Synthesis and Characterization of Well‐Defined Mid‐Chain Functional Macrophotoinitiators of Polystyrene by Combination of ATRP and “Click” Chemistry

A combination of ATRP and “click” chemistry is employed for efficient preparation of a novel well‐defined mid‐chain functional macrophotoinitiator of polystyrene. Bromo‐terminated polystyrene (PSt‐Br) is prepared by ATRP of styrene using a methyl‐2‐bromopropanoate initiator with CuBr/PMDETA. Subsequently, PSt‐Br is converted to PSt‐N₃ by a simple nucleophilic substitution reaction. A dialkyne‐functionalized photoinitiator (alkyne‐PI‐alkyne) is synthesized using a dihydroxy‐functional photoinitiator and propargyl bromide. Then the “click” reaction between PSt‐N₃ and alkyne‐PI‐alkyne is performed by Cu(I) catalysis. Spectroscopic studies reveal that low‐polydispersity polystyrene with the desired photoinitiator functionality in the middle of the chain (PSt‐PI‐PSt) is obtained.

     

Synthesis of Well‐Defined Telechelic Macrophotoinitiator of Polystyrene by Combination of ATRP and Click Chemistry

A new well‐defined telechelic macrophotoinitiator of polystyrene was synthesized by combination of ATRP and click chemistry. The ATRP of styrene by means of 2‐oxo‐1,2‐diphenylethyl‐2‐bromopropanoate (PI‐Br) initiator with CuBr/2,2′‐bipyridine yields polystyrene with photoactive benzoin (PI) and bromine (Br) group (PI‐PSt‐Br). Subsequently, PI‐PSt‐Br was converted to PI‐PSt‐N₃ by simple nucleophilic substitution reaction. Alkyne functionalized benzoin (PI‐alkyne) was synthesized by using benzoin photoinitiator and propargyl bromide. Then the coupling reaction between PI‐PSt‐N₃ and PI‐alkyne was performed by Cu(I) catalysis. The spectroscopic studies revealed that low‐polydispersity polystyrene with desired photoinitiator functionality at both end of the chain, PI‐PSt‐PI, was obtained.

     

Polystyrene with Improved Chain‐End Functionality and Higher Molecular Weight by ARGET ATRP

The bromine chain‐end functionality of polystyrene (PSt) prepared by activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) was analyzed using 500 MHz ¹H nuclear magnetic resonance (NMR). Bulk polymerization of styrene (St) was carried out with 50 ppm of copper in the presence of tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) ligand and tin(II) 2‐ethylhexanoate [Sn(EH)₂] reducing agent at 90 °C. Due to the use of a low concentration of an active Cu/ligand catalyst complex, it was possible to significantly decrease the occurrence of catalyst‐based side reactions (β‐H elimination). As a result, compared to PSt prepared via normal ATRP, PSt with improved chain‐end functionality was obtained. For example, at 92% monomer conversion in normal ATRP only 48% of chains retained chain‐end functionality, whereas 87% of the chains in an ARGET ATRP still contained halogen functionality. PSt with controlled molecular weight ( = 11 600 g · mol^?1, = 9 600 g · mol^?1) and narrow molecular weight distribution ( = 1.14) was prepared under these conditions. In addition, as a result of decreased frequency of side reactions in ARGET ATRP, PSt with relatively high molecular weight was successfully prepared ( = 185 000 g · mol^?1, = 1.35).

     

Tailor‐Made Soluble Polymer Supports: Synthesis of a Series of ATRP Initiators Containing Labile Wang Linkers

A series of functional initiators for atom transfer radical polymerization (ATRP) was prepared. These structures contain an ATRP initiating site, a labile p‐alkoxybenzyl ester Wang linker and a functional end‐group (i.e., ? COOH, ? N₃, ? OH, ? C?CH, or ? NHFmoc). These novel initiators can be utilized for synthesizing well‐defined soluble polymer supports. For instance, the azide‐, alcohol‐, alkyne‐, and NHFmoc‐ derivatives were tested as initiators for the bulk ATRP of styrene. SEC, MALDI‐TOF‐MS, and NMR measurements indicated that well‐defined polystyrene samples with defined end‐groups have been synthesized in this process. Moreover, it was demonstrated that the labile Wang linkers could be easily cleaved with a mild trifluoroacetic acid treatment.

