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.

     

On the Monolayer Adsorption of Thiol‐Terminated Dendritic Oligothiophenes onto Gold Surfaces

The self‐assembled monolayer formation of a series of thiophene dendron thiols with different generations and alkyl chain lengths onto gold surfaces is studied. Average film thicknesses and dielectric constants were calculated from SPR using a two‐subphase differential method. The in situ adsorption of the thiophene dendron thiols was monitored by SPR kinetics measurements and fitted using an empirical three‐step model. Electrochemical redox molecular probing experiments provided additional insight into surface coverage, which showed different abilities to block electron transfer at the monolayer/electrode interfaces. The surface coverage of the films was also estimated by QCM measurements and supported by static WCA measurements.

     

ABA and BAB Triblock Copolymers Based on 2‐Methyl‐2‐oxazoline and 2‐n‐Propyl‐2‐oxazoline: Synthesis and Thermoresponsive Behavior in Water

Inspired by the well‐known amphiphilic block copolymer platform known as Pluronics or poloxamers, a small library of ABA and BAB triblock copolymers comprising hydrophilic 2‐methyl‐2‐oxazoline (A) and thermoresponsive 2‐n‐propyl‐2‐oxazoline (B) is synthesized. These novel copolymers exhibit temperature‐induced self‐assembly in aqueous solution. The formation and size of aggregates depend on the polymer structure, temperature, and concentration. The BAB copolymers tend to agglomerate in water, with the cloud point temperature depending on the length of poly(2‐n‐propyl‐2‐oxazoline) chain. On the other hand, ABA copolymers form smaller aggregates with hydrodynamic radius from 25 to 150 nm. The dependence of viscosity and viscoelastic properties on the temperature is also studied. While several Pluronic block copolymers are known to form thermoreversible hydrogels in the concentration range 20–30 wt%, thermogelation is not observed for any of the investigated poly(2‐oxazoline)s at the investigated temperature range from 10 to 50 °C.

     

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).     

Functionalization of Gold and Silicon Surfaces by Copolymer Brushes Using Surface‐Initiated ATRP

Surface‐initiated ATRP was used for step‐by‐step growth of poly(butyl methacrylate)‐co‐poly(2,2‐dimethylaminoethyl methacrylate) (PBMA‐co‐PDMAEMA) brushes from gold and silicon substrates. A one‐step procedure was found to have high efficiency for initiator anchoring. The polymer brushes were characterized in situ by contact angle measurements, ellipsometry, and X‐ray photoelectron spectroscopy (XPS). Detachment of the polymer brushes from both substrates allowed an exact determination of molecular weight and polydispersity indexes given by GPC. ¹H NMR confirmed the chemical structure of the detached brushes. Comparison of theoretical predictions and experimental data showed that the first PBMA block had a folded conformation while copolymerization of the second DMAEMA induced stretching of the brushes.

     

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 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.     

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.     

π‐Conjugated Polymers Consisting of 9,10‐Dihydrophenanthrene Units

π‐Conjugated polymers consisting of 9,10‐disubstituted 9,10‐dihydrophenenthrene, with the substituents octyl, 2‐ethylhexyl, ‐OSiBu₃, etc., units are prepared by organometallic polycondensation. Homopolymers ( PH₂Ph(9,10‐R) ) have a π‐conjugation system similar to that of polymers of 9,9‐dialkylfluorene and show UV‐Vis peaks at ≈380 nm. In addition to the peak at ≈380 nm, some homopolymers give rise to a peak at a longer wavelength, suggesting molecular assembly of the polymers. X‐ray diffraction data support the molecular assembly. The homopolymers show photoluminescence (PL) with PL peaks at ≈430 nm, and PL spectrum of the polymer film is essentially unchanged after heating the polymer film at 150 °C in air. The homopolymers undergo electrochemical p‐doping at about 1.5 V versus Ag⁺/Ag.     

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.

     

Macroporous Materials from Self‐Assembling Synthetic Cyclic Peptide‐Based Compounds and Deposition of Dipeptide‐Capped Gold Nanoparticles on the Surfaces

Two cyclic peptides are separately self‐assembled, one on top of the other, utilizing non‐covalent interactions – mainly intermolecular hydrogen bonding – to form a one‐dimensional array. These one‐dimensional arrays are further self‐assembled to construct macroporous materials. This is shown from TEM, AFM and FE‐SEM analyses. These materials have been used for adsorption and desorption of nitrogen gas. Moreover, they can act as suitable templates for the deposition of dipeptide capped gold nanoparticles on the surfaces of macroporous structures.

     

Telechelic polystyrene α,ω-macrozwitterions, 1. Synthesis and characterization

Telechelic α,ω-macrozwitterions — narrowly distributed polystyrene chains oppositely charged at each end — were synthesized via anionic polymerization using direct functionalization with the initiator and the termination agent. The resulting products were purified (zwitterion content ≥ 0,95) and characterized with gel permeation chromatography, viscometry, static and dynamic light scattering and small-angle neutron scattering. In unpolar solvents as toluene, the polymeric zwitterions form clusters with molecular weights depending on concentration. In the dilute case, the clusters are relatively small and consist of approximately 8 zwitterions. The structure of these clusters is discussed by their scattering behaviour. Above a critical concentration being in the range of 0,05 g/cm³, an infinite aggregate is formed. Zwitterions in N,N-dimethylformamide behave differently: due to the attenuation of dipolar forces, no clusters are formed. In this case, the behaviour in dilute solution can be described by the formation of polymeric rings consisting of one polymer molecule, only.     

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 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].     

