Oxa‐ and Thiazolidine‐Containing Polymers Derived via the Asinger Four‐Component Reaction: the Ring Matters

Novel structural motifs in macromolecular chemistry are introduced by the use of the Asinger multicomponent reaction. The combination of ammonia, acetone, α‐chloroisobutyraldehyde, and either water or sodium hydrosulfide, leads to an oxazoline or thiazoline scaffold, respectively, which is subsequently modified with 10‐undecenol and 10‐undecenoyl chloride to obtain heterocycle‐functionalized α,ω‐dienes. These substrates are used as monomers in an acylic diene metathesis (ADMET) or thiol‐ene step‐growth polymerization. The thus‐obtained polymers are studied in post‐polymerization modifications, like hydrogenation and oxidation. Here, the thiazolidine‐ and oxazolidine‐containing polymers show dramatically different chemical stability due to the heterocyclic moieties.

     

α,ωn‐Heterotelechelic Hyperbranched Polyethers Solubilize Carbon Nanotubes

The synthesis of novel linear‐hyperbranched (linhb) polyether block copolymers based on poly(ethylene oxide) and branched poly(glycerol), bearing a single pyrene or myristyl moiety at the α‐position of the linear chain is described. The polymers exhibit low polydispersity ( < 1.3) and controlled molecular weights ( = 5 000 g · mol^?1). The mainly hydrophilic block copolymers with multiple hydroxyl end groups readily dissolve multiwalled carbon nanotubes (MWCNTs) in water by mixing and subsequent sonification, resulting in noncovalent attachment of the linhb hybrid structure to the carbon nanotubes (CNTs). Transmission electron microscopy (TEM) was employed to visualize the solubilized nanotubes; after sulfation of the multiple hydroxyl groups the polymer layer was detected in the TEM images.

     

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.     

Synthesis and Hydrolysis of α,ω‐Perfluoroalkyl‐Functionalized Derivatives of Poly(ethylene oxide)

Summary: Two series of novel α,ω‐perfluoroalkyl terminated esters of poly(ethylene oxide) (PEO) (R_F‐PEO) having the general structure C_mF_2m+1? COO? (CH₂? CH₂? O)_n? OC? C_mF_2m+1, with m = 1,2,3,4 or 5 have been synthesized. The influences of the PEO molar mass, the length of the perfluoroalkyl group (R_F) and temperature on the cleavage of the ester bridge in aqueous solution and the effect of the hydrolysis process on the size of aggregates formed in water were studied. According to ¹H and ¹⁹F NMR measurements the degree of functionalization obtained (up to 96 mol‐%) increases with the decrease in the length of the R_F group. All of the derivatives showed ester cleavage in water in short time scales. The rates of hydrolysis of the ester bridge in aqueous solution were determined from pH‐measurements. It was verified that the rate law for hydrolysis corresponds to a pseudo‐first order type. The hydrolysis kinetic constant k increased with a decrease in the length of the R_F group ranging from 0.2 × 10^?3 s^?1 for the longest R_F group (C₅F₁₁? ) up to 1.2 × 10^?2 s^?1 for the shortest R_F group (CF₃? ). The value of k depended almost exclusively on the length of the perfluoroalkyl chain and was independent of the length of the PEO backbone (1 000 or 2 000 g · mol^?1), as long as no additional phenomenon such as phase separation was present. It was also found that the change in the value of k with temperature followed a non‐Arrhenius pattern and there was an evident relationship between the non‐linearity in the ln k vs. 1/T relation with increasing temperatures and the occurrence of a macroscopic phase separation of LCST type. Dynamic light scattering measurements showed the coexistence of unimers with associated species with apparent hydrodynamic radii (R_h) of approximately 20–45 nm for all samples in aqueous solutions. These species might correspond to aggregates of a few micelles. For some samples also larger aggregates were found with R_h in the 100–500 nm range, which might be attributed to clusters of micelles.

