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The re-entrance sites, successive chain-folding number ⟨n⟩, and chain-folding fraction ⟨F⟩ of the chain-folding (CF) structure of ¹³C CH₃-labeled isotactic poly(1-butene) (iPB1) with an weight-averaged molecular weight (⟨M_w⟩ = 37 K g/mol) in solution- and melt-grown crystals as a function of crystallization temperature (T_c) were determined using solid-state (SS) NMR. The solution- and melt-grown crystals possessed adjacent re-entry structures between the right- and left-handed stems along the (100) and (010) planes, which were invariant as a function of T_c. The adjacent re-entry structures in the former exhibited long-range order (⟨n⟩ ≥ 8) compared with that in the latter (⟨n⟩ ≥ 1.7–2). These results indicated that the concentration and entanglement of polymers play significant roles in the CF process and structural formation during the initial stage of crystallization, whereas kinetics does not. Transmission …