Macromonomer Preparation by Radical Polymerization and Copolymerization of the Unsaturated Tetramer of Methyl Acrylate

Abstract

The unsaturated tetramer of methyl acrylate (CH2=CXCH2CHXCH2CHXCH2CH2X, where X = CO2Me: MATe) was homo- and copolymerized by radical means as a polymerizable acrylic ester bearing a bulky α-substituent. MATe homopolymerization in bulk yielded low molecular weight polymer consisting of the MATe units and 2-carbomethoxy-2-propenyl (CH2=C(CO2Me)CH2–) ω-end groups as a result of addition of propagation and simultaneous β-fragmentation of propagating radicals, expelling •CHXCH2CHXCH2CH2X which adds to MATe to initiate a new chain. The end groups, introduced almost quantitatively in bulk at 60 °C or above, were partly consumed by propagating radical addition. Copolymerizations of MATe with cyclohexyl acrylate (CHA) revealed that MATe is as reactive as CHA toward the poly(CHA) radical, and MATe is less reactive than CHA radical toward poly(MATe) radical by a factor of only 1.4. These results suggest that the poly(MATe) bearing the unsaturated end group can be a macromonomer copolymerizable with CHA to yield a highly branched structure because of the similarity in structure with the unsaturated end group of MATe. Comparison of MATe with unsaturated trimer and dimer of methyl acrylate indicated that the more significant steric hindrance of the α-substituent of MATe in homo- and copolymerization considerably facilitates introduction of the propenyl end group.