In this work, we showed that the self-assembly behavior of the macro-chain transfer agent P(DMA69-b-NIPAM60)-S?(C?S)?S?C12H25 [dodecyltrithiocarbonate (DTTC)] was very different to P(DMA68-b-NIPAM62)-S?(C?S)?S?C4H9 [butyltrithiocarbonate (BTTC)], resulting in very different water-based nanoreactor polymerizations. The DTTC diblock formed small aggregates below the lower critical solution temperature (LCST), which increased slightly above the LCST. This is in contrast to the BTTC diblock, in which unimers existed below the LCST and large aggregates of coreshell nanoreactors were present above the LCST. Polymerization of styrene in the DTTC diblock nanoreactors afforded fast rates of polymerization with the production of narrow molecular weight and particle size distributions. We found a direct relationship between the size and the targeted molecular weight; the greater the targeted the molecular weight the greater the particle size. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012