Year: 2026
Type: preprint
Abstract: Rigid foams earn their place in structural applications through a specific balance of stiffness and density. Reproducing that balance without isocyanates has proven far harder than replacing the chemistry itself. Water-blown polyhydroxyurethane (PHU) foams are the most credible isocyanate-free alternatives to conventional polyurethanes, but toxic base catalysts and weak mechanical properties have stalled their adoption. Brønsted acid catalysis, long dismissed on the expectation that amine protonation suppresses urethane formation, proves effective instead: a dynamic equilibrium of transient protonation and thermal amine regeneration widens the rheological window for water-driven CO2 release while carrying the network to full conversion. Acidic conditions additionally activate vinyl ethers, converting the pendant and vicinal hydroxyls responsible for moisture plasticization into acetal crosslinks. The resulting poly(hydroxyurethane)–polyacetal (PHU–PAC) foams show a sixteenfold (16x) higher rubbery modulus, a fourfold higher compressive modulus (4 → 18 MPa), and halved water uptake relative to the PHU benchmark. Normalized peak heat release rate falls nearly eightfold below that of a commercial PU foam, and on an Ashby plot of specific strength versus stiffness, PHU–PAC approaches HDPE and PVC. Addressing catalyst tractability, moisture uptake, and mechanical performance in one formulation, acid-catalyzed PHU–PAC reframes non-isocyanate foams as tunable structural materials and positions catalyst design as a lever for the next generation of sustainable cellular materials.
Source: ChemRxiv
Language: English
Subfield: Polymers and Plastics
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Award: G3104770371
OpenAlex ID: W7213879233