Facile Synthesis of Amphiphilic Heterografted Copolymers with Crystalline and Amorphous Side Chains

An amphiphilic polymer brush with PB and PEO side chains is prepared by combined “grafting‐onto” and “grafting‐from”. The linear and star‐shaped heterografted copolymer synthesized is of controlled molecular weight and has a narrow molecular weight distribution (M _w/M _n < 1.2). A DSC study of this heterografted copolymer containing crystalline and amorphous chains shows that it displays “fractionated crystallization” behavior. The study on isothermal crystallization kinetics of the copolymer is carried out in isothermal step crystallization (ISC) experiments, in which two crystallization exothermic peaks at low temperatures are observed. The critical micelle concentration (cmc) of the amphiphilic brush polymer in an aqueous solution is determined by a fluorescence technique. The results show that this amphiphilic brush forms aggregates in the system.

     

Micelle Behavior of Copolymers Composed of Linear and Hyperbranched Blocks in Aqueous Solution

Multi‐arm poly(THF)‐b‐polyglycerol linear‐hyperbranched copolymers consisting of a linear hydrophobic poly(THF) block and a hyperbranched hydrophilic polyglycerol block were synthesized by ring opening polymerization of tetrahydrofuran with silver trifluoromethane sulfonate as a catalyst and the consecutive polymerization of glycidol. Initiators with different geometries that propagated into different numbers of arms (e.g., 1, 2 or 4) were used to investigate the dependence of the micelle properties of the copolymers on the number of arms. The critical micelle concentration (CMC) first decreased and then increased with increasing numbers of arms showing a minimum CMC at an arm number of 2. A minimum CMC was difficult to obtain using multi‐arm block copolymers composed of linear polymers with the small number of arms investigated in this study. DLS showed that the 4‐arm poly(THF)‐b‐polyglycerol copolymer had a micelle size of approximately 83 nm under aqueous conditions, and the micelle size of the copolymers with different numbers of arms was similar. Unimolecular micelles could eventually be obtained using this system by increasing the number of arms, they are considered an ideal drug delivery carrier due to the concentration‐independent stability in the blood stream.

     

Polydopamine – A Versatile Coating for Surface‐Initiated Ring‐Opening Polymerization of Lactide to Polylactide

An efficient way for covering various surfaces with poly(lactic acid) (PLA) is discussed. In a first step, the material is coated with polydopamine (PDA) by air oxidation of dopamine. The resulting PDA layer acts as an initiator for ring‐opening polymerization (ROP) of lactide resulting in an outer PLA shell. Since PDA sticks to almost every solid material, the methodology has a wide scope. The strategy is demonstrated with magnetic nanoparticles and non‐magnetic powders.

     

One‐Pot Combination of eROP and ROMP for the Synthesis of Block Copolymers

The one‐pot combination of enzymatic ring‐opening polymerization (eROP) and ring‐opening metathesis polymerization (ROMP) is successfully established to construct block copolymers. cis‐1,4‐Diacetoxy‐2‐butene is employed both as a precursor to initiate eROP of ε‐caprolactone or 15‐pentadecanolide and as a chain transfer agent in ROMP. The obtained polymers are systematically characterized by NMR, GPC, DSC, and microTOF‐QII MS. An evaluation of the reaction kinetics indicates the presence of two stages during the one‐pot eROP/ROMP process. Compared with cascade methods, this one‐pot method exhibits many advantages for preparing well‐defined block copolymers, such as mild reaction conditions and the elimination of complex purification steps for intermediates. Thus, this one‐pot combination approach has the potential to be widely used in preparing biocompatible polymeric materials, especially for biological and pharmaceutical applications.

