Isotactic Polybutene-1 Research Articles

Analysis of formation mechanism of crystal form I in isotactic polybutene-1 based on a melting memory method

Analysis of formation mechanism of crystal form I in isotactic polybutene-1 based on a melting memory method

Deuterated Isotactic Polybutene-1 Exhibits Fast Form II to I Transition at Isothermal Crystallization Temperatures

Deuterated Isotactic Polybutene-1 Exhibits Fast Form II to I Transition at Isothermal Crystallization Temperatures

Dramatically Accelerating II-I Crystal Phase Transition of Polybutene‑1 by In Situ Incorporation of H-Shape Long-Chain-Branching Structures.

This communication reports an effective strategy helping address the long-troubling melt processing issue of isotactic polybutene-1 (i-PB) caused by its extremely slow II-I crystal phase transition. The solution lies in a facile synthesis of i-PB containing H-shape long-chain-branching structures (LCB-i-PB) by applying a so-called ω-alkenylmethyldichlorosilane copolymerization-hydrolysis (ACH) chemistry to butene-1 polymerization with Ziegler-Natta or metallocene catalysts. It is evident that the H-shape LCB structures effectively enhance chain entanglements of i-PB and induce an over-the-board acceleration of the overall melt crystallization process including nucleation, form II crystallization, and form II-form I phase transition. As i-PB usually requires up to a week to reach equilibrium of the II-I phase transition, it is found that with LCB-i-PB such a transition is almost finished within as short as 24 h to even higher degrees.

Tensile yield behavior of isotactic polybutene-1

Relative to polyethylene or polypropylene, isotactic polybutene-1 (iPB-1) in form I is of high value for commercial applications due to its excellent mechanical properties; whereas, it tends to exhibit inconspicuous yield behavior closely related to poor energy consumption and thus weak toughness when subjected to uniaxial stretching. Regret, few studies had addressed how to control iPB-1 tensile yield behavior. As the tensile yield behavior of form I iPB-1 depended on the applied annealing temperature Ta and time ta as well as cyclic loading-unloading conditions, iPB-1 three-phase structure evolution was carefully characterized by wide-line solid-state 1H NMR. With Ta or ta increasing, the weakening tensile yield behavior of iPB-1 was accompanied by a decreasing rigid phase content which can be recognized by 1H NMR rather than DSC, revealing that a higher rigid phase content in iPB-1 favors a more significant typical tensile yield behavior. Furthermore, the weakening tensile yield behavior of iPB-1 due to annealing at a higher temperature can slowly recover back while further annealing at a lower temperature, implying the reversibility of destroyed rigid phase. Cyclic loading-unloading under a suitable fixed strain can promote formation of rigid phase in iPB-1, favoring appearance of the typical yield behavior. Therefore, the mutual contact possibility, dislocation and slip of iPB-1 rigid phase were proposed to be responsible for the tensile yield behavior. The results are of significance for understanding the structural origin of tensile yield behavior of iPB-1 and further tuning toughness of iPB-1 for its industrial applications.

In situ synthesis of novel trans‐1, 4‐polyisoprene/isotactic polybutene reactor blends with multi‐component structure

AbstractIn this paper, a series of novel trans‐1, 4‐polyisoprene/isotactic polybutene (TPI/iPB) in‐reactor blends were synthesized by isoprene and butene sequential two‐stage polymerization technology with spherical TiCl4/MgCl2 type Ziegler‐Natta catalyst. The components, structures, and properties of the as‐obtained TPI/iPB reactor blends were characterized by gel permeation chromatography, Fourier transform Infrared spectroscopy, and differential scanning calorimetry. The active trans‐1, 4‐polyisoprene (TPI) particles obtained in the initial isoprene polymerization by the Z‐N catalyst can be acted as microreactors to initiate butene polymerization subsequently. The TPI/iPB reactor blends with varied components were in situ synthesized within the reactor. The preparative‐temperature rising elution fractionation (p‐TREF) technique was used to fractionate the TPI/iPB reactor blends based on the elution temperature ranged from −40°C to 90°C. The weight distribution and microstructure of each fraction were investigated. The reactor blends are composed of crystallizable high trans‐1, 4‐uint polyisoprene obtained from the first‐stage isoprene polymerization, high isotactic polybutene obtained from the second‐stage butene polymerization and TPI‐b‐iPB block copolymer with different sequence structure obtained from the initial time of the second stage. This work is expected to propose the possible polymerizations of a‐olefins and conjugated dienes by using heterogeneous Ziegler‐Natta catalyst and provide a kind of novel rubber/plastic reactor blend materials.Highlights The first synthesis of the trans‐1, 4‐polyisoprene/isotactic polybutene reactor blends. p‐TREF technique was used to analyze the composition of TPI/iPB reactor blends. Detailed structure characterization of the fractions including GPC and NMR TPI‐b‐iPB block copolymer can be obtained through the sequential polymerization. Rubber/plastic reactor blend materials were fabricated by the Z‐N catalyst.

