers from MA [268] and AcS [259] with 102.…”

Synthesis and characterization of high molecular weight and low dispersity polystyrene homopolymers by RAFT polymerization

“…However, high molecular weight PS (with Mw > 10 5 g/mol) has rarely been reported using RAFT polymerization, even though such high molecular weight polystyrene homopolymers have been synthesized by free-radical polymerizations [17][18][19]. For examples, PS with Mw ~ 10 4 g/mol was synthesized from the firstly reported RAFT reactions by Rizzardo et al [9], PS with Mw ~ 10 4 g/mol was synthesized using RAFT for assessing rate coefficients by Davis et al [17], and PS with Mw ~ 10 3 g/mol was synthesized using RAFT for studying the polymerization mechanism using MALDI-TOF-MS by Harruna et al [16].…”