Solvent effect on single-chain collapse of poly(methyl methacrylate) in tert-butyl alcohol

Kinetic and static properties of the coil-globule transition of poly(methyl methacrylate) (PMMA) in pure tert-butyl alcohol were determined by static light scattering and compared with those of PMMA in the mixed solvent tert-butyl alcohol+water(2.5 vol %) in order to examine the effect of water on the chain collapse. The measurements were carried out for the molecular weight Mx10(-6)=4.1 and 12.2 in the concentration range of 0.6x10(-4)-2.6x10(-4) g/cm(3), and the mean-square radius of gyration <s(2)> was determined as a function of the time after an abrupt decrease of temperature. PMMA chains collapsed to equilibrium globules within 90 min after quenching for M=1.22x10(7) and within 30 min for M=4.1x10(6). Chain aggregation due to phase separation became noticeable after the collapse of the chain because of an increase of observed molecular weight. For PMMA in the mixed solvent tert-butyl alcohol+water(2.5 vol %), the chain collapse process has been observed for periods from hours to weeks depending on the molecular weight and temperature, and the chain aggregation was negligibly small in the chain collapse process. The expansion factor alpha(2)=<s(2)>/<s(2)>(0) obtained for fully collapsed chains in pure tert-butyl alcohol was represented by the theoretical prediction alpha(3)-alpha-C(alpha(-3)-1)=B(1-theta/T)M-1/2 with the coefficients of B=0.0179 and C=0.054. For PMMA in the mixed solvent, the coil-globule transition curve has been expressed by the same equation with B=0.0164 and C=0.049, close to the above values. The small amount of water in the mixed solvent caused a drastic slowdown in the chain-collapse rate but had little effect on the coil-globule transition curve. (C) 2003 American Institute of Physics.