     

Facile and Efficient Synthesis of Fluorescence‐Labeled RAFT Agents and Their Application in the Preparation of α‐,ω‐ and α,ω‐End‐Fluorescence‐Labeled Polymers

The novel fluorescence‐labeled RAFT agents 2‐(4‐benzyl)benzoxazole benzodithioate (BBB) and 2‐(4‐benzyl)benzoxazole 9H‐carbazole‐9‐carbodithioate (BBCC) were synthesized via a nucleophilic substitution reaction between commercially available 2‐(4‐(chloromethyl)phenyl)benzoxazole (CMPB) and excessive carbodithioate or dithiocarbamate salts. BBB bearing benzoxazole at R‐group and BBCC carrying benzoxazole and carbazole at R‐ and Z‐group can be applied to directly obtain α‐ and α,ω‐end‐fluorescence‐labeled polymers, respectively. Considering the mild reaction conditions and readily available dyes, the reactions between CMPB and dithiocarbamate or carbodithioate salts should be a very simple and promising approach to synthesize fluorescent RAFT agents and polymers.     

Successive Synthesis of Multiarmed and Multicomponent Star‐Branched Polymers by New Iterative Methodology Based on Linking Reaction between Block Copolymer In‐Chain Anion and α‐Phenylacrylate‐Functionalized Polymer

A series of multiarmed and multicomponent miktoarm (μ‐) star polymers have been successfully synthesized by developing a new iterative methodology based on a specially designed linking reaction of the block copolymer in‐chain anions, whose anions are positioned between the blocks, with α‐phenylacrylate (PA)‐functionalized polymers. The iterative methodology involves the following two reaction steps: a) introduction of two different polymer segments by the linking reaction of a block copolymer in‐chain anion with a PA‐functionalized polymer and b) regeneration of the PA reaction site. By repeating this reaction sequence, two different polymer segments are advantageously and successively introduced into the μ‐star polymer. In practice, repetition of the reaction sequence affords well‐defined 3‐arm ABC, 5‐arm ABCDE, 7‐arm ABCDEFG, and even 9‐arm ABCDEFGHI μ‐star polymers, composed of polystyrene, polystyrenes substituted with functional groups, polyisoprene, and poly(alkyl methacrylate) arms, respectively.

     

Controlled synthesis of anthracene‐labeled ω‐amine polystyrene to be used as a probe for interfacial reaction with mutually reactive PMMA

Anthracene‐labeled polystyrene (PS) end‐capped by a primary amine has been synthesized by atom transfer radical copolymerization of styrene with 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (m‐TMI). The m‐TMI co‐monomer (5.7 mol‐%) does not perturb the control of the radical polymerization of styrene. The pendant isocyanate groups of the copolymer chains of low polydispersity (M _w/M _n = 1.25) and controlled molecular weight (up to 35 000) have been derivatized into anthracene by a reaction with 9‐methyl(aminomethyl)anthracene. The anthracene‐labeled PS (ca. 2 mol‐% label) has been conveniently analyzed by size‐exclusion chromatography with a UV detector (SEC‐UV). Moreover, the ω‐bromide end‐group of the copolymer chains has been derivatized into a primary amine, making the labeled PS chains reactive towards non‐miscible poly(methyl methacrylate) (PMMA) chains end‐capped by an anhydride. The interfacial coupling of the mutually reactive PS and PMMA chains has been studied under static conditions (i.e., at the interface between thin PS and PMMA films) and successfully analyzed by SEC‐UV.

SEC‐UV traces for anth‐PS‐NH₂ (80 μg · ml⁻¹; sample A5; Table 1 ), and PMMA‐anh (80 μg · ml⁻¹; sample B1; Table 1 ).     

Synthesis of New Homopolyester and Copolyesters by Anionic Ring‐opening Polymerization of α,α′,β‐Trisubstituted β‐Lactones

Summary: Novel polyester and copolyesters have been prepared by anionic ring‐opening polymerization of racemic 4‐alkyloxycarbonyl‐3,3‐dimethyl‐2‐oxetanones that had been synthesized in five steps from diethyl oxalpropionate used as chemical precursor. The anionic polymerizations, realized in bulk or in solution with tetraethylammonium benzoate as initiator, led to a homopolymer and copolymers with high molecular weights and polydispersity indices close to unity. These features can be explained by the presence of two methyl groups on the same carbon atom in the lactone, preventing transfer reactions to the monomer. Preparation of seeds and re‐initiation by addition of fresh monomer confirmed a living process. The hydrolysis of poly[(R,S)‐3,3‐dimethylmalic acid] under physiological conditions yielded (R,S)‐3,3‐dimethylmalic acid. A terpolymer was also prepared for biological studies related to its use as biodegradable materials for tissue regeneration.

