英语翻译We need polymers that have a controlled average molecula

英语翻译
We need polymers that have a controlled average molecular weight and a molecular weight distribution.Thus,the polymerization reactions must have an “off” switch as well!The chains may be terminated by two mechanisms.First the ends of two growing chains may be joined.This process,called combination,creates a single large chain from two smaller chains.Second,the active end of one chain may remove a hydrogen atom from a second chain by a process known as disproportionation.This reaction terminates two chains,rather than combining two chains into one larger chain.Sometimes,compounds known as terminators are added to end the polymerization reactions.In general,for thermoplastics,the higher then average molecular weight the higher will be the melting temperature and the higher will be the Younger’s modulus of the polymer.The following example illustrates an addition polymerization reaction.