Role of amorphous phase in II-I transition of iPB-1/iPP blends

Isotactic polybutene-1 (iPB-1) possesses excellent physical and mechanical properties, but its applications are limited owing to the slow II-I transition after melt processing. The concerned II-I transition mechanism is a long-lasting hot topic. After an isotactic polypropylene (iPP) was melt-blended into iPB-1, a good model system for II-I transition study to discuss on roles of amorphous phase was consequently obtained with amorphous phase tuned but form II crystalline structures almost kept fixed according to the affected crystallization and melting behaviors of iPB-1 in iPB-1/iPP blends. Both DSC and FTIR results revealed the enhanced II-I transition behaviors of iPB-1 in the blends and FTIR results especially confirmed form I direct crystallization from amorphous phase of iPB-1/iPP blends prior to form II consumption due to II-I transition. The earlier the direct form I crystallization, the faster II-I transition of iPB-1 in the iPB-1/iPP blends. It was proposed that form I direct crystallization of the iPB-1 chain segments which have ability to crystallize but remained in the amorphous phase lowered the energy barrier of transition from adjacent form II crystals to packed-mesophases due to the local volume contract resulting in a stretch to iPB-1 chains with parts contained in the adjacent form II crystals. Consequently, the II-I transition of adjacent form II crystals were triggered to start and it generated a ripple effect on the entire II-I transition process. The results are of great significance on understanding of iPB-1 II-I transition process and also of importance for iPB-1 industrial applications.

Transition of iPB-1 with low molecular weight crystallized from solutions.

The dimension or entanglement of polymer chains is crucial to chain dynamics, and the polymer chains can be diluted and disentangled in a solution by reducing the interaction with each other. This letter addresses the role of solution concentration in the crystal transition of isotactic polybutene-1 (iPB-1) with low molecular weight crystallized from solution. It turned out that the transition of iPB-1 obtained from the higher concentration of the solution is faster than that obtained from the lower one. In addition, the disparity in the transition between the early stage and later stage for samples prepared from solutions with and without stirring was characterized. DSC and X-ray experiments revealed that initial temperatures for the solution-crystallized iPB-1 to melt and crystallize into form II dominated the transition. The role of entropy in the transition was proposed as a primary factor influencing the iPB-1 transition. Increasing the concentration of the solution or stirring during crystallization increases the supersaturation for iPB-1 to crystalize from the solution and form less stable crystals. The less stable iPB-1 crystals cause the formation of form II at lower temperatures during heating. Therefore, the lower entropy in amorphous regions resulted in an enhanced propensity for the helical conformation with a lower entropy and consequently accelerated the crystal transition.

Form II to form I transition in solution-crystallized isotactic polybutene-1.

Different polymer chains in a solution or melt have different conformations with corresponding entropy at each moment, which would be confined after crystallization. Equilibrium concept-based conformation or conformational entropy depends on chain dynamics, which is related to the effect of energy on conformational changes in polymer chains. Herein, an isotactic polybutene-1 (iPB-1) crystal was crystallized from solution by adding a precipitant at various temperatures. The solution-crystallized iPB-1 crystal was heated to 100 °C to obtain form II at different heat rates and the transition of form II was characterized. It was found that the form II to form I transition was not only related to the precipitation temperature but also to the heating rate of the solution-crystallized iPB-1. Thus, both precipitation temperature and heating rate determine the formation temperature of form II, i.e., form II that crystallized at lower temperature would transform faster. The results indicate that the conformation or conformational entropy of the amorphous region in iPB-1 is important to understand crystal transition.

