Methylene Sequences Research Articles

Hydrocarbon generation mechanism of lamalginite- and telalginite-dominated source rocks in a saline lake basin: A case study of the Permian Lucaogou formation in the Jimusaer Sag, Junggar Basin

The hydrocarbon generation of source rocks is significantly influenced by organic matter type, chemical element composition, and structural characteristics of kerogen. We classified the organic matter types in the shale of the Lucaogou Formation, Jimusar Sag, Junggar Basin, using organic petrology and rock pyrolysis as well as kerogen element and Fourier transform infrared (FT-IR) spectroscopy analyses, and compared the hydrocarbon generation mechanisms of source rocks with different types of organic matter. The organic matter of the Lucaogou Formation contains mostly two types of hydrocarbon generating macerals, the lamalginite and the telalginite based on physical and optical properties (texture, fluorescence, and optical reflectance). The lamalginite is a continuous sheet of less than 5 μm thick and greater than 50 μm in length. It has strong yellow fluorescence. The telalginite occurs as discontinuous short strips or pear-shaped objects with length of 10–30 μm and relatively weak fluorescence. The lamalginite-dominated shale has higher atomic H/C and lower atomic O/C ratios, indicating better hydrocarbon generation potential, whereas the telalginite-dominated shale has higher N and S heteroatom contents. The results of FT-IR spectroscopy of the kerogen indicate that the lamalginite-dominated shale is rich in aliphatic groups with long linear methylene sequences. The aromatic groups content is relatively low, but the carboxyl/carbon group (CO) content is high. The aliphatic group content of the telalginite-dominated shale is relatively low, with short-branched chains. The aromatic group content is relatively high. The methyl vibration signal directly connected to the benzene ring is strong, and the sulfoxide (SO) group has a high-intensity peak. Our results provide new insights into distinguishing organic matter types in the Lucaogou Formation and understanding the hydrocarbon generation mechanisms of source rocks in saline lake basins.

Long Chain Polyamides: Influence of Methylene Sequence Length and External Forces on Structural Features

AbstractCrystallographic studies on a series of even–even polyamides PA10.n (12, 14, 16, and 18) with variable methylene sequence length (n − 2) are performed. Temperature‐dependent X‐ray diffraction studies show that a triclinic α phase is the preferred polymorph after slow cooling to room temperature like in many other even–even polyamides. For PA10.12 and PA10.14 the pseudo‐hexagonal high temperature phase γ is observed between the Brill transition temperature TB and melting point TM. For both higher members a distinct Brill transition is absent below TM. The influence of temperature on the packing state of the stems during cooling is discussed and compared to related polymers. An analysis of well oriented crystalline states in annealed fibers reveals that the crystalline state achieved under ambient conditions is influenced by external forces due to small energetic differences between different α and β polymorphs. All PA10.n samples show in the fiber‐oriented state a prominent β polymorph which is dominant in PA10.12 and PA10.14 but superimposed with a significant α fraction in both higher members. The consequences of changes in the polymorphic state under the influence of external forces for crystalline states achieved under application relevant processing conditions are considered.

Preparation of highly branched polyolefins by controlled chain‐walking olefin polymerization

AbstractA series of α‐diimine nickel(II) catalysts bearing different para‐substituted groups, {[(4‐R‐2,6‐Me2‐C6H2NC)2Nap]NiBr2, Nap: 1,8‐naphthdiyl; R = CHMePh (C1); R = CHPh2 (C2); R = tBu (C3); R = Br (C4); R = Me (C5)}, were synthesized and characterized. The molecular structures of C1 and C3 were determined by single crystal X‐ray analysis and show distorted tetrahedron geometry with C2v symmetry. The catalytic behaviors of these catalysts toward ethylene polymerization were investigated in the presence of diethylaluminum chloride (Et2AlCl) as a cocatalyst. The fast chain‐walking process in N,N‐chelated nickel system can be efficiently modulated via the introduction of para‐sec‐phenethyl substituents with improved thermal stability and catalytic performance. C1‐Et2AlCl exhibited high thermal stabilities and high activities reaching 4.61 × 106 g PE (mol Ni h)−1, producing highly branched amorphous polyethylenes (up to 143 branches/1000C) with high molecular weight and narrow polydispersity. This catalyst system conducted successfully conducted 2‐octene polymerization in comparison with the corresponding 1‐octene polymerization. The result demonstrated 2‐octene polymerized slower than 1‐octene and produced the highly‐branched poly(2‐octene)s with approximately 120 branches/1000C, including methyl, ethyl, amyl, and hexyl branches and a small amount of the long methylene sequence due to monomer isomerization.

