Synthesis and Dilute Solution Properties of Well-Defined H-Shaped Polybutadienes

Abstract

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° and 90°) light scattering detector, and a Viscotek differential viscometer in tetrahydrofuran at 40 °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.

Detecting Structural Polydispersity in Branched Polybutadienes

“…Moreover, a previous study on the branching parameter g for our samples showed very good to fair agreement with literature values on H-shaped polystyrene. 2 However, the RI elution profiles for the same final products characterized by SEC-2, as shown in Figure 3, had double peaks except for HA12B40. The molecular weights at the two peaks are in a ratio of about 1:2, indicating the presence of 1 / 2 -H molecules, which are equivalent to asymmetric 3-arm stars, implying that most of the samples were actually mixtures of H molecules and asymmetric 3-arm stars ( 1 / 2 -H).…”

Analytical Rheology of Polymer Melts: State of the Art

“…The primary impediments are that (i) synthesizing well-defined and well-characterized BPs is highly nontrivial [7,[215][216][217][218][219][220][221], (ii) the process of testing and calibrating the rheological models exposes many weaknesses of the tube model that are not manifested for LPs [158,159], and (iii) there is no counterpart to the "double reptation" model because of the complexity of the computational models. Even so, the past few years have seen tremendous progress.…”

Chain Architecture as an Orthogonal Parameter To Influence Block Copolymer Morphology. Synthesis and Characterization of Hyperbranched Block Copolymers: HyperBlocks

“…Predominantly these studies have been aimed at understanding the impact of chain branching upon the melt rheology of such polymers. Commonly studied branched architectures include the simplest branched structure, star polymers [1][2][3][4][5] , and increasingly complex architectures such as miktoarm stars 6,7 , graft/comb polymers [8][9][10][11][12][13] , H-shaped polymers [14][15][16][17] and dendritically long-chain branched polymers [18][19][20][21][22][23][24][25][26][27][28] . Chain-branching in block copolymers has also been explored with a view to understand the influence of architecture upon phase separation.…”