热敏聚氨酯膜及其透汽、透湿性的研究

Thermo-sensitive Polyurethane Membranes and Their Water and Vapor Permeabilities

比较了普通聚氨酯PU（a）和两种热敏聚氨酯（Thermo-Sensitive Polyurethane）PU（b）和PU（C）微相结构和性能的差异，并采用示差扫描量热分析仪（DSC）和正电子湮没谱仪（PAL）分别对3种聚氨酯的相转变温度，自由体积分数，自由体积空洞半径随温度的变化规律以及自由体积空洞半径的变化对薄膜透汽、透湿性的影响进行了研究。结果表明：热敏聚氨酯PU（b）和PU（c）在设定温度范围内（20～50℃）具有明显的两相分离结构；在其可逆相相转变温度前后，其自由体积空洞平均半径R、自由体积分数均发生了显著变化，自由体积分数均由20℃的1．6％左右提高到50℃时9％以上，自由体积空洞的平均半径由20℃时的0．23nln提高至50℃时的0．4nm以上，且均高于水蒸汽分子的平均半径（R=0．4nm）。相似地，热敏聚氨酯薄膜PU（b）和PU（C）的透汽、透湿性也发生了显著的变化，在相转变前后其透湿量分别提高了130％，160％，表现出了明显的热敏特性。

Differences of morphological structure and properties of common polyurethane （PU（a） ） and thermo-sen- sitive polyurethanes（ TSPU （b） and TSPU （ c ） ） were investigated. Differential Scanning Calorimetry （DSC）, Positron Annihilation Lifetimes （PAL）and water vapor permeability （WVP） were employed to investigate the phase transitions of polyurethanes and evaluate the temperature influence on the free volumes （FV） and the WVPs of all PU membranes. TSPU（b） with a glass transition reversible phase and TSPU（c） with a crystalline transition reversible phase showed an obvious phase-separated structure and a phase-transition in designed temperature range（20 - 50℃ ）. In addition, PAL study indicated that the radius of free volume holes（R） and the fractional free volume （f,） of TSPU are closely related to the phase-transition temperature （defined as switch temperature, T8）, phase transition leads to dramatic changes in R andfv. When the temperature exceeds the T8, the f, change from 1.6% to more than 9.0%, the average radius of free volume holes change from 0.23 nm to above 0.4 nm （Rb =0.418 nm, Rc = 0.467 nm） and become larger than that of the water vapor （ R,, = 0.4 nm）. Simultaneously, the WVPs of TSPU （b） and TSPU（c） membranes also showed a dramatic increase by 130%, 160% respectively and thermosensitive characteristics.