Memory Effect on the Form II to I Phase Transition of Isotactic Polybutene-1 in a Flow Field

Memory Effect on the Form II to I Phase Transition of Isotactic Polybutene-1 in a Flow Field

Accelerated crystallization and crystal-crystal transition of PB induced by PP with optimized content

Isotactic polybutene-1 (PB)/isotactic polypropylene (PP) blends, typical crystalline/crystalline polymer blends with low-melting-temperature (Tm) PB and high-Tm PP, exhibit complicated interactions between their components in both molten and solid states. However, the intrinsic influences of PP component on crystallization of PB form II, form II-I transformation, and the dependence of these phase transitions on PP content are unclear. In this work, the influences of PP content ranged from 5 wt% to 40 wt% on PB crystallization were investigated. It was found that the content of PP played significant roles on the phase morphologies of the blends in molten state and then the subsequent crystallization of PB whatever in form II or form I. The PP components with ≤20 wt% addition acting as heterogeneous nucleation sites promoted crystallization nucleation, increased the crystallinity and lamellar thickness of PB, accelerated PB form II-I transformation and increased transformation degree with the increase in PP content. Whereas, the PP components with ≥30 wt% incorporation reduced the crystallinity and lamellar thickness of PB, retarded PB form II-I transformation and transformation degree with the increase in PP content. Interestingly, the PB/PP (80/20) blend presented the fastest II-I transformation rate as well as the highest transformation degree of PB. The dependence of crystallization and crystal structures of PB form II, form I, and form II-I transformation kinetics on PP concentration was discussed. PB form I′ was not observed in the present study. This work provides a theoretical and practical guide for the preparation of novel PB materials with desired structures and excellent performance, especially with anxiously accelerated crystal-crystal transition and transition degree of PB.

Effect of crystalline transformation on supercritical CO2 foaming and cell morphology of isotactic polybutene-1

As a polycrystalline polymer, isotactic polybutene-1 (iPB-1) will form different crystalline structures when it crystallizes under different conditions. In this work, we found a simple method to manipulate the cell structure of iPB-1 foams by controlling the annealing time of crystalline form II at room temperature and employing supercritical CO2 foaming. As the content of crystalline form II increases, the storage modulus (G′) and complex viscosity (|η * |) increase, and the solubility of CO2 in iPB-1 increases. Crystalline form II has a wider foaming temperature window compared to crystalline form I and exhibits a more uniform cell structure at temperatures between 95 °C and 125 °C. The average cell diameters of crystalline form II and I are 33.9 µm and 11.2 µm at 115 °C and 15 MPa CO2, respectively. A small amount of crystalline form I acts as a heterogeneous nucleation agent during the foaming process, resulting in the formation of a “petal-like” cell structure. During the foaming saturation process, the melted portion of iPB-1 with unstable crystalline form II transforms into crystalline form I′ under high-pressure CO2, while the unmelted portion transforms into crystalline form I. As the pressure increases, the cell structure of iPB-1 undergoes a transition from “petal-like” to bimodal cell structure, ultimately achieving a more uniform structure. Moreover, increasing foaming pressure can also change the cell structure of the foamed material from closed-cell to open-cell. The occurrence of bimodal melting peaks in the foamed samples is beneficial for the adhesion of beads during the molding process.

