Study of phase separation in blends of polystyrene and poly(α-methylstyrene) in the glass transition region using quantitative thermal analysis

Abstract

Differential scanning calorimetry of 11 solution blends of polystyrenes of molecular masses from 3 X 103 to 1 X 107 daltons with poly(a-methylstyrenes) of molecular masses from 1.9 X 104 to 5.1 X 105 daltons was carried out between 300 and 500 K. The various blends covered the ranges from miscibility to immiscibility. The glass transition temperatures, their ranges, and the change in heat capacity with composition in the transition ranges have been measured. Long before phase separation is macroscopically noticeable, it is possible to detect phase instability from a broadened glass transition region. This broadening is discussed in terms of concentration fluctuations.

Calorimetric study of block-copolymers of poly(n-butyl acrylate) and gradient poly(n-butyl acrylate-co-methyl methacrylate)

“…This is not the case in random copolymers where the glass transition also changes, but the breadth of the glass transition does not exceed that of the homopolymers, as was shown for example for increas ingly brominated poly(2,6-dimethyl-1,4-phenylene oxide) [20]. For complete solubility of both components in block copolymers, as well as for blends of homopolymers, there is only one, broad glass transition and the beginning of the lower and the end of the upper glass transition move closer to each other, but never reaches the narrow glass transition range of a random copolymer, as was also documented on the styrene/a-methylstyrene system of homopolymers of varying molar mass by DSC [21].…”

Multiple glass transitions and local composition effects on polymer solvent mixtures

“…For the polymeric component there will be a local enrichment in self-composition because of chain connectivity. The impact of this effect on the glass transitions for a polymer blend was described some time ago by Lau et al 1 and Chung et al, 2 and quantified by Lodge and McLeish. 3 Their arguments would evidently apply as well to the polymeric component in a polymer-solvent mixture.…”

An addition scheme of heat capacities of linear macromolecules. Carbon backbone polymers

“…The heat capacity measurements [6] Weight fraction MS Fig. 2 Additivity of the heat capacity of or-methyl styrene and styrene blocks in the solid phase (at 330 K below the glass transition of both blocks) and in the liquid phase (melt, 470 K, above the glass transition of both blocks).…”

“…Of particular interest was that copolymer heat capacities could be generated from the heat capacities of the homopolymer constituents [1]. Heat capacities of multiphase polymers, such as partially crystallized polymers [4] and phase separated block copolymers [5] and blends [6] could also be analyzed by comparison with heat capacities derived from additivity of the components [7]. Even the increase in heat capacity at the glass transition was found to be additive and empirically predictable in terms of the rigid atomic groupings, "beads", in the macromolecule [8].…”