     

Self‐Assembling of Block Copolymers with Alternative Solvents

Block copolymer (BCP) lithography is one of the most technologically intriguing and scientifically interesting strategies for achieving nanometer‐sized features. This method usually exploits toluene as solvent for the deposition of BCPs in all the processing steps. However, this chemical has some technical disadvantages, such as high toxicity and hygroscopicity. The first aspect can limit its use on the industrial scale because of the protocols on the environmental and operator risks, while the second causes aging effects that can alter the results. In order to overcome these intrinsic limitations, a BCP self‐assembly (BCP‐SA) strategy is presented by using alternative deposition solvents in place of toluene. A preliminary study, based on the physical characteristics, such as volatility, polarity, and hygroscopicity, is carried out to explore two new alternative solvents, ethyl acetate and tetrahydrofuran. The effects on the BCP‐SA due to the new solvents are studied by SEM analysis supported by suitable software for the images elaboration. The results achieved show very promising outcomes for the polymer solutions obtained with ethyl acetate, in terms of uniformity of geometrical features, ordered areas extension, and homogeneity of the pattern obtained, making this chemical a good alternative to toluene.     

Controlled ROMP Synthesis of Ferrocene‐Containing Amphiphilic Dendronized Diblock Copolymers as Redox‐Controlled Polymer Carriers

Novel well‐defined redox‐responsive Ferrocene (Fc)‐containing amphiphilic dendronized diblock copolymers are synthesized by the ring‐opening metathesis polymerization technique using Grubbs’ third‐generation olefin metathesis catalyst as the initiator. These dendronized block copolymers can self‐assemble into spherical micelles in aqueous solution. The size of self‐assembled micelles can be modulated by the composition (namely, the ratio of hydrophobic and hydrophilic segments) and concentration of the dendronized copolymers. The obtained micelles show reversible redox‐controlled self‐assembly behaviors using FeCl₃ as oxidant and glutathione as reductant. Furthermore, the model molecule Rhodamine B is successfully loaded in these micelles, and the oxidation‐triggered controllable release is achieved by changing the type of oxidants (FeCl₃ and H₂O₂) and their concentrations. This is the first example of redox‐responsive micelles self‐assembled by novel amphiphilic dendronized Fc‐containing block copolymers, and the present micelles are visualized to be potential candidates in many fields, especially in stimuli‐responsive drug delivery systems.     

Synthesis of Amphiphilic Comb‐Shape Copolymers Via Ring‐Opening Polymerization of a Macromonomer

Amphiphilic comb‐shape copolymers PCL‐co‐P(MTC‐mPEG₁₆) (where PCL, MTC, and mPEG refer to poly(ε‐caprolactone), 2‐methyltrimethylene carbonate, and methoxy poly(ethylene glycol), respectively) are synthesized by ring‐opening polymerization of ε‐caprolactone and cyclic carbonate‐terminated PEG macromonomer (MTC‐mPEG₁₆) with benzyl alcohol as an initiator and Sn(Oct)₂ as a catalyst. Amphiphilic copolymers PCL‐co‐P(MTC‐mPEG₁₆) can form micelles in aqueous solution by self‐assembly. The diameters of PCL‐co‐P(MTC‐mPEG₁₆) micelles characterized by dynamic light scattering area few dozens of nanometers with a narrow size distribution and the morphology of the micelles observed through transmission electron microscopy are nanosized spheres. The in vitro drug release of comb‐shape copolymer PCL‐co‐P(MTC‐mPEG₁₆) micelles is more stable and sustained than that of linear block copolymers mPEG‐b‐PCL.

     

A Feasible Synthetic Route for Linear PTHF‐Hyperbranched Poly(phenyl sulfide) Block Copolymers

The linear‐hyperbranched block copolymers, in which the linear polytetrahydrofuran (PTHF) is linked to the apex of hyperbranched poly(phenylene sulfide) (HPPS‐SH), have been synthesized, and the synthesis includes condensation polymerization of 2,4‐dichlorobenzenethiol, subsequent transformation of the resultant HPPS‐SH to HPPS‐OH, and then the cationic ring‐opening polymerization of tetrahydrofuran (THF) using HPPS‐OH as a macrotransfer agent and BF₃ · OEt₂ as a catalyst. The resultant HPPSs have excellent thermal stability, the PTHF and HPPS chains were decomposed at 361 and 402 °C, respectively. HPPS can be dissolved in THF in the form of aggregates with R_h = 90 nm, which is larger than that (R_h = 55 nm) formed from the corresponding linear PTHF‐HPPS block copolymer.