Thermal Fractionation of Ethylene/1-Octene Multiblock Copolymers from Chain Shuttling Polymerization

Ethylene/1-octene statistical multiblock copolymers (OMBCs) consisting of the alternation of crystalline, hard blocks and amorphous, soft blocks, with ≈0.5 and 20 mol % of 1-octene units, respectively, are subjected to thermal fractionation resorting to successive self-nucleation and annealing (SSA). The study is extended to random copolymers (RCs) of high (44 kDa) and low (3.4 kDa) number average molecular mass Mn, mimicking in 1-octene content the crystalline hard blocks and to the OMBC fractions extracted in boiling n-hexane and cyclohexane through a suitable solution fractionation protocol. For all the samples, the melting endotherms are well resolved in a multiplicity of peaks corresponding to the melting of crystals of different thicknesses generated in the SSA protocol that reflect the distribution of the methylene sequence length (MSL) in between consecutive interruptions along the chains. It is shown that, regardless of molecular mass, the MSL distributions of the RC samples are shifted toward greater values than those of the OMBC samples, and that also the shapes of the distributions are different. Since the MSL distribution depends on the frequency and distribution of the defects along the chains, and the defects act as interruption points, the higher fraction of long crystallizable sequences in the RC samples suggests that whereas for the RC samples the interruptions are merely represented by the 1-octene units that are rejected outside the crystals, for the OMBCs, the interruption of the regular methylene sequences belonging to the crystalline hard blocks due to the amorphous soft blocks linked to them should also play a role. Indeed, due to the partial miscibility of the hard and soft blocks, the hard blocks of major length tend to crystallize in a confined environment. This prevents the formation of thicker crystals and induces decrease of the MSL values as well as changes in the shape of the MSL distributions (topological confinement). On the other hand, the hard blocks of shorter length tend to crystallize, crossing the hard block rich regions and causing melting point depression and consequent shift of the MSLs toward lower values with respect to RCs (diluent effect). It is shown that differences in the MSL distribution of OMBCs are the result of the interplay between topological confinement and diluent effect, which in turn reflects differences in the OMBC chain microstructure, that is, differences in the distribution of block length at the inter- and intra-chain level.

The Properties of Poly(ester amide)s Based on Dimethyl 2,5-Furanedicarboxylate as a Function of Methylene Sequence Length in Polymer Backbone.

A series of poly(ester amide)s based on dimethyl furan 2,5-dicarboxylate (DMFDC), 1,3-propanediol (PDO), 1,6-hexylene glycol (HDO), and 1,3-diaminopropane (DAP) were synthesized via two-step melt polycondensation. The phase transition temperatures and structure of the polymers were studied by differential scanning calorimetry (DSC). The positron annihilation lifetime spectroscopy (PALS) measurement was carried out to investigate the free volume. In addition, the mechanical properties of two series of poly(ester amide)s were analyzed. The increase in the number of methylene groups in the polymer backbone resulted in a decrease in the values of the transition temperatures. Depending on the number of methylene groups and the content of the poly(propylene furanamide) (PPAF), both semi-crystalline and amorphous copolymers were obtained. The free volume value increased with a greater number of methylene groups in the polymer backbone. Moreover, with a lower number of methylene groups, the value of the Young modulus and stress at break increased.

