Polar, functionalized diene-based material. III. Free-radical polymerization of 2-[(N, N-dialkylamino)methyl]-1,3-butadienes

The bulk free-radical polymerization of 2-[(N, N-dialkylamino)methyl]-1,3-butadiene with methyl, ethyl, and n-propyl substituents was studied. The monomers were synthesized via substitution reactions of 2-bromomethyl-1,3-butadiene with the corresponding dialkylamines. For each monomer the effects of the polymerization initiator, initiator concentration, and reaction temperature on the final polymer structure, molecular weight, and glass-transition temperature (Tg) were examined. Using 2,2′-azobisisobutyronitrile as the initiator at 75 °C, the resulting polymers displayed a majority of 1,4 microstructures. As the temperature was increased to 100 and 125 °C using t-butylperacetate and t-butylhydroperoxide, the percentage of the 3,4 microstructure increased. Differential scanning calorimetry indicated that all of the Tg, values were lower than room temperature. The Tg values were higher when the majority of the polymer structure was 1,4 and decreased as the percentage of the 3,4 microstructure increased. The Diels-Alder side products found in the polymer samples were characterized using NMR and gas chromatography-mass spectrometry methods. The polymerization temperature and initiator concentration were identified as the key factors that influenced the Diels-Alder dimer yield.