Structure of poly[(R,S)‐3,3‐dimethylmalic acid].     

Efficient Synthesis of α,ω‐Divinyl‐Functionalized Polyolefins

A facile one‐step olefin metathesis‐mediated ethenolysis reaction on polyolefins containing 1,4‐inserted butadiene units yields α,ω‐divinyl telechelic polymers. These reactions can be successfully performed with well‐defined thermally stable ruthenium catalysts to yield essentially complete metathesis of internal double bonds. The reaction progress is monitored by ¹H NMR spectroscopy over time, by tracking the disappearance of the signal due to internal unsaturation of 1,4‐butadiene at ca. 5.5 ppm in toluene‐d₈ solvent. The reaction conditions are optimized for ethylene pressure, temperature, catalyst loading, and reaction time. Catalyst loading of 45:1 1,4‐butadiene unsaturation to catalyst at 90 °C with 25 psi ethylene pressure is successful in removing internal unsaturation with no detectable isomerization side reactions. High‐temperature gel‐permeation chromatography (GPC) analysis of the depolymerized product correlates to the calculated molecular weight based on the number of internal double bonds observed in the ¹H NMR analysis of the starting polyolefin. This method offers a single step, rapid, and clean route toward divinyl‐terminated telechelic polymers based on commodity materials in high yields.

     

Synthesis,Characterization, and Intramolecular End‐to‐End Ring Closure of α‐Isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal Polystyrene‐block‐polyisoprene Block Copolymers

Cyclic polystyrene‐block‐polyisoprenes of controlled dimensions have been synthesized for the first time by the direct coupling of α‐isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal‐heterodifunctional linear polystyrene‐block‐polyisoprene precursors previously prepared by living anionic polymerization. Cyclization is achieved under high dilution by intramolecular coupling of the polymer ends under acid catalyst conditions. Using this strategy polystyrene‐block‐polyisoprene macrocycles of controlled chain dimensions are prepared in high yield (> 90%). Pure cycles were finally recovered by flash chromatography. The synthesis and characterization of both the linear α,ω‐heterodifunctional polystyrene‐block‐polyisoprenes block copolymers precursors and of the corresponding cyclized chain architectures are reported.

200 MHz ¹H NMR spectrum (CDCl₃) of cyclized polystyrene‐block‐polyisoprene copolymer (M _n = 12 000).     

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.     

Molecular Motions in the Supramolecular Complexes between Poly(ε‐caprolactone)‐Poly(ethylene oxide)‐Poly(ε‐caprolactone) and α‐ and γ‐Cyclodextrins

The structure and molecular motions of the triblock copolymer PCL‐PEO‐PCL and its inclusion complexes with α‐ and γ‐cyclodextrins (α‐ and γ‐CDs) have been studied by solid‐state NMR. Different cross‐polarization dynamics have been observed for the guest polymer and host CDs. Guest–host magnetization exchange has been observed by proton spin lattice relaxation T₁, proton spin lattice frame relaxation T_1ρ and 2D heteronuclear correlation experiments. A homogeneous phase has been observed for these complexes. Conventional relaxation experiments and 2D wide‐line separation NMR with windowless isotropic mixing have been used to measure the chain dynamics. The results show that for localized molecular motion in the megahertz regime, the included PCL block chains are much more mobile than the crystalline PCL blocks in the bulk triblock copolymer. However, the mobility of the included PEO block chains is not very different from the amorphous PEO blocks of the bulk sample. The cooperative, long chain motions in the mid‐kilohertz regime for pairs of PCL‐PEO‐PCL chains in their γ‐CD channels seem more restricted than for the single PCL‐PEO‐PCL chains in the α‐CD channels, however, they are not influencing the more localized, higher frequency megahertz motions.     

Synthesis of α,ω‐Isocyanate–Telechelic Poly(methyl methacrylate)

The preparation of α,ω‐isocyanate–telechelic poly(methyl methacrylate) using RAFT polymerization and two postpolymerization modification steps is presented. The synthetic strategy includes the RAFT polymerization of methyl methacrylate, which results in a hetero telechelic polymer. In the first modification step by radical exchange, a carboxylic acid homo telechelic PMMA was successfully prepared. Second, the carboxylic acid end groups are reacted with hexamethylene diisocyanate in excess and magnesium chloride as a catalyst. Under mild reaction conditions (80 °C, 4 h), the isocyanate homo telechelic PMMA is obtained. A conversion of 86% of the carboxylic acid end groups was achieved.     

