No abstract

Melt mixing of polyamides results in exchange reaction and generation of copolymers. In this work, Monte Carlo method is used to simulate the time evolution of molecular weight distribution (MWD) and copolymer composition during the exchange reaction process between polyamides with AA and BC structure. The influences of initial composition and molecular weight have been investigated. Decrease in the difference between the average molecular weight of two kinds of polyamides results in faster approach of the MWD toward Flory's dis-tribution and higher probability of producing copolymers. When the ratio between the numbers of initial molecules of two homopolymers is increased, the number of generated copolymers is reduced and the wider MWD is obtained.

ABSTRACT:Measurements of the change of the pour point depression (⌬T PP ) were performed for the wax solutions made of four solvent mixtures: ethyl acetate/hexane (EA/HEX), 1,2-dichloroethane/cyclohexane (DCE/CYH), butanone/heptane (MEK/ HEP), and acetone/chloroform (AC/CF) doped with EVA polymers. The values of ⌬T PP increase significantly with increasing of the selective solvent EA, DCE, MEK, and AC components, for the vinyl acetate (VA) segment in EVA copolymers, in the solvent mixtures. The solvent effect of ⌬T PP occurring in wax solutions can also come from the solutions of EVA polymer, which were prepared by solvent mixtures with various compositions and used as parent solutions of EVA pour point depressant. From the experimental results such as the NMR of EVA macromolecules; viscosities of EVA, waxes, and their blends; and solubilities of wax with and without EVA macromolecules in the solvent mixtures, the complexation between wax molecules and ordered ethylene segment, and wax solubilization within ordered ethylene segments in EVA macromolecules are suggested for qualitative description of the observed significant variation of ⌬T PP .

Ultrasonic disassociation of the ethylene-vinyl acetate (EVA) random copolymer in 1,2-dichloroethane (DCE), cyclohexane (CYH), and their solvent mixtures was investigated using viscometry and dynamic laser light scattering (DLLS). It was found that the disassociation of the EVA aggregates in solutions increases with increasing the time and intensity of ultrasonic shearing and approaches invariant finally. This phenomenon is especially marked for the EVA copolymer with low vinyl acetate (VA) content in the polar solvent of DCE at higher concentration and lower temperature. This is attributed to disassociation of the ethylene segment of the EVA random copolymer in dilute solutions.

ABSTRACT:The morphology evolution of miscible blends of a semicrystalline polyamide 6 (PA6) and an amorphous polyamide 6Ico6T (PA6IcoT) was investigated using an internal Brabender mixer at a temperature range 220-260 C. Morphology of the blends was characterized by scanning electron microscopy (SEM) and laser particle analysis. Temperature rising dissolution was used to separate the different phases of the blends and the phase compositions were determined by Fourier transform infrared (FTIR) spectroscopy. The particle size evolution of the dispersed phase (PA6) was calculated and agreed well with experimental observation. It was found that the particle size was quickly reduced to nanometer scale after several minutes of processing. A convection-diffusion model was adopted to study the phase evolution during meltmelt mixing stage and compute the dimension of each phase. The results strongly support the notion of existence of distinct phases during blending, whose development can be well described by the model. The dispersed phase is reduced mainly by stretching of flow, while the broadening of the blending phase can be primarily attributed to molecular diffusion. The study also suggests the possibility to prepare novel polymer blends with nanometer sized domain of high uniformity.