Synthesis of 4-, 8-, 12-arm star-branched polybutadienes with three different chain-end functionalities using a functionalized initiator

An array of well-defined 4-, 8-, and 12-arm, chain-end functionalized, star polymers and their deuterated analogs has been synthesized using a t-butyldimethylsiloxy-functionalized alkyllithium initiator and anionic polymerization. The design of the synthesis provides for unusually well-defined comparisons of the behavior of the polymers with different chain-end functionality. For each star architecture three polybutadiene polymers were synthesized with the same labeling, the same well-defined degree of branching and molecular weight, but different chain end functionality. Deprotection of the t-butyldimethylsiloxypropyl chain ends of the stars as first synthesized provided stars with hydroxypropyl chain ends. The hydroxypropyl chain ends were further converted to trifluoroethanesulfonyloxypropyl chain ends by tresylation with 2,2,2-trifluoroethanesulfonyl chloride. Measurements of intrinsic viscosities for the hydrogenous and deuterated linear PBs made in the course of characterizing the star functionalities confirm that the dimensions of the linear chains are not affected by isotopic substitution.