The non-equilibrium dynamics of linear and star-shaped cis-1,4 polyisoprenes confined within nanoporous alumina is explored as a function of pore size, d, molar mass, and functionality (f = 2, 6, and 64). Two thermal protocols are tested: one resembling a quasi-static process (I) and another involving fast cooling followed by annealing (II). Although both protocols give identical equilibrium times, it is through protocol I that it is easier to extract the equilibrium times, t eq, by the linear relationships of the characteristic peak frequencies with time and rate, respectively, as log­(fmax) = C 1 – k log­(t) and log­(fmax) = C 2 + λ log­(β). Both thermal protocols establish the existence of a critical temperature (at T c, where k → 0 and λ → 0) below which non-equilibrium effects set-in. The critical temperature depends on the degree of confinement, 2R g/d, and on molecular architecture. Strikingly, establishing equilibrium dynamics at all temperatures above the bulk, T g, requires 2R g/d ∼ 0.02, i.e., pore diameters that are much larger than the chain dimensions. This reflects non-equilibrium configurations of the adsorbed layer that extent away from the pore walls. The equilibrium times depend strongly on temperature, pore size, and functionality. In general, star-shaped polymers require longer times to reach equilibrium because of the higher tendency for adsorption. Both thermal protocols produced an increasing dielectric strength for the segmental and chain modes. The increase was beyond any densification, suggesting enhanced orientation correlations of subchain dipoles.

The dynamics of a series of cis-1,4-polyisoprene stars located inside nanoporous alumina was investigated as a function of functionality, f (2 ≤ f ≤ 64), arm molar mass, M (2.6 ≤ M ≤ 13.5 kg•mol −1 ), and degree of confinement (0.01 ≤ 2R g /d ≤ 0.6; where R g is the radius of gyration and d is the pore diameter) by dielectric spectroscopy. In the bulk, dielectric spectroscopy revealed broadening of the chain modes with the increasing functionality. In addition, a slower dielectric process was found in the vicinity of the soft-colloidal process identified earlier by rheology. The latter associates with the cooperative reorganization of the stars and involves rotational and translational motions. The effect of confinement on the dynamics of stars was stronger than for linear chains. First, the dielectric strength of the normal modes was reduced in the stars and, second, the chain dynamics were slower. The reduced dielectric strength was employed as a measure of the thickness of the interfacial layer. Based on the dielectric strength, we can account for the possible arm star configurations in the vicinity of the pore walls. The slower chain dynamics reflect the increased entanglement density near the pore walls due to extra topological constraints imposed by the adsorbed arms. Functionalization of the pore walls partially restored the dielectric strength of the chain modes. Overall, star-shaped polymers are more prone to adsorption effects when confined in nanopores as compared to linear chains.

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