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

Chain transfer constants have been determined for an unsaturated methyl methacrylate trimer, CH2C(CO2Me)CH2[C(CO2CH3)(CH3)CH2]2H (MMA3), in polymerizations of methacrylate esters (ethyl, EMA; n-butyl, BMA; tert-butyl, tBMA; 2-ethylhexyl, 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.