The self-assembly of poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymers (PCL n PEO44 and PCL n PEO113) with narrow polydispersity in aqueous medium was studied using transmission electron microscopy. In this system, the formed micelles are composed of a crystalline PCL core and a soluble PEO corona. We demonstrated that the PCL-b-PEO block copolymers can form micelles with abundant morphologies, depending on the lengths of the blocks and composition. It is observed that for PCL n PEO44 the micellar morphology changes from spherical, rodlike, wormlike, to lamellar, as the length of the PCL block increases. In contrast, most of PCL n PEO113 (n = 21−147) block copolymers form spherical micelles, and only PCL232PEO113 exhibits mixed spherical and lamellar micellar morphologies. The effect of microstructure on micellar morphology was semiquantitatively interpreted in terms of reduced tethering density (σ). It is found that lamellar micelles are formed when σ is smaller than a critical value of between 3.0 and 4.8. A larger σ indicates crowding of the tethered chain, and spherical micelles tend to be formed.

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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 1 H NMR spectra) and 99.0% (based on 13 C NMR spectra), respectively. PPMTC samples have number-average molecular weight (M 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 olefinic blocky copolymers (OBCs) were quenched from different mixing states in the melt, and crystallization kinetics and morphology at various crystallization temperatures (T cs) and corresponding mechanical properties were studied. It is observed that, at lower T cs, premesophase separation in the melt accelerates crystallization of OBC-A with a weak segregation strength and a larger fraction of the crystalline hard blocks due to enrichment of the hard blocks in the hard-block-rich domains. By contrast, premesophase separation retards crystallization of OBC-B with a stronger segregation strength and lower fraction of the hard blocks because of the prevailing confinement effect at lower T cs. Moreover, since the hard blocks dissolved in the soft-block-rich domains can crystallize at lower T cs, which can bridge the crystals formed in different hard-block-rich domains, the crystal growth is not restricted. At higher T cs, OBC-A crystallizes more slowly from the premesophase-separated melt than that from the homogeneous melt, which is attributed to the weaker crystallizability of the hard blocks dissolved in the soft-block-rich domains and thus the restricted crystal growth. Nevertheless, mesophase separation always takes place prior to crystallization at higher T cs for OBC-B because of the faster rate of mesophase separation. Therefore, the mixing state in the melt has little effect on crystallization and morphology of OBC-B at higher T cs. It is found that the mechanical properties of OBCs can be regulated in a wide range by alteration of crystallization conditions. Better mechanical properties can be achieved when OBCs crystallize from the homogeneous melt and at a lower T c.

Poly(vinylidene difluoride)/organically modified montmorillonite (PVDF/OMMT) composite nanofibers were prepared by electrospinning the solution of PVDF/OMMT precursor in DMF. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) show that in the bulk of the PVDF/OMMT precursor OMMT platelets are homogeneously dispersed in PVDF and can be both intercalated and exfoliated. It is found that the diameter of the PVDF/OMMT composite nanofibers is smaller than that of the neat PVDF fibers because the lower viscosity of PVDF/OMMT solution, which is attributed to the possible adsorption of PVDF chains on OMMT layers and thus reduction in number of entanglement. The crystal structure of the composite nanofibers was investigated using WAXD and Fourier transform infrared (FT-IR) and compared with that of thin film samples. The results show that the nonpolar alpha phase is completely absent in the electrospun PVDF/OMMT composite nanofibers, whereas it is still present in the neat PVDF electrospun fibers and in the thin films of PVDF/OMMT nanocomposites. The cooperative effect between electrospinning and nanoclay on formation of polar beta and gamma crystalline phases in PVDF is discussed. The IR result reveals that electrospinning induces formation of long trans conformation, whereas OMMT platelets can retard relaxation of PVDF chains and stabilize such conformation due to the possible interaction between the PVDF chains and OMMT layers. This cooperative effect leads to extinction of nonpolar alpha phase and enhances the polar beta and gamma phases in the electrospun PVDF/OMMT composite nanofibers.

The degradation and reuse of epoxy thermosets have significant impact on the environments. We report that an epoxy−amine thermoset embedded with Diels−Alder (DA) bonds was transformed into soluble polymers via sonochemistry under mild temperature (ca. 20 °C) for the first time. Sonication could effectively induce the position-oriented cleavage of DA bonds (i.e., retro-DA) of the fully swelled epoxy thermoset in dimethyl sulfoxide (DMSO), leading to the soluble polymers. Of importance, such sonochemical process could be regulated on demand via switching on-and-off of the sonication. The obtained soluble polymers could be recured to form epoxy−amine thermosets via DA reaction. This sonochemical method might provide an unprecedented and efficient way to the controlled degradation and recycling of the epoxy thermosets containing the dynamic covalent bonds likes DA groups.

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Four R 1 R 2 Si(OMe) 2 type compounds were added as an external electron donor (De) in propylene polymerization with TiCl 4 /Di/MgCl 2 type supported Ziegler−Natta catalysts (Di = internal donor). Each polypropylene (PP) sample was fractionated into three parts (atactic, medium-isotactic and isotactic PP), and the number of active centers ([C*]/[Ti]) in each PP fraction was counted using 2-thiophenecarbonyl chloride as the quenching and tagging agent. The gradual decrease of [C*]/ [Ti] with De/Ti ratio is ascribed to competitive and reversible coordination of De on either central Ti of the active center or Mg adjacent to the central Ti. The former coordination leads to deactivation of C*, and the latter one leads to still living C*. The chain propagation rate constant (k p ) of the active centers producing atactic, medium-isotactic and isotactic PP change with De/ Ti in different ways. Only the k p of active centers producing isotactic PP was evidently increased by De. Enhancement in isotacticity of PP product is found to be a combined result of both deactivation of active centers by De and selective activation of the active centers that produce isotactic PP. Changing the alkyl groups of R 1 R 2 Si(OMe) 2 leads to an altered balance between the deactivation and activation effects of De.