Mesophase Separation and Rheology of Olefin Multiblock Copolymers

Coordinative Chain Transfer and Chain Shuttling Polymerization

Coordinative chain transfer polymerization, CCTP, is a degenerative chain transfer polymerization process that has a wide range of applications. It allows a highly controlled synthesis of polyolefins, stereoregular polydienes, and stereoregular polystyrene, including (stereo)block as well as statistical copolymers thereof. It also shows a green character by allowing catalyst economy during the synthesis of such polymers. CCTP notably allows the end functionalization of both the commodity and stereoregular specialty polymers aforementionned, control of the composition of statistical copolymers without adjusting the feed, and quantitative formation of 1-alkenes from ethene. A one-pot one-step synthesis of the original multiblock microstructures and architectures by chain shuttling polymerization (CSP) is also an asset of CCTP. This methodology takes advantage of the simultaneous presence of two catalysts of different selectivity toward comonomers that produce blocks of different composition/microstructure, while still allowing the chain transfer. This affords the production of highly performant functional polymers, such as thermoplastic elastomers and adhesives, among others. This approach has been extended to cyclic esters' and ethers' ring-opening polymerization, providing new types of multiblock microstructure. The present Review provides the state of the art in the field with a focus on the last 10 years.

Strong synergistic toughening and compatibilization enhancement of carbon nanotubes and multi-functional epoxy compatibilizer in high toughened polylactic acid (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) blends

Different carbon nanotubes (CNTs) contents on high-toughness polylactic acid (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) blends were prepared by one-step melt blending using multifunctional epoxy oligomers (ADR) as reactive compatibilizer. During reactive blending, the PLA or PBAT chains were grafted onto the CNTs by allowing the carboxyl or hydroxyl groups to react with epoxy groups and form a branched CNTs-based copolymer. The branched copolymer at the interface between PLA and PBAT was dispersed through emulsion to improve the polymer-polymer or polymer-nanoparticle entanglement between the molecular chains. Interfacial adhesion, interface layer stability, and system viscoelasticity and compatibility were improved as indicated by rheological curves and dynamic mechanical analysis. The strength and toughness of the sample were simultaneously improved by the addition of CNTs and ADR. The impact strength reached 35.3 kJ/m2, which was approximately 7 times that of the PLA/PBAT blend, and the tensile strength was also increased from 33.6 MPa to 42.8 MPa. The properties of PLA/PBAT blend synergistically modified by ADR and CNTs were obviously better than those of PLA/PBAT blend modified by ADR or CNTs. The toughening synergistic effect of ADR and CNTs on PLA/PBAT was observed with efficiency reaching 3.05. With the further understanding of the toughening mechanism, the branched CNTs-based copolymers and CNTs clusters induce a synergistic effect, which increased the interfacial adhesion and ability of energy dissipation and stress transmission.

Microphase separation/crosslinking competition-based ternary microstructure evolution of poly(ether-b-amide)

The temperature dependence of the rheological properties of poly(ether-b-amide) (PEBA) segmented copolymer under oscillatory shear flow has been investigated. The magnitude of the dynamic storage modulus is affected by the physical microphase separation and irreversible crosslinking network, with the latter spontaneously forming between the polyamide segments and becoming the dominant factor in determining the microstructural evolution at temperatures well above the melting point of PEBA. From the rheological results, the initial temperature of the rheological properties dominated by the microphase separation and crosslinking (T cross) structures were determined, respectively. Based on the two obtained temperatures, the microstructure evolution upon the heating can be separated into the ternary microstructure domains: homogenous (temperature below ), microphase separation dominating (between and T cross), and crosslinking dominating domains (above T cross). When the PEBA is heated to above T cross, the content of crosslinking network increases with time and temperature, leading to an irreversible and non-negligible influence on the rheological, crystallization, and mechanical properties. A more pronounced strain-hardening phenomenon during the uniaxial stretching is observed for the sample with a higher content of crosslinking network.

Effect of PMMA/Silica Hybrid Particles on Interfacial Adhesion and Crystallization Properties of Poly(lactic acid)/Block Acrylic Elastomer Composites

Poly(lactic acid) (PLA) is a relatively brittle polymer, and its low melt strength, ductility, and thermal stability limit its use in various industrial applications. This study aimed to investigate the effect of poly(methyl methacrylate) (PMMA) and PMMA/silica hybrid particles on the mechanical properties, interfacial adhesion, and crystallization behavior of PLA/block acrylic elastomer. PLA/block acrylic elastomer blends exhibit improved flexibility; however, phase separation occurs between PLA and block acrylic elastomer domains. Valid time-temperature superposition (TTS) measurements of viscoelastic behavior were obtained and exhibited interfacial adhesion with the addition of PMMA or PMMA/silica in PLA/block acrylic elastomer blends. In particular, the phase separation temperature was increased by the incorporation of PMMA/silica hybrid particles, which suggests a potential role for these particles in improving the phase stability. In addition, PMMA inhibits crystallization, while PMMA/silica acts as a nucleating agent, thus increasing the crystallization rate and crystallinity degree.

