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Light Scattering Study of Internal Dynamics of Hyperbranched Polymers with Controlled Branching Patterns and Low Polydispersities in Dilute Solutions

Hao, Nairong, Zhu, Mo, Li, Lianwei
Macromolecules 2019 v.52 no.10 pp. 3794-3804
fractal dimensions, light scattering, polystyrenes
Internal dynamics of flexible polymer chains is one of the most important fundamental problems in polymer physics. Although numerous efforts have been devoted to the understanding of internal dynamics for linear polymers, little attention was paid to branched systems. This work aims to elucidate how the branching effect quantitatively influences the internal motions of long-subchain hyperbranched polymers in dilute solution. By light scattering study of four hyperbranched polystyrene samples with controlled branching patterns and low polydispersities (Mw/Mₙ < 1.40 and Mw ∼ 10⁷ g/mol), we quantified and analyzed the asymptotic behavior of the reduced first cumulant [Γ* = Γ(q)/(q³kBT/η₀)], the value of Γ* at high q-regime [the approximate values of Γ*(∞)], the scattering vector (q) dependence of linewidth [Γ(q)], the number of relaxation modes in Γ(q)-distribution curves, the characteristic relaxation time (τ₁) of the first internal mode, and the q-dependent relative strength of internal motions. Our results reveal: (i) Γ*(∞) is not sensitive to the branching density, but more related to the fractal dimension of a given system; (ii) the asymptotic power law in the intermediate qRₕ regime (1.5 < qRₕ < 3.0), compared to Γ*(∞), is a better indicator, which could reflect the structural details of different branched systems; (iii) the branching effect could lead to the suppression of overall internal motions, but the introduction of moderate branching could enhance the contribution of some energetically favorable internal modes in linewidth distribution; (iv) by comparing the experimentally determined and theoretically calculated τ₁, the result provides direct experimental evidence supporting that the classical theory is not applicable to hyperbranched polymer systems. The present work not only helps clarify some long-standing controversial issues existed in previous studies, but also provides useful experimental data for further theoretical calculations of internal dynamics for branched systems.