Crystallization Behavior of Isotactic Propylene−Ethylene and Propylene−Butene Copolymers:  Effect of ComonomersversusStereodefects on Crystallization Properties of Isotactic Polypropylene

Abstract

Isotactic propylene−ethylene (iPPEt) and propylene−butene (iPPBu) copolymers have been prepared with different metallocene catalysts. The different influences of stereodefects (isolated rr triads), ethylene and butene comonomeric units on the crystallization of the α and γ forms of isotactic polypropylene (iPP) have been discriminated. Both iPPEt and iPPBu copolymers crystallize from the melt as mixtures of the α and γ forms. The amount of the γ form increases with increasing crystallization temperature, comonomer concentration, and content of rr stereodefects. In iPPBu copolymers, the amount of the γ form decreases for concentration of butene units higher than 10−14 mol % and is always lower than that crystallized in iPPEt copolymers. Butene units, therefore, favor crystallization of the γ and α forms at low and high concentrations, respectively. These data have indicated that the crystallization of the γ form of iPP is not only related to the value of the average length of the regular propylene sequences 〈L iPP〉, but is also related to the inclusion of stereodefects and constitutional defects in the crystals of iPP. Very different proportions of ethylene and butene units are included in crystals of the α and γ forms of iPP. Butene units are included indifferently in crystals of the α and γ forms, but probably more easily in the α form at high concentrations. Therefore, at low butene concentration, up to nearly 10 mol %, the effect of shortening of the length of regular isotactic propylene sequences prevails and induces crystallization of the γ form. For butene concentrations higher than 10 mol %, the effect of inclusion of butene units in crystals of the α form prevails, producing a decrease of the amount of the γ form and crystallization of the pure α form for butene contents higher than 30 mol %.

Application of a multi-phase multi-morphology crystallization model to isotactic polypropylenes with different molecular weight distributions

“…It is well known that the γ-form is able to host more defects in its crystal structure (see Refs. [8,9]), therefore its growth for the iPPs object of this study, is expected to be favoured over the typically stable α-form, especially in the high temperature range. Therefore, the under estimation of the amount of γ-form could be related to the aforementioned underestimation of the crystal growth rate of the γ-form, and only experimental data collected for metallocene iPPs could solve the issue in the future.…”

“…De Rosa et al investigated the crystallization behavior of isotactic polypropylene from metallocene catalysis and different stereo-regularity [8] and comonomer content [9] and found an increase in the amount of γ-form with decreasing the average length of isotactic sequences or with increasing comonomer content.…”

“…The β modification is usually formed using specific nucleating agents [2][3][4] or from oriented α-crystals created by moderately strong flow [5]. Elevated pressure and high crystallization temperatures induces the γ-phase [6,7], which is found also in iPPs with stereo-and/or regio-errors [8][9][10] or small amount of α-olefines comonomer [11]. Elevated cooling rates (>100°C/s) inhibit the stable monoclinic modification in favour of a mesomorphic form [1,12].…”

Structure and Properties of Low-Isotacticity Polypropylene Elastomeric Fibers Prepared by Sheath-Core Bicomponent Spinning

“…Conventionally, PE and PP have been polymerized applying Ziegler-Natta catalyst. Development of metallocene catalyst provided the technologies for designing new types of polymers such as those with narrow molecular weight and composition distributions, controlled stereo regularity [1][2] , copolymerization [3][4][5][6][7] etc. Especially, development of polymers with elastomeric characteristics is widely investigated recently [8][9][10][11][12][13].…”

Copolymerization of 4-methyl-1-pentene with α,ω-alkenols

“…However, if the chain length of the comonomer is closer to the main monomer, the impact would become weak. The change of the melting temperature of the propylene copolymer with 1-butene [36], 1-hexene [37,38], 1-octene [37] and 1-decene [37] showed that, the incorporation of the shorter comonomer would be less efficient to decrease the melting temperature of the copolymer. Previous research revealed that 1-butene was more inclined to be incorporated into the crystalline phase than ethylene, 1-hexene and 1-octene for propylene copolymers [39].…”