Identifying a Mesomorphic Boundary Zone within Polybutene-1 Single Crystals Emerging During a Crystal–Crystal Transformation

We present experimental evidence that the transformation from one solid phase to another solid phase within a faceted polymer single crystal passes through a transient mesomorphic phase. This phase exists in the boundary zone separating the two crystalline phases of isotactic polybutene-1 (PB-1), i.e., Form II and Form I of PB-1. Employing real-time atomic force microscopy in tapping mode (TM-AFM), we followed the crystal–crystal transformation in time. TM-AFM measurements performed at about 20 °C under a nitrogen atmosphere with high humidity have allowed through differences in viscoelastic properties and associated changes in thickness to distinguish the two crystalline phases as well as the boundary zone. Measurements at an elevated temperature of 90 °C (which was far below the melting temperatures of both Form II and Form I crystals) further revealed that this boundary zone shows a transient and diffuse character and a distinctly increased thickness. Using high-resolution phase imaging of TM-AFM, we observed that within this rather extended boundary zone of up to some hundred nanometers at elevated temperatures, Form I crystals with a diameter of around 30 nm were growing in a softer and featureless matrix phase. The boundary zone and so the growth front of the Form I crystal advanced at an almost constant rate, suggesting that chains in the mesomorphic phase were considerably mobile. Our observation of an extended boundary zone probably indicates that compared to a direct crystal–crystal transformation, the corresponding free energy barrier for this transformation is lower within such a zone. Hence, our here presented model study sheds light on the poorly understood and complex pathways involved in a solid–solid transformation within a polymer single crystal.

Equilibrium Melting Temperature of the Hexagonal Crystals of Polybutene-1 and Its Copolymer

TheLamellar structures of form I in polymorphic isotactic polybutene-1 (iPB-1) and forms I and I′ in butene-1/ethylene random copolymer (iPB-1/C2) were investigated by studying their melting behavior using the combination of small-angle X-ray scattering (SAXS) and fast scanning chip calorimetry (FSC) techniques. Hexagonal form I was transformed from tetragonal form II obtained by crystallization of a homogeneous melt of iPB-1 and iPB-1/C2. Hexagonal form I′ was crystallized directly from a heterogeneous melt of iPB-1/C2. Despite the same hexagonal crystallographic structure, forms I and I′ have obviously distinct melting behaviors due to different ways of crystal formation. Well-defined linear dependences of the melting temperature against the reciprocal lamellar thickness were observed for forms I and I′ with frozen chain mobility in crystals. The slopes of the thus obtained melting lines for forms I and I′ are different. Their extrapolations to imaginary infinitely large lamellar thickness provide the equilibrium melting temperature Tm∞ for forms I and I′, which is associated with the stability of the lamellar crystals. In spite of crystal defects in form I′, a higher Tm∞ is observed for this form in iPB-1/C2 than Tm∞ for form I in both iPB-1 and iPB-1/C2. The difference in Tm∞ indicates a less perfect structure of form I crystal lamellae that is caused by the fragmentation of form II crystal lamellae during the polymorphic phase transition from form II to I. The lamellae broke into crystal blocks along the lamellar direction. The smaller lateral sizes of the fragmented lamellae clearly induce a decrease in the stability of crystals, as expressed in a lower Tm∞ for form I.

High-temperature creep behaviors of polybutene-1 with different chain microstructure and molecular weight

The creep resistance of polymer determines the dimensional stability of product under stress. The isotactic polybutene-1 (iPB) with outstanding high-temperature creep resistance and stress-crack resistance is applied widely in the field of hot-water pipes. Although the chain information including weight-average molecular weight (Mw) and aggregate structures of isotactic polybutene-1 (iPB) influence the creep resistance, the crucial factor affecting the creep behavior greatly is unclear. In this work, a series PB samples with varied Mw, isotacticity and configurational sequence were synthesized and characterized based on Gel Permeation Chromatography (GPC), solvent fractionation and Nuclear Magnetic Resonance Spectroscopy (NMR). The Differential Scanning Calorimetry (DSC), Wide-angle X-ray diffraction (WAXD) and Small angle X-ray scattering (SAXS) were used to characterize the aggregation structures of PB samples. The stress-strain behaviors and 95 °C creep deformation of these PB samples were testes by tensile test and Dynamic Mechanical Analysis (DMA), respectively. It was found that these PB samples showed different chain microstructures like 88–99 wt% high isotactic PB (HiPB) fractions, 90–97.6 mol% tetra-meso placements (mmmm) in HiPB fraction, and 50 × 104-160 × 104Mw. Increasing the molecular weight, isotacticity or configurational sequence mmmm enhanced the creep resistance of PB, while mmmm configurational sequence played more important role in creep resistance of PB through adjusting the aggregation structure (crystalline domains) of the final product greatly. Exploring the influencing factors of creep resistance provided guidance for the synthesis of high-performance PB for high-temperature pipe application.

