Model linear and star-shaped polyisoprenes with phosphatidylcholine analogous end-groups. Synthesis and association behavior in cyclohexane

Semitelechelic (ω-), telechelic (α,ω-), as well as 3- and 12-arm star polyisoprenes (PI), end-functionalized with the same dimethylamino group, were synthesized by aniomic polymenzation high vacuum techniques, using 3-dimethylaminopropyllithium as initiator and chlorosilanes as linking agents. The dimethylamino groups were transformed to phosphatidylcholine analogues through reaction with 2-ethoxy-2-oxo-1,3,2-dioxaphospholane. The association behavior of the phosphoro-zwitterionic PI (PZw-PI) was studied in cyclohexane by low angle laser light scattering, viscometry, and dynamic light scattering. The linear PZw-PIs present relatively low weight-average degree of association (N_w: 2-6), as compared with the corresponding sulfozwitterionic PI (N_w: 10-45). The N_w values decrease with increasing molecular weight of the PI. In the case of the star PZw-PI, the multiple intermolecular associations lead to the formation of gels, which break down by addition of a small amount of 1-heptanol. In very dilute solutions and for high arm molecular weight stars, intramolecular dominates over intermolecular association.