synopsisThe effects of vinyl acetate content on crystallinity of ethylene-vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystalliiity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene-vinyl alcohol copolymer) was also investigated. 103 98 77 44 112 113 107 110 Calcd by theory 106.2 97.6 72.0 44.0 100.2 97.6 72.0 44.0 12. L.

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The rates of spherulite and crystal growth in isotactic polystyrene have been studied as a function of temperature by microscopic, x‐ray, and density methods. The effects of molecular weight and degree of isotacticity upon the spherulite growth are shown. Degree of isotacticity is the predominant factor in growth rate. Maximum rate of spherulite growth was observed at 175°C., while the maximum rate of crystal growth was observed at 190°C. Some evidence exists that polystyrenes made with the use of heterogeneous catalysts of the Ziegler type consist of heterogeneous blocks of isotactic and atactic polymers rather than polyblends.

SynopsisThe dynamic mechanical properties of molded and cast polyacrylonitrile and copolymers have been measured by an automatic Rheovihron. The transitions are described for the amorphous, "paracrystalline," and crystalline phases. Based upon a number of polymer theories of multiple phases in polymeric systems, the transitions have been assigned to specific polymer motions. Three transitions are defined for the alpha transition region. The mechanical response is compared to x-ray diffraction and infrared to ascertain the transition assignments in decreasing order beginning with the highest temperature transition as (1) the main transition for the amorphous phase ( T I ) , (2) dipole-dipole interaction which is related to the "paracrystalline phase" (T2), and (3) secondary transition for the amorphous phase (7'3).