Simple analytical method for determination of microstructures of poly(ethylene-co-vinyl acetate) using the melting points

Abstract Microstructures of poly (ethylene-co-vinyl acetate) (EVA) are dependent on the distribution of VA units as well as the VA content. Simple analytical method to determine microstructure of EVA was established using melting points of EVA and correlationship with those of wax and its ester. EVAs with the VA contents of 9.5–40 wt% (3.3–17.8 mol%) were used. The melting points were analyzed using differential scanning calorimetry (DSC). EVAs had two melting points of Tm1 and Tm2 at 96–44 and 56 - 36 °C, respectively. The melting points were found to be closely related to the minimum carbon number participating in the crystal formation (CNmin). The crystalline size could be estimated by equation of CNmin = - ln [(106.7 - Tm)/214.8]/0.055 + 15. The CNmin1 and CNmin2 were 68–38 and 41–35, respectively. The CNmin1 decreased by about 4.5/mol% until 6.7 mol% of the VA content, while the CNmin2 slightly decreased by about 0.4/mol%. It was found that EVA would be generally composed of three ethylene block sizes of ∼VA-(CH2CH2)c1>20-VA-(CH2CH2)15