“…This mechanism of RAFT polymerization (Scheme ) should not be confused with the “iniferter” mechanism first described by Otsu et al That process relies on reversible photodissociation of the C−S bond of a dithiocarbamate derivative to provide a mechanism for chain activation and deactivation (Scheme ). Although it was originally considered that reversible chain transfer might occur during these polymerizations, subsequent work has shown that the transfer coefficient of N , N -dialkyldithiocarbamates in polymerizations of methacrylates and styrenes are very low (≪1). ,,− The thermal dissociation of the dithiobenzoates ( 2 ) analogous to Scheme is not detectable under our reaction conditions as demonstrated by control experiments that showed no polymer is formed in the absence of added initiator. 8 …”
Section: Resultsmentioning
confidence: 78%
“…Although it was originally considered that reversible chain transfer might occur during these polymerizations, 3 subsequent work has shown that the transfer coefficient of N,N-dialkyldithiocarbamates in polymerizations of methacrylates and styrenes are very low (,1). 17,36,[68][69][70] The thermal dissociation of the dithiobenzoates (2) analogous to Scheme 8 is not detectable under our reaction conditions as demonstrated by control experiments that Factors a and b should be directly reflected in the magnitude of the transfer coefficient of 2. Factor c should not directly affect the transfer coefficient.…”
Section: A Plot Of Log[initial Rate Of Polymerization] Vs Log[aibn]mentioning
Radical polymerization with reversible addition−fragmentation chain transfer (RAFT
polymerization) can be used to synthesize a wide range of polymers of controlled architecture and narrow
molecular weight distribution. The polymerizations use addition−fragmentation chain transfer agents
(RAFT agents) that possess high transfer coefficients in free radical polymerization and confer living
character on the polymerization. This paper explores the effect of the substituents R of dithiobenzoate
RAFT agents [SC(Ph)S−R] on the outcome of polymerizations of styrene, methyl methacrylate (MMA)
and butyl (BA) or methyl acrylate (MA). In MMA polymerization at 60 °C, effectiveness depends strongly
on R decreasing in the order where R is: −C(Alkyl)2CN ∼ −C(Me)2Ar > −C(Me)2C(O)O(alkyl) >
−C(Me)2C(O)NH(alkyl) > −C(Me)2CH2C(Me)3 ≥ −C(Me)HPh > −C(Me)3 ∼ −CH2Ph. Of these, only
the compounds with R = −C(Me)2Ph and −C(Me)2CN provided polymers with substantially narrowed
polydispersities in batch polymerization and gave molecular weight control of the form expected for a
living polymerization. These compounds have high transfer coefficients in MMA polymerization (transfer
coefficient >20 for 0.003 M RAFT agent in bulk MMA). Reagents with R = −C(Me)2C(O)O(alkyl),
C(Me)2C(O)NH(alkyl), −C(Me)2CH2C(Me)3, −C(Me)HPh, −C(Me)3, and −CH2Ph appear relatively
ineffective in MMA polymerization because they have much lower transfer coefficients (ca. 1.7, 0.7, 0.4,
0.15, 0.03, and 0.03 respectively). In polymerizations of styrene or acrylates at 60 °C, transfer coefficients
of RAFT agents are several orders of magnitude higher and all compounds in the above series yield narrow
polydispersity polymers. The transfer coefficients of benzyl dithiobenzoate in styrene and methyl acrylate
polymerization at 60 °C are ca. 50 (0.0093 M RAFT agent in bulk monomer) and 105 (with 0.003−0.006
M RAFT agent in 4.43 M monomer), respectively. The rate constant for addition to the thiocarbonyl
group does not depend strongly on R. Differences in activity depend on the properties of R and the
propagating chain as free radical leaving groups and on the partitioning of R• between adding to monomer
(to reinitiate) and adding to polymeric RAFT agent. When the reaction of R• with the polymeric RAFT
agent to reform the initial RAFT agent is significant, the transfer coefficient may reduce with concentration
of RAFT agent and with conversion. In these circumstances, the activity of RAFT agents is best
characterized by two transfer constants associated with the forward and reverse reactions. Steric factors,
polar factors, and the stability of R• all appear to play an important role in determining the transfer
coefficient and the effectiveness of RAFT agents.