Composition, hydrogen bonding and viscoelastic properties correlation for ethylene/α,ω-alkenol copolymers

The influence of composition of ethylene/ α,ω -alkenol ( α,ω -alkenol = 10-undecen-1-ol or 9-decen-1-ol) copolymers on comonomer distribution and dynamic rheological properties were investigated. Thermal fractionation revealed formation of multiple peaks corresponding to the presence of methylene sequences of different length in copolymers. The share of fraction with shorter methylene sequence increased with increasing comonomer content. It turned out that viscoelastic behavior of ethylene/ α,ω -alkenol copolymers was dependent on comonomer content incorporated into the polymer chain. The relaxation time of reptation increased with increasing comonomer content what confirmed that comonomer units acted as physically crosslinking agent. FT-IR investigation proved the appearance of inter- and intramolecular hydrogen bonds in ethylene copolymers with α,ω -alkenols. Higher relative content of inter- and intramolecular hydrogen bonds was observed in α,ω -alkenol with a longer hydrocarbon chain. In addition, activation energy of flow increased with increasing of the comonomer content. Moreover, incorporation of α,ω -alkenols into the polymer chain resulted in a decrease of the packing length of copolymers with increasing comonomer content, what proved that the inter- and intramolecular hydrogen bond played a significant role in viscoelastic properties. • Amount of α,ω -alkenol incorporated in copolymers affected comonomer distribution. • The content of α,ω -alkenol played a key role in rheological behavior of copolymers. • The FT-IR study showed the presence of hydrogen bonds in E/ α,ω -alkenol copolymers. • The effect of hydrogen bonding is dependent on structure of α,ω -alkenol comonomer.

Crystallization of Long-Spaced Precision Polyacetals III: Polymorphism and Crystallization Kinetics of Even Polyacetals Spaced by 6 to 26 Methylenes.

In this paper we extend the study of polymorphism and crystallization kinetics of aliphatic polyacetals to include shorter (PA-6) and longer (PA-26) methylene lengths in a series of even long-spaced systems. On a deep quenching to 0 °C, the longest even polyacetals, PA-18 and PA-26, develop mesomorphic-like disordered structures which, on heating, transform progressively to hexagonal, Form I, and Form II crystallites. Shorter polyacetals, such as PA-6 and PA-12 cannot bypass the formation of Form I. In these systems a mixture of this form and disordered structures develops even under fast deep quenching. A prediction from melting points that Form II will not develop in polyacetals with eight or fewer methylene groups between consecutive acetals was further corroborated with data for PA-6. The temperature coefficient of the overall crystallization rate of the two highest temperature polymorphs, Form I and Form II, was analyzed from the differential scanning calorimetry (DSC) peak crystallization times. The crystallization rate of Form II shows a deep inversion at temperatures approaching the polymorphic transition region from above. The new data on PA-26 confirm that at the minimum rate the heat of fusion is so low that crystallization becomes basically extinguished. The rate inversion and dramatic drop in the heat of fusion irrespective of crystallization time are associated with a competition in nucleation between Forms I and II. The latter is due to large differences in nucleation barriers between these two phases. As PA-6 does not develop Form II, the rate data of this polyacetal display a continuous temperature gradient. The data of the extended polyacetal series demonstrate the important role of methylene sequence length on polymorphism and crystallization kinetics.

Crystallization of Poly(ethylene)s with Regular Phosphoester Defects Studied at the Air-Water Interface.

Poly(ethylene) (PE) is a commonly used semi-crystalline polymer which, due to the lack of polar groups in the repeating unit, is not able to form Langmuir or Langmuir–Blodgett (LB) films. This problem can be solved using PEs with hydrophilic groups arranged at regular distances within the polymer backbone. With acyclic diene metathesis (ADMET) polymerization, a tool for precise addition of polar groups after a certain interval of methylene sequence is available. In this study, we demonstrate the formation of Langmuir/LB films from two different PEs with regular phosphoester groups, acting as crystallization defects in the main chain. After spreading the polymers from chloroform solution on the water surface of a Langmuir trough and solvent evaporation, the surface pressure is recorded during compression under isothermal condition. These π-A isotherms, surface pressure π vs. mean area per repeat unit A, show a plateau zone at surface pressures of ~ (6 to 8) mN/m, attributed to the formation of crystalline domains of the PEs as confirmed by Brewster angle and epifluorescence microscopy. PE with ethoxy phosphoester defects (Ethoxy-PPE) forms circular shape domains, whereas Methyl-PPE-co-decadiene with methyl phosphoester defects and two different methylene sequences between the defects exhibits a film-like morphology. The domains/films are examined by atomic force microscopy after transferring them to a solid support. The thickness of the domains/films is found in the range from ~ (2.4 to 3.2) nm depending on the transfer pressure. A necessity of chain tilt in the crystalline domains is also confirmed. Grazing incidence X-ray scattering measurements in LB films show a single Bragg reflection at a scattering vector qxy position of ~ 15.1 nm−1 known from crystalline PE samples.

