Synthesis and characterization of macrocyclic vinyl aromatic homopolymers and block copolymers

The synthesis of well-defined narrow molecular weight (MW) distribution macrocyclic poly(9,9-dimethyl-2-vinylfluorene) (PDMVF) containing single 1,4-benzylidene or 9,10-anthracenylidene unit is reported. Narrow MW distribution PDMVF macrocycles and the matching linear polymers with number average degree of polymerization (DP_n) between 12 and 142 are synthesized via potassium naphthalide initiated anionic polymerization of 9,9-dimethyl-2-vinylfluorene (DMVF) in THF at −78°C followed by end-to-end coupling with 1,4-bis(bromomethyl)benzene (DBX) or 9,10-bis(chloromethyl)anthracene (BCMA) under high dilution condition (anion concentration 10−5∼10 −6 M). These macrocycles are distinguished from their matching linear polymers by the smaller hydrodynamic sizes (9–29%) determined by size exclusion chromatography (SEC), with the largest polymer showing the greatest difference. The glass transition temperatures (T_g's) of small PDMVF macrocycles are much higher (up to 45 degrees) than those of their linear analogues, but decrease slightly as MW's increase, giving a 14 degrees lower T_g for the DP_n = 142 cycle compared to the matching linear polymer. Macrocyclic PDMVF exhibits better thermal stability under non-oxidative condition than the linear analogue. Hypochromic effects have been observed for both linear and cyclic PDMVF polymers compared to 9,9-dimethyl-2-ethylfluorene (DMEF) model compound and high MW polymers are affected more. Hypochromism have also been found for PDMVF cycles compared to the matching linear polymers and are more pronounced for larger cycles.; For the first time narrow molecular weight (MW) distribution macrocyclic polystyrene-b-poly(9,9-dimethyl-2-vinylfluorene) (PS- b-PDMVF) containing single 9,10-anthracenylidene unit is prepared via anionic block copolymerization followed by end-to-end coupling with BCMA. The first block, DMVF block, appears to be a well-defined DMVF oligomer block consist of largely DMVF dimer and trimer. The macrocycles appear to have higher fluorenyl absorptivities than their matching linear polymers. Energy transfer from the 9,9-dimethyl fluorenyl donors to the 9,10-anthracenylidene acceptor has been observed in fluorescence emission spectra and the smaller macrocycle tends to have higher energy transfer efficiency.