Abstract
Effects of branches on the crystallization kinetics of polypropylene-g-polystyrene (PP-g-PS) and polypropylene-gpoly( n-butyl acrylate) (PP-g-PnBA) graft copolymers with well-defined molecular structures were systematically investigated by DSC. The Avrami equation was used to analyze the isothermal crystallization process, while the analysis of nonisothermal crystallization process was based on the Jeziorny-modified Avrami model and Mo model. The kinetics results of isothermal and nonisothermal crystallization verified the peculiar effects of branches on the crystallization process of PP backbones in PP-g-PS and PP-g-PnBA graft copolymers: on one hand, the interaction between branches (π-π interaction between PS branches, or dipole-dipole interaction between PnBA branches) restrained the mobility and reptation ability of the PP backbones, which hindered the crystallization process; on the other hand, the heterogeneous nucleation effect resulting from the branched structure and fluctuation-assisted nucleation mechanism (caused by microphase separation between the PS or PnBA rich phase and the PP rich phase) became more pronounced with increasing branch length, which facilitated the crystallization process.
Highlights
Isotactic polypropylene is one of the most widespread commercial polymers due to its outstanding physical and chemical properties
We systematically studied the isothermal and nonisothermal crystallization kinetics of polypropylene-g-poly(ethylene-co-1-butene) (PP-g-EBR) graft copolymers with well-defined molecular structures, and found that the crystallization rate increased first and decreased with increasing the branch level[24]
At a given crystallization temperature, the t1/2 value of PP-g-PS and PP-g-PnBA graft copolymers increased first and decreased with the enhancement of branch length. This verified the peculiar effects of branches on the crystallization process of PP backbones in PP-g-PS and PP-g-PnBA graft copolymers: on one hand, the interaction between branches (π-π interaction between PS branches, or dipole-dipole interaction between PnBA branches) restrained the mobility and reptation ability of the PP backbones, which hindered the crystallization process; on the other hand, the heterogeneous nucleation effect resulting from the branched structure[29−31] and fluctuation-assisted nucleation mechanism[32, 33] became more pronounced with increasing branch length[24], which facilitated the crystallization process
Summary
Isotactic polypropylene (iPP) is one of the most widespread commercial polymers due to its outstanding physical and chemical properties. We systematically studied the isothermal and nonisothermal crystallization kinetics of polypropylene-g-poly(ethylene-co-1-butene) (PP-g-EBR) graft copolymers with well-defined molecular structures, and found that the crystallization rate increased first and decreased with increasing the branch level[24].
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