Precise Isotactic or Atactic Pendant Alcohols on a Polyethylene Backbone at Every Fifth Carbon: Synthesis, Crystallization, and Thermal Properties

A semi-crystalline precision polymer with a high molar mass (>100 kg mol^–1), a moderate dispersity (∼1.6), and an isotactic alcohol pendant on each and every fifth carbon of a linear polyethylene backbone is synthesized through highly regioregular ring-opening metathesis polymerization of (S) or (R)-3-(tert-butyldimethylsiloxy)­cyclopentene followed by olefin hydrogenation and alcohol deprotection. The thermal and semi-crystalline properties of these materials are compared to analogues with atactic alcohol pendants and varying degrees of head-to-tail (HT) regioregularity. For atactic polymers with HT from 77 to 99%, the change in glass transition temperature (T_g) is minimally affected (47 ± 2 °C), but the crystalline melting temperature (T_m) increases substantially from 96 to 137 °C. When highly isotactic alcohol pendant groups are present (90% enantiopure monomer and HT = 96%), the T_g increases slightly to ∼53 °C, but the T_m increases dramatically to 190 °C. Although the wide-angle X-ray diffraction patterns of atactic and isotactic materials are similar and infer equivalent crystal unit cell packing, the isotactic sample develops ∼40% crystallinity, which is double that observed for an atactic sample (20%) with high HT = 99%. The thermal stability of all samples was >360 °C. Such investigations present unexplored insights on how isotactic and precision microstructure affect material properties of polymeric systems outside the two-carbon branch periodicity of isotactic polymers from vinyl monomers. Synthesis, structural characterizations, thermal properties in addition to intermolecular hydrogen bonding, and other crystalline structural data are discussed comparatively based on tacticity.