     

Synthesis and ATRP Activity of New TREN‐Based Ligands

Summary: Ligands suitable for atom transfer radical polymerization (ATRP) were prepared by the Michael addition of several acrylates (allyl, benzyl, butyl, 2‐ethylhexyl, and 3‐(dimethoxymethylsilyl)propyl acrylates) with tris(2‐aminoethyl)amine (TREN). These ligands, readily prepared from inexpensive precursors, were used for the preparation of catalyst complexes suitable for polymerization of (meth)acrylates and styrene, providing activity comparable to catalysts currently used for these monomers. Catalysts containing ligands with a dimethoxymethylsilyl substituent were examined for copper removal after the reaction mixture was contacted with silica gel.

     

Porous Semi‐Interpenetrating Hydrogel Networks Based on Dextran and Polyacrylamide With Superfast Responsiveness

AAm was free‐radical polymerized at various temperatures in the presence of N,N'‐methylenebisacrylamide as a cross‐linker and dextran resulting in novel Dx/PAAm semi‐IPNs. The structure and morphology of networks were investigated by means of FTIR, DSC, and ESEM. In comparison to the PAAm network, the interior network structures of the novel semi‐IPNs prepared at ?18 °C exhibit a heterogeneous morphology consisting of pores of sizes about 80 µm, while those formed at +5 and +25 °C have pores with sizes about 3 µm. The Dx/PAAm semi‐IPNs exhibited higher swelling ratios, than those without Dx, irrespective of the gel preparation temperature. Moreover, Dx/PAAm semi‐IPN hydrogels formed at ?18 °C attain the equilibrium state in water within 15 s.

     

Synthesis and Dielectric Study of New Liquid‐crystalline Polysiloxanes Presenting a Thioether Spacer

Three new cyanobiphenyl polysiloxanes presenting long thioether spacers have been carried out. This type of spacer leads to very stable liquid‐crystalline polymers at room temperature and remove the crystallinity phenomenon. Dielectric analysis results show that the thioether spacer brings much more molecular flexibility to the system.

Example of an “interdigitated” structure observed by X‐ray analysis.     

Block Copolymers from Organomodified Siloxane‐Containing Macroinitiators by Atom Transfer Radical Polymerization

Alternating copolymers of 1,3‐diisopropenylbenzene and 1,1,3,3‐tetramethyldisiloxane were synthesized by hydrosilylation–polyaddition. These linear copolymers were functionalized at both ends with 2‐bromoisobutyryl or benzyl chloride moieties. Subsequently, the obtained organomodified siloxane‐containing macroinitiators were successfully used for the preparation of ABA‐type block copolymers by atom transfer radical polymerization (ATRP) of styrene and tert‐butyl acrylate. The high chain‐end functionality of the macroinitiators was confirmed by ¹H NMR analysis of the macroinitiators and GPC measurements of the obtained ABA‐type block copolymers. The macroinitiator peaks disappeared in GPC traces after ATRP, and the obtained block copolymers showed a significantly narrower molecular‐weight distribution than the macroinitiators.

Synthesis of ABA‐type block copolymers by means of ATRP using organomodified siloxane‐containing, benzyl chloride functionalized macroinitiators.     

Tunable Shell Thickness in Silica Nanospheres Functionalized by a Hydrophobic PMMA‐PSt Diblock Copolymer Brush via Activators Generated by Electron Transfer for Atom Transfer Radical Polymerization

An improved strategy to synthesize SiO₂‐PMMA nanoparticles with tunable shell thickness is demonstrated, via iron (III) catalyst‐mediated activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP). To investigate the effect of the content monomer and ligand on the PMMA shell thickness, hydrophobic PMMA‐PSt diblock copolymer brushes on the surface of the silica nanospheres are designed and synthesized by AGET ATRP. Transmission electron microscopy (TEM) and field‐emission scanning electron microscopy (FESEM) show that the product has a core‐shell‐like structure and that the average shell thickness of the PMMA can easily be tuned by simply adjusting the amount of monomer or ligand. In addition, the M _n of the PMMA can be tuned from 37 800 to 62 400 g mol^?1 by changing the shell thickness, and the PDI is 1.213–1.473. These results confirm the living nature of the polymerization.

