Alternating chain sequence weakening of interfacial molecular interactions enhances the Tg confinement effect of polymers

Confinement alters polymer dynamics and results in a marked T-g confinement effect, i.e., a reduction in the glass-transition temperature (T-g) of a polymer under confinement. The T-g confinement effect is related to dynamic enhancement at the air interface caused by reductions in intermolecular cohesion forces at the interface. Thus, tuning molecular interactions at the interface allows modification of the T-g confinement effects of polymers. In this work, using interfacial-sensitive sumfrequency generation (SFG) spectroscopy, we demonstrated that incorporation of bulky and polar maleic anhydride (MA) into polystyrene (PSt) chains in an alternating manner, forming an alternating copolymer of P(St-alt-MA), led to reductions in pi-pi and dipolar interactions at the air interface relative to those in the bulk. This reduction in molecular interactions led to greater mobility enhancement at the interface compared with the sluggish dynamics in the bulk, and accordingly, the P(St-alt-MA) alternating copolymer experienced a distinctly greater T-g confinement effect. These results demonstrated the impacts of local conformations and molecular interactions at the interface on the confinement effects of polymers and reinforced the idea of effective manipulation of confined polymer dynamics by changing the packing of molecules and functional groups at the interface.

Automated summary

Confinement alters polymer dynamics and leads to a reduction in the glass-transition temperature (T-g) of a polymer. The reduction in T-g is related to the enhancement of dynamics at the interface caused by changes in molecular interactions. This study demonstrated that tuning molecular interactions and conformation at the interface can effectively manipulate the confinement effects of polymers, resulting in a greater T-g reduction.