Influence of Ionic Species on the Microphase Separation Behavior of PCL‑<i>b</i>‑PEO/Salt Hybrids

The microphase separation behavior of the hybrids of poly­(ε-caprolactone)-b-poly­(ethylene oxide) (PCL-b-PEO) with different inorganic salts at various doping ratios (r) was studied by temperature-variable SAXS. It was observed that the salts could induce microphase separation to form ordered structure in the originally miscible melt of PCL-b-PEO. The effects of the metal ion and anion were correlated with the competitive interactions of PEO/salt and PCL/salt, which were characterized by FT-IR and DSC, respectively. It was found that at lower doping ratios the salts preferentially interacted with PEO. The larger association number of the metal ion and stronger association between PEO and salt led to a lower onset doping ratio for formation of ordered structure (r0). At higher doping ratios the salt interacted with PCL as well. When the metal ion exhibited a highly selective interaction toward PEO, a more ordered structure with a higher order–order transition temperature (TODT) tended to be formed. The anion in the salt also affected the interactions of PEO/salt and PCL/salt. Weaker Lewis basicity of the anion would result in a stronger interaction of PEO/salt and thus a lower r0. The results showed that the microphase separation behavior of the PCL-b-PEO/salt hybrids was sensitive to the competitive interactions of the salt with the PCL and PEO blocks

Crystallization-Driven Co-Assembly of Micrometric Polymer Hybrid Single Crystals and Nanometric Crystalline Micelles

In the present work, crystallization-driven coassembly of micrometric polymer single crystals and nanometric block copolymer micelles was achieved. The hybrid single crystals are first formed by cocrystallization of polyethylene (PE) homopolymer and polyethylene-<i>b</i>-poly­(<i>tert</i>-butyl acrylate) (PE-<i>b</i>-P<i>t</i>BA) block copolymer (BCP) in DMF or DMF/<i>o</i>-xylene mixed solvent. The morphology of the obtained hybrid single crystals can be regulated via changing the solvent composition, crystallization temperature and mass ratio of BCP/homopolymer. Because of the difference in crystallization rate, the distribution of PE-<i>b</i>-P<i>t</i>BA BCP in the hybrid single crystals may be inhomogeneous, leading to a concave gradient surface structure. The hybrid single crystals have a double-layer structure, in which PE homopolymer chains adopt extended conformation and the PE blocks in PE-<i>b</i>-P<i>t</i>BA are probably once-folded. After the PE homopolymer is consumed, cylindrical micelles of PE-<i>b</i>-P<i>t</i>BA can further epitaxially grow on the lateral surface of the hybrid single crystals and “ciliate paramecium-like” coassemblies are yielded. The single crystal/micelles coassemblies can be prepared either by one-step method, in which PE and PE-<i>b</i>-P<i>t</i>BA are added together in a single step, or by two-step method, in which the hybrid single crystals are prepared in the first step and extra PE-<i>b</i>-P<i>t</i>BA is added in the second step to grow BCP micelles. This work provided a simple route to construct hierarchical assemblies composed of objects with different scales by using crystallization as the key driving force

Specific Disassembly of Lamellar Crystalline Micelles of Block Copolymer into Cylinders

Specific Disassembly of Lamellar Crystalline Micelles of Block Copolymer into Cylinder

Understanding the Seeded Heteroepitaxial Growth of Crystallizable Polymers: The Role of Crystallization Thermodynamics

Seeded heteroepitaxial growth is a “living” crystallization-driven self-assembly (CDSA) method that has emerged as a promising route to create uniform segmented nanoparticles with diverse core chemistries by using chemically distinct core-forming polymers. Our previous results have demonstrated that crystallization kinetics is a key factor that determines the occurrence of heteroepitaxial growth, but an in-depth understanding of controlling heteroepitaxy from the perspective of crystallization thermodynamics is yet unknown. Herein, we select crystallizable aliphatic polycarbonates (PxCs) with a different number of methylene groups (xCH2, x = 4, 6, 7, 12) in their repeating units as model polymers to explore the effect of lattice match and core compatibility on the seeded growth behavior. Seeded growth of PxCs-containing homopolymer/block copolymer blend unimers from poly(ε-caprolactone) (PCL) core-forming seed platelet micelles exhibits distinct crystal growth behavior at subambient temperatures, which is governed by the lattice match and core compatibility. A case of seeded growth with better core compatibility and a smaller lattice mismatch follows epitaxial growth, where the newly created crystal domain has the same structural orientation as the original platelet substrate. In contrast, a case of seeded growth with better core compatibility but a larger lattice mismatch shows nonepitaxial growth with less-defined crystal orientations in the platelet plane. Additionally, a case of seeded growth with poor core compatibility and larger lattice mismatch results in polydisperse platelet micelles, whereby crystal formation is not nucleated from the crystalline substrate. These findings reveal important factors that govern the specific crystal growth during a seeded growth approach by using compositionally distinct cores, which would further guide researchers in designing 2D segmented materials via polymer crystallization approaches

