Influence of dibutyl phthalate on the mechanical, thermal, and relaxation behaviour of poly (methyl methacrylate) for denture-base soft liners

Abstract

Methyl methacrylate and six solutions of methyl methacrylate/dibutyl phthalate (nominally 5 to 30% v/v) were polymerized into thin sheets using gamma radiation. Dynamic mechanical spectra of the storage modulus, loss modulus and loss tangent, as well as changes in length, were investigated as a function of temperature. From these measurements, the depression of the storage modulus and glass-transition temperature were obtained. Subsequently, differential scanning calorimetry (DSC) and cross-polarization-magic-angle-spinning NMR were used to obtain additional glass-transition and relaxation-time measurements. Based upon these experiments, a specific form of the rule of mixtures described the depression of the glass-transition temperature. From storage-modulus measurements, antiplasticization was evidenced at very low temperatures and at compositions greater than 25% v/v. Solid-state NMR confirmed that plasticization causes an increase in polymer main-chain motion via the physical loosening of secondary bonds between polymer chains.