Tuning layered superstructures in precision polymers

An approach to influence and control layered superstructures by varying the methylene sequence length between two consecutive functional groups in linear precision polymers containing 2,6-diaminopyridine (DAP) groups is presented. Layered superstructures with repeating units involving three monomeric units along the chain direction with very high coherence lengths upto 110 nm are observed in case of shorter alkyl segments, (16 and 18 {hbox {CH}}_{2} units), while more conventional layer superstructures incorporating only one monomer are found for related polymers with 20 {hbox {CH}}_{2} units per methylene sequence. A building block model explaining the unusually large periodicity of three monomeric units is proposed wherein layers containing crystalline or amorphous methylene sequences occur in different combinations. Occurrence of different layered structures depending on crystallization conditions, methylene sequence length as well as functional group type is explained by a competition of H-interactions between the DAP groups and the van der Waal forces between the hydrophobic methylene groups.

Selectivity of Thermal Analysis in the Branching Analysis of Low Density Polyethylene

AbstractLow density polyethylene (LDPE) exhibits a complex branching architecture that is characterized by the numbers and lengths of the branches. In previous work, it has been demonstrated that comprehensive microstructural information on LDPE can only be obtained via multiple preparative fractionations and subsequent advanced analysis of the fractions. In this work, microstructural differences of LDPE with similar molar masses but different melt flow indexes are addressed. The samples are fractionated using the multiple preparative fractionation concept to generate narrowly distributed branch and molar mass fractions, respectively. The individual fractions are cross‐fractionated by stepwise recrystallization using successive self‐nucleation and annealing to obtain endotherms with multiple peaks (seeds). Each seed represents a population of chains with similar branching structure or crystallizable methylene sequences. The methylene sequence lengths (MSLs) and the seed contents of the seeds with the highest population are compared for fractions with similar fractionation characteristics. Fractions showing significant differences in their MSL and/or seed content are investigated further using advanced analytical techniques and 2D liquid chromatography (2D‐LC), to correlate MSL or seed content to the branching structure.

Characterization of Ethylene-butene Polyethylene Copolymers by DSC and SSA

Two copolymers of M1 and M2 were studied by DSC and SSA. The SSA test was applied to characterized the distribution of methylene sequence length (MSL) in the M1 and M2 copolymers. The butene comonomer contents of M1 and M2 were 4.66 mol% and 4.83 mol%, respectively. The content of butene comonomer of M1 and M2 is low, and the distribution of MSL increases monotonously with that of MSL. The longest MSL of M1 is 195.4, and the mole fraction is 0.96%, which is higher than M2. The influence of MSL and distribution on the crystallinity and Tm is greater than that of the total monomer content, which are different with traditional opinions.

Dominant Effects of Short-Chain Branching on the Initial Stage of Nucleation and Formation of Tie Chains for Bimodal Polyethylene as Revealed by Molecular Dynamics Simulation.

