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

Abstract

The coil−globule transition was studied for poly(methyl methacrylate) (PMMA) in acetonitrile with molecular weights M w = 6.4 × 106 and 11.4 × 106 by static light scattering. Because of the very slow phase separation, the mean-square radius of gyration was determined reliably in the temperature range from above the ϑ temperature at 44.0 °C down to 5 °C. PMMA chains in acetonitrile collapsed slowly to equilibrium globules, and the collapse processes were measured for time periods of 30 min to 7 days depending the molecular weight and temperature. The behavior of the equilibrium expansion factor was represented as a function of (1 − ϑ/T)M 1/2 and compared with the theoretical predictions by Birshtein and Pryamitsyn and those by Grosberg and Kuznetsov. The second and third virial coefficients for segment interactions were estimated from the observed coil−globule transition curve by using the theories and were comparable with literature values due to the second and third virial coefficients of the dilute solution.

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

“…2 and 3 in Ref. 13. The chain collapse processes for M w = 6.4ϫ 10 6 at 15.0°C and for M w = 1.14ϫ 10 7 at 20.0°C have nearly the same values of ␣ eq 2 as 0.26 and 0.25, respectively, and can be used to determine ␥ m .…”

“…For a comparison, the coil-globule transition curve for PMMA of M w = 6.4ϫ 10 6 and 1.14ϫ 10 7 in pure AcN is shown with filled squares and filled circles, respectively. 13 The coilglobule transition in the mixed solvent is much sharper than that in pure AcN.…”

“…13 The weight-average molecular weights M w of M21A-F5 and M21F8 were determined to be 6.4ϫ 10 6 and 1.14ϫ 10 7 at the temperature of 44.0°C in pure AcN by static light scattering, respectively. The molecular weight distributions of M21A-F5 and M21-F8 were determined to be M w / M n = 1.25 and 1.34 by analytical gel permeation chromotography, respectively.…”

“…The chain collapse processes for M w = 6.4ϫ 10 6 at 30.0°C and for M w = 1.14ϫ 10 7 at 35.0°C have nearly the same values of ␣ eq 2 as 0.17 and 0.18, respectively. In a previous study, 13 we carried out measurements on the same samples as the present ones in pure AcN and obtained the chain collapse processes shown in Figs. 2 and 3 in Ref.…”

“…The chain collapse processes in AcN + water ͑10 vol % ͒ were determined by static light scattering, while the chain collapse processes in pure AcN have been obtained in a previous study. 13 The solvent dependence and the molecular weight dependence of the chain collapse were determined independently, and consequently, the characteristic time was conjectured as exp ϳ M 3 , where represents the nature of the solvent. The value of in AcN was larger by about ten times than that in AcN + water ͑10 vol % ͒.…”