We map out the solid-state morphologies formed by model soft-pearl-necklace polymers as a function of chain stiffness kb, spanning the range from fully flexible to rodlike chains. In the flexible limit, systems form RWCP crystals: monomers close-pack while chains retain random-walk-like order. In the rodlike limit, systems from NCP crystals: nematic chain ordering typical of lamellar precursors coexists with close-packing. At intermediate values of bending stiffness, systems glass-form, despite the fact that they also possess an NCP ground state. The range of kb over which glass formation occurs increases with the thermal cooling rate employed in our molecular dynamics simulations. Values of kb between the glass-forming and rodlike ranges produce complex ordered phases such as close-packed spirals. This may be associated with the fact that the onset of intermediate-range nematic order with increasing kb in this regime coincides with a sharp increase in the solidification temperature, altering the character of the energy-entropy competition.
We then connect these results to kb-dependent differences in these systems’ melt dynamics. Flexible and rodlike chains display simple melt dynamics with Arrhenius temperature dependence and a discontinuous change upon solidification (crystallization). Intermediate-stiffness chains are fragile glass-formers displaying Vogel-Fulcher dynamical arrest. To connect this difference in dynamics to the differing microstructure of the melts, we examine how various measures of structure, including cluster-level metrics recently introduced in studies of colloidal systems, vary with chain stiffness and temperature. No clear static-structural cause of the dynamical arrest is found. Instead, the differences likely result from intermediate-stiffness systems’ energy landscapes being much rougher due to a competition between paths leading to RWCP and NCP ordering. We also find that the intermediate-stiffness chains display qualitatively different dynamical heterogeneity. Specifically, their stringlike motion (cooperative rearrangement) is correlated along chain backbones in a way not found for either flexible or rodlike chains. This activated “crawling” motion is clearly associated with the dynamical arrest observed in these systems, and illustrates one way in which factors controlling the crystallization versus glass formation competition in polymers can depend nonmonotonically on chain stiffness.