Compositional effects on mechanical properties and viscosity in UDMA-MMA blends

Photo-cured adhesives based on methyl methacrylate (MMA) are common, but MMA has a low molecular weight and low viscosity which is not ideal in some situations. The addition of high molecular weight of diurethane dimethacrylate (UDMA) is an attractive proposition as it increases viscosity and reduces photo-cure times. Photo-cured blends with 30, 40, 50, 60, and 70 wt.% UDMA in MMA plus camphorquinone (CQ) and ethanol were tested by nanoindentation, tensile testing, viscosity measurements, and vibrational spectroscopy. Changes in mechanical properties with composition ranged from hardness which showed a small increase with UDMA wt.%, to indentation modulus which was largely unchanged, to tensile modulus which showed a small decrease. The hardness increase is counter to the other mechanical changes and may be due to increased hydrogen bonding as seen in the vibrational spectra. Higher UDMA percentages gave a noticeable decrease in tensile strength, but an increase in the viscosity of the uncured liquid. The blends were all superior mechanically to UDMA on its own. Spectroscopy indicated a decreasing degree of conversion of double bonds as UDMA increases, which explains many of the property changes. The results show MMA-UDMA composition can be tuned for specific applications where viscosity and photo-curing time is important while still maintaining good mechanical properties. Compositions in the range 30–50 wt. % UDMA offer a balance of good mechanical properties, relatively short photo-cure times, and low viscosity which are needed to penetrate deep, narrow gaps.