附录 A 高分子缩写 B 一些重要商用高分子材料的典型性能 C 塑料和橡胶的ASTM标准 D SI单位和物理常数
精彩书摘
The exact sequence of monomer units along the chain can vary widely depending uponthe relative reactivities of each monomer during the copolymerization process. At the ex-tremes, monomer placement may be totally random or may be perfectly alternating, as illus-trated in Figure 1-4. The actual sequence of monomer units is determined by the relative reac-tivities of the monomers as will be described in Section 2.2.1. Under special circumstances,it is possible to prepare copolymers that contain a long block of one monomer (A) followedby a block of the other monomer (B). These are called AB-block copolymers. Tfiblock co-polymers have a central B block joined by A blocks at the end. A commercially importantABA-triblock copolymer is polystyrene-block-polybutadiene-block-polystyrene (SBS), athermoplastic elastomer (see Section 9.2.3). In addition to these copolymer structures, graftcopolymers can be prepared by polymerizing a monomer in the presence of a fully formedpolymer of another monomer. Graft copolymers are important as elastomeric (e.g., SBR) andhigh-impact polymers (e.g. high-impact polystyrene and ABS).