39) We thank Dr. I. Voigt-Martin for kindly supplying us with the electron micrographs.(40) The previously reported SALS patterns for this series of quenched samples1" indicates that the quenching temperature corresponded to about 70 °C. (41) Our previous report10 suffers from this deficiency, and the enthalpies of fusion are lower than the correct values. This error can be rectified, to a very good approximation, by adding 0.10 to the degree of crystallinities previously calculated from the enthalpy of fusion measurements. (42) It should be noted that the premise of interface-controlled growth makes no assumption or imposes any requirements on the interfacial structure. In particular, identification with a regularly folded interface is unnecessary and incorrect.
2-Hydroxyethyl methacrylate (HEMA) (branch)-methyl acrylate (MA) (backbone) comb-type graft copolymers were synthesized by grafting an amino-semitelechelic oligo (HEMA) to a methacrylate (GMA) random copolymer. From electron microscope observation, it was found that these graft polymeric membranes had microphase separated structures. Pervaporation of a benzene-cyclohexane mixture through these membranes was carried out in order to study the effect of microphase separated structures on selective permeability. Benzene was found to preferentially permeate through the membranes. Moreover, the pervaporation rate of benzene increased with increasing MA mole fraction in the graft copolymers. It was found that the continuous phases ofpoly(MA) domains functioned as permeating pathways for benzene and that the selectivity of the graft polymeric membranes occurred in the process of dissolution of the solvent into the membranes. The microphase separated structure was found to effectively enhance the selectivity as a result of its suppressing the plasticizing effect of benzene. KEY WORDS Pervaporation I Benzene-Cyclohexane Azeotropic Mixture I Membrane I Graft Copolymer I 2-Hydroxyethyl Methacrylate I Methyl Acrylate I Microphase Separated Structure I Plasticizing Effect I Separation I
Micelle formation and the hydrophobic domain structure of a water-soluble ABA-type block copolymer of hydrophobic poly(2-hydroxyethyl methacrylate) (PHEMA) and hydrophilic polyethylene oxide) (PEO) were investigated by means of small-angle X-ray scattering and a fluorometric analysis using fluorescent dyes as probes for the hydrophobic region. The emission Xm"T of a fluorescent dye added to a block copolymer solution exhibits a distinct two-step blue shift with an increase in polymer concentration. The concentration at which the second transition takes place is consistent with the critical concentration for the intermolecular association determined from light scattering. The first transition in the emission Xmax indicates that the hydrophobic domain of the contracted PHEMA chain was formed within a molecule, suggesting the formation of a monomolecular micelle. Subsequent intermolecular association through PHEMA chains appears to bring about further aggregation of PHEMA chains within the hydrophobic domain. The fluorescence spectra exhibit a remarkable temperature dependence and the emission Xm" was shifted toward shorter wavelength on lowering the temperature in both the monomolecular and polymolecular micelles. As for the polymolecular micelle, X-ray scattering data reveal that a considerable extent of the intermixing phase exists in the interfacial region between the core and the shell and also that the width of the intermixing phase decreases with a lowering of the temperature. This suggests that a demixing of the constituent blocks results in an enhancement of the hydrophobicity of the PHEMA chains within the core of the micelle. The state of the PHEMA chains in the intermixing phase is discussed.
ABSTRACT:The water-soluble ABA-type block copolymer composed of a hydrophobic poly(2-hydroxyethyl methacrylate) and a hydrophilic poly(ethylene oxide) was synthesized. The correlation between the structure of the block copolymer in dilute aqueous solution and its hydrophobic interaction was studied in comparison with random copolymers whose hydrophobic groups are statistically distributed along the chain. Fluorometric measurements using ANS as a probe for hydrophobic region were carried out on the aqueous solution of the block copolymer in the monomolecular state. The hydrophobic domain structure of the monomolecular block copolymer is discussed with respect to the change in the thermodynamic parameters for the binding process of ANS to the polymer chain. The binding ability of the block copolymer for an ANS molecule was found to be larger than that of corresponding random copolymers. This indicates that the mode of the arrangement of hydrophobic groups along the chain affects the hydrophobic interaction and that the block copolymer forms the large hydrophobic region which results from the aggregation of these hydrophobic blocks. It was observed that the temperature dependence of the binding constant of the block copolymer displayed a sharp transition within a narrow temperature range, indicating that the structural change takes place within a molecule. The thermodynamic parameters for both states of the block copolymer below and above the transition temperature were determined independently from the temperature dependence of the binding constant. This means that the hydrophobic domain of the block copolymer becomes larger in the lower temperature range than in the higher, presumably because of the segregation between the hydrophobic and the hydrophilic blocks.KEY WORDS Water-Soluble Block Copolymer / Telomerization / 2-Hydroxyethyl Methacrylate / Poly(ethylene oxide) / Hydrophobic Interaction / Fluorescent Probe / Hydrophobic Domain / Segregation / Polymers consisting of both the hydrophilic and hydrophobic portions have characteristic properties,1 often referred to as the amphiphilic property. Only a few papers, however, have been published on the relation between the polymer structure and this property. The condition for the occurrence of either the hydrophilic or the hydrophobic functions still remains unclear and so it is desirable to study more extensively the influence of intramolecular interaction on the solution properties. may thus be expected that the mode of arrangement of hydrophobic groups in a polymer chain affects the occurrence of hydrophobicity in polymers.It has been reported that the hydrophobic interaction of a water-soluble amphiphilic polymer is influenced not only by the chemical structure and composition of the hydrophobic groups but also by the distribution of these groups along the chain. 2 • 3 ItThe study on the conformation and intramolecular interaction of block copolymers consisting of an incompatible homopolymer pair in dilute solution has been the subject of extensive investigati...
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