Perfectly Linear α,ω‐Hydroxy‐Terminated Polyethylene with Near‐Ideal Crystallinity

Abstract

Abstract A novel 1,5‐(bis‐borinane)pentane (1,5‐BBP) has been developed for polyhomologation (C1 polymerization), enabling the synthesis of well‐defined α,ω‐hydroxy polymethylene (PM) with controlled molar masses and narrow polydispersity at elevated temperatures. The structural integrity and complete difunctionality of the PM were confirmed by 1 H NMR, 1 1 B NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS), and SEC analyses. Achieving perfectly linear polyethylene (PE), an analog to PM, without branching remains a longstanding synthetic challenge, as even trace defects disrupt lamellar packing and reduce crystallinity. We address this limitation through the introduction of a monomer purification strategy for dimethyl sulfoxonium methylide in C1 polymerization that, for the first time, reduces residual branching to <0.04%, as confirmed by quantitative 1 3 C NMR. The resulting nascent PM exhibits exceptional properties, including enthalpies of fusion up to 290 J·g −1 , melting temperatures of 138 °C–143.15 °C, and crystallinity values of 93.8%–99.1% (DSC) and 92.0%–95.9% (WAXS). Solid‐state 2D 1 H‐ 1 3 C cross‐polarization magic angle spinningwide‐line separation (CP–MAS WISE) NMR spectra further confirm predominantly crystalline domains with minimal amorphous content. This study demonstrates that precise control over initiator design, monomer purity, and reaction conditions enables α,ω‐hydroxy‐terminated PM with crystallinity approaching the theoretical limits.