自由基聚合Radical polymerization

链引发：偶氮二异丁腈（AIBN）或过氧化苯甲酰（BPO）受热分解为初级自由基，再与单体加成生成单体自由基，这是决速步。链增长：自由基迅速与单体加成，通常头-尾连接。链终止：两个增长链自由基偶合或歧化终止，因此聚合物“死”了。链转移：自由基夺取溶剂、单体或链转移剂上的原子，使分子量下降。在稳态假设下，聚合速率与 [M][I]^½ 成正比。

Initiation: AIBN or benzoyl peroxide decomposes on heating to primary radicals that add to monomer, the rate-determining step. Propagation: the radical adds monomer rapidly, usually head-to-tail. Termination: two growing radicals combine or disproportionate, leaving 'dead' polymer. Chain transfer: a radical abstracts an atom from solvent, monomer or a transfer agent, lowering molar mass. Under the steady-state assumption the rate is proportional to [M][I]^½.

工业上有四种实施方法：本体聚合（有机玻璃板）、溶液聚合（涂料树脂）、悬浮聚合（单体分散为液滴，得到 PVC、聚苯乙烯颗粒）和乳液聚合（在乳化剂胶束中进行，得到丁苯橡胶、乳胶漆）。本体聚合后期黏度剧增导致终止变慢、速率猛增，称为“凝胶效应”或自加速效应，需注意散热防止爆聚。

Four process types are used: bulk (acrylic sheet), solution (coating resins), suspension, in which monomer droplets give PVC and polystyrene beads, and emulsion, in surfactant micelles, giving SBR rubber and latex paint. In bulk polymerisation the late rise in viscosity slows termination and the rate surges, the gel or Trommsdorff effect, so heat must be removed to prevent runaway.

传统自由基聚合难以控制分子量分布和链结构。1990 年代发展的氮氧稳定自由基聚合（NMP）、原子转移自由基聚合（ATRP，松本、王锦山 1995 年）和可逆加成-断裂链转移聚合（RAFT，1998 年）通过休眠种与活性种的快速可逆平衡，实现了窄分布和嵌段共聚物的精确合成。

Conventional radical polymerisation offers little control over molar-mass distribution or architecture. In the 1990s nitroxide-mediated polymerisation (NMP), atom transfer radical polymerisation (ATRP, Matyjaszewski and Jin-Shan Wang, and independently Sawamoto, 1995) and reversible addition–fragmentation chain transfer (RAFT, 1998) achieved narrow distributions and precise block copolymers through fast reversible exchange between dormant and active chains.