     

Physical Properties of PBMA‐b‐PBA‐b‐PBMA Triblock Copolymers Synthesized by Atom Transfer Radical Polymerization

The physical properties of well‐defined poly(butyl methacrylate)‐block‐poly(butyl acrylate)‐block‐poly(butyl methacrylate) (PBMA‐b‐PBA‐b‐PBMA) triblock copolymers synthesized by atom transfer radical polymerization (ATRP) are reported. The glass transition and the degradation temperature of copolymers were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC measurements showed phase separation for all of the copolymers with the exception of the one with the shortest length of either inner or outer blocks. TGA demonstrated that the thermal stability of triblock copolymers increased with decreasing BMA content. Dynamic mechanical analysis was used for a preceding evaluation of adhesive properties. In these block copolymers, the deformation process under tension can take place either homogeneously or by a neck formation depending on the molecular weight of the outer BMA blocks and on the length of the inner soft BA segments. Microindentation measurements were also performed for determining the superficial mechanical response and its correlation with the bulk behavior.

Stress‐strain curves for the different PBMA‐b‐PBA‐b‐PBMA specimens at room temperature and at 10 mm/min.     

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.

     

Synthesis and Characterization of PDMS‐, PVP‐, and PS‐Containing ABCBA Pentablock Copolymers

Amphiphilic ABCBA pentablock copolymers based on PVP, PS, and PDMS were synthesized using a combination of ATRP and RAFT polymerizations. The PVP‐block‐PS‐block‐PDMS‐block‐PS‐block‐PVP pentablock copolymer was characterized using a variety of chromatography and spectroscopic methods which showed that a high degree of end group and molecular weight control can be achieved. Preliminary analysis of the aqueous solution behavior of the pentablock copolymer showed that it self‐assembles in water in order to shield the PDMS and PS segments from the water.

     

Novel polymeric surfactants: Synthesis of semi‐branched,non‐ionic triblock copolymers using ATRP

This article reports the synthesis of novel amphiphilic triblock copolymers with a semi‐branched PLURONIC^®7R structure by atom transfer radical polymerization (ATRP) in aqueous media. Poly(ethylene oxide)s (PEOs) with molecular weights 10 000 and 16 000 were end‐functionalized and used as bifunctional macroinitiators for the polymerization of oligo(propylene oxide) monomethacrylate by ATRP in a 1/3 v/v water/methanol mixture and in a 1/1 v/v water/1‐propanol mixture. Deviations from first‐order kinetics with respect to the monomer concentration were observed indicating that termination reactions were taking place. However, linear plots were obtained, when ln[M]₀/[M] was plotted against time^2/3 as suggested by Fischer. The effect on the control of the polymerization by adding Cu(II)Br₂ to the polymerization medium has been investigated. When 10 mol‐% of Cu(II)Br₂ was substituted for Cu(I)Br, normal first‐order kinetics were observed. A large reduction in the rate of polymerization was observed for the polymerization initiated by bifunctional PEO10 000 initiator, but almost no reduction in the rate of polymerization was observed, when the bifunctional PEO16 000 initiator was used. When the polymerizations were conducted in 1/1 v/v water/1‐propanol, unexpectedly high rates of polymerization were observed.

Synthesis of amphiphilic block copolymers with a semi‐branched PLURONIC^®R architecture using ATRP.     

Synthesis and Optical Properties of π‐Conjugated Polymers Composed of Benzo[1,2‐b:4,5‐b′]dithiophene and Thiophenes Bearing Electron‐Deficient Ethenyl Groups in the Side Chains

π‐Conjugated polymers composed of dialkoxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophenes bearing cyano‐alkoxycarbonylethenyl [? CH?C(CO₂R)CN] and bis(alkoxycarbonyl)ethenyl groups [? CH?C(CO₂R)₂] were prepared. The optical properties of the obtained polymers were investigated by UV‐vis and photoluminescence spectroscopy to demonstrate that the absorption maxima of the polymers were tunable by varying the substituent of thiophene unit. The photoluminescence wavelengths and intensities of the polymer in solution were significantly dependent on the polymer side chain. The HOMO energy level of the polymer was lowered by up to ?5.51 eV by introducing electron‐deficient cyano groups. Polymer solar cells based on the new polymers were fabricated to achieve a PCE of 1.90%.

