Rheological behavior of amine-functionalized liquid polybutadiene

Varying quantities of hydrogen-bonding stickers (amines) are introduced to liquid polybutadiene through the hydroaminoalkylation method. Amination significantly affects both the glassy and rubbery dynamics of these materials. The amination process results in a delay of the transition from the glassy to rubbery state, attributed to the lower mobility of hydrogen-bonding sites compared to the backbone segments. As the density of stickers increases, a liquid to solid transition is observed, and the emergence of a plateau rubbery modulus due to hydrogen bonding between amine functional groups. Rheological analysis reveals a failure in time-temperature superposition near the gel point. This failure is due to the decrease in the intensity of the elastically effective network strands with rising temperature from the weakening of the strength of hydrogen bonds. Moreover, the terminal relaxation timescale lengthens considerably as the degree of gelation increases, indicating the impact of many cooperative intermolecular associations. Compared to high molecular weight polybutadiene, the functionalized low molecular weight polybutadienes possess similar plateau modulus, highlighting the effectiveness of post-polymerization modifications in enhancing the mechanical properties of the amine-functionalized low molecular weight polybutadiene.