“…This mechanism of RAFT polymerization (Scheme ) should not be confused with the “iniferter” mechanism first described by Otsu et al That process relies on reversible photodissociation of the C−S bond of a dithiocarbamate derivative to provide a mechanism for chain activation and deactivation (Scheme ). Although it was originally considered that reversible chain transfer might occur during these polymerizations, subsequent work has shown that the transfer coefficient of N , N -dialkyldithiocarbamates in polymerizations of methacrylates and styrenes are very low (≪1). ,,− The thermal dissociation of the dithiobenzoates ( 2 ) analogous to Scheme is not detectable under our reaction conditions as demonstrated by control experiments that showed no polymer is formed in the absence of added initiator. 8 …”
Section: Resultsmentioning
confidence: 78%
“…Although it was originally considered that reversible chain transfer might occur during these polymerizations, 3 subsequent work has shown that the transfer coefficient of N,N-dialkyldithiocarbamates in polymerizations of methacrylates and styrenes are very low (,1). 17,36,[68][69][70] The thermal dissociation of the dithiobenzoates (2) analogous to Scheme 8 is not detectable under our reaction conditions as demonstrated by control experiments that Factors a and b should be directly reflected in the magnitude of the transfer coefficient of 2. Factor c should not directly affect the transfer coefficient.…”
Section: A Plot Of Log[initial Rate Of Polymerization] Vs Log[aibn]mentioning
Radical polymerization with reversible addition−fragmentation chain transfer (RAFT
polymerization) can be used to synthesize a wide range of polymers of controlled architecture and narrow
molecular weight distribution. The polymerizations use addition−fragmentation chain transfer agents
(RAFT agents) that possess high transfer coefficients in free radical polymerization and confer living
character on the polymerization. This paper explores the effect of the substituents R of dithiobenzoate
RAFT agents [SC(Ph)S−R] on the outcome of polymerizations of styrene, methyl methacrylate (MMA)
and butyl (BA) or methyl acrylate (MA). In MMA polymerization at 60 °C, effectiveness depends strongly
on R decreasing in the order where R is: −C(Alkyl)2CN ∼ −C(Me)2Ar > −C(Me)2C(O)O(alkyl) >
−C(Me)2C(O)NH(alkyl) > −C(Me)2CH2C(Me)3 ≥ −C(Me)HPh > −C(Me)3 ∼ −CH2Ph. Of these, only
the compounds with R = −C(Me)2Ph and −C(Me)2CN provided polymers with substantially narrowed
polydispersities in batch polymerization and gave molecular weight control of the form expected for a
living polymerization. These compounds have high transfer coefficients in MMA polymerization (transfer
coefficient >20 for 0.003 M RAFT agent in bulk MMA). Reagents with R = −C(Me)2C(O)O(alkyl),
C(Me)2C(O)NH(alkyl), −C(Me)2CH2C(Me)3, −C(Me)HPh, −C(Me)3, and −CH2Ph appear relatively
ineffective in MMA polymerization because they have much lower transfer coefficients (ca. 1.7, 0.7, 0.4,
0.15, 0.03, and 0.03 respectively). In polymerizations of styrene or acrylates at 60 °C, transfer coefficients
of RAFT agents are several orders of magnitude higher and all compounds in the above series yield narrow
polydispersity polymers. The transfer coefficients of benzyl dithiobenzoate in styrene and methyl acrylate
polymerization at 60 °C are ca. 50 (0.0093 M RAFT agent in bulk monomer) and 105 (with 0.003−0.006
M RAFT agent in 4.43 M monomer), respectively. The rate constant for addition to the thiocarbonyl
group does not depend strongly on R. Differences in activity depend on the properties of R and the
propagating chain as free radical leaving groups and on the partitioning of R• between adding to monomer
(to reinitiate) and adding to polymeric RAFT agent. When the reaction of R• with the polymeric RAFT
agent to reform the initial RAFT agent is significant, the transfer coefficient may reduce with concentration
of RAFT agent and with conversion. In these circumstances, the activity of RAFT agents is best
characterized by two transfer constants associated with the forward and reverse reactions. Steric factors,
polar factors, and the stability of R• all appear to play an important role in determining the transfer
coefficient and the effectiveness of RAFT agents.