The molecular mechanism of short-chain branching (SCB), especially the effects of methylene sequence length (MSL) and short-chain branching distribution (SCBD) on the initial stage of nucleation, the crystallization process, and particularly the tie chain formation process of bimodal polyethylene (BPE), were explored using molecular dynamics simulation. This work constructed two kinds of BPE models in accordance with commercial BPE pipe resins: SCB incorporated in the long chain or in the short chains. The initial stage of nucleation was determined by the MSL of the system, as the critical MSL for a branched chain to nucleate is about 60 CH2. SCB incorporated in the long chain led to a delay of the initial stage of nucleation relative to the case of SCB incorporated in the short chains. The increase of branch length could accelerate the delay to nucleation. The location of short chain relative to the long chain depended on the MSL of the short chain. As the MSL of the system decreased, the crystallinity decreased, while the tie chains concentration increased. The tie chains concentration of the BPE model with branches incorporated in the long chain was higher than that with branches incorporated in the short chain.

Study of the Kinetics of the Phase Transition of the First Order in Tetracosane C24H50 by Fourier-Transform IR Spectroscopy

The kinetics of the development of the structural phase transition of the first order in monodisperse samples of tetracosane C24H50 has been studied using Fourier-transform IR spectroscopy. Temperature dependences of frequencies and intensities of rocking (in the region of ν ~ 720 cm–1) and bending (in the region of ν ~ 1470 cm–1) vibration modes of CH2 groups in trans methylene sequences in crystalline cores of elementary lamellae has been analyzed. It has been shown that the solid-phase transition of the first order develops by the heterogeneous mechanism in a narrow temperature interval ΔT ~ 2 K according to the theory of diffuse phase transitions of the first order and is caused by changes in the symmetry of crystallographic cells.

Chain-walking polymerization of 3-heptene with phenyl substituted α-diimine nickel catalysts

The first example of a 3-alkene polymerization has been successfully achieved with 3-heptene in the presence of phenyl-substituted α-diimine nickel precatalysts activated by dMMAO, and compared with the corresponding linear alkenes, i.e., 1-pentene, 2-hexene and 4-octene polymerizations. The microstructures of the produced poly(3-heptene), which consists of ethyl, propyl and butyl branches indicated the 3,4- and 4,3-insertion, followed by chain-walking, with incorporation of a small fraction of long methylene sequences of 1,7-enchainment via monomer-isomerization.Late-transition metal catalyzed polymerization reactions of internal alkenes to synthesize novel polyolefin materials are highly important and also highly challenging. Upon activation with dried modified methylaluminoxane (dMMAO), the first example of a 3-alkene polymerization has been successfully achieved for 3-heptene catalyzed by phenyl-substituted α-diimine nickel complexes in comparison, and compared with the polymerizations of the corresponding linear alkenes, i.e., 1-pentene, 2-hexene and 4-octene. The results indicate that the polymerization of 3-heptene was achieved via chain-walking to generate branched amorphous polymers with glass transition temperature of ca. −68 °C. The microstructures of the produced poly(3-heptene) indicated the 3,4- and 4,3-insertion followed by chain-walking, the latter being predominant. The NMR analyses of the polymers showed that the obtained poly(3-heptene) possessed ethyl, propyl and butyl branches and a small amount of the long methylene sequence of 1,7-enchainment via monomer-isomerization. The branches structures were significantly dependent on the polymerization temperature, and the content of propyl branches derived from 3,4-insertion decreased with an increase in the polymerization temperature.

Crystallization of Long-Spaced Precision Polyacetals I: Melting and Recrystallization of Rapidly Formed Crystallites

Rapidly melt-crystallized polyethylenes with acetal groups (−O–CH2–O−) precisely spaced by 12, 18, 19, or 23 methylene backbone carbons exhibit two reorganizations and three melting endotherms on heating at relatively low heating rates. Real-time wide-angle X-ray diffraction (WAXD) experiments further confirm that these transitions are associated with a reorganization to a different crystalline structure. The differential scanning calorimetry endotherms are associated with melting of the initially formed disordered (or hexagonal) phases, followed by melting of Form I and by melting of Form II crystals with increasing temperature. In parallel with these structural changes, the long spacing undergoes a discrete step increase at the polymorphic transitions. Upon the transition from disordered to Form I crystals, the core crystal thickness increases by one repeating unit, whereas the crystal thickness remains basically unchanged during the transition from Form I to Form II crystallites. The effect of even vs odd CH2 spacer on the observed melting temperatures is prevalent for spacer <10 CH2 units. The even or odd number of methylenes between acetals also affects the type and kinetics of packing assembly in layered crystallites. Although a disordered mesomorphic-like structure develops under fast cooling in odd-spaced polyacetals (PA-19, PA-23), the formation of Form I crystals cannot be bypassed in PA-12 and PA-18. Furthermore, some differences are also found in the WAXD patterns of Form II between odd- and even-spaced polyacetals, denoting that staggering of the acetals in the crystallites is affected by the configuration of consecutive acetals with respect to the methylene sequence.

