Synthesis and evaluation of new dicarboxylic acid functional trithiocarbonates:: RAFT synthesis of telechelic poly(n-butyl acrylate)s

We report herein the synthesis of three new diacid functional trithiocarbonates (TTCs) in which the substitution pattern about the TTC functionality is varied and compare their effectiveness alongside examples of previously reported trithiocarbonates as mediating agents in the RAFT polymerization of n-butyl acrylate. For direct comparative purposes we show that at an initial TTC concentration: initial AIBN concentration ([TTC](0):[AIBN](0)) of 20 2-(2-carboxyethylsulfanylthiocarbonylsulfanyl)propionic acid (TTC5) and 2-(2-carboxyethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (TTC6) perform as well as 3-benzylsulfanylthiocarbonylsulfanylpropionic acid (TTC3) with respect to kinetics and molecular weight control. In contrast, 2-(1-carboxy-1-methylethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (TTC1)-mediated homopolymerization deviates from "ideal" behavior due, we speculate, to steric crowding of the central TTC core. Additionally, 3-(2-carboxyethylsulfanylthiocarbonylsulfanyl)propionic acid (TTC4) fails to confer any control on the homopolymerization of nBA with the polymerization exhibiting complex characteristics, as evidenced in the resulting molecular weight distribution, which may be indicative of hybrid behavior. Subsequently, we examine the effect of [TTC](0):[AIBN](0) for TTC5 and TTC6 and show that lower ratios result in faster polymerizations, consistent with previous reports. Finally, we demonstrate the ability to form block copolymers with high reinitiating efficiency. These new TTCs thus offer access to the direct synthesis of AB diblock dicarboxylic acid telechelic (co)polymers.