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 polymer microspheres with mercapto groups by polycondensation of α,ω-alkanedithiol and α,ω-dibromoalkane in the presence of a polystyrene latex

Polymer microspheres with mercapto groups were synthesized by the polycondensation of α,ω-alkanedithiol and α,ω-dibromoalkane in the presence of a polystyrene latex (PSt) and a nonionic surfactant. The immobilization of the mercapto group onto the microsphere was studied using dithiols with various alkylene chain lengths and PSt seed particles with different diameters. When small-sized PSt seed particles (0,40 μm) were used, the mercapto group content was high. In contrast, the use of large seed particles (0,89 μm) in the polycondensation reaction resulted in microspheres with low mercapto group content in spite of the use of an excess amount of dithiol. The polycondensation with 1,4-butanedithiol afforded microspheres with high mercapto group content. Silver ions were found to be adsorbed onto the microspheres with mercapto groups.     

Synthesis of polymer microspheres with mercapto groups by polycondensation of α,ω‐alkanedithiol and α,ω‐dibromoalkane in the presence of a poly[styrene‐N‐(hydroxymethyl)acrylamide] latex

Polymer microspheres with mercapto groups were synthesized by polycondensation of α,ω‐alkanedithiol and α,ω‐dibromoalkane in the presence of a poly[styrene‐N‐(hydroxymethyl)acrylamide] latex (PS‐HMAm). Monodisperse microspheres were obtained in quantitative yield. The sulfur content of the microspheres was comparable to that calculated from the feed ratio, indicating that the polycondensation proceeds in the polymer particles. The immobilization of the mercapto group onto the microsphere is significantly influenced by the molar ratio of dithiol to dibromide and the diameter of the PS‐HMAm particles used in the polycondensation. The mercapto group content of the microsphere increases with the molar ratio of dithiol to dibromide. The polycondensation with small seed particles (0,127 μm) afforded microspheres with high mercapto group contents. On the contrary, upon use of large ones (0,456 μm) the mercapto group content is decreased.     

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.     

Well‐Defined Miktocycle Eight‐Shaped Copolymers Composed of Polystyrene and Poly(ε‐caprolactone): Synthesis and Characterization

A series of well‐defined miktocycle number‐eight‐shaped copolymers composed of cyclic polystyrene (PS) and cyclic poly(ε‐caprolactone) (PCL) have been successfully synthesized by a combination of atom transfer radical polymerization (ATRP), ring‐opening polymerization (ROP), and “click” reaction. The synthesis involves three steps: 1) preparation of tetrafunctional initiator with two acetylene groups, one hydroxyl group and a bromo group; 2) preparation of two azide‐terminated block copolymers, N₃‐PCL‐(CH?C)₂‐PS‐N₃, with two acetylene groups anchored at the junction; and 3) intramolecular cyclization of the block copolymer through “click” reaction under high dilution. The ¹H NMR, FT‐IR, and gel permeation chromatography (GPC) techniques are applied to characterize the chemical structures of the resulting intermediates and the target polymers. Their thermal behavior is investigated by differential scanning calorimeter (DSC). The decrease in chain mobility of eight‐shaped copolymers restricts the crystallization of PCL.

     

Influence of Hydrogen on the Polymerization of Ethylene with Nickel‐α‐diimine Catalyst

The performance of 1,4‐bis(2,6‐diisopropylphenyl)acenaphtenediimine‐dichloronickel(II) ( 1 ) in the polymerization of ethylene was controlled by the addition of molecular hydrogen in the gas feed. Productivities obtained at 10°C with the system 1 /triisobutylaluminium decreased with the addition of hydrogen, from 499 to 6.7 kg polymer·mol^–1·h^–1, the molecular weight average of the polyethylene dropped from 365 to 18.6 kg·mol^–1, the polydispersity index dropped from 3.0 to 1.8 but the branching degree increased from 48 to 75 branches/1 000 backbone carbon atoms. With trimethylaluminium as cocatalyst more complex behaviors were observed.