Structure and molecular mobility of nascent isotactic polypropylene powders
نویسندگان
چکیده
The detailed structure and molecular mobility of nascent isotactic polypropylene (iPP) powder was investigated using differential scanning calorimetry, transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). The crystallinity of the nascent iPP powder is approximately 33%, which is much lower than that of melt-quenched or isothermally crystallized iPP. Peaks from the variable temperature-cross-polarization and magic-angle spinning spectra at high temperature for the noncrystalline component of nascent powder (POW) were enhanced over those of the melt-crystallized samples. Pulse NMR experiments indicated that the mobility of the rigid component of the POW was easily activated with temperature. No lamellar structures were observed in the TEMs of the POW. The annealing treatment of the POW induced the development of a lamellar structure and temperature independence in the rigid component mobility. From these results, one can conclude that the crystalline size of the POW is extremely small and that the intermediate component is easily affected by the surrounded noncrystalline component. Polymer Journal (2012) 44, 764–771; doi:10.1038/pj.2012.121; published online 20 June 2012
منابع مشابه
A first principles investigation of isotactic polypropylene
Bulk isotactic polypropylene in the a form was studied using density functional theory-based computations. The computed physical structure of this system is in excellent agreement with available experimental data. The electronic band structure, ionization potential, and electron affinity were also determined. The impact of various types of chemical imperfections (including double bond, hydroxyl...
متن کاملSemicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design.
We report the design, synthesis, morphology, phase behavior, and mechanical properties of semicrystalline, polyolefin-based block copolymers. By using living, stereoselective insertion polymerization catalysts, syndiotactic polypropylene-block-poly(ethylene-co-propylene)-block-syndiotactic polypropylene and isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene...
متن کاملCrystal structure of the trigonal form of isotactic polypropylene as an example of density-driven polymer structure.
Propene-hexene copolymers crystallize in a new polymorphic form of isotactic polypropylene when the concentration of hexene is higher than nearly 10-15 mol %. The hexene units are included in the crystals, inducing an increase of density that allows crystallization of 3-fold helical chains in a trigonal unit cell according to the space group R3c or Rc, where the helical symmetry of the chains i...
متن کاملSupercritical CO₂ Foaming of Radiation Cross-Linked Isotactic Polypropylene in the Presence of TAIC.
Since the maximum foaming temperature window is only about 4 °C for supercritical CO₂ (scCO₂) foaming of pristine polypropylene, it is important to raise the melt strength of polypropylene in order to more easily achieve scCO₂ foaming. In this work, radiation cross-linked isotactic polypropylene, assisted by the addition of a polyfunctional monomer (triallylisocyanurate, TAIC), was employed in ...
متن کاملMesoporous silica-supported zirconocene catalysts for highly isotactic polypropylene.
A new bis(indenyl)zirconocene bearing a pendant Si-Cl anchor has been grafted onto MCM-41, SBA-15, MCM-48 and a disordered mesoporous silica for the polymerisation of ethylene and propylene, producing polymers with very high molecular weights, low polydispersities and, in the case of polypropylene, higher levels of isotacticity than obtainable with analogous homogeneous systems.
متن کامل