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.

     

Synthesis of Diverse Asymmetric α,ω‐Dienes Via the Passerini Three‐Component Reaction for Head‐to‐Tail ADMET Polymerization

The Passerini three‐component reaction is applied to synthesize, in a one‐step procedure, diverse asymmetric α,ω‐dienes containing an acrylate and a terminal olefin. Such monomers are well known to undergo head‐to‐tail acyclic diene metathesis (ADMET) polymerization due to the high cross‐metathesis selectivity between acrylates and terminal olefins. Additionally, amphiphilic block copolymers are synthesized using a monofunctional PEG₄₈₀ monoacrylate, which acts as a selective chain‐transfer agent during the polymerization process. Thus, control over the molecular weight of the amphiphilic ADMET polymers is shown by using different ratios of mono­mer and chain‐transfer agent. All the polymers are thoroughly characterized, and their ability to form nanoparticles in aqueous solution is studied.

     

Poly(ε‐caprolactone)‐graft‐poly(2‐(dimethylamino)ethyl methacrylate) Amphiphilic Copolymers Prepared via a Combination of ROP and ATRP: Synthesis,Characterization, and Self‐Assembly Behavior

Poly(ε‐caprolactone)‐graft‐poly(2‐(dimethylamino) ethyl methacrylate) (PCL‐g‐PDMAEMAs), a kind of amphiphilic graft copolymer, was prepared by combination of ROP and ATRP. The FTIR, ¹H NMR, and GPC results indicate that well‐defined polymers with controlled graft density and length of side chain were successfully synthesized. We prepared PCL‐g‐PDMAEMA nanoparticles by employing a nanoprecipitation technique. The pH‐ and thermosensitive properties of PCL‐g‐PDMAEMA nanoparticles were investigated by ¹H NMR, TEM, and DLS. It was found that the nanoparticles with an average size of 120 nm presented core–shell structure in aqueous dispersion. Furthermore, the nanoparticles are sensitive to temperature in base while not in an acidic environment.

     

Synthesis and Characterization of α,ω‐Telechelic Polymers by Atom Transfer Radical Polymerization and Coupling Processes

Initiators for atom transfer radical polymerization (ATRP) bearing different functional groups (aldehyde, aromatic hydroxyl, dimethyl amino) were synthesized and characterized. Monotelechelics with low molecular weight were obtained by ATRP of styrene using these initiators in the presence of the CuBr/bpy catalytic complex. α,ω‐Telechelic polymers with double molecular weights with respect to the starting materials were prepared by coupling of monotelechelics under atom transfer radical generation conditions, in the absence of monomer, using CuBr as catalyst, tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) as a ligand, under Cu⁰ mediated reductive conditions and with toluene as solvent. Terminal Br atoms present in monotelechelic polystyrenes (PS) as a consequence of the ATRP mechanism also offer other routes for preparing telechelic polymers. Aldehyde functionalized polymer was etherified with hydroquinone furnishing telechelic PS with a molecular weight that was two times higher. All polymers were characterized by spectral methods (NMR, IR spectroscopy) as well as by GPC.

Synthesis of initiators for atom transfer radical polymerization bearing different functional groups, for example, aldehyde, aromatic hydroxyl, dimethyl amino.     

A Tandem Controlled Radical Polymerization Technique for the Synthesis of Poly(4‐vinylpyridine) Block Copolymers: Successive ATRP,SET‐NRC,and NMP

Poly(methyl methacrylate)‐block‐poly(4‐vinylpyridine), polystyrene‐block‐poly(4‐vinyl pyridine), and poly(ethylene glycol)‐block‐poly(4‐vinylpyridine) block copolymers are synthesized by successive atom transfer radical polymerization (ATRP), single‐electron‐transfer nitroxide‐radical‐coupling (SET‐NRC) and nitroxide‐mediated polymerization (NMP). This paper demonstrates that this new approach offers an efficient method for the preparation of 4‐vinylpyridine‐containing copolymers.

