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

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Synthesis

Background:

• Synthesizing perfectly linear polyethylene (PE) and its analogs, like polymethylene (PM), is challenging due to branching defects.
• These defects hinder lamellar packing, reduce crystallinity, and limit material properties.
• Existing C1 polymerization methods struggle to achieve high linearity and controlled polymer architectures.

Purpose of the Study:

• To develop a novel initiator for polyhomologation (C1 polymerization) to synthesize well-defined α,ω-hydroxy polymethylene (PM).
• To achieve unprecedented control over molar mass, polydispersity, and linearity in PM.
• To investigate the properties of PM synthesized with minimized branching.

Main Methods:

• Development and application of a novel 1,5-(bis-borinane)pentane (1,5-BBP) initiator for C1 polymerization.
• Implementation of a monomer purification strategy for dimethyl sulfoxonium methylide to reduce branching.
• Characterization using ¹H NMR, ¹¹B NMR, MALDI-TOF MS, SEC, quantitative ¹³C NMR, DSC, WAXS, and solid-state 2D NMR.

Main Results:

• Successfully synthesized α,ω-hydroxy-terminated PM with controlled molar masses and narrow polydispersity at elevated temperatures.
• Achieved residual branching below 0.04% in PM, confirmed by quantitative ¹³C NMR, a significant improvement over previous methods.
• The resulting PM exhibited exceptionally high crystallinity (up to 99.1%), melting temperatures (up to 143.15 °C), and enthalpies of fusion (up to 290 J·g^-1).

Conclusions:

• The novel 1,5-BBP initiator and monomer purification strategy enable the synthesis of highly linear PM via C1 polymerization.
• Precise control over initiator design, monomer purity, and reaction conditions is key to achieving theoretical limits in polymer crystallinity.
• This work provides a pathway to advanced polymeric materials with superior thermal and mechanical properties due to enhanced crystallinity.