Nucleation process and coil-globule transition of poly(methyl methacrylate in dilute solutions)

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Phase separation occurs very slowly for the dilute solutions of poly(methyl methacrylate) (PMMA) in isoamyl acetate (System I) and PMMA in the mixed solvent ter-butyl alcohol + water(2.5 vol%) (System II). Taking advantage of this slow phase separation, the coil-globule transition and the initial stage of phase separation were studied by light scattering measurements, which were carried out in the concentration range from 0.6 x 10ィイD1-4ィエD1 g/cmィイD13ィエD1 to 6.0x10ィイD1-4ィエD1. For the system I with the molecular weight MィイD2wィエD2 x 10ィイD1-6ィエD1 = 2.4 and 4.4, polymer chains contracted to equilibrium sizes in the first, 30 min after quench. For the system II with MィイD2wィエD2 x 10ィイD1-6ィエD1 = 8.4 and 12.2 , polymer chains contracted very slowly and took a few hundred minutes to a few thousand minutes to attain equlilibrium globules. The contraction of polymer chains occurred in a single stage and was represented by a power law. For the system I with MィイD2wィエD2 x 10ィイD1-6ィエD1 = 2.4 and 4.4 and system II with MィイD2wィエD2 x 10ィイD1-6ィエD1 = 1.57, phase separation process was measured in time periods from a few hours to a few days. The obtained light scattering data were analyzed by the Guinier plot, which yielded the weight average molecular weight, <M>ィイD2wィエD2 and z-average square radius <RィイD12ィエD1>ィイD2zィエD2 of clusters of polymer chains. Both the plots of In<M>ィイD2wィエD2 and In<RィイD12ィエD1>ィイD2zィエD2, versus time were represented by straight lines, whose slopes were proportional to the concentration. The slow phase separation was concluded to be due to the the reaction limited cluster aggregation. Since the aggregation of polymer chains stems from the reaction between segments, tho slow chain contraction was also found to be due to the reaction limited aggregation between segments.