Cooperative effect through different bridges in nickel catalysts for polymerization of ethylene

A series of mononuclear (M1 and M2) and dinuclear (C1–C6) Ni α‐diimine catalysts activated by modified methylaluminoxane were used in polymerization of ethylene. Catalyst C2 bearing the optimum bulkiness showed the highest activity (1.6 × 106 g PE (mol Ni)−1 h−1) and the lowest short‐chain branching (32.5/1000 C) in comparison to the dinuclear and mononuclear analogues. Although the mononuclear catalysts M1 and M2 polymerized ethylene to a branched amorphous polymer, the dinuclear catalysts led to different branched semicrystalline polyethylenes. Homogeneity and heterogeneity in the microstructure of the polyethylene samples was observed. Different trends for each catalyst were assigned to syn and anti stereoisomers. In addition, thermal behavior of the samples in the successive self‐nucleation and annealing technique exhibited different orders and intensities from methylene sequences and lamellae thickness in respect of each stereoisomer behavior. Higher selectivity of hexyl branches obtained by catalyst C2 showed a cooperative effect between the centers. The results also revealed that for catalysts C5 and C6, selectivity of methyl branches led to very high endotherms and crystalline sequences with melting temperatures higher than that of 100% crystalline polyethylene indicating ethylene/propylene copolymer analogues. For catalysts C3 and C4, more vinyl end groups were a result of the long distance between the Ni centers. Kinetic profiles of polymerization along with a computational study of the precatalysts and catalysts demonstrated that there is a direct relation between rate constant, energy interval of catalyst and precatalyst, and interaction energy of Et···methyl cationic active center (Et···MCC or π–Comp.). Based on this, narrow energy interval (activation energy) of precatalyst and catalyst leads to fast and higher activation rate (catalyst M2), and strong interaction of ethylene and catalyst leads to high monomer uptake and productivity (catalyst C2). Moreover, theoretical parameters including electron affinity, Mulliken charge on Ni, chemical potential and hardness, and global electrophilicity showed optimum values for C2.

Microstructure characterization of one high-speed extrusion coating polyethylene resin fractionated by solvent gradient fractionation

One low density polyethylene (LDPE) resin with high-speed extrusion coating property is fractionated through solvent gradient fractionation (SGF) technique using 1,2,4-trimethylbenzene (TMB) and ethyl cellosolve (ECS) as good/poor solvent pair at 115 °C. The pristine sample and its fractions are characterized by high-temperature gel permeation chromatography (HT-GPC) coupled with triple detectors (refractive index RI, light scattering LS, viscometer VIS), 13C–nuclear magnetic resonance spectroscopy (13C–NMR), differential scanning calorimetry (DSC) and successive self-nucleation/annealing (SSA) thermal fractionation. By adjusting the ratio of good/poor solvent, the obtained fractions show their molecular weight from 1.58 × 103 g/mol to 4.76 × 105 g/mol. It is found that the fractions with high molecular weight (fractions 10–13) occupy about 55.85% in resin. Particularly, the molecular weight distribution (MWD) of most fractions is in the range of 1.1–1.2. Each fraction contains more short chain branch (SCB) and less long chain branch (LCB) simultaneously. With increasing the molecular weight, the branching content shows no regular change. The lowest SCB and total branch content regions correspond to molecular weight 1.97 × 104 to 4.10 × 104 g/mol. The melting and crystallization temperatures of fractions firstly increase and then decrease with the molecular weight. The crystallinity decreases gradually from 51.7% to 31.1%. In the SSA thermal fractionation, each fraction shows a broad range of endotherm with multiple melting peaks in DSC curve corresponding to the different methylene sequence length (MSL) (L n and L w ). The longest L n (L w ) region occurs in the molecular weight of 8.95 × 103 to 3.14 × 104 g/mol. The relationship between chain microstructure and properties is also discussed.

