Enhanced Mechanophore Activation within Micelles

We describe the enhanced mechanophore activation within nanosized core–shell micelles, which also present temperature and ultraviolet (UV) light-responsive properties. The model micelle was fabricated by the self-assembly of an amphiphilic block copolymer of poly­(<i>tert</i>-butyl acrylate-<i>b</i>-<i>N</i>-isopropyl­acrylamide) with one spiropyran (SP) moiety at the midpoint of chain [SP-(<i>t</i>-BA₈₈-<i>b</i>-NIPAM₆₂)₂, <b>P2</b>]. Micellization of <b>P2</b> in tetrahydrofuran (THF)/water mixed solvent enhanced the reactivity of the electrocyclic ring-opening reaction of SP to merocyanine (MC) isomer under sonication because micellization caused SP-centered P<i>t</i>BA block entangled and partially swelled in the micellar core and the increase of the dielectric constant of the medium around the SP, which could facilitate the conversion of SP to MC. This new enhanced mechanophore activation model demonstrated here is valuable as a probe to detect stress activation within nanosized particles and to design multiple-responsive materials

Hydrogen-Bonding-Mediated Fragmentation and Reversible Self-assembly of Crystalline Micelles of Block Copolymer

Two hydrogen (H)-bond donors, phenol and l-threonine, were added into the aqueous solutions containing crystalline micelles of a poly­(ε-caprolactone)-<i>b</i>-poly­(ethylene oxide) (PCL-<i>b</i>-PEO) block copolymer, respectively. Dynamic light scattering (DLS) characterization showed that the micellar size became smaller after addition of phenol. Transmission electron microscopy (TEM) results revealed that the long crystalline cylindrical micelles formed in the neat aqueous solution were fragmented into short cylinders and even quasi-spherical micelles, as the phenol concentration increased. By contrast, the spherical PCL-<i>b</i>-PEO crystalline micelles could be transformed into short cylinders and then long cylinders after addition of l-threonine. Reversible morphological transformation was realized for the PCL-<i>b</i>-PEO crystalline micelles by adding these two H-bond donors alternately. It is confirmed that both phenol and l-threonine could form H-bonds with PEO. We proposed that, the micellar corona was swollen by phenol, leading to fragmentation of the micellar core, whereas the PEO blocks in the micellar corona was dynamically cross-linked by l-threonine beacuse of its multiple H-bond-donation groups, resulting in a smaller reduced tethering density

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

Fabrication of High χ‑Low <i>N</i> Block Copolymers with Thermally Stable Sub‑5 nm Microdomains Using Polyzwitterion as a Constituent Block

In this work, we used zwitterionic poly­(4-vinylpyridine) propane-1-sulfonate (PVPS) as a constituent block to construct high χ-low N block copolymers (BCPs) with different neutral polymers as the other block, including polystyrene (PS), poly­(ethylene oxide) (PEO), and poly­(l-lactide) (PLLA). Lamellar structures with sub-5 nm microdomains were observed in all three types of BCPs. Due to the tendency of self-aggregation induced by electrostatic interaction in polyzwitterion, the Flory–Huggins parameters (χ) between PVPS and most neutral polymers are relatively high, which provides a facile and efficient way to fabricate high χ-low N BCPs. In addition, the dimension of the sub-5 nm structures formed in PVPS-containing BCPs showed high thermal stability with a small fluctuation (±0.1 nm) of domain spacings upon heating

Regioselective and Alternating Copolymerization of Carbonyl Sulfide with Racemic Propylene Oxide

We report the first example of a regioregular and fully alternating poly (propylene monothiocarbonate) (PPMTC) from the well-controlled copolymerization of two asymmetric monomers, carbonyl sulfide and racemic propylene oxide, using (Salen)­CrCl in conjunction with bis­(triphenylphosphoranylidene)­ammonium chloride. The maximum turnover of frequency of this catalyst system was 332 h^–1 at 25 °C. The contents of monothiocarbonate and tail-to-head linkages of PPMTC were up to 100% (based on ¹H NMR spectra) and 99.0% (based on ¹³C NMR spectra), respectively. PPMTC samples have number-average molecular weight (<i>M</i>_n) up to 25.3 kg/mol with polydispersity index of 1.41. The very low decomposition temperature of 137 °C and high refractive index of 1.63 of PPMTC make it a potential scarifying optical adhesive