     

Polylactide/Perfluoropolyether Block Copolymers: Potential Candidates for Protective and Surface Modifiers

Perfluoropolyethers are a well known and widely used family of polymers, suitable as protectives. Their main drawback is the lack of solubility, which is complete only in chlorofluorocarbons. In this work a series of A‐B‐A block copolymers (FluoPLA), with a relative low molecular weight, were prepared by ROP of L ‐ and D ,L ‐lactide (PLA) in the presence of a hydroxy‐terminated perfluoropolyether as macroinitiator. In fact the use of block copolymers leads to different advantages, i.e. a limited segregation phenomena and higher polymer solubility. The resulting polymers were characterized (by NMR, IR, HPLC‐SEC, DSC, LS) and tested as potential protective and surface modifiers for cultural heritage (ESEM‐EDS, solar‐box technique, colorimeter analysis).

     

Stereocomplex Formation in Polylactide Multiarm Stars and Comb Copolymers with Linear and Hyperbranched Multifunctional PEG

A systematic comparison between graft poly(l‐ lactide) copolymers with different topologies and their ability to form stereocomplexes with poly(D ‐lactide) (PDLA) is performed. Comb and hyperbranched copolymers based on functional poly(ethylene glycol) and poly(l‐ lactide) with molecular weights in the range of 2000–90 000 g mol^?1 and moderate molecular weight distributions (M _w/M _n = 1.08–1.37) are prepared via the combination of anionic and ring‐opening polymerization. Two “topological isomers,” a linear poly(ethylene oxide)/poly(glycerol) (PEG/PG) copolymer and a branched PEG/PG copolymer are used as backbone polymers. Furthermore, the stereocomplex formation between PDLA and the hyperbranched and comb copolymers containing poly(l‐ lactide) arms is studied. Stereocomplex formation is confirmed by DSC as well as by Fourier transform IR (FTIR) and Raman spectroscopy.

     

Controlled Synthesis of “Reverse Pluronic”‐Type Block Copolyethers with High Molar Masses for the Preparation of Hydrogels with Improved Mechanical Properties

Hydrogels based on Pluronics (EO_n/2‐PO_m‐EO_n/2, EO = ethylene oxide, PO = propylene oxide) have been frequently investigated, yet key limitations still remain, including a propensity for quick erosion and insufficient mechanical robustness. This issue can be alleviated by creating “reverse Pluronics” (PO_n/2‐EO_m‐PO_n/2), which is proposed to enable the formation of physical cross‐links via a micellar network. Until recently, however, efforts in this direction were aggravated by synthetic difficulties, specifically prohibiting the realization of poly(propylene oxide) (PPO)‐moieties with a high DP. In this study, an organocatalytic polymerization method is employed to synthesize “reverse Pluronics,” resulting in highly defined polymers (Ð_M ≤ 1.02–1.07, M_n up to 35 000 g mol^?1) with exceptionally long PPO blocks. The higher molar mass and the reverse constitution of the polyether combine to enable the generation of thermoresponsive hydrogels with a storage modulus that is increased tenfold relative to reference samples. Gelation temperature and maximum storage modulus (G′_max) are readily influenced by the choice of the polyether (down to 5 wt%). The improved mechanical properties are accompanied by an increased resistance toward erosion in water. Isotactic enrichment is presented as an additional tuning parameter for hydrogel properties.     

Selectivity of PEO‐block‐PPO Diblock Copolymers in the Microwave‐Accelerated,Anionic Ring‐Opening Polymerization of Propylene Oxide with PEG as Initiator

Diblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were synthesized by the anionic ring‐opening polymerization of propylene oxide (PO), with controlled microwave heating in sealed vessels. A detailed study was carried out to investigate the effects of different parameters on the formation of unwanted byproducts. Parameters that were considered include temperature; the concentration of NaH, monomer and hydroxy groups in the feed; and the polarity of the reaction medium. A continuous decrease of internal pressure during the sealed‐vessel experiment reflected the consumption of PO monomer and the completion of the reaction was confirmed by a drop of the internal pressure to zero when reactions were performed in bulk. The products were characterized by using different chromatographic techniques. A comparison of the reaction times and composition of the polymers prepared by microwave and conductive heating is given.