“…The significant reduction in the overall molecular weight, the number‐average molecular weight was reduced from 1,470,000 to 139,000 g/mol, was consistent with the elimination of autoacceleration. In addition to the circumvention of autoacceleration, this polymerization mechanism was chosen for its ease of use in bulk polymerizations, as no solvent was required, its negligible addition of impurities such as heavy metals, and previously demonstrated use in polymerizations of 2‐hydroxyehtyl methacrylate and MMA 28–31…”
Oxide methanesulfonates of Mo, U, Re, and V have been prepared by reaction of MoO(3), UO(2)(CH(3)COO)(2)·2H(2)O, Re(2)O(7)(H(2)O)(2), and V(2)O(5) with CH(3)SO(3)H or mixtures thereof with its anhydride. These compounds are the first examples of solvent-free oxide methanesulfonates of these elements. MoO(2)(CH(3)SO(3))(2) (Pbca, a=1487.05(4), b=752.55(2), c=1549.61(5) pm, V=1.73414(9) nm(3), Z=8) contains [MoO(2)] moieties connected by [CH(3)SO(3)] ions to form layers parallel to (100). UO(2)(CH(3)SO(3))(2) (P2(1)/c, a=1320.4(1), b=1014.41(6), c=1533.7(1) pm, β=112.80(1)°, V=1.8937(3) nm(3), Z=8) consists of linear UO(2)(2+) ions coordinated by five [CH(3)SO(3)] ions, forming a layer structure. VO(CH(3)SO(3))(2) (P2(1)/c, a=1136.5(1), b=869.87(7), c=915.5(1) pm, β=113.66(1)°, V=0.8290(2) nm(3), Z=4) contains [VO] units connected by methanesulfonate anions to form corrugated layers parallel to (100). In ReO(3)(CH(3)SO(3)) (P1, a=574.0(1), b=1279.6(3), c=1641.9(3) pm, α=102.08(2), β=96.11(2), γ=99.04(2)°, V=1.1523(4) nm(3), Z=8) a chain structure exhibiting infinite O-[ReO(2)]-O-[ReO(2)]-O chains is formed. Each [ReO(2)]-O-[ReO(2)] unit is coordinated by two bidentate [CH(3)SO(3)] ions. V(2)O(3)(CH(3)SO(3))(4) (I2/a, a=1645.2(3), b=583.1(1), c=1670.2(3) pm, β=102.58(3), V=1.5637(5) pm(3), Z=4) adopts a chain structure, too, but contains discrete [VO]-O-[VO] moieties, each coordinated by two bidentate [CH(3)SO(3)] ligands. Additional methanesulfonate ions connect the [V(2)O(3)] groups along [001]. Thermal decomposition of the compounds was monitored under N(2) and O(2) atmosphere by thermogravimetric/differential thermal analysis and XRD measurements. Under N(2) the decomposition proceeds with reduction of the metal leading to the oxides MoO(2), U(3)O(7), V(4)O(7), and VO(2); for MoO(2)(CH(3)SO(3))(2), a small amount of MoS(2) is formed. If the thermal decomposition is carried out in a atmosphere of O(2) the oxides MoO(3) and V(2)O(5) are formed.
“…The polymerisation of St in the presence of these reagents has all the main features of `pseudo-living' polymerisation. 173,174 An EPR study of the photo decomposition of S-benzyl N,Ndiethyldithiocabamate and PS containing a terminal dithiocarbamate group induced by UV radiation (l = 365 nm, 25 8C) has shown 120,211 that decomposition follows the same mechanism with rupture of the C7S bond to give reactive benzyl (or polystyrene) and stable N,N-diethyldithiyl radicals.…”
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