Synthesis of ring-shaped macromolecules

Cyclic polymers: Synthetic strategies and physical properties

“…9 Systematic studies of syntheses and properties of cyclic polymers based on polycondensation methods began around 1980, almost simultaneously and independently by several research groups. [10][11][12][13] Since then, a weak but steady flow of publications dealing with cyclic polymers has continued. Meanwhile, several review articles dealing with syntheses and properties of circular polymers have appeared, but these articles do not clearly distinguish between synthetic methods and synthetic strategies.…”

“…This relationship was used by numerous organic chemists for the preparation of monodisperse macrocycles (e.g., 10-40 atoms in the ring), which were purified from cycles or linear chains having higher molar masses by chromatographic methods or recrystallization. The same approach was used by polymer chemists in 1980, [10][11][12][13] and later for the preparation of cyclic polymers with low polydispersity. The discussion of synthetic methods presented below is subdivided according to the functionalities of the (polymers) monomers into ''a 2 þb 2 '' polycondensations, ''aÀb'' polycondensations, and finally, ''a 2 '' polycondensations.…”

“…[10][11][12][13] The most widely used reaction sequence begins with the preparation of a bisanionic initiator (Bi in Schemes 10-12) followed by a living anionic polymerization of styrene yielding bisanionic polystyrenes (PSs) of low polydispersity. These polymeric bisanions were then condensed with dichloro-or dibromo-alkanes including CH 2 Cl 2 , CH 2 Br 2, and CH 2 J 2 or with 1,2-and 1,4-bis(chloromethyl) and bis(bromomethyl) benzenes, so that yields around or above 50% were obtained.…”

“…This combination of properties allowed for a separation of the quasi monomeric cycles (containing one PS chain) from the higher cyclic or linear polycondensation products by means of size-exclusion chromatography (SEC). [10][11][12][13][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] The optimum iMC was calculated via eq 5, 13 which correlates the molecular weight of the bifunctional polymer chains with a concentration (C eq ) where rates of cyclization and chain growth are equal C eq ¼ a ¼ 1 in eq 3. For bisanionic PS of M n 10 kDa a C eq value around 10 À3 mol/L was calculated.…”

“…For bisanionic PS of M n 10 kDa a C eq value around 10 À3 mol/L was calculated. 13 To obtain yields of the SCHEME 10 Syntheses of cyclic polystyrenes by ''a 2 þ b 2 '' (poly)condensation at low initial monomer concentration (iMC % 10 À5 mol/L). Bi ¼ bifunctional initiator.…”