Effect of poly (acrylic acid)architecture on setting and mechanical properties of glass ionomer cements

Objective. This work focuses on the influence of poly(acrylic acid)(PAA)architecture (linearor branched)on setting behavior and compressive strength of glass ionomer cements (GICs).Methods. Branched and linear poly(acrylic acid)s were synthesized according to the Strath-clyde methodology or by free radical polymerization. They were characterized by1H-NMRspectroscopy and size exclusion chromatography to determine their molecular weightand size distribution. GIC setting was characterized by oscillating rheometry and time-dependent FTIR spectroscopy. In addition, compressive strength was tested on cylindricalsamples (6 × 4 mm; n = 8/cement composition)after storage in deionized water at 37?C forone day.Results. We used two different routes to prepare PAA. One direct route in order to providestraightforward access to branched PAA and a two-step approach in order to get more controlabout the PAA molecular weight using tert-butyl acrylate (tBA)for polymerization with sub-sequent deprotection. Using the second approach we obtained several linear PAA of which amixture was used in order to mimic the molecular weight and size distribution of branchedPAA. This allowed the direct comparison of properties relying only on the polymer architec-ture. Comparing linear PAA to branched samples in general led to faster setting but at thesame time decreased the compressive strength. Increasing molecular weight of branchedPAA resulted in even faster GIC setting while increasing compressive strength and this cor-relates well with the trends reported for linear PAA in literature. Mixing of branched andlinear PAA, however, turned out to be an effective way of tailoring GIC properties. Signifi-cance: our results suggest that both molecular weight and dispersity need to be consideredwhen choosing suitable PAA architecture for obtaining specific GIC properties.