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

Abstract

Kinetic and static properties of the coil-globule transition of poly͑methyl methacrylate͒ ͑PMMA͒ in pure tert-butyl alcohol were determined by static light scattering and compared with those of PMMA in the mixed solvent tert-butyl alcoholϩwater͑2.5 vol %͒ in order to examine the effect of water on the chain collapse. The measurements were carried out for the molecular weight M ϫ10 Ϫ6 ϭ4.1 and 12.2 in the concentration range of 0.6ϫ10 Ϫ4 -2.6ϫ10 Ϫ4 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 ϭ1.22 ϫ10 7 and within 30 min for M ϭ4.1ϫ10 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 alcoholϩwater͑2.5 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 ␣ 2 ϭ͗s 2 ͘/͗s 2 ͘ 0 obtained for fully collapsed chains in pure tert-butyl alcohol was represented by the theoretical prediction ␣ 3 Ϫ␣ϪC(␣ Ϫ3 Ϫ1)ϭB(1Ϫ /T)M 1/2 with the coefficients of Bϭ0.0179 and Cϭ0.054. For PMMA in the mixed solvent, the coil-globule transition curve has been expressed by the same equation with Bϭ0.0164 and Cϭ0.049, 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.

Coil−Globule Transition of Poly(methyl methacrylate) in Acetonitrile

“…Data points in the globule region in Figure 5 may be fitted by the broken straight line, which gives values of the parameters P and Q, and, correspondingly, values of v and w as shown in the first row in Table 1. We also analyzed data of the coil-globule transition curve for PMMA in IAA, 10 in TBA, 13 and in the mixed solvent TBA + water (2.5 vol %) 14 and for PS in cyclohexane. 22 The obtained values of the parameters P, Q, v, and w are listed in Table 1.…”

Kinetics of chain collapse in dilute polymer solutions: Molecular weight and solvent dependences

“…[11][12][13][14] It was found that the transition curve depends markedly on the solvent species and is represented by the equation of the mean-field theory as 18,19 ␣ eq 3 − ␣ eq − C͑␣ eq −3 − 1͒ = BM 1/2 , ͑3͒…”

“…12 The chain collapse in pure AcN is extremely slow and accelerated by an addition of water, while the chain collapse in pure TBA is very fast and decelerated by an addition of water. A comparative study on the systems of PMMA in AcN + water and in TBA+ water would provide a hint on the dynamics of chain collapse.…”

“…Experimental studies of the chain collapse have been carried out on solutions of polystyrene, 8 poly͑N-isopropyl acrylamide͒, 9,10 and poly͑methyl methacrylate͒ ͑PMMA͒. [11][12][13][14] The chain collapse in the former two solutions was too fast to be measured accurately. As for PMMA solutions, the chain collapse was observed to occur much slower than the theoretical predictions and to depend strongly on the molecular weight as well as the solvent species and the quench depth.…”

“…In previous studies, [11][12][13][14] we have measured chain collapse processes in the dilute solutions of PMMA in the single solvents of isoamyl acetate, tert-butyl alcohol ͑TBA͒, acetonitrile, and in the mixed solvent of TBA+ water ͑2.5 vol % ͒ by static light scattering. Since the solutions underwent very slow phase separation and remained transparent for long time periods from hours to weeks depending on the molecular weight, the solvent species, and the quench depth, the chain collapse process could be measured without being disturbed by the chain aggregation for the periods.…”