Structure formation in nanophase-separated systems with lamellar morphology: Comb-like vs. linear precision polymers

We report findings of a comparative study of a comb-like polymer, poly(1,4-phenylene-2,5-n-didecyloxy terephthalate) [PPDOT] and a linear chain precision polymer consisting of a methyl protected 2,6-diaminopyridine group after every 20th methylene unit of a linear saturated polyethylene chain [PDAPS20]. Both polymers exhibit lamellar morphologies related to a nanophase separation of the methylene sequences from ring-like sub-units as seen in X-ray diffraction data. Although their chain architecture is different, investigations on oriented samples of both PPDOT and PDAPS show that their lamellae orient in such a way that their surface normals tend to be perpendicular to the shear fields leading to different average chain orientations. A novel approach considering the volume occupied per CH2 unit in the alkyl nanodomain calculated on the basis of unit cell considerations is employed to understand the packing state of the alkyl segments. While modification B of PPDOT exhibits densely packed alkyl nanodomains, modification A of PPDOT and PDAPS20 show a relatively loose packing. At the end, we attempt to bring together these two classes of polymers exhibiting nanophase-separated morphologies by means of a classification scheme based on the structural arrangement of the sub-units within their respective domains, highlighting their similarities and differences.

Synthesis and Characterization of Isotactic Poly(1-hexene)/Branched Polyethylene Multiblock Copolymer via Chain Shuttling Polymerization Technique

Understanding from the underlying mechanism of chain shuttling polymerization (CSP) is limited due to scarceness of successful reports and incompetence of traditional characterization techniques to distinguish blocky structures. Here, a simple synthesis approach for production of an isotactic poly(1-hexene)/branched polyethylene multiblock copolymer from a 1-hexene monomer is presented. Resulting copolymers can be easily characterized because of their solubility in most organic solvents. This novel blocky architecture is synthesized using ansa-ethylenebis(1-η5-indenyl)zirconium dichloride and α-diimine nickel(II) bromide catalysts. While the former participates in 1,2-enchainment of monomers and produces amorphous segments, the latter forms methylene sequences through chain walking reaction. A quasi-living polymerization is established by reversible transfer of growing chains between catalyst components, as manifested by narrowing molecular weight distribution. 13C NMR analysis confirms that the blocky st...

Infrared Spectroscopy and X-ray Diffraction Characterization of Dimorphic Crystalline Structures of Polyethylenes with Halogens Placed at Equal Distance along the Backbone.

Polyethylenes with halogens placed on each and every 21st, 15th, or ninth backbone carbon display crystallization patterns enabled by the size of the halogen and by changing crystallization kinetics. The different structures have been identified from X-ray patterns combined with a detailed analysis of the infrared spectra of series containing F, Cl, or Br atoms that were either fast or isothermally crystallized from the melt. Under both crystallization modes, all specimens develop layered crystallites that accommodate 5-9 repeating units along the chain's axis. The size of the halogen and intermolecular staggering to maximize packing symmetry are responsible for striking structural differences observed between the series and between the two modes of crystallization. While the small size of the F atom causes a small perturbation to the crystal lattice and the orthorhombic structure is maintained for all members of the series either fast or isothermally crystallized, each Cl or Br-containing system presents dimorphism. Under fast crystallization, Cl and Br containing samples adopt the all-trans conformation (planar Form I), while in slowly crystallized samples gauche conformers set for bonds of the backbone carbons adjacent to the carbon with the halogen due to a close intermolecular staggering of halogens (herringbone Form II). In both forms the methylene sequence betweenhalogens maintains the all-trans conformation. The structural details are extracted from the analysis of the C-halogen stretching region of the IR spectra, and from adherence to the n-alkane behavior of CH2 rocking, CH2 wagging, and C-C stretching progression modes.