Reactivities of ω‐Unsaturated Methacrylate Oligomers toward tert‐Butoxy Radicals: Investigation of the Effect of Degree of Polymerization and Ester Alkyl Group

Abstract

The reactivities of ω‐unsaturated methacrylate oligomers (RMA‐n; n = 2–5) toward tert‐butoxy radicals (t‐BuO·) as a model of the addition step in addition‐fragmentation chain transfer (AFCT) have been investigated by the nitroxide trapping technique in combination with HPLC and electrospray ionization mass spectrometry. The ratio of the rate coefficients for the addition of ω‐unsaturated methyl methacrylate oligomers (MMA‐n) to t‐BuO· to the β‐fragmentation of t‐BuO· (kadd/kβ), where kβ can be treated as a constant, has been shown to decrease with increasing n due to increased steric hindrance of the α‐substituents. However, the value of kadd/kβ reaches a constant value at n = 3–4, and the greatest extent of suppression of the addition rate compared with MMA is less than a factor of four. Comparison of the values of kadd/kβ for ω‐unsaturated cyclohexyl methacrylate oligomers (CHMA‐n; n = 2 and 3) with MMA‐n revealed that the extent of suppression increased with increasing n without regard to the ester alkyl group. Hydrogen abstraction by t‐BuO· from RMA‐n appears to occur mainly at the ester alkyl groups, and the extent is much greater from CHMA‐n than from MMA‐n.

One-Step Synthesis of Thermally Curable Hyperbranched Polymers by Addition–Fragmentation Chain Transfer Using Divinyl Monomers

“…In all feed ratios, the consumption ratio of the pendant methacryloyl group was higher than that of the 2-carbomethoxy-2-propenyl group and tended to increase with increasing EGDMA conversion, whereas the consumption ratio of the 2-carbomethoxy-2-propenyl group was almost constant below 15%. The rate coefficient for the addition of radicals to the pendant methacryloyl group is expected to be slightly larger than that to the 2-carbomethoxy-2-propenyl group . It was also reported that the 2-carboalkoxy-2-propenyl groups bonded to methacrylate oligomers undergo AFCT to generate an another 2-carboalkoxy-2-propenyl group (forward β-fragmentation) or regenerate an original 2-carboalkoxy-2-propenyl group (backward β-fragmentation), in the polymerization of methacrylates. , This apparently results in low consumption ratio of the 2-carboalkoxy-2-propenyl groups.…”

“…The rate coefficient for the addition of radicals to the pendant methacryloyl group is expected to be slightly larger than that to the 2-carbomethoxy-2-propenyl group. 37 It was also reported that the 2-carboalkoxy-2-propenyl groups bonded to methacrylate oligomers undergo AFCT to generate an another 2carboalkoxy-2-propenyl group (forward β-fragmentation) or regenerate an original 2-carboalkoxy-2-propenyl group (backward β-fragmentation), in the polymerization of methacrylates. 21,23 This apparently results in low consumption ratio of the 2-carboalkoxy-2-propenyl groups.…”

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

“…There are no direct data on k add for the reaction of propagating radicals with RMA n. However, we anticipate that the values of k add for dimers (RMA 2 ) should be similar or greater than that of trimers (RMA 3 ) and macromonomers (RMA n ) ( k add ∼40% k p see above). The values of k add for tert -butoxy radicals adding MMA 2 and CMA 2 are reported to be approximately 2-fold higher than those for adding MMA 3 and CMA 3 respectively ,,, The increase in transfer constant of RMA 2 with increasing temperature is attributed to the partitioning of the adduct becoming less selective.…”

Macromonomer synthesis using α‐(2‐methyl‐2‐phenylpropyl)acrylates as addition–fragmentation chain‐transfer agents expelling the cumyl radical

“…In order to avoid the formation of a mixture of structural isomers of crossdimers, as in crossdimerization with a cobalt catalyst,21 methyl α‐(2‐mehyl‐2‐phenypropyl)acrylate (MS‐2) and cyclohexyl α‐(2‐mehyl‐2‐phenypropyl)acrylate (CHS‐2) were synthesized by the reaction of 2,3‐dimethyl‐2,3‐diphenylbutane25 with MMA‐2 and cyclohexyl α‐(2‐methyl‐2‐carbocyclohexylpropyl)acrylate,26 respectively, for 6 h at 250 °C. α‐(2‐Methyl‐2‐carbomethoxypropyl)styrene (SM‐2), a structural isomer of MS‐2, was prepared by the reaction of dimethyl 2,2′‐azobisisobutyrate with the dimer of AMS for 3.5 h at 90 °C.…”