     

Poly(N‐hydroxyethylacrylamide) Prepared by Atom Transfer Radical Polymerization as a Nonionic,Water‐Soluble,and Hydrolysis‐Resistant Polymer and/or Segment of Block Copolymer with a Well‐Defined Molecular Weight

N‐Hydroxyethylacrylamide (HEAA) was polymerized using the atom transfer radical polymerization (ATRP) with ethyl 2‐chloropropionate (ECP), copper(I) chloride (CuCl), and tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) in ethanol/water, producing poly(N‐hydroxyethylacrylamide) (PHEAA) with well‐defined molecular weights. The thermogravimetric analysis (TGA) indicated that the obtained PHEAA broadly decomposed with a two‐stage weight loss. The first loss was due to the decomposition of the hydroxyethyl groups, which started at temperatures ranging from 249.2 to 277.1 °C. The remaining polyacrylamide backbones started to decompose at temperatures ranging from 352.5 to 383.4 °C. The differential scanning calorimetry (DSC) indicated that PHEAA had a glass transition temperature (T_g) ranging from 70.6 to 117.8 °C. The ability of the obtained PHEAA as a prepolymer to initiate other acrylamide derivatives is described. N,N‐Dimethylacrylamide (DMAA), N‐acyloylmorpholine (NAM), and N‐[3‐(dimethylamino)propyl]acrylamide (DMAPAA) were subsequently added to the solutions after the polymerization of HEAA with ECP/CuCl/Me₆TREN, producing the corresponding block copolymers.

     

A Novel Macroinitiator for the Synthesis of Triblock Copolymers via Atom Transfer Radical Polymerization: Polystyrene‐block‐poly(bisphenol A carbonate)‐block‐polystyrene and Poly(methyl methacrylate)‐block‐poly(bisphenol A carbonate)‐block‐poly(methyl methacrylate)

Summary: Bis(hydroxy)telechelic bisphenol A polycarbonate (PC) was prepared via melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC) using lanthanum(III ) acetylacetonate as a catalyst for transesterification. Subsequently, the polycarbonate was converted to a bifunctional macroinitiator for atom transfer radical polymerization (ATRP) with the reagent, α‐chlorophenylacetyl chloride. The macroinitiator was used for the polymerization of styrene (S) and methyl methacrylate (MMA) to give PS‐block‐PC‐block‐PS and PMMA‐block‐PC‐block‐PMMA triblock copolymers. These block copolymers were characterized by NMR and GPC. When styrene and methyl methacrylate were used in large excess, significant shifts toward high molecular weights were observed with quantitative consumption of the macroinitiator. Several ligands were studied in combination with CuCl as the ATRP catalyst. Kinetic studies reveal the controlled nature of the polymerization reaction for all the ligands used.

Formation of a bifunctional ATRP macroinitiator by esterification of bis(hydroxy)telechelic PC with α‐chlorophenylacetyl chloride.     

Double‐Hydrophilic Polymer Brushes: Synthesis and Application for Crystallization Modification of Calcium Carbonate

Summary: A water‐soluble diblock copolymer composed of poly(ethylene glycol) (PEG) and a cylindrical poly(acrylic acid) (PAA) brush is reported. It is prepared by a ‘grafting from’ approach using stepwise atom transfer radical polymerization combined with group transformation. Uniform molecular brushes, PEG₁₁₃‐b‐P(MA‐g‐PAA₂₆)₁₆₉, are thus prepared as indicated by atom force microscopy analysis. This PAA densely grafted polymer is used to induce the crystallization of calcium carbonate in aqueous solution. Different experimental conditions, fast mixing reactions and static diffusion methods, are applied to explore the effect of polymer brushes on the crystallization, which is characterized by scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis.

AFM image of the polymer brushes on mica and an SEM image of CaCO₃ particles prepared in its presence.     

