Polymers are typically immiscible with one another, that is phase separated, in the absence of specific favorable intermolecular interactions, because the combinatorial entropy of mixing is small. Copolymers, polymer molecules containing more than one type of monomer unit, are frequently used to induce miscibility in homopolymer mixtures. Extensive work has previously established the importance of the copolymer composition, though the sequence of monomers within the copolymer has received less attention. Copolymers with random and with alternating sequences of monomers have been synthesized and mixed with homopolymers to evaluate the importance of the sequence distribution on blend miscibility. Blend miscibility determinations using differential scanning calorimetry and visual inspection can be erroneous when the glass transition temperatures of the phases are similar or the domains are small compared to the wavelength of light. Thus, we have used transmission electron microscopy to study the phase behavior of these polymer blends.Blend samples (∼30 mg) of poly(styrene-co-methyl methacrylate) (PS-PMMA), homopolystyrene (PS), homopoly(methyl methacrylate) (PMMA) were prepared by casting from tetrahydrofuran and annealing at 150°C for 7 days.
Copolymer Sequence Distribution in Which Monomer Unit Sequence and Its Cotacticity Both Obey Correlatively the First Order Markov Process. Applications to Poly(acrylonitrile-co-methyl methacrylate) and Poly(acrylonitrile-co-ethyl methacrylate)
