Design of Bimodal PCL and PCL‐HA Nanocomposite Scaffolds by Two Step Depressurization During Solid‐state Supercritical CO2 Foaming

This communication reports the design and fabrication of porous scaffolds of poly(ε‐caprolactone) (PCL) and PCL loaded with hydroxyapatite (HA) nanoparticles with bimodal pore size distributions by a two step depressurization solid‐state supercritical CO₂ (scCO₂) foaming process. Results show that the pore structure features of the scaffolds are strongly affected by the thermal history of the starting polymeric materials and by the depressurization profile. In particular, PCL and PCL‐HA nanocomposite scaffolds with bimodal and uniform pore size distributions are fabricated by quenching molten samples in liquid N₂, solubilizing the scCO₂ at 37 °C and 20 MPa, and further releasing the blowing agent in two steps: (1) from 20 to 10 MPa at a slow depressurization rate, and (2) from 10 MPa to the ambient pressure at a fast depressurization rate. The biocompatibility of the bimodal scaffolds is finally evaluated by the in vitro culture of human mesenchymal stem cells (MSCs), in order to assess their potential for tissue engineering applications.

     

Fabrication of Compositional‐Gradient Biodegradable Polymeric Films Showing Self‐Bending Deformation

A compositional graded film of poly(ε‐caprolactone) (PCL) with 4,4′‐thiodiphenol (TDP), in the film thickness direction, was fabricated by self‐diffusing of TDP in the PCL melt. We found out the self‐bending deformation of the gradient film, which bent into a rolled‐up shape by itself. The initial shape of the film was flat when the sample was quenched from the melt. Upon the fast crystallization of PCL, the gradient film bent to the side with low TDP content. Then, after PCL crystallized the film bent to the opposite direction, that is, to the side with high TDP content. This bending to the TDP rich region was induced by not only the crystallization of PCL but also mass transfer due to the diffusion of TDP from TDP rich region to poor region.

     

High‐Molecular‐Weight Polycarbonates Synthesized by Enzymatic ROP of a Cyclic Carbonate as a Green Process

High‐molecular‐weight PTeMC and PHMC were prepared by the lipase‐catalyzed polymerization of butane‐1,4‐diol or hexane‐1,6‐diol and diphenyl carbonate via the formation of a cyclic dimer by a green process. Cyclic carbonate dimers were prepared by the lipase‐catalyzed condensation of diphenyl carbonate with butane‐1,4‐diol or hexane‐1,6‐diol in dilute toluene solution using an immobilized lipase from Candida antarctica, and was followed by the ring‐opening polymerization of the cyclic dimer in bulk with the same lipase to produce PTeMC with = 119 000 g · mol^?1 and PHMC with = 399 000 g · mol^?1, respectively. Additionally, enzymatic polymerization of cyclic carbonate dimer was analyzed with respect to the K_m and V_max for the lipase.

     

Regulation of Micellar Morphology of PCL‐b‐PEO Block Copolymers by Crystallization Temperature

The effect of crystallization temperature on the micellar morphology of PCL‐b‐PEO block copolymers in water has been studied. It is found that the micellar morphology of PCL_nPEO₄₄ and PCL_nPEO₁₁₃ changes with crystallization temperature in different ways because of two competitive factors: perfection of the PCL crystals in the core and deformation of the soluble PEO block. For PCL_nPEO₄₄, perfection of the PCL crystals dominates the micellar morphology and lamellar micelles are formed at a higher crystallization temperature. For PCL_nPEO₁₁₃ the micellar morphology is mainly determined by the tethering density and spherical micelles or cylindrical micelles with a larger length/diameter ratio are formed at a higher crystallization temperature because of the larger tethering density.

     

Surface Hydrophilicities and Enzymatic Hydrolyzability of Biodegradable Polyesters, 2

Control of the surface hydrophilicities and enzymatic hydrolyzability of hydrophobic aliphatic polyesters such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) [i.e. poly(L ‐lactic acid) (PLLA)] was attempted by coating with hydrophilic poly(vinyl alcohol) (PVA). The PVA coating was carried out by immersion of the PCL and PLLA films in PVA solutions. The effects of PVA coating on the hydrophilicities were monitored by dynamic contact angle measurements, while the enzymatic hydrolyzability of the PVA‐coated PCL and PLLA films was evaluated by the weight losses after Rhizopus arrhizus lipase‐ and proteinase K‐catalyzed hydrolysis, respectively. It was found that the PVA coating successfully enhanced the hydrophilicities of the aliphatic polyester films and significantly suppressed enzymatic hydrolyzability of the aliphatic polyester films, excluding the PCL film coated at a very low concentration such as 0.01 g · dL^?1 and the crystallized PLLA film coated at 1 g · dL^?1, for which slight enhancement and no significant enhancement, respectively, were observed in the enzymatic hydrolyzability. Moreover, the hydrophilicities and enzymatic hydrolyzability of the aliphatic polyester films were controllable to some extent by varying the PVA solution concentration and the film crystallinity.

