Spontaneous copolymerization of acrylic acid with 4-vinylpyridine and microscopic acid dissociation of the alternating copolymer

A large amount of heat was generated by mixing concentrated acrylic acid an d concentrated 4 -vinylpyridine, which led to carbonized products. When the y were mixed within the limited concentration range, however, the polymeriz ation took place spontaneously, and gave the alternating copolymer a relati vely low molecular weight. The copolymerization was accelerated by a cation ic catalyst, and inhibited by butylamine although it was not accelerated by a radical initiator and was not inhibited by a radical inhibitor. These fi ndings suggest that the spontaneous copolymerization proceeds via cationic mechanism. However, copolymerization is accelerated by water, which is a ty pical inhibitor of ionic polymerization. Macroscopic and microscopic acid dissociation constants of the alternating copolymer were determined by pH-titration method. The relative concentratio ns of respective microscopic forms were calculated using the relation betwe en micro-constants and hydrogen ion concentration. The fraction of the prot onated form, which exists exclusively in the lower pH range, decreases with increasing pH value, and fully vanishes at pH approximate to 6, while the deprotonated form begins to appear from about pH = 9. The zwitterionic and neutral molecule forms coexist over a wide range of pH, and the latter form is predominant regardless of the pH value. Macro- and micro-constants were also measured for the system of monomer mixtures, and homopolymer mixtures as well. (C) 2001 Elsevier Science Ltd. ll rights reserved.