Additionally, we observe that low MW PLGA 75:25 (Figure ) has a much higher T g,β value compared to that of the low MW 50:50 co-polymer. Previous work has shown that an increase in lactic acid monomer (i.e. relatively more methyl groups present) reduces polymer mobility due to the steric hindrance introduced by the methyl side groups. We observe this effect for low MW PLGA 75:25, for which the increased number of methyl side groups effectively restrict the rotations around the C-O bonds in the PLGA backbone which results in an increase in T g,β . For the α-relaxation, apart from overcoming potential energy barriers, sufficient free volume is required for large-scale motions to take place. The raised T g,α value of low MW PLGA 75:25 reflect the fact that the steric effects dominate, attributed to the high entanglement of the increased number of methyl groups and the copolymer backbone.