Advancing contact angle (θ_a) of PCL, PLLA‐C, and PLLA‐A films before and after the PVA coating by immersion in 1 g · dL^?1 solution.     

Synthesis of π‐Conjugated Polymer Consisting of Pyrrole and Fluorene Units by Ru‐Catalyzed Site‐Selective Direct Arylation Polycondensation

Polycondensation of 1‐(2‐pyrimidinyl)pyrrole with 2,7‐dibromo‐9,9‐dioctylfluorene via Ru‐catalyzed direct arylation gives the corresponding conjugated polymer with a molecular weight of 19 800 in 86% yield. The introduction of directing group, 2‐pyrimidinyl substituent, into the pyrrole monomer induces ortho‐metalation and provides the site‐selective direct arylation polycondensation at the α‐position of pyrrole unit without the protection of β‐position. The removal of 2‐pyrimidinyl substituent on the pyrrole unit proceeds efficiently and results in the enhancement of coplanarity along the main chain of the polymer.

     

Urease‐Catalyzed Carbonate Precipitation inside the Restricted Volume of Polyelectrolyte Capsules

A new biomimetic approach for performing CaCO₃ synthesis exclusively inside micron‐sized polyelectrolyte capsules, based on the fermentative formation of a precipitative agent (CO₃²⁻ anion) by urease‐catalyzed urea hydrolysis, was developed. Precipitated CaCO₃ completely fills the interior capsule volume and has a metastable vaterite phase.

     

Ordered Honeycomb‐Structured Films from Dendronized PMA‐b‐PEO Rod‐Coil Block Copolymers

Summary: Fabrication of honeycomb‐patterned films from amphiphilic dendronized block copolymer (PEO₁₁₃‐b‐PDMA₈₂) by ‘on‐solid surface spreading’ and ‘on‐water spreading’ method is reported. Highly ordered honeycomb films with quasi‐horizontally paralleled double‐layered structure can be fabricated by the on‐solid surface spreading method. This work raises the possibility that such structures can be formed in amphiphilic dendronized block copolymers and extends the family of source materials.

     

Biomimetic Mussel Adhesive Inspired Clickable Anchors Applied to the Functionalization of Fe3O4 Nanoparticles

The functionalization of magnetite (Fe₃O₄) nanoparticles with dopamine‐derived clickable biomimetic anchors is reported. Herein, an alkyne‐modified catechol‐derivative is employed as the anchor, as i) the catechol‐functional anchor groups possess irreversible covalent binding affinity to Fe₃O₄ nanoparticles, and ii) the alkyne terminus enables further functionalization of the nanoparticles by the grafting‐onto approach with various possibilities offered by ‘click’ chemistry. In the present work, azido‐end group functionalized Rhodamine and poly(ethylene glycol) (PEG) are utilized to coat the iron oxide nanoparticles to make them fluorescent and water soluble.

     

The Strength of the Macromonomer Strategy for Complex Macromolecular Architecture: Molecular Characterization,Properties and Applications of Polymacromonomers

The efficiency of the macromonomer (MM) synthetic strategy for the creation of nonlinear complex macromolecular architectures (miktoarm stars, α,ω‐branched polymers, random/exact comb and graft copolymers, dendritic polymers, molecular brushes) is reviewed. In addition, the solution/bulk properties and the potential applications of polymacromonomers (PMM), as well as new synthetic ideas are presented. The synthesis of macromonomers and living polymacromonomers in situ leads to many novel linear and nonlinear structures, as for example PMM‐b‐PS‐b‐PMM, (PS)₂PMM. The use of multichlorosilylstyrenes as monomer/linking agents opens new ways for structures with multichain macromonomeric building blocks.

The use of multichlorosilylstyrenes as monomer/linking agents opens new ways for structures having multichain macromonomeric building blocks.     

Ultrasound‐Assisted Synthesis of Hybrid Vanadium Oxide/Polyaniline Nanowires

A single‐step sonochemical procedure to synthesize hybrid vanadium oxide/polyaniline nanowires starting from crystalline V₂O₅ and aniline in aqueous medium is presented. The synthesis explores the effect of high power ultrasounds on heterogeneous solid–aqueous phases, which leads to 30 nm width wires of 5 to 10 µm in length. Monomer intercalation and oxidative polymerization within the inorganic matrix proceed simultaneously with morphological changes. The electronic conductivity of hybrid nanowires reaches 0.8 S · cm⁻¹ at room temperature.