A New Versatile Radical Addition on α, ω‐Dimethacrylate Poly(ethylene oxide)

Summary: The synthesis of α,ω‐di(2‐methyl‐6‐pyrenyl‐2‐succinimidylhexanoic ester)poly(ethylene oxide) (Py(S)‐EO_n‐(S)Py) was obtained by a new radical reaction between 4‐pyrenylbutanoate N‐hydroxysuccinimidyl ester and α,ω‐dimethacrylate poly(ethylene oxide). The reason for the choice of such bulky groups is a possible application of this reaction to the synthesis of polyrotaxane from polypseudorotaxane. Two reaction media were examined, heterogeneous in water at room temperature using persulfate as initiator, or homogeneous in DMSO at 60 °C using AIBN as initiator. Structural characterization of the functionalization products was carried out by SEC, MALDI TOF, and NMR spectroscopies. It was shown that two types of α,ω‐dipyrenyl PEO could be obtained, one corresponding to the expected product (Py(S)‐EO_n‐(S)Py), the other corresponding to the same structure but without the succinimidyl substituent (Py(H)‐EO_n‐(H)Py). It was also shown that in the soluble system macrocycles could be formed and this last aspect has been assigned to intramolecular interactions existing between the pyrenyl groups. An interesting aspect of this synthesis is the possibility to find conditions giving high yields without crosslinking and fairly reduced amount of coupling.

     

Interconversion of Alternating Poly(ester amide)s and Cyclic Ester Amides from Adipic Anhydride and α,ω‐Amino Alcohols

Poly(esters amide)s from adipic anhydride and α,ω‐amino alcohols were obtained by polycondensation of α‐carboxyl‐ω‐hydroxyl amides under mild conditions in solution or by bulk polycondensation at elevated temperatures. For the polycondensation in bulk the influence of catalyst and of temperature on the number‐average molecular weight was studied. At a temperature of 170 °C the polycondensation process is followed by a ring‐closing depolymerisation and the formation of cyclic ester amides. Ten‐ to fourteen‐membered cyclic ester amides were obtained and characterized. The ring‐opening polymerisation of these cyclic ester amides leads, in a controlled mode, to poly(ester amide)s. The interconversion of poly(ester amide)s and cyclic ester amides by ring‐closing depolymerisation and ring‐opening polymerisation is possible. The poly(ester amide)s from adipic anhydride and homologous α,ω‐amino alcohols H₂N? (CH₂)_x? OH (x = 2–6) are semicrystalline materials, their melting points show the odd/even effect observed for [n]‐polyamides and [n]‐polyurethanes.

Synthesis of alternating poly(ester amide)s.     

Oligo(thiophénylènes-1,4) α,ω-difonctionnalisés, 3. Oligomères α,ω-diaminés et copolyamides qui en dérivent

Polyamides 7a and 7b were prepared from α-(4-aminophenyl)-ω-aminopoly(thio-1,4-phenylene)s (3a) by reaction with 1,12-dodecanedioic acid (6) , tribloc copolymers 9 from 3a and 11 aminoundecanoic acid (8) , and multibloc copolymers 10 from 3a, 6 , and 8 . The properties of these copolymers were studied by DSC and compared with those of N, N'-lauroyl derivatives of 3a as model compounds. Phase separations were observed with products containing at least four phenylene units in the thiophenylene blocs. However, the T_g was found to increase with increasing number of phenylene units.     

π‐Conjugated Polymers Consisting of Isothianaphthene and Dialkoxy‐p‐phenylene Units: Synthesis,Self‐Assembly,and Chemical and Physical Properties

A series of π‐conjugated alternating copolymers consisting of Th‐ITN‐Th and p‐C₆H₂(OR)₂ units were synthesized. XRD indicated that the copolymers assume an interdigitation packing mode, and UV‐Vis spectra revealed a strong tendency for self‐assembly. Upon molecular assembly of the copolymer, the UV‐Vis absorption shifted by about 100 nm to a longer wavelength from that of the single molecule. The copolymers underwent electrochemical oxidation (or p‐doping) and reduction (or n‐doping) at 0.2 and ?2.0 V versus Ag⁺/Ag, respectively. A p‐doped copolymer film showed an electrical conductivity of 182 S · cm^?1, and the temperature dependence of electrical conductivity was measured. The copolymer showed piezochromism and served as a p‐channel material for a field‐effect transistor.

     

Novel Fluorinated Hybrid Polymer by Radical Polyaddition of Bis(α‐trifluoromethyl‐β,β‐difluorovinyl) Terephthalate onto Dialkoxydialkylsilanes

To develop the radical polyaddition of bisperfluoroisopropenyl esters, the reactions of bis(α‐trifluoromethyl‐β,β‐difluorovinyl) terephthalate [CF₂?C(CF₃)OCOC₆H₄COOC(CF₃)?CF₂] (BFP) with dialkoxydialkylsilane were examined to prepare fluorinated hybrid polymers bearing dialkylsilyl groups in the main chain. Prior to polyaddition, the radical addition reaction of 2‐benzoyloxypentafluoropropene [CF₂?C(CF₃)OCOC₆H₅] (BPFP) has been investigated to afford the results that diethoxydimethylsilane (DEOMS) or dimethoxydimethylsilane with BPFP initiated by oxo radical are the best combination for the preparation of polymers. The mechanism of the addition reaction was proposed. Radical polyaddition of BFP with DEOMS initiated by benzoyl peroxide or di‐tert‐butyl peroxide has yielded polymers of up to molecular weight 1 × 10⁶ with rather broad molecular weight distribution. A mechanism for the polyaddition reaction is proposed based on the radical addition reaction between BPFP and DEOMS. The step‐growth polymerization is initiated by hydrogen abstraction of DEOMS to add a perfluoroisopropenyl group, followed by a 1,7‐shift of the radical in the intermediate. The relationship between addition reaction mechanism and polyaddition mechanism was also discussed.

     

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.