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FTIR Microanalysis and Phase Behaviour of Ethylene/1‐Hexene Random Copolymers
Author(s) -
Pracella Mariano,
D'Alessio Aldo,
Giaiacopi Simone,
Raspolli Galletti Anna,
Carlini Carlo,
Sbrana Glauco
Publication year - 2007
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200700028
Subject(s) - copolymer , crystallinity , polymer chemistry , fourier transform infrared spectroscopy , crystallization , materials science , differential scanning calorimetry , branching (polymer chemistry) , monomer , nucleation , glass transition , ethylene , analytical chemistry (journal) , chemistry , crystallography , chemical engineering , polymer , thermodynamics , catalysis , organic chemistry , physics , engineering , composite material
Ethylene/1‐hexene random copolymers with 1‐hexene content in the range of 1–5 mol‐%, synthesised in the presence of new heterogeneous catalyst systems based on bis‐carboxylato and ‐bis‐chloro‐carboxylato titanium chelate complexes, have been characterised by FTIR microspectroscopy (FTIR‐M), DSC calorimetry and X‐ray scattering. The co‐monomer content and sequence distribution in the various samples were determined by means of both FTIR‐M and 13 C NMR spectroscopy. The deformation bands of methyl groups in the region of 1 400–1 330 cm −1 were used for the structural analysis of these copolymers. The effect of composition on the crystallinity and phase transitions of copolymers was analysed both in 1 500–1 300 and 760–690 cm −1 frequency ranges as a function of the annealing temperature. A neat variation of the absorbance ratio of methyl band at 1 378 cm −1 was recorded between 110 and 130 °C corresponding to the melting range of the copolymer crystals. The crystallisation behaviour of the copolymers was examined by DSC in dynamic and isothermal conditions; the isothermal kinetics were analysed according to the Avrami model. A marked decrease in the bulk crystallisation rate, accompanied by changes in the nucleation and growth of crystals, was found with an increase in the co‐monomer content. The melting behaviour of isothermally crystallised samples was also investigated and the melting temperatures of the copolymers at equilibrium conditions were related to the composition; the experimental data were consistent with the Flory exclusion model of side branches from the crystalline phase. The lowering of crystal growth rate in the copolymers has been accounted for by an increase in the free energy of formation of critical size nuclei due to the effect of the side branches.