     

Enzymatic degradations of copolymers of L-lactide with cyclic carbonates

Syntheses and biodegradation of random copolymers of L -lactide (L -LA) with trimethylene carbonate (TMC), 1,1-dimethyltrimethylene carbonate (1,1-DTMC) and 2,2-dimethyltrimethylene carbonate (2,2-DTMC) were investigated at various monomer ratios using SmMe(C₅Me₅)₂THF as an initiator at 80 °C for 24 h in toluene. Enzymatic degradation of these polymers were performed using cholesterol esterase, lipoprotein lipase, and proteinase K. Poly(TMC) was effectively biodegraded by cholesterol esterase and lipoprotein lipase, while poly(2,2-DTMC) and all the copolymers were hardly degraded using these enzymes. Biodegradations of poly(L -LA-co-TMC) (97:3) and poly(L -LA-co-2,2,DTMC) (95:5) show rapid degradations using TES buffer, a compost and proteinase K. The physical properties of these copolymers were also examined.

Enzymatic degradation of L -LA/2,2-DTMC copolymers by proteinase K in Tricine buffer (pH 8.0) at 37 °C: a 98:2, b 82:18, c 100:0, d 66:34, e 34:66, f 0:100.     

Crystallization of Poly(ε‐caprolactone)/Poly(vinyl chloride) Miscible Blends Under Strain: The Role of Molecular Weight

Summary: The effect of poly(ε‐caprolactone) (PCL) molecular weight on the orientation of crystalline PCL in miscible poly(ε‐caprolactone)/poly(vinyl chloride) (PCL/PVC) blends, melt crystallized under strain, has been studied by a combination of wide angle X‐ray diffraction (WAXD) and small angle X‐ray scattering (SAXS) studies. An unusual crystal orientation with the b‐axis parallel to the stretching direction was observed in miscible PCL/PVC blends with PCL of high molecular weight (>21 000). SAXS showed the presence of nanosize confined PCL in the PCL/PVC blends, which could be preserved at temperatures higher than the T_m of PCL but lower than the T_g of PVC. A mechanism based on the confinement of PCL crystal growth was proposed, which can explain the formation of b‐axis orientation in PCL/PVC blends crystallized under strain.

SAXS pattern of stretched PCL/PVC blend after annealing at 90 °C for 5 min.     

Ring‐Opening Polymerization of ε‐Caprolactone by Poly(ethylene glycol) by an Activated Monomer Mechanism

Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et₂O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.

The non‐metal catalyzed living ring‐opening polymerisation of ε‐caprolactone by PEG.     

Chain Transfer and Efficiency of End‐Group Introduction in Free Radical Polymerization of Methyl Methacrylate in the Presence of Poly(methyl methacrylate) Macromonomer

Summary: Experimental and modeling studies of addition–fragmentation chain transfer (AFCT) during radical polymerization of methyl methacrylate in the presence of poly(methyl methacrylate) macromonomer with 2‐carbomethoxy‐2‐propenyl ω‐ends (PMMA‐CO₂Me) at 60 °C are reported. The results revealed that AFCT involving PMMA‐CO₂Me formed in situ during methyl methacrylate polymerization has a negligible effect on the molecular weight distribution.

     

Phenoxy–Ether Ligated Ti Complexes for the Polymerization of Ethylene

Summary: Bis(phenoxy–ether) Ti complexes were investigated as ethylene polymerization catalysts. The complexes, combined with iBu₃Al/Ph₃CB(C₆F₅)₄ or methylaluminoxane (MAO) cocatalysts, can be highly active single‐site catalysts, which display activities ( turnover frequency, max. 2 065 min⁻¹) comparable with that of a highly active bis(phenoxy–imine) Ti complex/MAO system, and provide very high molecular weight polyethylenes ( 2 040 000–5 420 000) at 25 °C under atmospheric pressure.

Synthesis of polyethylene using bis(phenoxy–ether) Ti complexes, an example of which is shown.     

Glass Transition Temperature Depression at the Percolation Threshold in Carbon Nanotube–Epoxy Resin and Polypyrrole–Epoxy Resin Composites

Summary: The glass transition temperatures of conducting composites, obtained by blending carbon nanotubes (CNTs) or polypyrrole (PPy) particles with epoxy resin, were investigated by using both differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). For both composites, dc and ac conductivity measurements revealed an electrical percolation threshold at which the glass transition temperature and mechanical modulus of the composites pass through a minimum.

DC conductivity, σ_dc, as a function of the conducting filler concentration of the CNT– (▪) and PPy– (○) epoxy resin composites.