Diffusion controlled stereoregular polymerization in granule reactors - Reaction kinetic of Pr/Bt sequence polymerization with TiCl4/MgCl2 Ziegler-Natta catalyst

Diffusion controlled stereoregular polymerization was studied to understand the relations between fragmentation and growing of catalyst granules and its catalytic features for olefin polymerizations. In this work, propylene (Pr) polymerization kinetics and Pr/butene-1 (Bt) sequence polymerization kinetics with spherical TiCl4/MgCl2 Ziegler-Natta catalyst were investigated by monitoring catalytic activity (CA), the number of active centers ([C*]/[Ti]) and microstructure of polymers. It was found that the increase in Pr polymerization time benefiting to the catalyst granule fragmentation, had different influences on the [C*]/[Ti] and catalytic efficiency (CE) for Bt-stage polymerization in different stage. Anyway, the isotacticity and weight-average molecular weight (Mw) of isotactic polybutene-1 (iPB) fractions decreased gradually with the increase in Pr polymerization time. It was deduced that the easy solubility of polybutene-1 (PB) brought difficulties in further fragmentation of catalyst particles to expose more active centers, and Bt was more sensitive to the chemical and steric environment around the active species. This work provides further understanding of the catalytic characteristics of granule reactors in the initial polymerization stage, which will guide the novel polyolefin alloy production.

Utilization of supercritical CO2 for controlling the crystal phase transition and cell morphology of isotactic polybutene-1 foams

Isotactic polybutene-1 (iPB-1) is a semi-crystalline polymer with multiple crystal forms. In this work, we found a novel method to obtain and adjust the expansion ratio and bimodal cellular structures of iPB-1 foams with annealing and foaming using supercritical CO2. The form I′ can be obtained via the supercritical CO2 annealing, and the ratio of form I and I′ can be adjusted by controlling simply the annealing time. The effects of crystal form ratio on the thermal behavior, rheological behavior and cell morphology of foams were analyzed. Energy storage modulus (G′) and complex viscosity (|η*|) decrease with the increased content of form I. Crystal form I′ has a lower foaming temperature window and bubble growth resistance than form I, resulting in larger cell diameter and expansion ratio. The bimodal cell structure can be observed in the samples with 1:1 form I′/form I, where the average large and small cell size are 122 and 40 µm at 109 °C and 10 MPa CO2, respectively. To regulate the cell distribution, various ratios of mixed crystal phases were applied to investigate their effect on the foaming behavior and bimodal cells structure at different temperatures. Even with a similar expansion ratio, significantly different cell distributions of bimodal cell structure can be easily prepared by simply adjusting the content of form I′, which can broaden the application range of iPB-1 foams.

Crystallization studies on heterogeneous melts of polybutene-1

The heterogeneous melts of isotactic polybutene-1 (iPB-1) containing Form I or Form II seeds with uniform size and random distribution were prepared by selective melting of melt crystallized and transformed samples, respectively. Compared with a reference blank melt, the remnant Form I or II seeds are able to significantly reduce the half-time of crystallization under isothermal conditions. Besides, the nucleation efficiency of Form II seeds is much higher than that of Form I seeds because of the lower lateral surface energy and highly lattice match. Furthermore, a great number of tiny spherulites with submicrometer radius nucleate and grow simultaneously, offers an opportunity to follow the development of spherulites at the very early stage. The analysis of the differential scanning calorimetry (DSC) curves confirms that the mass fraction for faster primary crystallization of heterogeneous melts is lower than that of blank melt, which clearly indicates that growth rate of spherulites is decreasing before impingement. The radius of spherulites was not much larger than the diffusion length provides the foundation for the observed non-linear growth of spherulites. This quantitative comparison of the crystallization kinetics of blank melt and heterogeneous melts can therefore be applied as a method to improve our understanding of nucleation and the diffusion-controlled growth of polymer.

