Chain Transfer Activity of ω-Unsaturated Methacrylic Oligomers in Polymerizations of Methacrylic Monomers

Abstract

Chain transfer constants have been determined for an unsaturated methyl methacrylate trimer, CH2dC(CO2Me)CH2[C(CO2CH3)(CH3)CH2]2H (MMA3), in polymerizations of methacrylate esters (ethyl, EMA; BMA; tBMA; EHMA) and for the analogous trimers of butyl methacrylate (BMA3) and methacrylic acid (MAA3), a hydroxyethyl methacrylate dimer (HEMA2), a hydroxyethyl methacrylate-methyl methacrylate-hydroxyethyl methacrylate trimer (HEMA-MMA-HEMA), and a HEMA macromonomer in methyl methacrylate (MMA) polymerization. These data have been assessed with reference to our previously reported data on chain transfer of MMA macromonomers in MMA polymerizations. The transfer constants (Ctr) for MMA3 in polymerizations of methyl, ethyl, n-butyl, tert-butyl, and 2-ethylhexyl methacrylate at 60 °C are similar (∼0.18). The Ctr of MAA3 (0.28 at 60 °C in 2-butanone solvent) in MMA polymerization is ca. 50% higher than that of MMA3 under similar conditions. Other trimers (BMA3, HEMA-MMA-HEMA) and a low molecular weight HEMA macromonomer (degree of polymerization ca. 7) have Ctr similar to that of MMA3. The transfer constants for the various trimers show no significant temperature dependence over the range 60-100 °C. The Ctr of the dimers (MMA2, HEMA2) in MMA polymerization are an order of magnitude lower than those of the corresponding trimers. The Ctr of HEMA2 (0.018 at 60 °C) in MMA polymerization is ca 50% higher than that of MMA2 (0.013 at 60 °C). The Ctr of both dimers increases with increasing temperature between 60 and 100 °C (Ctr HEMA2 0.031, MMA 0.018 at 60 °C). Issues relating to the synthesis and characterization of trimers (RMA3) by catalytic chain transfer are discussed. Methods for synthesis of di-end-functional trimers MAA-MMA-MAA, HEMA-MMA-HEMA based on selective hydrolysis and reesterification are described. These trimers may find use in telechelic synthesis.

Synthesis of optically active methacrylic oligomeric models and polymers bearing the side-chain azo-aromatic moiety and dependence of their chiroptical properties on the polymerization degree

“…Then, they have been hydrolyzed in the presence of an excess of KOH in absolute ethanol to give the corresponding methacrylic acid oligomers (MA acid oligomers) in high yield (Scheme 1). The MA acid dimer and trimer have been recently reported as obtained by selective alkaline hydrolysis in water of the related MMA oligomers after 16 h reaction [22]. By using ethanol as solvent, instead, we have been able to obtain the desired products in about 1 h, in quantitative yield.…”

Living Radical Polymerization by the RAFT Process

“…[22,23] We first reported the use of addition-fragmentation chain transfer agents to control polymerization in the mid 1980s. [7,32,33] The agents include macromonomers, [24][25][26] allyl sulfides, [27] allyl bromides, [28] allyl peroxides, [29] vinyl ethers, [30] and thionoesters. [31] We also reported that living characteristics (narrow polydispersities, block synthesis) could be achieved with the use of macromonomer RAFT agents in emulsion polymerization of methacrylate monomers in 1995 (the acronym RAFT was not used at that time).…”

“…[44] Analogous behaviour is observed for macromonomer RAFT agents. [25,26] For similar reasons, RAFT agent 6 (R = t-butyl) is poor with respect to RAFT agent 7 (R = t-octyl). [44] These differences in RAFT agent activity are attributed to steric factors.…”

Chain Transfer and Efficiency of End‐Group Introduction in Free Radical Polymerization of Methyl Methacrylate in the Presence of Poly(methyl methacrylate) Macromonomer

“…[15] The chain-transfer activity is also significantly influenced by the partitioning of the adduct radical, that is, whether it fragments to expel a new radical or to regenerate the same propagating species and the original AFCT agent (Scheme 1). [13,[15][16][17] The fragmentation mode whereby the bulkier radical is expelled tends to be favored, thereby explaining why the chaintransfer constant of the MMA dimer is smaller than for the MMA trimer and tetramer in methacrylate polymerization. [13,15] A low rate of exchange (that is, a low rate constant of addition to macromonomer) is essentially what makes a poly(methacrylate) macromonomer/methacrylate monomer system different from a reversible AFCT (RAFT) system [18] based on dithioesters in terms of its ability to induce a controlled/living polymerization.…”