2,5-distyrylpyrazine four-center-type polymerization

The photopolymerization of diolefinic crystals was discovered in the case of the [2+2] photocyclopolymerization of 2,5-distyrylpyrazine (DSP) crystals and was named four-center-type polymerization (see Scheme 10.21) [36, 37]. 

Hasegawa, M., Suzuki, Y., Suzuki, F., and Nakanishi, H. Four-center type photopolymerization in the solid state. I. Polymerization of 2,5-distyrylpyrazine and related compounds. J. Polymer Sci. A7, 743-752 (1968). 

In 1967, Hasegawa identified the solid-state photochemical transformation of distyrylpyrazine 0 as a four center polymerization to a crystalline polymer with cyclobutane rings. Extensive crystallographic and mechanistic studies of this process have been reported (50). This type of four center photopolymerization has been extended to give a quantitative asynunetric induction (51). Laser Raman techniques have been used to study monomer-to-polymer conversion of these photopolymerizations and other processes as well (52). 

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