The Use of ε‐Caprolactone as a Polymerizable Solvent for the Atom Transfer Radical Polymerization of MMA at Low Temperature

This paper reports on the decisive effect that solvent has on the atom transfer radical polymerization of methyl methacrylate (MMA) at low temperature. In butanone and in the presence of a copper(I)/bipyridine complex, the polymerization is controlled and the molecular weight distribution is narrow, at 0°C and even lower. This control is maintained when ε‐caprolactone (CL) is substituted for butanone. The use of this polymerizable solvent together with a novel dual initiator, 2‐hydroxyethyl, 2′‐methyl‐2′‐bromopropionate, is an efficient strategy to prepare PMMA‐b‐PCL diblock polymers in a one‐pot process.     

Living Alternating Copolymerization of a Methylenecyclopropane Derivative with CO to Afford Polyketone with Dihydrophenanthrene‐1,10‐diyl Groups

Summary: Pd complexes prepared from [PdCl(Me)(L)] (L = N‐ligands) and NaBARF catalyze the alternating copolymerization of 7‐methylenedibenzo[a,c]bicyclo[4.1.0]heptane with CO to produce the polyketone. Pd complexes with substituted 1,10‐phenanthroline ligands produce the polymer with narrow molecular weight distribution. Addition of 4‐tert‐butylstyrene to the growing polymer after consumption of the initially charged monomer, results in polymer growth to afford an AB‐type block copolyketone. A Pd complex with an optically active bisoxazoline ligand produces the optically active polymer with narrow polydispersity. The addition of DBU to a solution of polyketone converts the cis‐fused six‐membered rings into the trans‐fused rings via epimerization of the CH carbon attached to the carbonyl group.

Addition of I to cationic Pd complexes catalyzes the ring‐opening copolymerization of the monomer with CO to produce the polyketone, ? (C(?CH₂)? C₁₄H₁₀? CO)_n? ( II ).     

Characterization of Linear and 3‐Arm Star Block Copolymers by Liquid Chromatography at Critical Conditions

Summary: LCCC for polyMA homopolymers was established in order to analyze the polyMA‐polySt linear and star block copolymers. The validity of the assumption that under the LCCC for polyMA, the polyMA segment in the polyMA‐containing block copolymer is chromatographically “invisible” was verified. It was found that within the scale of investigation ( ), the molecular weight and architecture of the polyMA segments had no evident influence on the retention behavior of the polySt‐polyMA block copolymers and the polyMA block in the copolymer was “invisible”. The critical conditions of polyMA were used for quantitative analysis of the polySt block in the linear and 3‐arm star polyMA‐polySt block copolymers, which were synthesized by AGET ATRP in miniemulsion. It was shown that the copolymer had completely different elution peak from its MI. The calculated molecular weights of polySt blocks in the block copolymers were similar to those obtained from normal SEC analysis. Transferring the eluates from the LCCC (the first dimension) column to a SEC column (the second dimension) produced LCCC × SEC two‐dimensional chromatogram, which contained information on both chemical composition and molecular weight of the synthesized copolymers. The combination of these liquid chromatography methods clearly confirmed the high initiation efficiency of the polyMA MIs during the synthesis of block copolymers and the presence of a byproduct formed by radical‐radical coupling.

     

Synthesis of Polystyrene‐block‐Poly(methyl methacrylate) with Fluorene at the Junction: Sequential Anionic and Controlled Radical Polymerization from a Single Carbon

Polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) has been synthesized by sequential anionic and reverse atom transfer radical polymerization (ATRP) or a variation of nitroxide mediated polymerization (NMP) from a single initiating site, specifically the 9‐carbon on 2,7‐dibromofluorene or fluorene. The addition of the second arm (PS) relied on thermal decomposition of 2,2′‐azoisobutyronitrile (AIBN) to generate radicals, abstracting the 9‐H on the polymer‐bound fluorene species to form the initiating radical. Styrene was not present in the reaction mixture when AIBN was decomposed, preventing competition between addition across the monomeric alkene and hydrogen abstraction from the fluorene. After 1 h, styrene was introduced and mediation of the subsequent radical polymerization was achieved by the presence of CuCl₂/ligand or TEMPO. Characterization of the diblock copolymers by gel permeation chromatography (GPC) revealed substantial shifts in number average molecular weight ( ) values compared to the anionically prepared PMMA macroinitiator, while polydispersity indices (PDI's) remained relatively low (typically < 1.5). Characterization by UV detection with GPC (at 310 nm) verified that the diblock polymer is chromophore‐bound, which was further verified by UV‐vis spectroscopy of the isolated diblock.

