Crystallization Properties and Polymorphic Behavior of Isotactic Poly(1-Butene) from Metallocene Catalysts: The Crystallization of Form I from the Melt

Abstract

A study of the crystallization from the melt and of the polymorphic behavior of isotactic poly(1-butene) (iPB) prepared with metallocene catalysts is presented. Samples of isotactic polybutene of different stereoregularity, containing different concentrations of stereodefects (rr triads defects) and regiodefects (4,1 units) have been prepared with different C 2 -and C 1 -symmetric metallocene catalysts. The concentration of defects and the molecular mass are controlled through a rational choice of the catalyst structure and conditions of polymerization. Highly isotactic samples with concentration of rr stereodefects lower than 2 mol %, crystallize from the melt in the metastable form II. This is a common polymorphic behavior observed in iPB samples prepared with Ziegler-Natta catalysts and extensively reported in the literature. More stereodefective iPB samples, containing concentration of stereodefects higher than 2 mol %, crystallize form the melt as mixtures of form II and form I, the fraction of crystals of form I increases with increasing concentration of defects and decreasing cooling rate from the melt, and samples with concentration of rr defects of 3-4 mol % crystallize from the melt in the pure form I at low cooling rates. This is the first experimental observation of the crystallization of the stable trigonal form I of iPB from the melt at atmospheric pressure. This result may be of interest because the crystallization of the metastable form II from the melt and the spontaneous transformation at room temperature of form II into the stable form I has been considered for long time an unavoidable problem that stands in the way of the industrial development of the Ziegler-Natta iPB.

Critical roles of molecular dynamics in the superior mechanical properties of isotactic-poly(1-butene) elucidated by solid-state NMR

“…Among the previous characterizations, only DSC detected a large difference in the T m s (T m ¼130 1C for form I and 80-95 1C for form I¢). 33,42 This result provided direct evidence that form I¢ and I are different polymorphs. It was suggested from a large difference in their T m s that form I¢ is structurally disordered form I.…”

“…Very recently, De Rosa et al 33 reported that the low isotacticity sample directly crystallizes into form I¢ from the melt state. Here the stereoregularity effects on lamellar thickness /lS were investigated.…”

“…Here we will use two samples of iPB1 and low isotactic PB1 (low_iPB1) (/mmmmS¼78%). Very recently, De Rosa et al 33 found that low tacticity iPB bypasses crystallization into form II and directly crystallizes into the trigonal form (form I¢). The two iPB1 samples used in this study display different crystallization mechanisms (through or bypassing form II).…”

Kinetics of the Polymorphic Transition in Isotactic Poly(1-butene) under Uniaxial Extension. New Insights From Designed Mechanical histories.

“…24 ■ RESULTS AND DISCUSSION Mechanical properties. The polymorphic transformation occurring in i-PBu upon storage fresh (form II) samples at room temperature is associated with profound changes in the mechanical response of the material.…”

“…The parameter R takes into account the differences in the diffraction power of the two families of planes, and it has been estimated equal to 0.36. 24 The amorphous halo has been determined from WAXD pattern of an atactic poly(1-butene) sample. The resulting weight fraction of form I is considered in the following discussion on transformation kinetics.…”