The role of defect microstructure in the crystallization behavior of metallocene and MgCl2-supported Ziegler-Natta isotactic poly(propylenes)

Abstract

The intermolecular defect distribution of poly(propylenes) of the Ziegler-Natta (ZN) and metallocene (M) types is assessed by classical fractionation and analysis of the fractions by GPC and 13C NMR. In addition, the linear growth rates, a property sensitive to differences in defects distribution in the poly(propylene) chain, are used to infer the stereoblock-like intramolecular distribution of defects in industrial type ZN iPPs and their fractions. The behavior of fractions from a matched metallocene iPP provide direct evidence of the single-site nature of the catalyst. Metallocene poly(propylenes) enable a quantitative assessment of the molecular, thermodynamic and kinetic factors that govern the formation and concentrations of the a and g polymorphs. Short continuous crystallizable sequences and high crystallization temperatures favor the formation of this polymorph in homo poly(propylenes) and random propylene copolymers. Differences in the partitioning of the comonomer between the crystalline and non-crystalline regions leads to contents of the gamma phase that differ among the copolymers at any given crystallization temperature. Qualitatively these differences can be used to assess the degree to which a counit participates in the crystallite

Variations in Microstructural and Physicochemical Properties of Candelilla Wax/Rice Bran Oil–Derived Oleogels Using Sunflower Lecithin and Soya Lecithin

“…Sy3 showed the highest rate of crystallization among all prepared samples. Although Sy3 showed improved crystallinity, which is evident from the brightness of the PLM micrograph, the high rate of crystallization may have resulted in the formation of fat crystals with defects [ 55 ].…”

Melt Memory Effect in Polyethylene Random Terpolymer with Small Amount of 1-Octene and 1-Hexene Co-Units: Non-Isothermal and Isothermal Investigations

“…Typical examples are ethylene-1-alkene copolymers, which are widely used in many different fields, such as pipes for water, oil, and gas transportation, packing films for foods and goods, structural materials for furniture or containers, and so on [ 1 , 7 ] These varieties of applications require a wide range of mechanical properties of the final polyethylene products. The presence of a chain of co-units at random positions, stereo defects, or noncrystallizable second polymers in the melt cannot be included in the crystal lattice, but it affects the crystallization and melting properties [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ].…”

“…The crystallization process of copolymers is often accompanied by the melt memory effect, which is correlated with self-seeds that increase the crystallization rate of copolymers [ 27 , 28 , 30 ]. If a copolymer is melted and then crystallized again, the time required for the subsequent crystallization process often changes with the previous melt temperature and the duration of the molten stage [ 1 , 11 , 16 , 17 , 19 , 22 , 23 , 27 , 28 , 29 ]. The parameters, such as comonomer content, distribution, and melt temperature reached, will affect the strength and tendency of the melt memory effect [ 16 , 18 , 19 ].…”

Uma revisão sobre polimerização de olefinas usando catalisadores Ziegler-Natta heterogêneos

“…molar, distribuição de massas molares e taticidade); iii) permitirem o controle da macroestrutura do polímero (distribuição do tamanho da partícula, morfologia e porosidade); iv) permitirem o controle das propriedades finais do polímero (resistência à tração, rigidez, transparência, etc. ), resultando em uma ampla faixa de aplicações [22] .…”