     

One‐Pot Synthesis of PTFEMA‐b‐PMMA‐b‐PTFEMA by Controlled Radical Polymerization with a Difunctional Initiator in Conjugation with Photoredox Catalyst of Ir(ppy)3 Under Visible Light

Visible‐light‐induced free radical polymerization of methyl methacrylate (MMA) and 1,1,1‐trifluoroethyl methacrylate (TFEMA) with a difunctional initiator, dimethyl 2,6‐dibromoheptanedioate (DMDBHD), conjugated with a photoredox catalyst, tris(2‐phenylpyridinato)iridium(III) (fac‐[Ir(ppy)₃]), is investigated. Kinetic studies demonstrate that homopolymerizations of both MMA and TFEMA are controlled radical polymerizations. The linear increase of molecular weights with monomer conversion and the narrow PDIs (1.2–1.4) reveal a good living character. In addition, PTFEMA‐b‐PMMA‐b‐PTFEMA triblock copolymer is prepared by a one‐pot process with sequential monomer addition. The of the triblock copolymers increases linearly with monomer conversion and the PDI of block copolymers is still maintained around 1.2–1.4. Experimental data confirm that the products are pure block polymers. Furthermore, the molar fraction of the TFEMA monomeric unit in the block copolymer is about 21.96%, close to the theoretical value 21.00% calculated from the monomer conversion.

     

Effect of the End‐Positioning of a Lithium Sulfonate Group on the Aggregation and Micellization Behavior of ω‐Lithium Sulfonate Polystyrene‐block‐polyisoprenes

Summary: ω‐Lithium sulfonate polystyrene‐block‐polyisoprenes were synthesized by anionic polymerization high vacuum techniques and a post‐polymerization reaction with 1,1‐diphenylethylene and 1,3‐propane sultone. The solution properties of ω‐lithium sulfonate block copolymers were studied in a low polarity solvent (CCl₄) which is a good solvent for both blocks. The study revealed the formation of aggregates due to the association of the lithium sulfonate groups (SuLi). The mass, size and shape of the aggregates were studied by static and dynamic light scattering and viscometry. The aggregation number decreased as the length of the chain increased and the aggregates showed a behavior similar to that of star polymers. The micellization of ω‐functionalized block copolymers was also studied in a polar selective solvent for polystyrene, N,N‐dimethylacetamide (DMA). Micelles formed from block copolymers containing the sulfonate group at the polyisoprene end exhibited an association number which was about 80% of that of the neutral block copolymer and had a higher critical micelle concentration. The samples having the polar group at the PS end showed a similar behavior.

The structures of the end‐functionalized block copolymers studied.     

Amphiphilic Multi‐Arm Star‐Block Copolymers for Encapsulation of Fragrance Molecules

Novel amphiphilic multi‐arm star‐block copolymers with a hyperbranched core, a hydrophobic inner shell, and a hydrophilic outer shell have been prepared from a commercial hyperbranched polyester macroinitiator by ring‐opening polymerization of ε‐caprolactone, followed by atom transfer radical polymerization of tert‐butyl acrylate (tBuA). Hydrolysis of the tert‐butyl groups was then used to convert the poly(tBuA) blocks to poly(acrylic acid), resulting in stable amphiphilic core‐shell structures with significantly higher degrees of functionality than reported so far in the literature. A strong correlation between the maximum concentration of selected hydrophobic guest molecules and the concentration of amphiphilic star‐block copolymer in aqueous solution was observed by ¹H NMR, demonstrating the capacity of these copolymers to encapsulate and disperse significant loadings (up to about 27 wt.‐%) of volatile hydrophobic molecules such as fragrances in water.

