화학공학소재연구정보센터
Macromolecules, Vol.41, No.21, 8225-8230, 2008
Synthesis and Dilute Solution Properties of Well-Defined H-Shaped Polybutadienes
A novel and advantageous approach to synthesis of H-shaped polybutadienes (H-PBd) is reported. The synthetic strategy employs classical anionic polymerization using high-vacuum techniques and utilizes a difunctional linking agent 4-(dichloromethylsilyl)diphenylethylene (DCMSDPE). The synthesis involves (a) growing a living PBd chain using s-BuLi as initiator in benzene at room temperature, (b) titration of DCMSDPE with living PBdLi, (c) addition of s-BuLi to activate the double bond of DPE, (d) subsequent addition of butadiene to generate a living "1/2 H", which has two arms and half of the final cross-bar, and (e) finally coupling the two "1/2 H" molecules with dichlorodimethylsilane to produce an H-PBd, which has two arms attached to each end of the cross-bar. The weight-average molecular weight, number-average molecular weight, molecular weight distribution, intrinsic viscosity, and radius of gyration were characterized by multidetector size exclusion chromatography (SEC) coupled with a refractive index detector, a two-angle (15 degrees and 90 degrees) light scattering detector, and a Viscotek differential viscometer in tetrahydrofuran at 40 degrees C. The H-PBds showed narrow and symmetrical molecular weight distributions (polydispersity indices, PDI = 1.03-1.06). Furthermore, the use of light scattering detectors showed that there were no detectable high molecular weight, more highly branched components present in these materials. This is an important advantage of this novel approach over previous synthetic routes to H-polymers. The values of the branching parameters g (0.58-0.77) and g' (0.60-0.75) in the thermodynamically good solvent, tetrahydrofuran, are consistent with values reported previously by Roovers and Toporowski for H polystyrenes in the good solvent toluene. Effects of architecture on the branching parameters are elucidated.