Two Growth Modes of Semicrystalline Cylindrical Poly(ε-caprolactone)‑<i>b</i>‑poly(ethylene oxide) Micelles

The micelles of a poly­(ε-caprolactone)-<i>b</i>-poly­(ethylene oxide) block copolymer (PCL₅₉-<i>b</i>-PEO₁₁₃) in different mixed solvents were held at 53 °C for 5 min, and seed solutions with different micellar morphologies and amounts of micellar semicrystalline seeds were prepared. The crystallinity of these seed micelles was identified by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that mostly amorphous spherical micelles are formed by heating micellar solutions in H₂O/THF (5/1 v/v) and H₂O/dioxane (5/1 v/v) mixed solvents, a mixture of amorphous spherical micelles and short semicrystalline cylindrical micelles is yielded in H₂O/DMF (5/1 v/v), whereas mostly short semicrystalline cylindrical micelles are obtained in H₂O/DMSO (5/1 v/v) mixed solvent. The seed solutions were placed at 4 °C for micellar growth. Transmission electron microscope (TEM) shows that micellar growth driven by epitaxial crystallization of core-forming PCL chains takes place and the length of grown cylindrical micelles increases with time. Two growth modes are observed. One is the growth of unimers (or amorphous spherical micelles) on the active ends of semicrystalline cylindrical micelles in micellar solution in H₂O/DMF (5/1 v/v) at the initial growth period. The other is the growth by end-to-end coupling of cylindrical micelles in H₂O/DMSO (5/1 v/v). The kinetics of micellar growth is strongly dependent on the growth mechanism. The growth of the cylindrical micelles in the H₂O/DMF (5/1 v/v) solution is much faster than that in the H₂O/DMSO (5/1 v/v) solution. On long time scale, micellar growth by end-to-end coupling of semicrystalline cylindrical micelles occurs with slow rate in both H₂O/DMF (5/1 v/v) and H₂O/DMSO (5/1 v/v) solutions, and the growth rate in H₂O/DMF (5/1 v/v) solution is even slower than that in H₂O/DMSO (5/1 v/v)

Carbon Dioxide/Epoxide Copolymerization via a Nanosized Zinc–Cobalt(III) Double Metal Cyanide Complex: Substituent Effects of Epoxides on Polycarbonate Selectivity, Regioselectivity and Glass Transition Temperatures

In this study, we describe the substituent effect of epoxides on CO₂/epoxide copolymerization catalyzed by a nanosized zinc–cobalt­(III) double metal cyanide complex [Zn–Co­(III) DMCC]. The Zn–Co­(III) DMCC catalyzed the copolymerization of CO₂ with 11 epoxides with alkyl or aryl groups at 50–60 °C within 15 h. The reaction afforded various CO₂/epoxide copolymers with high epoxide conversion efficiencies up to 100%. The alternating degree (<i>F</i>_CO₂) of the resulting copolymer was solely decided by the steric hindrance of the substituents of the epoxides regardless of their electron-donating or withdrawing properties. Substituents with large steric hindrances (2, 2-dimethyl, <i>tert</i>-butyl, cyclohexyl, decyl, and benzyl) led to highly alternating degrees (up to 100%). The regioselective CO₂/epoxide copolymerization was dominated by the electron induction effect of the substituent. The electron-withdrawing substituent such as phenyl and benzyl induced regioselective ring-opening at the methine site of the epoxide. For CO₂/isobutene oxide copolymerization, the regioselective reaction occurred at the methylene site of the isobutene oxide because of the strong electron-donating ability and steric hindrance of the two methyls of the isobutene oxide. The linear alkyl groups of the epoxides could not induce the regioselective reaction during copolymerization. The glass transition temperatures (<i>T</i>_gs) of the CO₂/epoxide copolymers with linear alkyl substituent groups decreased from +6 to −38 °C with increasing alkyl length, but increased from 6 to 84 °C with increasing steric hindrance of the epoxide substituents. Thus, various CO₂/epoxide copolymers with a wide <i>T</i>_g range from −38 to +84 °C were provided and could be applied as elastomers or plastics

Fully Degradable and Well-Defined Brush Copolymers from Combination of Living CO₂/Epoxide Copolymerization, Thiol–Ene Click Reaction and ROP of ε-caprolactone

Fully Degradable and Well-Defined Brush Copolymers from Combination of Living CO2/Epoxide Copolymerization, Thiol–Ene Click Reaction and ROP of ε-caprolacton