Well-Defined Bilayered Molecular Cobrushes with Internal Polyethylene Blocks and ω‑Hydroxyl-Functionalized Polyethylene Homobrushes

Novel well-defined bilayered molecular cobrushes with internal polyethylene blocks, P­(PE_core-b-PS_corona) (PE: polyethylene; PS: polystyrene), and ω-hydroxyl-functionalized polyethylene homobrushes, P­(PE-OH), were synthesized through the macromonomer strategy. Two main steps were involved in the synthesis of the P­(PE_core-b-PS_corona) bilayered cobrushes: (i) formation of norbornyl-terminated macromonomer (Nor-PE-b-PS) by esterification of PS-b-PE-OH (combination of anionic polymerization, hydroboration, and polyhomologation) with 5-norbornene-2-carboxylic acid and (ii) ring-opening metathesis polymerization (ROMP) of Nor-PE-b-PS. The synthesis of P­(PE-OH) was achieved by (i) hydroboration of tert-butyl­dimethyl­silyl-protected allyl alcohol, followed by polyhomologation of dimethyl­sulfoxoniun methylide with the formed tri­[3-(tert-butyl­dimethyl­silyl­oxyl)­propyl]­borane initiator, oxidation/hydrolysis, and esterification of the TBDMS-O-PE-OH with 5-norbornene-2-carboxylic acid to afford the macromonomer TBDMS-O-PE-Nor, and (ii) ROMP of TBDMS-O-PE-Nor, followed by deprotection. Nuclear magnetic resonance spectroscopy (¹H and ¹³C NMR) and high temperature gel permeation chromatography (HT-GPC) were used to characterize all macromonomers/molecular brushes and differential scanning calorimetry (DSC) to study the thermal properties. The molecular brush P­(PE-b-PS) showed lower melting point (T_m) and better solubility in toluene than the corresponding macromonomer PS-b-PE-Nor. In the case of homobrushes, the thermal properties were strongly affected by the presence of the PE end-groups.