Examination of Models for Carbocationic Polymerization:  Influence of Chain Length on Carbocation Reactivities

Mayr, Herbert; Roth, M.; Faust, Rudolf

doi:10.1021/ma9602379

Cited by 25 publications

(20 citation statements)

References 28 publications

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“…In the case of EBP and EBiB the PMMA • is more stable due to the back strain effect, in which the release of steric strain from the dormant PMMA-Br species as it undergoes transformation from a sp 3 hybridized to sp 2 hybridized configuration through activation makes the formation of the radical more enthalpically valuable. 47,48 Taken altogether, this data concludes that in the case of acrylates, all three initiators result in narrow molecular weight distributions although clearly MBPA is less ideal due to much slower polymerization rates. On the contrary, in the case of methacrylates only MBPA can facilitate a well-controlled polymerization delivering polymers of low dispersity.…”

Section: Resultsmentioning

confidence: 72%

Cu(0)-RDRP of methacrylates in DMSO: importance of the initiator

et al. 2018

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The controlled radical polymerization of methacrylates\ud via\ud Cu(0)-mediated RDRP is challenging in comparison to acrylates with most reports illustrating higher dispersities, lower monomer conversions and poorer end group fidelity relative to the acrylic analogues. Herein, we present the successful synthesis of poly(methyl methacrylate) (PMMA) in DMSO by judicious selection of optimal reaction conditions. The effect of the initiator, ligand and temperature on the rate and control of the polymerization is investigated and discussed. Under carefully optimized conditions enhanced control over the molecular weight distributions is obtained furnishing methacrylic polymers with dispersities as low as 1.10, even at very high conversions. A range of methacrylates were found to be tolerant to the optimized polymerization conditions including hydrophobic, hydrophilic and functional methacrylates including methyl and benzyl methacrylate, ethylene glycol methyl ether methacrylate and glycidyl methacrylate. The control retained during the polymerization is further highlighted by in situ chain extensions yielding well-defined block polymethacrylates

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Section: Resultsmentioning

confidence: 72%

Cu(0)-RDRP of methacrylates in DMSO: importance of the initiator

et al. 2018

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“…Similar effects were previously reported on the solvolysis of alkyl halides and ionization of alkyl halides to sp 2 -hybridized carbocations. 31,32 The presence of a penultimate unit effect was reported earlier in propagation studies. At 60°C, the rate constant of addition of the H-MMA • radical (i.e., methyl isobutyryl radical) to MMA was 3.9 times higher than that of the H-MMA-MMA • dimeric radical and 17 times higher than a value of k p from PLP measurements.…”

mentioning

confidence: 57%

Effect of Penultimate Unit on the Activation Process in ATRP

2003

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Atom transfer radical polymerization (ATRP) is among the most successful processes for controlled radical polymerization. [1][2][3][4][5] The catalytic cycle in ATRP involves a transition metal complex reversible switching between two oxidation states as shown in Scheme 1. The activator is typically a copper(I) halide complex formed with a nitrogen-based ligand. [6][7][8][9][10][11][12][13][14][15] Homolytic cleavage of the alkyl-halogen bond (R-X) by the Cu I complex generates an alkyl radical R • and the corresponding X-Cu II complex. The radical R • can initiate and subsequently propagate with a propagation rate constant k p by adding across the double bond of a vinyl monomer. The radicals can either terminate by coupling or disproportionation (k t ) or be reversibly deactivated by the X-Cu II complex (k deact ). Since the equilibrium is strongly shifted toward the dormant species (k act , k deact ), radical concentration is low and termination is suppressed. As a result of the persistent radical effect, 16 polymers with predictable molecular weights, narrow molecular weight distributions, and high functionalities have been synthesized.The evaluation of all the reaction parameters such as k act , k dact , and k p (or k i ) are crucial for development of a deeper understanding of the process leading to better control over this catalytic system. Values of the rate constant of activation, k act , for polymeric and monomeric systems can be measured by suppressing the deactivation process in the presence of fast radical traps (T • in Scheme 1) such as 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO). [17][18][19][20][21][22][23][24] We recently reported that for both Cu(I)/bpy 23 and Cu(I)/PMDETA 24 catalysts reactivity of tert-butyl 2-bromopropionate (H-tBA-Br) is 3.4 times smaller than that of either ethyl or methyl 2-bromopropionate (H-MA-Br) and 45 times smaller than that of ethyl 2-bromoisobutyrate (H-EMA-Br, where H represents a hydrogen atom). These compounds could be considered as models of dormant species present in the ATRP homopolymerization of tert-butyl acrylate (tBA), methyl acrylate (MA), and methyl methacrylate (MMA). However, it was reported earlier that although H-MABr or H-tBA-Br is a good initiator for ATRP of MA and tBA, H-EMA-Br is a rather poor initiator for ATRP of MMA, plausibly due to the higher reactivity of the dormant polymeric species, ascribed to the B-strain effect. 25-27 Thus, it is of interest to compare activation rate constants for the "monomeric" and "dimeric" dormant species and expand these studies to mixed dimeric species which will model copolymerization systems. 2,28-30 Figure S-12 in the Supporting Information illustrates the structures of all studied monomeric, dimeric, and the related dormant polymeric species.The activation process was studied using the TEMPO trapping methodology and chromatography described earlier. [20][21][22][23][24] Pseudo-first-order conditions were used, with an excess of the CuBr/2bpy catalytic system, to simplify the kinetic analysis. 18,23,24 Tabl...

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“…Mayr et al reported on models for carbocationic polymerizations employing similar end group functionalized polyisobutylenes. [14] Accordingly, we have checked the synthesis of a block copolymer by cationic initiation with the bis(4-methoxyphenyl)methylium-head group functionalized PIBVE on silica. The use of carbenium head group functionalized polymers for block copolymer synthesis, which are obtained by a hydride transfer reaction, has not yet been reported in the literature.…”

Section: Resultsmentioning

confidence: 99%

Surface Mediated Hydride Transfer Reaction of a Diarylmethyl Head Group Functionalized Poly(isobutyl vinyl ether) with Triphenylmethylium

Spange¹,

Eismann

2001

Macromol. Chem. Phys.

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Poly(isobutyl vinyl ether) (PIBVE) with bis(4‐methoxyphenyl)methyl‐head‐group is transformed into a cationically active macro initiator by a hydride transfer reaction with silica surface coordinated triphenylmethylium as the hydride acceptor. The formation of the macrocation is investigated directly by UV/Vis spectroscopy on the surface of the silica particles and by GPC analysis of the surrounding solution. The hydride transfer reaction can be observed on the surface of the silica in a narrow temperature window between –5 and + 5°C. The use of the novel silica supported macrocation for a block copolymer synthesis with N‐vinylcarbazol (NVC) is demonstrated.

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Examination of Models for Carbocationic Polymerization: Influence of Chain Length on Carbocation Reactivities

Cited by 25 publications

References 28 publications

Cu(0)-RDRP of methacrylates in DMSO: importance of the initiator

Cu(0)-RDRP of methacrylates in DMSO: importance of the initiator

Effect of Penultimate Unit on the Activation Process in ATRP

Surface Mediated Hydride Transfer Reaction of a Diarylmethyl Head Group Functionalized Poly(isobutyl vinyl ether) with Triphenylmethylium

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