共聚物Copolymer

无规共聚物中单元随机分布（如丁苯橡胶 SBR）；交替共聚物中两种单元严格交替（如苯乙烯-马来酸酐）；嵌段共聚物由长段的不同单元依次连接（如 SBS）；接枝共聚物在主链上接出另一种高分子支链（如 ABS 中聚丁二烯接枝苯乙烯-丙烯腈）。链式共聚中，两单体的竞聚率 r₁、r₂ 决定组成与序列分布：r₁r₂ ≈ 1 为理想无规，r₁r₂ ≈ 0 倾向交替。马约-刘易斯方程给出瞬时共聚物组成。

In random copolymers the units are distributed randomly (styrene–butadiene rubber, SBR); in alternating copolymers they strictly alternate (styrene–maleic anhydride); block copolymers join long runs of each unit (SBS); graft copolymers carry side chains of another polymer on the backbone (ABS, styrene–acrylonitrile grafted on polybutadiene). In chain copolymerisation the reactivity ratios r₁ and r₂ set composition and sequence: r₁r₂ ≈ 1 gives ideal random copolymers and r₁r₂ ≈ 0 tends to alternation. The Mayo–Lewis equation gives the instantaneous composition.

1930 年代德国法本公司开发丁苯橡胶（Buna S）和丁腈橡胶（Buna N）。二战期间美国大规模生产丁苯橡胶以替代天然橡胶。1944 年马约和刘易斯、阿尔弗雷和戈德芬格分别建立共聚组成方程。1948 年起 ABS 塑料问世，1960 年代壳牌开发 SBS 嵌段共聚物。

In the 1930s IG Farben developed styrene–butadiene rubber (Buna S) and nitrile rubber (Buna N), and during the Second World War the United States mass-produced SBR to replace natural rubber. In 1944 Mayo and Lewis, and Alfrey and Goldfinger, derived the copolymer composition equation. ABS plastic appeared from 1948, and Shell developed SBS block copolymers in the 1960s.

共聚是改性高分子的主要手段：乙烯中加入少量 1-丁烯或 1-辛烯得到线型低密度聚乙烯，更柔韧；氯乙烯与醋酸乙烯酯共聚改善加工性；乙烯-醋酸乙烯酯（EVA）用于热熔胶和鞋底。嵌段共聚物的不相容链段发生纳米尺度的微相分离，形成球状、柱状、层状等有序结构。

Copolymerisation is the main way to modify polymers: adding a little 1-butene or 1-octene to ethylene gives tougher linear low-density polyethylene; vinyl chloride–vinyl acetate copolymers process more easily; ethylene–vinyl acetate (EVA) goes into hot-melt adhesives and shoe soles. Incompatible blocks in block copolymers microphase-separate on the nanoscale into ordered spheres, cylinders and lamellae.