Synthesis and Crystallization Behavior of Equisequential ADMET Polyethylene Containing Arylene Ether Defects: Remarkable Effects of Substitution Position and Arylene Size

A new series of polyethylene (PE) containing arylene ether units as defects in the main chain, which were precisely separated by 20 CH2 units, were synthesized via acyclic diene metathesis (ADMET) polymerization. The thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking were investigated with TGA, DSC, WAXD, and SAXS. It is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and their location in the solid phase. The ortho-substituted phenylene units are excluded from the crystal phase, leading to a low melting temperature (Tm). In contrast, the para-substituted phenylene units can be included into the crystal, leading to a high Tm. The meta-substituted phenylene units can be partially included into the crystal, resulting in mixed crystal structures and an intermediate Tm. Such an effect of substitution position in precision PEs is different from that in poly­(ethylene oxide) reported in the literature, which can be ascribed to the matchable configuration of the defects in the main chain with the conformation of PE in the crystals. When the defects become naphthylene ether units, the crystallization and melting behaviors of the polymers are similar to or different from those of the precision PEs with phenylene ether defects, depending on the substitution position. This shows that both the substitution position in the arylene ether defects and the defect size exert effects on crystallization, melting behaviors, and chain stacking of precision PEs

Poly(trimethylene monothiocarbonate) from the Alternating Copolymerization of COS and Oxetane: A Semicrystalline Copolymer

A semicrystalline poly­(trimethylene monothiocarbonate) (PTMMTC) has been synthesized via the selective and alternating copolymerization of carbonyl sulfide and oxetane. This reaction was catalyzed by (salen)­CrCl accompanied by organic bases over a wide range of temperatures from 40 to 130 °C. PTMMTC is shown to exhibit similar crystallization behavior to high-density polyethylene (HDPE), i.e., being spherulite and possessing melting temperatures (Tm) up to 127.5 °C and a degree of crystallinity (Xc) of up to 71%. Moreover, PTMMTC has a wide processing temperature window of ca. 100 °C

Design and Regulation of Lower Disorder-to-Order Transition Behavior in the Strongly Interacting Block Copolymers

Lower disorder-to-order transition (LDOT) phase behavior is seldom observed in block copolymers (BCPs). Design of LDOT BCPs is important for broadening the applications and improving the high temperature properties of BCPs. In this work, the LDOT phase behavior was first achieved in the strongly interacting BCPs consisting of poly­(ethylene oxide) (PEO) and poly­(ionic liquid) (PIL) blocks (EO_<i>m</i>-<i>b</i>-(IL-X)_<i>n</i>, X: counterion) by introducing two extra strong forces (hydrogen-bonding and Coulombic interaction) with different temperature dependences. It is also found that the LDOT phase behavior of the EO_<i>m</i>-<i>b</i>-(IL-X)_<i>n</i> BCPs can be regulated by molecular weight (related to mixing entropy), counterion, and salt doping. Increasing counterion size and salt content shifts the disorder-to-order transition temperature (<i>T</i>_DOT) to higher temperature, whereas a higher molecular weight leads to a lower <i>T</i>_DOT. Based on our findings, some general rules for design of LDOT phase behavior in the strongly interacting BCPs were proposed. Moreover, the conductivity of the EO_<i>m</i>-<i>b</i>-(IL-X)_<i>n</i> BCPs was correlated with the LDOT phase behavior. A remarkable increase in conductivity after LDOT, i.e., a thermo-activated transition, is observed for the EO_<i>m</i>-<i>b</i>-(IL-X)_<i>n</i> BCPs, which can be attributed to the cooperative effects of temperature rising and LDOT

Closed-Loop Phase Behavior of Block Copolymers in the Presence of Competitive Hydrogen-Bonding and Coulombic Interaction

The closed-loop phase behavior, where a lower disorder-to-order transition (LDOT) takes place first, followed by an upper order-to-disorder transition (UODT) upon heating, is seldom observed in block copolymers (BCPs). In this work, we prepared a model BCP, LiClO₄-doped poly­(ethylene oxide)-<i>b</i>-poly­(<i>tert</i>-butyl acrylate-<i>co</i>-acrylic acid) (PEO-<i>b</i>-P­(<i>t</i>BA-<i>co</i>-AA)), in which the hydrogen (H)-bonding between the PEO and AA units and the Coulombic interaction in salt-doped PEO block have opposite effects on the miscibility of BCPs. The relative strength of the H-bonding and Coulombic interaction can be easily tuned by the hydrolysis degree (<i>D</i>_H) of the P<i>t</i>BA block and the amount of doped salt. Various phase behaviors are observed by changing relative strength of different forces. Especially, the closed-loop phase behavior can be achieved when H-bonding, Coulombic interaction, and mixing entropy reach a delicate balance