Self-Assembling Behavior of Butadienyllithium Headgroups in Benzene via SANS Measurements

Abstract

The self-assembling behavior of butadienyllithium (−CH2−CHCH−CH2−Li) headgroups in benzene has been studied via the use of small-angle neutron scattering (SANS). The carrier polystyrene chain molecular mass was 2.6K. Previous work has shown that the styryllithium headgroup can simultaneously form aggregated architectures encompassing tetramers and dimers along with a small number, ∼0.1%, of chains engaged in the formation of large scale mass fractal aggregates. That aggregation behavior contradicts the long entrenched belief that the sole self-assembled state of styryllithium headgroups is dimeric. This study shows that the butadienyllithium active centers exhibit more complicated aggregation tendencies than their styryllithium counterparts. For example, the butadienyllithium headgroup can form star-shaped structures with mean functionalities as large as 10 in addition to dimers. This structural versatility is in obvious conflict with the current propagation model that requires tetramers as the solitary aggregation state.

Dynamics of Monofunctional Polybutadienyl Lithium Chains Aggregated in Benzene

“…In addition, the strong increase of the LS intensity of the living chains in the low-q regime (q < 0:01 nm À1 ) demonstrates the existence of a small amount of large aggregates, as well known for living chains in nonpolar solvents. [8][9][10][16][17][18] These large aggregates should have existed in all living PB solutions examined.…”

“…These small aggregates coexist with a minor amount of large aggregates with f > 100, as revealed from light/neutron scattering experiments. [8][9][10][16][17][18] Recently, the neutron scattering and 1 H NMR studies were conducted during the polymerization process of PBLi in heptane to reveal an interesting decrease of f with increasing conversion (from f of the order of 100 to f ¼ $ 4 for the main component of the aggregates). This decrease was intimately related to the NMR-determined initiation/polymerization rates.…”

Bimodality of molecular mass distribution of polydienes obtained under the action of dilithium initiators in hydrocarbon media: the reasons, mathematical simulations, and their experimental testing

“…It would be rather useful to establish dependence of the association degree and the equilibrium constants of dissociation on the chain length for the very short chains experimentally, including polystyryl lithium. Thus for example, Unauthenticated Download Date | 5/12/18 11:12 AM Stellbrink et al [30] found out that the degree of the polybutadienyl lithium active sites association of the very short chains (MW about 2500) is much more than the tetramerous { up to decamerous one. Thus, the initial gel-fraction can be cross-linked to the much greater degree and more less swelled than in the case of tetramerous association.…”

Determination of the interaction parameter and topological scaling features of symmetric star polymers in dilute solution

“…This effect was first modeled using a double extrapolation to zero scattering angle and to zero concentration in the Zimm plot [1]. The modified Zimm approach of Stein and Hadziioannou [38], later justified by the random phase approximation (RPA) of de Gennes [39], could model scattering at all concentrations and angles [40][41][42]. This approach is limited to Gaussian, linear chains (d f = 2) since it utilizes Eq.…”