     

pH‐Sensitive Poly(ethylene glycol)/Poly(ethoxyethyl glycidyl ether) Block Copolymers: Synthesis,Characterization, Encapsulation,and Delivery of a Hydrophobic Drug

Curcumin is a natural polyphenolic compound known for its numerous pharmacological properties. However, its low water solubility and instability at neutral pH are serious drawbacks preventing its use as an oral drug. Well‐defined amphiphilic poly(ethylene glycol)‐block‐poly(ethoxyethyl glycidyl ether) (PEG‐b‐PEEGE) block copolymers carrying acid‐labile acetal groups are synthesized by anionic ring‐opening polymerization and investigated as potential pH‐sensitive nano‐carriers for delivery of curcumin to cancer cells. The nanoparticles, resulting from copolymer self‐assembly in aqueous media, are characterized by dynamic light scattering and cryo‐transmission electron microscopy. The nanoparticles’ stabilities are evaluated in three different phosphate buffers (pH = 7.2, 6.4, and 5.3). The stability decreases at lower pH and a complete disappearance of the nanoparticles is noticed after 4 days at pH 5.3. Curcumin is encapsulated in hydrophobic core of mPEG₄₀‐b‐PEEGE₂₅ nanoparticles allowing significant enhancements of curcumin solubility in water and lifetime at neutral pH. In vitro curcumin release is studied at different pH by UV‐spectroscopy and high‐performance liquid chromatography (HPLC). The cytotoxicity of curcumin and curcumin encapsulated in micelles is evaluated by cell viability 3‐(4,5‐Dimethyl‐2‐thiazolyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide (MTT) assay on MDA‐MB‐231 human breast cancer cells.     

“Tree‐Shaped” Copolymers Based on Poly(ethylene glycol) and Atactic or Isotactic Polylactides: Synthesis and Characterization

“Tree‐shaped” copolymers constituted by an m‐PEG trunk and poly(L ‐lactide) or poly(D ,L ‐lactide) branches were obtained. The m‐PEG was functionalized at the terminal chain with two (G1) and four (G2) hydroxyl groups, then reacted with Al(CH₃)₃ to produce aluminum alkoxide species, active as initiators in the ROP of L‐ or D ,L‐ lactide. Copolymers were characterized by ¹H and ¹³C NMR, GPC and DSC, and compared with analogous linear copolymers. Characterization of a low‐molecular‐weight G1 copolymer confirmed the architecture. GPC curves showed monomodal and narrow molecular weight distribution for all the samples, while the melting points of the copolymers seemed more correlated to the architecture than to the composition.

     

Toughening Polylactide with Phase‐Separating Complex Copolymer Architectures

Polylactide (PLA) is a commercially produced potentially sustainable plastic that holds promise to replace petroleum‐sourced materials. Unfortunately, the brittle nature of PLA limits its current utility to disposable packaging. Melt blends of PLA and a rubbery material can rubber toughen the plastic, but often require the addition of a compatibilizer and generate opaque materials. Current efforts explore using block and graft copolymers with a majority PLA block and minority rubbery block that phase separate on the nanometer length scale to rubber toughen PLA. With these complex architectures, the polymer matrix, the minor rubbery component, and the compatibilizer are present in one molecule. Many block and graft copolymers rely on non‐sustainable rubbery blocks, which limits the sustainability of these materials. Recent work has utilized polyisoprene (PI) as the sustainable backbone for PLA graft copolymers. Post‐polymerization functionalization and copolymerization of PI provides a method to create fully sustainable PLA/PI graft copolymers that phase separate on the nanometer‐scale to make potentially tough, sustainable plastics.

     

Amphiphilic Polyoxazoline‐block‐Polypeptoid Copolymers by Sequential One‐Pot Ring‐Opening Polymerizations

