A study of thermodynamically favorable crystals in branched polymers: A disentangled and crystallizable interphase

Ankur Rastogi, Ann E. Terry, Vincent B.F. Mathot, Sanjay Rastogi

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10 Scopus citations

Abstract

The paper addresses the crystallization behavior of homogeneous branched polyethylenes, where the branches cannot be incorporated within the lattice. The polymer was chosen to investigate the morphology achievable by polymers where the chains cannot extend, which is considered to be a requisite to minimize the surface free energy. Pressure-temperature conditions similar to those necessary to form extended chain crystals in linear polyethylenes are applied. In-situ wide-angle X-ray diffraction and Raman spectroscopy are used to follow the structural and conformational changes during crystallization. The hexagonal phase is not observed in these polymers unlike in linear polyethylene. However, crystallization at elevated pressures results in a structural organization of the interphase and the fold surface; this provides adjacent reentry, where the branches will also possess structural order. Crystallization of these components leads to the formation of an incompressible open-orthorhombic phase (a = 7.56 Å, b = 5.03 Å, c = 2.55 Å, density = 960 kg/m3) in addition to the existing orthorhombic crystalline domain. With the crystallization of the chains at the interphase and on the fold surface, a contraction in the parent orthorhombic phase or its transformation into the monoclinic phase is observed. Our experimental data suggest that in such a class of polymers the thermodynamically stable state will be crystals with an ordered interphase that can be achieved ultimately by disentanglement of the chains in the amorphous region. The disentangled nature of the amorphous component is further supported by solid-state mechanical deformation of samples. © 2005 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)4744-4754
Number of pages11
JournalMacromolecules
Volume38
Issue number11
DOIs
StatePublished - May 31 2005
Externally publishedYes

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