Melt pre-shear induced orientation crystallization of PB and PB/HMwPB blend

Shear flow is important to understand the relationship between processing and properties of polymer products. In this work, the influences of shearing and high-molecular-weight polybutene-1 (HMwPB) on the evolution of oriented crystal's morphologies of isotactic polybutene-1 (PB) were investigated by shearing at a temperature slightly above the nominal melting temperature under different shear rate and shear duration. The shear thickening presented in primary normal stress revealed the presence of a gel-like network of shish-precursors, in which a birefringence region was observed in polarized optical microscopy (POM) images after crystallization in both PB and PB/HMwPB blend. Those shish-precursors enhanced the crystallization temperature and directly influenced the crystal structures of PB form II, and these crystal structures could be preserved from the form Ⅱ to form Ⅰ. The rheological, one-dimensional scattering, and DSC data reach a plateau with the shear duration, indicating that all the PB chains achieve their ultimate oriented state. The addition of a small amount of HMwPB caused the earlier formation of shish-precursors, the higher crystallization temperature of PB form Ⅱ, thicker lamellae, higher melting temperature, and degree of orientation of PB form Ⅰ. • Shear conditions for different crystal structures formation were given. • Shish-precursors formation and oriented crystal evolution were investigated using rheology methods combining optical microscopy and scattering technology. • The effect of HMwPB on shish-precursors formation and oriented crystal evolution was investigated.

Attapulgite Structure Reset to Accelerate the Crystal Transformation of Isotactic Polybutene.

Isotactic polybutene (iPB) has a wide application in the water pipe field. However, the most valuable form I, needs 7 days to complete the transformation. In this study, the attapulgite (ATP), which produces lattice matching of the iPB form I, was selected to prepare an iPB/ATP composite. The Fischer–Tropsch wax (FTW) was grafted with maleic anhydride to obtain MAFT, and the ATP structure was reset by reactions with MAFT to the prepared FATP, which improved the interface compatibility of the ATP and iPB. The Fourier transform infrared spectroscopy (FT-IR) and the water contact angle test confirmed the successful synthesis of FATP. X-ray diffraction (XRD) verified that the graft of MAFT did not affect the crystal structure of ATP. The iPB + 5% FATP had the maximum flexural strength, which was 12.45 Mpa, and the flexural strength of the iPB + 5% FATP annealing for 1 day was much higher than others. Scanning electron microscope (SEM) photographs verified that FATP and iPB had good interface compatibility. The crystal transformation behavior indicated that the iPB + 5% FATP had the fastest crystal transformation rate, which proved that the reset structure, ATP, greatly accelerated the crystal transformation of iPB. This was a detailed study on the effect of lattice matching, interfacial compatibility and internal lubrication of the reset structure, ATP, in the nucleation and growth stages of iPB form I. The result was verified by XRD, differential scanning calorimetry (DSC), Avrami kinetics and polarizing microscope (POM) analysis.

The formation of highly stable form of isotactic polybutene-1 electrospun membrane via self-seeding

The non-isothermal crystallization behavior from the incomplete melting of isotactic polybutene-1 (iPB-1) electrospun (e-spun) membranes is investigated. The standard sample of e-spun iPB-1 contains the concomitant form II and I′, which are less stable than form I. So, we adopted a pathway of treating a nucleation stage of concomitant polymorphs. Cross-nucleation was observed when a stable polymorph nucleates and grows on a formerly existing polymorph. The present outcomes revealed that upon non-isothermal crystallization of a partially molten state, an appropriate Domain of self-seeding temperature (Ts) 115 °C to 125 °C directed towards forming highly stable iPB-1 form I. Such phenomena might be typified to the memory effect of their pristine crystalline structure and the inter-lamella confinement effect in that particular and constrained environment of the partially molten state. In addition, the influence of variable applied voltage on the self-nucleation mechanism was also considered comparatively. Based on their morphology, spectral, and thermal analysis, samples spun at 11 kV were relatively preeminent to proceed with the self-seeding route.