We present experiments and theory on the melt dynamics of monodisperse entangled polymers of H-shaped architecture. Frequency-dependent rheological data on a series of polyisoprene H-polymers are in good agreement with a tube model theory that combines path-length fluctuation (like that of star polymer melts) at high frequency, with reptation of the self-entangled “cross-bars” at low frequencies (like that of linear polymer melts). We account explicitly for mild polydispersity. Nonlinear step-strain and transient data in shear and extension confirm the presence of a relaxation time not seen in linear response, corresponding to the curvilinear stretch of the cross-bars. This time is very sensitive to strain due to the exponential dependence of the branch-point friction constants on the effective dangling path length. Strain-induced rearrangements of the branch points are confirmed by small-angle neutron scattering (SANS) on stretched and quenched partially deuterated samples. We develop an extension of melt-scattering theory to deal with the presence of deformed tube variables to interpret the SANS data.

The dynamic dilution theory of stress relaxation, quantitative for star polymer melts, cannot be directly applied to star−linear blends. The linear chains on their reptation time scale τd release constraints on the star arms, resulting in constraint-release Rouse motion for the star arms not described by dynamic dilution. We present a microscopic theory without adjustable parameters for stress relaxation in such blends, which is in excellent agreement with dynamic rheology data for the full range of blend fractions.

We present experiments and theory on the melt dynamics of monodisperse entangled polymers of comb-shaped architecture. Frequency-dependent rheological data on a series of comb polymers are in good agreement with a tube-model theory that combines star polymer melt behavior at high frequency with modified linear polymer reptation behavior at low frequencies. Taking into account mild polydispersity and by incorporating the high-frequency Rouse modes, we are able to model quantitatively the entire frequency range. Qualitatively distinct dynamical features of the comb architecture are compared to those of the simpler star and H-topologies.