Sustainable polyacetals from erythritol and bioaromatics

Abstract

The polymerization of biorenewable molecules to polymers with hydrolyzable main‐chain functionality is one approach to identifying sustainable replacements for common, environmentally unsound packaging plastics. Bioaromatic polyacetals were synthesized via acid‐catalyzed acetal formation from dialdehydes and tetraols. Ethylene linked dialdehyde monomers VV and SS were constructed from bioaromatics vanillin and syringaldehyde, respectively. Tetraol monomers included biogenic erythritol (E), along with pentaerythritol (P), and ditrimethylolpropane (D). Four copolymer series were prepared with varying tetraol content: E/P‐VV; E/D‐VV; E/P‐SS; and E/D‐SS. Number average molecular weights (Mn) ranged from 1,400 to 27,100 Da. Generally, the copolymerization yields were inversely proportional to the feed fraction of erythritol (E), implying that tetraols P and D react more readily. The materials were typically amorphous and exhibited glass transition temperatures (Tg) ranging from 57 to 159 °C, suitably mimicking the Tg values of several commodity plastics. The syringaldehyde‐based copolymers exhibited a higher Tg range (71–159 °C) than the vanillin‐based copolymers (57–110 °C). Accelerated degradation studies in aqueous HCl (3 M, 6 M, concentrated) over 24 h showed that degradation (Mn decrease) was proportional to the acid concentration. A one‐year degradation study of E50/D50‐SS (from 50% feed of erythritol) in seawater, deionized water, tap water, or pH 5 buffer showed no Mn decrease; but in pH 1 buffer, the decrease was 40% (18,800 to 11,200). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44089.

Synthesis and material properties of elastomeric high molecular weight polycycloacetals derived from diglycerol and meso‐erythritol

“…Incorporation of the latter tetraols into the polymer backbone was expected to impart less flexibility than diglycerol, which could provide control over the tensile properties of the resulting polyacetals. Meso ‐erythritol was of particular interest because, like diglycerol, it is biocompatible and biorenewable,9a but has been used only sparingly to date to prepare polyesters or polyacetals 9a…”

“…On the other hand, use of 1,3‐, and 1,4‐cyclohexanedione led to brittle materials, and terephthalaldehyde generated a relatively flexible solid but with weaker properties when compared to the glutaraldehyde‐based polyacetal. Lastly, the biorenewable divanillin monomer developed by Miller and coworkers provided a hard, but brittle polyacetal. All of these materials displayed relatively low glass transition temperatures ( T g ) and no discernible melting points, with the exception of the polyketal derived from 1,4‐cyclohexanedione and diglycerol, which exhibited a well‐defined T m of 207 °C.…”

“…We attribute this drop in molecular weight to a reduction in polymer solubility in the reaction medium, likely stemming from the increased rigidity of meso ‐erythritol compared to diglycerol. In fact, Miller and coworkers demonstrated that meso ‐erythritol has a propensity to be incorporated as a rigid 1,3;2,4‐bisacetal (Figure ), 9a which would support our hypothesis. In contrast, the diglycerol isomers presumably form a bisacetal separated by a flexible ether linkage.…”

“…While the molecular weight values were comparable, the polyacetal prepared with 25% pentaerythritol displayed increased tensile strength of 2.0 MPa compared to 0.5 MPa for the same level of meso ‐erythritol (Table , entry 2 vs entry 6). We suspect that this increase in strength stems from increased chain rigidity due to the bicyclic acetal spirocarbon center formed as pentaerythritol is incorporated in the polymer backbone . Given this improvement in strength, we are actively working to develop reaction conditions that permit higher incorporations of pentaerythritol.…”

“…For example, Miller and coworkers prepared biorenewable polyalkylene acetals via acetal metathesis polymerization of α,ω‐diols . This research team also synthesized a variety of polycycloacetals incorporating bioaromatic backbone structures through polycondensation of tetraols and aromatic dialdehydes, with number averaged molecular weights ( M n ) reaching 27,100 g/mol . Isosorbide is another intriguing monomer for synthesis of polyacetals, and the resulting polymers displayed degradation rates that correlated with the length of the aliphatic spacer between acetal linkages .…”