Connectivity-Dependent Mechanics of Main-Chain Oligomers in Side-Chain Liquid-Crystalline Polyacrylate Networks

Liquid-crystalline elastomers (LCEs) combine orientational order with polymer-network elasticity, yet the influence of molecular connectivity on their mechanics across different timescales remains poorly understood. Side-chain polyacrylate LCEs containing main-chain liquid-crystalline oligomers with different end connectivity are investigated: network-bound diacrylate-terminated DA-LCO and non-network-bound end-capped LCO. Both oligomers lower the glass-transition temperature while preserving nematic order, but their connectivity produces distinct mechanical responses. DA-LCO maintains a higher rubbery modulus, whereas LCO produces softer, more extensible networks. Both systems exhibit similar strain-rate dependences at short and intermediate deformation times, indicating that physically confined LCO remains mechanically engaged. At longer times, LCO exhibits an additional terminal relaxation associated with progressive release of physical constraints; no corresponding process is observed in DA-LCO before fracture. At moderate temperatures, LCO and the PEG-crosslinked reference network show comparable Arrhenius dependences with apparent activation energies around 60" " kJ" " mol^(-1), while LCO terminal relaxation shifts to shorter times at elevated temperatures. Molecular connectivity therefore acts as a timescale-dependent design parameter: non-network-bound oligomers can provide short-time mechanical support while enabling additional long-time stress dissipation. Oligomer end connectivity thus offers a molecular strategy for tuning mechanics and relaxation in nematic polymer networks.