Improvement in the Transience and Mechanical Performance of Flexible Poly(phthalaldehyde) Substrates

Cyclic poly(phthalaldehyde) (PPHA) is a metastable polymer that depolymerizes to ortho-phthalaldehyde (o-PHA) at ambient temperatures. Both high molecular weights and a long shelf-life can be achieved. After an external stimulus trigger has been activated to break polymer backbone bonds, PPHA undergoes rapid depolymerization from the solid state. Flexible PPHA substrates can be made by mixing the polymer with traditional non-volatile plasticizers, however the solubility of plasticizers in PPHA is sometimes poor, and any solid products left behind after depolymerization can hinder the transience of the mixture. Hansen solubility parameters for PPHA were obtained and used to predict the solubility of plasticizers in PPHA. The freezing point of the degraded remnants is proportional to the total mole fraction of additives present in any given PPHA formulation. The colligative properties of o-PHA were obtained and used to estimate the freezing point depression of the transient remnants for multi-component mixtures. A single additive approach to plasticizing PPHA is presented in this study using diethyl adipate (DEA). Mechanical properties of PPHA films containing DEA were characterized. Glass transition temperature (Tg) values between 99.5 °C and 12.5 °C can be achieved using THF solvent to cast the PPHA-DEA film. A Tg of 187 °C was extrapolated for pure PPHA with no residual solvent. The flexibility of the DEA loaded PPHA films greatly improved at high DEA loadings. DEA also improved the transient depolymerization performance of DEA loaded PPHA resulting in complete liquification after depolymerization.