The living anionic polymerization of isocyanates carried out using conventional initiators is associated with side reactions due to rapid initiation rates as well as back-biting by the growing chain, resulting in a lack of control on the molecular weight (MW) and molecular weight distribution (MWD) of the polymers. Successful control over the reaction was possible by using additives that could prevent back-biting. We find an initiator in sodium benzanilide (Na-BA), which has a slow initiation rate combined with additive function, so that use of an external additive is eliminated. The initiator has resulted in polymers with high yields and an unprecedented control over the MW and MWD. It is possible to introduce a number of functionalities at the termini of the polymer by using Na-BA derivatives as well as suitable terminating agents, leading to macromonomer, reactive and chiral polymers, and chiral macromonomer in approximately 100% yields. In the process, the finding has expanded the scope of polyisocyanates in diverse applications.

We report the synthesis and characterization by temperature gradient interaction chromatography (TGIC) and rheometry of a symmetric H-shaped polybutadiene (PBd) that we call “HA20B40”, and of a symmetric star-shaped synthetic precursor of HA20B40, and the use of these characterization data to test and validate advanced tube models (the hierarchical and, to a lesser extent, the BOB models) for long-chain branched polymers. Furthermore, by deliberately adding additional well-characterized linear and star-branched polymers into HA20B40, we mimic the effect of impurities in the sample to test the ability of the hierarchical model to account for the effect of similar such impurities, which are detected by TGIC. Our modeling predictions for HA20B40 and its blends with star and linear polymers show very good agreement with measured rheological data, indicating that the modeling validation is successful for the symmetric H-shaped polymers. We then test the hierarchical model further using literature data for symmetric H-PBds, for which the TGIC and experimental rheology data were published. We find that as long as the polymer composition is accurately determined, the hierarchical model can calculate the rheological behavior accurately. The theory can therefore be used to help to identify the composition or impurities, which are almost always present at low levels at least in such topologically complex samples.

Rod-coil-rod triblock copolymers of 2-vinylpyridine (2VP) and n-hexyl isocyanate (HIC) were synthesized by living anionic polymerization. The homopolymerization of 2VP was carried out at -78 °C in THF by using bidirectional initiators sodium naphthalenide (Na-Naph) and potassium naphthalenide (K-Naph). Block copolymerization with HIC was performed at -98 °C in the presence of sodium tetraphenylborate additive. While K-Naph yields copolymers of broad molecular weight distribution, Na-Naph was quite effective in facilitating a high degree of control over the copolymerization. The block copolymers containing higher rod volume fraction showed lamellar microphase separation in THF, a common solvent for both the rod and the coil blocks. The self-organization of the copolymer in solvents selective for one block was quite fascinating in that in CHCl 3 solid micelles of ∼20 nm were formed, whereas large hollow micelles of ∼200 nm were generated in CH 3 OH.

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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.