Other Approaches to Graft Copolymers

A telechelic polystyrene containing two carboxyl groups at one end of a polymer can be used as a macromonomer in a step polymerization with a diol or diamine to yield a polyester or polyamide containing graft chains of polystyrene. The required telechelic polymer is obtained by radical polymerization of styrene in the presence of 2-mercaptosuccinic acid. 

Macromonomers containing a norbornene group have been polymerized by ROMP (Sec. 7-8) to form graft copolymers [Breunig et al., 1995 Heroguez et al., 1997]. 

Most of the methods for synthesizing block copolymers were described previously. Block copolymers are obtained by step copolymerization of polymers with functional end groups capable of reacting with each other (Sec. 2-13c-2). Sequential polymerization methods by living radical, anionic, cationic, and group transfer propagation were described in Secs. 3-15b-4, 5-4a, and 7-12e. The use of telechelic polymers, coupling and transformations reactions were described in Secs. 5-4b, 5-4c, and 5-4d. A few methods not previously described are considered here. 

Block copolymers have been obtained from polymeric radicals, which—unlike those employed for graft polymerization—have the radical centers at the ends of the polymer chains. This can be achieved by breaking chemical bonds in the polymer backbone by mastication (mixing) of the polymer [Ceresa, 1973, 1976, 1978 Sakaguchi and Sohma, 1978]. If 

The former gives a mixture of the block copolymer with the two homopolymers since the polymer radicals combine randomly. The latter yields the block copolymer along with the homopolymer of Mj. 

---