Synthesis of a novel star liquid crystal polymer using trifunctional initiator via atom transfer radical polymerization

In this paper, two types of three-arm star mesogen-jacketed crystal polymers (MJLCPs) with different core (that is hard core and soft core) were synthesized by 2,5-bis(4-methoxyphenyl)oxycarbonyl]styrene (MPCS), which was initiated by two different trifunctional initiators 1,3,5-(2′-bromo-2′-methylpropionato)benzene (I_a) and 1,1,1-tris(2-bromoisobutyryloxymethyl)propane (I_b), respectively. Characterization of these polymers by ¹H NMR and GPC clearly supported the formation of a three-arm star-shaped PMPCS. The resulting three-arm star PMPCS possessed narrow molecular weight distribution, and its molecular weight (M_n,NMR) agreed well with the theoretical value, which reveals the quantitative initiation efficiency. The liquid-crystalline behaviors of the two types of three-arm star polymer with different structure were also investigated by differential scanning calorimeter (DSC) and polarized optical microscope (POM). We found that the liquid-crystalline behavior was incorrelated with structure of core but correlated with the length of three-arm star polymer arm. Only each arm of the three-arm star-shaped polymers with a M_n,GPC beyond 0.90 × 10⁴ g/mol could form a liquid crystalline phase,which was found to be stable up to the decomposition temperature of these tri-arm MJLCPs.