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Alternative approaches to treating subcutaneous abscesses-especially those associated with antibiotic-resistant pathogenic bacterial strains-that eliminate the need for antibiotics are urgently needed. This work descibes a chitosan (CS) derivative with self-doped polyaniline (PANI) side chains that can self-assemble into micelles in an aqueous environment and be transformed into colloidal gels in a process that is driven by a local increase in pH. These self-doped PANI micelles can be utilized as nano-localized heat sources, remotely controllable using near-infrared (NIR) light. To test the in vivo efficacy of the CS derivative as a photothermal agent, an aqueous solution thereof is directly injected at the site of infected abscesses in a mouse model. The injected polymer solution eventually becomes distributed over the acidic abscesses, forming colloidal gels when it meets the boundaries of healthy tissues. After treatment with an 808 nm laser, the colloidal gels convert NIR light into heat, causing the thermal lysis of bacteria and repairing the infected wound without leaving residual implanted materials. This approach has marked potential because it can provide colloidal gels with tunable spatial stability, limiting localized heating to the infected sites, and reducing thermal damage to the surrounding healthy tissues. [ABSTRACT FROM AUTHOR]

Abstract: Low polydispersity linear and cyclic poly(ε-caprolactone) with molecular weights of 2–7.5 kg/mol were synthesized. Differences in the morphology of cyclic and linear single crystals (obtained from solution at identical temperatures) indicate that cyclic PCL crystals were obtained at higher supercoolings than linear ones. Cyclic PCL crystals (both crystallized from solution and from the melt) exhibited higher melting point values (T m ) than analogous linear PCL lamellae. In addition, cyclic PCLs crystallize from the melt at higher rates than linear PCLs at identical crystallization temperatures. Results showed that cyclic PCLs possess a higher equilibrium melting point () than linear PCL crystals. A modified Thomson–Gibbs equation and a modified Hoffman–Weeks equation have been derived in this work to demonstrate that the higher of the cyclic polymer stemmed from the negative cyclization entropy associated with the absence of chain ends and the more collapsed conformation of the cyclic chain in the melt state. [Copyright &y& Elsevier]

We investigate the crystallization behavior of isotacticpolypropylene(iPP) under the influence of nanoscale confinement templated by themicrophase-separated structure of an iPP-based diblock copolymer system,isotactic polypropylene-block-atactic polystyrene(iPP-b-aPS). Three types of iPP microdomains, i.e.,lamellae, cylinder, and sphere, were generated by controlling thecomposition of the diblock. The effect of microdomain morphology onthe nucleation mechanism, crystallization kinetics, self-nucleationbehavior, the population of the helical sequence of iPP block in themelt state, and crystal orientation have been systematically studied.It was found that the crystallization rate of iPP was predominantlycontrolled by homogeneous nucleation when the crystallization processwas largely confined within the individual cylindrical and sphericalmicrodomains. Such a nucleation mechanism and the highly frustratedcrystal growth in the isolated microdomains led to the absence ofDomain II and atypical crystallization kinetics in Domain III in theself-nucleation study. The population of the longer helical sequenceof iPP block revealed by infrared spectroscopy was found to be affectedby temperature but not by the spatial confinement, chain stretching,and junction point constraint imposed by the microdomains. Finally,the orientation of α-form iPP crystals in the lamellae-formingiPP-b-aPS was identified over a broad range of crystallizationtemperatures (Tc). Different from othercrystalline–amorphous diblocks, a lamellar branching of α-formiPP was observed in the lamellar microdomains at Tclying between 15 and 80 °C, where the daughterlamellae developed from the perpendicularly orientated parent iPPcrystals with a specific angle of 80° or 100°. Once thesample was crystallized at Tc≤10 °C, the iPP crystals became randomly oriented. [ABSTRACT FROM AUTHOR]

