Glass transition of stereoregular poly(methyl methacrylate) at interfaces

The glass transition temperature (T-g) of layers of stereoregular poly(methyl methacrylate) (PMMA) spin-cast on silicon and aluminum surfaces has been investigated by ellipsometry. The interfacial specific interactions were highlighted and quantified by infrared reflection absorption spectroscopy. It was found that depending on PMMA tacticity, a strong correlation exists between the density of the polymer/surface interactions and the T-g of that polymer at the interface. Indeed, i-PMMA with a large density of interfacial interactions increases its T-g at the interface whereas s-PMMA with a lower value of bonded segments exhibits a T-g depression. It is suggested that a certain level of interfacial interactions associated with an increase of density of the layer will compensate for the increase of mobility resulting from a reduction of the entanglement density or a segregation of chain ends at an interface.