Studies on chain shuttling polymerization reaction of nonbridged half-titanocene and bis(phenoxy-imine) Zr binary catalyst system

In this contribution, olefin block copolymers were produced via chain shuttling polymerization (CSP), using a new combination of catalysts and a chain shuttling agent (CSA) diethylzinc (ZnEt₂). The binary catalyst system included nonbridged half-titanocene catalyst, Cp*TiCl₂(O-2,6-ⁱPr₂C₆H₃) (Cat A) and bis(phenoxy-imine) zirconium, {η ²-1-[C(H)=NC₆H₁₁]-2-O-3-^tBu-C₆H₃}₂ZrCl₂ (Cat B), as well as co-catalyst methylaluminoxane (MAO). In contrast to dual-catalyst system in the absence of CSA, the blocky structure was obtained in the presence of CSA and rationalized from rheological studies. The binary catalyst system could cause the CSP reaction to occur in the presence of CSA ZnEt₂, which yielded broad distribution ethylene/1-octene copolymers (M _w/M _n: 35.86) containing block polymer chains with high M _w. The presented dual-catalytic system was applied for the first time in CSP and has a potential to be extended to produce a library of olefin block copolymers that can be used as advanced additives for thermoplastics.

The Influence of DMDBS on Crystallization Behavior and Crystalline Morphology of Weakly-Phase-Separated Olefin Block Copolymer

Olefin block copolymer (OBC), with its low hard segments, can form unique space-filling spherulites other than confined-crystallization morphologies, mainly due to its weak phase-separation. In this work, 1,3;2,4-Bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), a well-known nucleating agent, was used to tailor the crystallization behavior and crystalline morphology of OBC. It was found that DMDBS can precipitate within an OBC matrix and self-assemble into crystalline fibrils when cooling from the melt. A non-isothermal crystallization process exhibited an increased crystallization rate and strong composition dependence. During the isothermal crystallization process, DMDBS showed a more obvious nucleating efficiency at a higher crystallization temperature. OBC showed typical spherulites when DMDBS was added. Moreover, a low addition of DMDBS significantly decreased the crystal size, while a large addition of DMDBS induced aggregates, due to the limited miscibility of DMDBS with OBC. The efficient nucleating effect of DMDBS on OBC led to an increased optical transparency for OBC/DMDBS composites.

Influence of Phase Separation on Performance of Graft Acrylic Pressure-Sensitive Adhesives with Various Copolyester Side Chains

Acrylic pressure-sensitive adhesives with various polyester side-chain lengths were synthesized to investigate the effect of branching on phase separation and polymer mechanical performance. The polyester macromonomers (MMs) were produced through ring-opening co-polymerizations of l-lactide (l-LA) and ε-caprolactone (ε-CL) initiated with 2-hydroxyethyl methacrylate (HEMA), which provides the polyester chains with terminal vinyl groups. By varying the HEMA content, a range of MM chain lengths constructed from L₁₀C₄ (five l-LA and four ε-CL units) to L₁₀₀C₄₀ were obtained at a constant monomer mole ratio. Copolymerization of 2-ethylhexyl acrylate and acrylic acid with these MMs at constant mass composition provided a series of comb copolymers consisting of acrylic backbones with polyester branches of various chain lengths. Characterization of thin films cast from the polymers using thermal analysis and scanning probe microscopy showed a transition from a homogeneous phase to the formation of distinct microphases with increasing branching chain lengths. Rheological analysis of the linear viscoelastic responses was also used through small-amplitude oscillatory shear, and dynamic master curves were constructed by time-temperature superposition. The rheological data were also consistent with phase separation for the longer side-chain lengths of L₅₀C₂₀ and L₁₀₀C₄₀. The extra elastic contribution at low frequency and the temperature dependence of a _T both show obviously effect of separated phases. Performance testing of polymer films showed that the chain extension resulted in a significant increase in both peel strength and shear resistance, which was accompanied by a modest decrease in film tackiness. The results demonstrate that tailoring branch chain structures provide a promising means for controlling the properties of the high-biomass content adhesive polymers.

Olefinic Thermoplastic Elastomer Gels: Combining Polymer Crystallization and Microphase Separation in a Selective Solvent

Since selectively swollen thermoplastic elastomer gels (TPEGs) afford a wide range of beneficial properties that open new doors to developing elastomer-based technologies, we examine the unique structure-property behavior of TPEGs composed of olefinic block copolymers (OBCs) in this study. Unlike their styrenic counterparts typically possessing two chemically different blocks, this class of multiblock copolymers consists of linear polyethylene hard blocks and poly(ethylene-co-α-octene) soft blocks, in which case, microphase separation between the hard and the soft blocks is accompanied by crystallization of the hard blocks. Here, we prepare olefinic TPEGs (OTPEGs) through the incorporation of a primarily aliphatic oil that selectively swells the soft block and investigate the resultant morphological features through the use of polarized light microscopy and small-/wide-angle X-ray scattering. These features are correlated with thermal and mechanical property measurements from calorimetry, rheology, and extensiometry to elucidate the roles of crystallization and self-assembly on gel characteristics and establish useful structure-property relationships.

Molecular relaxation and dynamic rheology of “cluster phase”-free ionomers based on lanthanum(iii)-neutralized low-carboxylated poly(methyl methacrylate)

La(iii)-neutralized low-carboxylated poly(methyl methacrylate)-based ionomers free of cluster phase exhibit a fluid-to-solid transition assigned to an interconnected multiplets network.

Liquid–solid transition in mesophase separated olefin multiblock copolymers during crystallization

A delayed liquid–solid transition has been found in strongly segregated olefin multiblock copolymers, compared to that in weakly segregated systems.