The crystallization kinetics and crystallization-inducedmorphologicalformation of an asymmetric double-crystalline block copolymer, syndiotacticpolypropylene-block-poly(ε-caprolactone) (sPP-b-PCL), have been investigated by time-resolved simultaneoussmall-angle and wide-angle X-ray scattering (SAXS/WAXS). The sPP-b-PCL under study exhibited hexagonally packed cylindermorphology in the melt state, where the minority sPP block formedthe cylindrical microdomains dispersed in the PCL matrix. The crystallizationbehavior was studied by imposing two types of crystallization histories:(1) two-stage crystallization, where the diblock was first cooledto the temperature TcsPPsituatingbetween the melting points of the two components (TmPCL< TcsPP< TmsPP) to allowsPP crystallization to saturation followed by cooling to TcPCL< TmPCLto induce PCL crystallization; (2) one-stage crystallization,where the system was cooled directly to Tc< TmPCLto allow the twocomponents to crystallize competitively. In both cases, the crystallizationof sPP block was in general able to disrupt the melt structure andtransformed it into a crystalline lamellar morphology. For the two-stagecrystallization process, the PCL block was found to exhibit a fastercrystallization at a given TcPCLwhen the sPP block was precrystallized at higher TcsPP. This “interactive crystallizationkinetics” was attributed to the mediation of the stretchingof PCL blocks by the thickness of sPP crystalline domains which dependedon TcsPP. In the one-stageprocess, the crystallization events of the two blocks became morecompetitive with decreasing Tc. The morphologicalperturbation induced by crystallization was also more hindered atlower Tc, such that a significant portionof sPP blocks remained confined within the cylindrical microdomainsso as to suppress the sPP crystallinity. [ABSTRACT FROM AUTHOR]

This study reports the creation of star-like chain architecture through complexation of a mono-amino terminated poly(ethylene oxide) (PEO-NH2) with a macrocyclic compound, 4-sulfonic calix[ n]arene ( n=4 and 8) (SCA- n). The complexes were prepared in aqueous solution to render proton transfer from the sulfonic acid groups in SCA- n to the amino groups in PEO-NH2, and thereby generated 4- and 8-arm star-like complexes with the PEO arms attached to the SCA- n cores via ionic bonding. Formation of the complexes was verified by titration, solubility test, and dilute solution viscometry. The intrinsic viscosities ([η]) of the complexes in toluene were 60% higher than that of neat PEO-NH2, showing that the star-like structure retained in nonpolar solvents. On the other hand, PEO arms dissociated from the cores in water, so that the complexes and neat PEO-NH2 displayed similar [η]. The star-like supramolecules showed a SAXS peak associated with the core-core correlation in the melt with the inter-core distance of 7.3 nm. The concentration fluctuation in the melt was completely destroyed upon the crystallization of PEO arms. In the semicrystalline state, the SCA- n cores were excluded from the crystal lattice and resided in the interlamellar amorphous regions. Measurements of the crystal thickness by SAXS indicated that the PEO chains in the crystals were once- and twice-folded in neat PEO-NH2 and the complexes crystallized at 40 °C, respectively. [ABSTRACT FROM AUTHOR]

Blending with homopolymer offers a facile approach for tuning the microdomain morphology of block copolymer, provided that the homopolymer chains are uniformly solubilized in the corresponding microdomain to swell the junction point separation. Here we studied the solubilization behavior of poly(4-vinyl pyridine) homopolymer (h-P4VP) in the lamellar microdomain formed by its blends with a poly(ethylene oxide)-block-poly(4-vinyl pyridine) (PEO-b-P4VP) showing the feature of lower critical ordering transition (LCOT) in terms of weaker segregation strength at lower temperature. We revealed that, while the conventional criterion of homopolymer-to-block molecular weight ratio for attaining uniform solubilization was applicable to LCOT blend, there was an excess swelling of junction point separation upon the addition of homopolymer, leading to a decrease of interdomain distance with increasing homopolymer composition. This anomalous phenomenon was attributed to the reduction of interfacial free energy due to the incorporation of P4VP homopolymer into the microdomain interface. [ABSTRACT FROM AUTHOR]