Structure-mechanical property relationships for polycarbonate urethane elastomers with novel soft segments

A series of eight aliphatic polycarbonate (PC) glycols with various methylene numbers (HO-[(CH₂)_mOC(=O)O]₂) _m-OH, m = 3, 4, 5, 6, 7, 8, 9, and 10) were employed as a soft segment for a synthesis of polyurethane elastomers (PUEs). First of all, viscosity, glass transition temperature, melting point, and crystalline structure of these new PC-glycols were investigated. The PC-glycol-based PUEs were synthesized using the PC-glycols, 4,4′-diphenylmethane diisocyanate, and 1,4-butanediol by a one-shot method. Differential scanning calorimetry and small-angle X-ray scattering measurements revealed that the degree of microphase separation of the PC-glycol-based PUEs became first weaker and then stronger with increasing number of methylene groups of PC-glycols. The threshold carbon number for the degree of microphase separation was six. In the tensile testing, Young's modulus of the PUEs decreased and increased with an increase in the methylene number, which can be explained by the degree of microphase separation. Tensile strength and elongation at break of the PC-glycol-based PUEs increased and decreased with increasing the number of methylene groups. These results are associated with the ease of packing of the PC-glycol chains.