     

Visible‐Light‐Induced Controlled Polymerization of Hydrophilic Monomers with Ir(ppy)3 as a Photoredox Catalyst in Anisole

With fac‐Ir(ppy)₃ as photoredox catalyst and ethyl 2‐bromoisobutyrate (EBiB) as initiator, the homopolymerization of methyl methacrylate (MMA) in different solvents, such as N,N‐dimethylformamide (DMF), acetonitrile, and anisole are run under irradiation of an LED lamp. The results show that anisole is a better solvent for the polymerization with regard to the polydispersity index (PDI). A well‐controlled polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) is demonstrated and the clean block copolymer of PMMA‐b‐PPEGMA is prepared with PDI less than 1.3; however, the 2‐(dimethylamino) ethyl methacrylate (DMAEMA) polymerization is poorly controlled. With the PMMA as macromolecular initiator, the block copolymer PMMA‐b‐PDMAEMA can be prepared with PDI around 2.0.

     

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.     

Use of Original ω‐Perfluorinated Dithioesters for the Synthesis of Well‐Controlled Polymers by Reversible Addition‐Fragmentation Chain Transfer (RAFT)

A series of five fluorinated dithioesters PhC(S)SRCH₂C_nF_2n+1 (where R represents an activating spacer and n = 6 or 8) was obtained in fair to high yields (57–88%). These transfer agents were successfully used in reversible addition‐fragmentation transfer (RAFT) of styrene (S), methyl methacrylate (MMA), ethyl acrylate (EA) and 1,3‐butadiene. Well‐chosen fluorinated dithioesters were able to lead to a good control of the radical polymerization of these monomers (i.e., molar masses of the produced polymers increased linearly with the monomer conversion and the polydispersity indexes ranging between 1.1 and 1.6 remained low). The relationship between the structures of the dithioesters and the living behavior of the radical polymerization of these above monomers is discussed and it is shown that the nature of the R group influences the living behavior from different contributions to radical stabilization. Furthermore, the RAFT process also yielded PMMA‐b‐PS and PEA‐b‐PS block copolymers bearing a fluorinated moiety.     

Polythioethers with Controlled α,ω‐End Groups Prepared by Visible Light Induced Thiol–Ene Click Polymerization of Dithiol and Divinyl Ether with 4‐(N,N‐diphenylamino)benzaldehyde as Organocatalyst

This study reports a step‐growth click‐polymerization of 1,4‐benzenedimethane (BDMT) and diethylene glycol divinyl ether (DEGVE) with 4‐(N,N‐diphenylamino)‐benzaldehyde (DPAB) as a photoredox catalyst under irradiation of visible light. DPAB exhibits a strong UV–vis absorption at 350 nm and a strong fluorescence emission at 480 nm in anisole. There is a strong fluorescence quenching between BDMT and DPAB. The molecular weight of the polythiolether can be controlled by reaction time and monomer feed ratios. More importantly, α,ω‐dithiol and α,ω‐divinyl telechelic polythiolether oligomers are successfully synthesized by simply changing the molar ratios of BDMT to DEGVE. ¹H NMR and MALDI‐TOF MS spectra demonstrate that the oligomers have high end group fidelity. In addition, strong fluorescence is observed when the α,ω‐dithiol terminated polythiolether adds with N‐(1‐pyrenyl) maleimide, indicating that the as‐prepared polythiolether bears reactive thiol end groups. Furthermore, high molecular weight polythiolether are prepared by chain extension with reactive polythiolether oligomers as macro‐monomers. For example, α,ω‐divinyl oligomer (M_n = 2000 g mol^?1) could further react with α,ω‐dithiol oligomer (M_n = 2400 g mol^?1) to form high molecular weight polythiolether (M_n = 6000 g mol^?1).