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

Abstract

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.

Crystal Structures of Isotactic and Atactic Poly(1-pentamethylene alcohol)

“…The indexing is essentially the same as that for it-PPMA. However, the a - and b -axial lengths are longer than those of it-PPMA case, thus indicating a more expanded lattice for at-PPMA in agreement with earlier predictions from WAXD patterns of non-oriented specimens . The ratio a / b = 1.73 suggests a pseudo-hexagonal packing of the molecular chains.…”

“…While the T g of both at-PPMA and it-PPMA is similar, ∼50 °C, the melting temperature ( T m ) and X c changed significantly. For at-PPMA and it-PPMA, T m = 125 and 190 °C, respectively, while the X c increased from 0.2 to 0.4 . One interesting feature from the comparative work was the effect of tacticity on segmental packing.…”

“…9 Using ROMP of trialkylsilyl-protected 2-cyclopentenol, followed by hydrogenation and deprotection, we recently synthesized atactic and isotactic poly(1-pentamethylene alcohol) (PPMA), both with extremely high levels of regioregularity (head to tail addition >97%). 23 The chemical structures are shown in Scheme 1 comparatively with the structure of an ethylene-vinyl alcohol statistical copolymer.…”

“…As described in ref 23, in addition to describing the synthesis in detail, a comparative study of the melting behavior and higher-order structures of the highly stereoregular atactic and isotactic PPMA species was reported. 23 While the T g of both at-PPMA and it-PPMA is similar, ∼50 °C, the melting temperature (T m ) and X c changed significantly. For at-PPMA and it-PPMA, T m = 125 and 190 °C, respectively, while the X c increased from 0.2 to 0.4.…”

Regiospecific Poly(ethylene-co-vinyl alcohol) by ROMP of 3-Acetoxycyclooctene and Postpolymerization Modification for Barrier Material Applications

“…Tuba et al 28 studied ROMP of 3-hydroxycyclopentene without protecting groups; however, the resulting polymer had a low molar mass, and hydrogenation was not attempted on the ROMP-derived material. Very recently, Guillory et al 29 reported stereo-and regioregular EVOH made by ROMP of 3tert-butyldimethylsiloxycyclopentene and its enantiomerically pure derivatives. These polymers all displayed varying thermal properties due to their differing ethylene and vinyl alcohol concentrations, regio-and stereochemistry, and degrees of hydrogenation.…”