     

Synthesis and Characterization of Red‐Emitting Poly(aryleneethynylene)s Based on 2,5‐Bis(2‐ethylhexyl)‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione (DPP)

Synthesis and characterization of a series of PAEs containing DPP units in the main chain are described. of the polymers was in the range 10 800–111 900. The polymers formed a deep blue solution in chloroform with absorption maxima between 589 and 645 nm and optical band gaps ranging from 1.61 to 1.74 eV. When excited at the absorption maxima, the polymer solutions showed red fluorescence with emission maxima between 656 and 676 nm. The polymers exhibited quasi‐reversible oxidation process with HOMO energy levels between ?5.60 and ?6.17 eV. EL properties of three polymers were investigated with device configuration ITO/PEDOT:PSS/Polymer/LiF/Al. When appropriate bias voltage was applied, a red EL with a maximum brightness of 17.5–24 cd · m^?2 could observe from the devices.

     

Mixed Alkyl‐ and Alkoxy‐Substituted Poly[(phenylene ethynylene)‐alt‐(phenylene vinylene)] Hybrid Polymers: Synthesis and Photophysical Properties

Summary: We report the synthesis, characterisation and photophysical properties of mixed alkyl‐ and alkoxy‐substituted poly[(phenylene ethynylene)‐alt‐(phenylene vinylene)] hybrid polymers with the general constitutional unit: (? Ph? C?C? Ph? C?C? Ph? CH?CH? Ph? CH?CH? )_n ( 7 ). The polymers were obtained through the Horner‐Wadsworth‐Emmons olefination reaction of alkyl‐substituted luminophoric dialdehydes, 5a–b , and alkoxy‐substituted bisphosphonates. Contrary to their alkoxy‐substituted congeners, 10a–b , which exhibit solution fluorescence quantum yields close to unity, dialdehydes ( 5a–b ) fluoresce poorly at room temperature, but show phosphorescence at 77 K. High molecular weight polymers were obtained showing poor solubility compared to solely alkoxy‐substituted polymers ( 11 ) of the same backbone constitutional units. The presence of alkyl side groups in 7 leads to a 15 nm blue shift of their absorption spectra relative to 11 . Both types of polymers show however identical emission spectra with only a slight blue shift (3–4 nm) of the emission peak of 7 relative to 11 . This clearly proves that the chromophore system responsible for the emission in both types of compounds is located around the lower‐energy, alkoxy‐substituted phenylene‐vinylene portion of the polymers as confirmed by fluorescence kinetics investigations.

     

Metathetic Selective Degradation of Polyisoprene: Low‐Molecular‐Weight Telechelic Oligomer Obtained from Both Synthetic and Natural Rubber

Summary: Degradation studies of cis‐1,4‐polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end‐functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well‐defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a range of from 10 000 to 30 000, with a polydispersity index of around 2.5.

Structure produced by the metathetic depolymerization of hydroxy telechelic cis‐1,4‐polyisoprene.     

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.     

Novel Side‐Chain Polyrotaxane with Cyclodextrin: Syntheses and Study of Water‐Soluble Copolymers Bearing Hydrophobically Associative Components

Summary: Novel water‐soluble hydrophobically associative polymers, comprising sodium 2‐acrylamido‐2‐methylpropansulfonate , N,N‐dimethylacrylamide and different amounts of a hydrophobically associative macromonomer, were synthesized in an aqueous medium. Formation of a rotaxane‐like complex of this macromonomer, with randomly methylated β‐cyclodextrin, was studied. In addition, a side chain of polyrotaxane, comprising this complex and methyl methacrylate, was synthesized via ATRP. These polymers were characterized by dynamic light scattering and fluorescent‐probe technique. Effects of methylated β‐cyclodextrin on micelle formation of the polymers were also studied.

The side‐chain polyrotaxane.     

Photocurable Shape‐Memory Copolymers of ε‐Caprolactone and L‐Lactide

Biodegradable and photocurable block copolymers of ε‐caprolactone and L ‐lactide were synthesized by polycondensation of PLLA diol ( = 10 000 g · mol^?1), PCL diol ( = 10 000 g · mol^?1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape‐memory properties. Random copolymers exhibited R_f and R_r values above 90% at 45 °C for an extremely large tensile strain of 1 000%.