Structure-property relationships in photopolymerizable polymer networks: Effect of composition on the crosslinked structure and resulting thermomechanical properties of a (meth)acrylate-based system

Photoinitiated polymer networks were formed by copolymerization of terf-butyl acrylate with di(ethylene glycol) dimethacrylate (DEGDMA) or poly(ethylene glycol) dimethacrylate (PEGDMA). The degree of crosslinking was systematically varied by modifying the weight fraction and molecular weight of the dimethacrylate crosslinking agent. An increase in effective crosslink density with increasing crosslinking agent concentrations was confirmed by decreasing equilibrium swelling ratios (q) and increasing rubbery moduli (E _R). Glass transition temperatures (T_g) varied from -22 to 124°C, increasing with increasing DEGDMA content and decreasing with increasing PEGDMA content. Tensile deformation behavior (at T_g) ranged from an elastomeric-like large-strain response for lightly crosslinked materials to a small-strain brittle response for highly crosslinked networks. At low cross-linking levels, the strain-to-failure of the network polymers decreased quickly with increasing crosslinking agent concentration. The stress at failure demonstrated a more complex relationship with crosslinking agent concentration. The effect of composition on network structure and resulting properties (q, E_R, strain-to-failure) decreased as the crosslinking agent concentration increased. The results reveal trade-offs in T_g, E_R, strain-to-failure, and failure stress with composition and network structure, and are discussed in light of the wide range of potential applications suggested in the literature for (meth)acrylate-based photopolymerizable polymer networks including biomaterials and shape-memory polymers.