Amphiphilic block copolymers possess great potential as biomaterials in drug delivery and gene therapy. Herein, pseudopeptidic‐type diblock copolymer of poly(2‐oxazoline)‐block‐polypeptoid (POx‐b‐POI) is presented and synthesized. Poly[2‐(3‐butenyl)‐2‐oxazoline]‐block‐poly(sarcosine) (PBuOx‐b‐PSar) comprising hydrophobic POx segment bearing alkenyl side chain and hydrophilic POI segment of N‐methyl glycine, viz., sarcosine, is prepared by ring‐opening polymerization (ROP) through a one‐pot and three‐step route. Diphenyl phosphate initiates ROP of BuOx, and then the living chain end of PBuOx is quenched by ammonia to obtain PBuOx‐ammonium phosphate in situ, the active ammonium group initiates ROP of sarcosine N‐carboxy anhydride. PBuOx‐b‐PSar with controlled molecular weights (4.7–10.8 kg mol⁻¹) and narrow dispersities (Ð _M 1.15–1.21) are characterized by ¹H NMR, ¹³C NMR, and size‐exclusion chromatography. Dynamic light scattering and transmission electron microscopy analysis reveal that PBuOx‐b‐PSar self‐assembles into nanostructures of average diameter D _H of 37–109 nm in aqueous solution. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide test demonstrates the cytocompatibility (relative cell viability > 80%) of the PBuOx‐b‐PSar. In view of the self‐assembly and biocompatibility, the readily prepared diblock copolymers may hopefully be used in biomedical applications.

     

Syntheses and Specific Interactions of Poly(ε‐caprolactone)‐block‐poly(vinyl phenol) Copolymers Obtained via a Combination of Ring‐Opening and Atom‐Transfer Radical Polymerizations

Summary: A series of PCL‐b‐PVPh diblock copolymers were prepared through combinations of ring‐opening and atom‐transfer radical polymerizations of ε‐caprolactone and 4‐acetoxystyrene, and subsequent selective hydrolysis of the acetyl protective group. This PCL‐b‐PVPh diblock copolymer shows a single glass transition temperature over the entire composition range, indicating that this copolymer is able to form a miscible amorphous phase due to the formation of intermolecular hydrogen bonding between the hydroxyl of PVPh and the carbonyl of PCL. In addition, DSC analyses also indicated that the PCL‐b‐PVPh diblock copolymers have higher glass transition temperatures than their corresponding PCL/PVPh blends. FT‐IR was used to study the hydrogen‐bonding interaction between the PVPh hydroxyl group and the PCL carbonyl group at various compositions.

FT‐IR spectra in the 1 680–1 780 cm^?1 for PCL‐b‐PVPh copolymers with various PVPh contents.     

Synthesis of Novel Linear PEO‐b‐PS‐b‐PCL Triblock Copolymers by the Combination of ATRP,ROP, and a Click Reaction

A new strategy to synthesize a series of well‐defined amphiphilic PEO‐b‐PS‐b‐PCL block copolymers is presented. First, bromine‐terminated diblock copolymers PEO‐b‐PS‐Br are prepared by ATRP of styrene, and converted into azido‐terminated PEO‐b‐PS‐N₃ diblock copolymers. Then propargyl‐terminated PCL is prepared by ROP of ε‐caprolactone. The PEO‐b‐PS‐b‐PCL triblock copolymers with from 1.62 × 10⁴ to 1.96 × 10⁴ and a narrow PDI from 1.09 to 1.19 are finally synthesized from these precursors. The structures of these triblock copolymers and their precursors have been characterized by NMR, IR, and GPC analysis.

     

Styrene–Ferrocenyldimethylsilane–Methyl Methacrylate Triblock Copolymers: Synthesis and Phase Morphology

Triblock copolymers were synthesized from styrene (S), dimethylsilaferrocenophane (FS), and methyl methacrylate (MMA) via sequential anionic polymerization, taking advantage of the dimethylsilacyclobutane‐mediated endcapping of the living PS‐b‐PFS precursors. Well‐defined materials were obtained, having molecular weights of around 100 000 g · mol^?1 and polydispersity indices of below 1.1. First investigations of the microphase behavior show that the materials selforganize in bulk morphologies where PMMA is the matrix while PS forms either spheres or cylinders. The central short PFS block forms either droplets or cylinders, which are placed at the surface of the PS domains.

     

Synthesis of PLLA‐MPEG Diblock Copolymers by Microwave‐Assisted Copolymerization of L‐Lactide and Methoxy Poly(ethylene glycol)

PLLA‐MPEG diblock copolymers with a controlled number‐average molar mass ranging from 7 330 to 117 610 g · mol^?1 and an L ‐lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100 °C by MPEG‐initiated ROP of L ‐lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA‐MPEG diblock copolymers with longer PLLA segments.