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Room temperature atom transfer radical polymerizations of N -isopropylacrylamide (NIPAM) carried out in 2-propanol ( i -PrOH) and tert -butyl alcohol ( t -BuOH) resulted in PNIPAMs with polydispersities between 1.1 and 1.2 and degrees of polymerization of up to 300. Methyl 2-chloropropionate (MCP), copper(I) chloride, and tris2-(dimethylamino)ethylamine (Me 6 TREN) were used as initiator, catalyst, and ligand in a 1:1:1 ratio. Conversions were as high as 91 and 79%, respectively, without the need for excess catalyst as was required in previous studies. Aqueous solutions of these narrow-disperse PNIPAMs showed a strong decrease of the phase transition temperature with increasing molecular weight, as measured by turbidimetry and differential scanning calorimetry. In low molecular weight samples, containing significant oligomeric fractions, the slightly hydrophobic methyl propionate end group becomes significant and further decreases the onset temperature of the phase transition.
Xia et al. (Wed,) studied this question.