Formation Kinetics and Scaling of “Defect-Free” Hyperbranched Polystyrene Chains with Uniform Subchains Prepared from Seesaw-Type Macromonomers

Using a facile approach, we successfully made large “defect-free” hyperbranched polystyrene (PSt) chains with uniform subchains between two branching points from the interchain “clicking” of a seesaw-type linear macromonomer [azide∼∼∼alkyne∼∼∼azide] prepared by ATRP with a following conversion of two bromine-ends into two azide-ends, where ∼∼∼ denotes a PSt chain (1.65–31.0 kg/mol). The “click” reaction kinetics monitored by a combination of size exclusion chromatography (SEC) and laser light scattering (LLS) reveals that the degree of self-polycondensation (DP) is related to the reaction time (t) as ln(DP+ 1)/2 = ([A]0kAB,0)/β arctan(βt), where [A]0 and kAB,0 are the initial alkyne concentration and the initial reaction rate between the azide and alkyne groups, respectively; β is a constant and its reciprocal (1/β) represents the time at which kAB = kAB,0/2. The results reveal that 1/β is scaled to the macromonomer’s molar concentration ([C]) and molar mass (M) as 1/β ∼ [C]−0.35M0.55, indicating that 1/β is governed by the interchain distance and diffusion, respectively. Each hyperbranched sample can be further fractionated into a set of narrowly distributed “defect-free” hyperbranched chains with different molar masses by precipitation. The LLS results show, for the first time, that the root-mean-square radius of gyration (⟨Rg⟩) and hydrodynamic radius (⟨Rh⟩) of “defect-free” hyperbranched polystyrenes in toluene at 25 °C are scaled to the weight-average molar mass (Mw) as ⟨Rg⟩ = 5.53 × 10–2Mw0.464 and ⟨Rh⟩ = 2.95 × 10–2Mw0.489, respectively, where the exponents are smaller than the predicted 1/2.