Water vapor transmission of poly(ethylene oxide)-based segmented block copolymers

This article discusses the rate of water vapor transmission (WVT) through monolithic films of segmented block copolymers based on poly(ethylene oxide) (PEO) and monodisperse crystallisable tetra-amide segments. The polyether phase consisted of hydrophilic PEO or mixtures of PEO and hydrophobic poly(tetramethylene oxide) (PTMO) segments. The monodisperse tetra-amide segments (T6T6T) were based on terephthalate units (T) and hexamethylenediamine (6). By using monodisperse T6T6T segments the crystallinity in the copolymers was high (∼ 85%) and, therefore, the amount of noncrystallised T6T6T dissolved in the polyether phase was minimal. The WVT was determined by using the ASTM E96BW method, also known as the inverted cup method. By using this method, there is direct contact between the polymer film and the water in the cup. The WVT experiments were performed in a climate-controlled chamber at a temperature of 30°C and a relative humidity of 50%. A linear relation was found between the WVT and the reciprocal film thickness of polyether-T6T6T segmented block copolymers. The WVT of a 25-μm thick film of PTMO2000-based copolymers was 3.1 kg m−2 d−1 and for PEO2000-based copolymers 153 kg m−2 d−1. Of all the studied copolymers, the WVT was linear related to the volume fraction of water absorbed in the copolymer to the second power. The results were explained by the absorption-diffusion model.