Kinetics of coil–globule transition of poly(methyl methacrylate) in isoamyl acetate

Abstract

The coil-globule transition was studied by static light scattering measurements on poly͑methyl methacrylate͒ with the molecular weight M w ϫ10 Ϫ6 ϭ2.35 and 4.4 in isoamyl acetate. Since the phase separation of the dilute solution occurred very slowly, the measurements could be made in the broad temperature range from near the ⌰ temperature 61°C to 0°C 30 min after a quench of the solution. The observed expansion factor ␣ 2 for the radius of gyration was represented as a function only of M 1/2 and showed a constant value at large ϪM 1/2 with being 1Ϫ⌰/T. A quantitative comparison between a recent theory for a contracted coil and the data of ␣ 2 revealed the coil-globule crossover phenomena. The behavior of plot of 1/␣ 3 versus ϪM 1/2 was distinctly different in the three ranges, i.e., coil range, globule range, and range of a constant ␣. The plot of the observed second virial coefficient A 2 against temperature yielded a minimum as predicted from a theory of A 2 below the ⌰ temperature. ͓S1063-651X͑97͒11809-8͔

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

“…In order to determine the molecular weight M w , the mean-square radius of gyration ͗s 2 ͘ and the second virial coefficient A 2 from the light-scattering data, the excess Rayleigh ratio R at an angle was analyzed by the scattering equation, 20 2 and q ϭ(4 n/ )sin( /2), where N A is Avogadro's number, is the wavelength of incident light in a vacuum, and n is the refractive index of solution. The plot of (Kc/R ) 1/a vs sin 2 ( /2) gives a straight line for an appropriate value of the constant a and ͗s 2 ͘ can be obtained from the slope of the plot according to Eq.…”

“…͑3͒. 2,20 The values of ͗s 2 ͘, A 2 , and M w were determined by using the Zimm plot with aϭ2 for the sample M19-F12 and aϭ1.5 for M21-F9. Figure 1 shows light-scattering data for the sample M19-F12 obtained at 30 min after quenching to 60.0°C.…”

“…[1][2][3][4] Since the solutions underwent very slow phase separation, the mean square radius of gyration ͗s 2 ͘ of PMMA chains was determined accurately in the temperature ranges from the temperature 61.0°C to 0°C in isoamyl acetate 1,2 and from the temperature 41.5°C to 20°C in the mixed solvent 3,4 by using solutions in the concentration range of 0.7ϫ10 Ϫ4 -5ϫ10 Ϫ4 g/cm 3 . PMMA chains in both of the solvents collapsed completely before the onset of phase separation.…”

“…The rate of chain collapse depended strongly on the molecular weight and was slower in the mixed solvent than in isoamyl acetate. 2,4 For M w ϭ1.22ϫ10 7 , chain collapse required a period of hours to weeks depending on the solvent and quench depth. The observed chain collapse process was fitted to a stretched exponential function, with which an expansion factor for totally collapsed chains was estimated.…”

“…These coefficients were determined to be Bϭ0.0041 and Cϭ0.073 for PMMA in isoamyl acetate 1,2 and Bϭ0.0164 and Cϭ0.049 in the mixed solvent tert-butyl alcoholϩwater͑2.5 vol %͒. 3,4 The coil-globule transition has been studied for some other polymer solutions, for which light scattering measurements have been carried out for very large molecular weights and at extremely low concentrations in order to minimize the effect of the phase separation.…”