聚丙烯Polypropylene

每个重复单元的甲基碳都是一个假手性中心。甲基全部在主链同一侧为等规（全同立构），交替排列为间规，无规排列为无规立构。等规聚丙烯链呈 3₁ 螺旋，能结晶（结晶度约 40–70%），熔点约 160–165 °C，坚硬有用；无规聚丙烯不能结晶，是柔软黏稠的无用材料。丙烯不能用自由基法得到高分子量聚合物，因为烯丙位氢容易被夺取发生退化链转移。

Each methyl-bearing carbon is a pseudo-stereocentre. With all methyls on one side the polymer is isotactic, with alternating sides syndiotactic, and with random placement atactic. Isotactic chains form 3₁ helices and crystallise (about 40–70%), melting near 160–165 °C, giving a useful rigid plastic; atactic PP cannot crystallise and is soft and tacky. Propylene cannot be radically polymerised to high polymer because its allylic hydrogens are easily abstracted, causing degradative chain transfer.

1954 年意大利化学家居里奥·纳塔用齐格勒催化剂（TiCl₄/AlEt₃）聚合丙烯，得到高结晶度的等规聚丙烯，并提出“等规”“间规”“无规”等术语。1957 年意大利蒙特卡蒂尼公司投产。纳塔与齐格勒共获 1963 年诺贝尔化学奖。1980 年代卡明斯基等发现甲基铝氧烷活化的茂金属催化剂，可精确控制立构规整性。

In 1954 the Italian chemist Giulio Natta polymerised propylene with a Ziegler catalyst (TiCl₄/AlEt₃) and obtained highly crystalline isotactic polypropylene, coining the terms isotactic, syndiotactic and atactic. Montecatini began production in 1957, and Natta shared the 1963 Nobel Prize in Chemistry with Ziegler. In the 1980s Kaminsky and others found methylaluminoxane-activated metallocene catalysts that control tacticity precisely.

聚丙烯密度低（约 0.90 g/cm³，最轻的通用塑料）、耐热（可蒸煮消毒和微波加热）、耐弯折疲劳（可做“活铰链”）、耐化学品。用于汽车保险杠和内饰、微波炉餐盒、注射器、包装薄膜（BOPP）、编织袋、地毯纤维，以及口罩的熔喷无纺布滤层。

Polypropylene is light (about 0.90 g/cm³, the lightest commodity plastic), heat resistant enough for steam sterilisation and microwaving, fatigue resistant enough for living hinges, and chemically resistant. It is used for car bumpers and interiors, microwave containers, syringes, packaging film (BOPP), woven sacks, carpet fibres and the melt-blown filter layer of face masks.