Synthesis and characterization of side‐chain liquid crystalline ABC triblock copolymers with p‐methoxyazobenzene moieties by atom transfer radical polymerization

A series of novel side‐chain liquid crystalline ABC triblock copolymers composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PMMAZO) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as a catalyst system. First, the bromine‐terminated diblock copolymer poly(ethylene oxide)‐block‐polystyrene (PEO‐PS‐Br) was prepared by the ATRP of styrene initiated with the macro‐initiator PEO‐Br, which was obtained from the esterification of PEO and 2‐bromo‐2‐methylpropionyl bromide. An azobenzene‐containing block of PMMAZO with different molecular weights was then introduced into the diblock copolymer by a second ATRP to synthesize the novel side‐chain liquid crystalline ABC triblock copolymer poly(ethylene oxide)‐block‐polystyrene‐block‐poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PEO‐PS‐PMMAZO). These block copolymers were characterized using proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatograph (GPC). Their thermotropic phase behaviors were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). These triblock copolymers exhibited a smectic phase and a nematic phase over a relatively wide temperature range. At the same time, the photoresponsive properties of these triblock copolymers in chloroform solution were preliminarily studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4442–4450, 2008     

Three‐Dimensional Structure of Olefinic Thermoplastic Elastomer Blends Using Electron Tomography

Summary: The present communication reports the first use of electron tomography in reconstructing the three‐dimensional morphology in thermoplastic elastomer blends. The blends investigated were dynamically vulcanized blends of ethylene‐propylene‐diene (EPDM) rubber/poly(propylene)/oil and polystyrene‐block‐(ethylene‐co‐butylene)‐block‐polystyrene (SEBS)/poly(propylene)/oil. An easy identification of blend morphology could be carried out at blend compositions, where conventional transmission electron microscopic imaging gives misleading information. This technique gives a higher resolution than any other microscopic technique, and is applicable to blends with dispersed as well as co‐continuous morphologies.

Example of a tomographic model of partially co‐continuous SEBS phases in a SEBS/PP/oil thermoplastic blend. Only the contours of the SEBS phase are shown.     

Photocrosslinked poly(vinylbenzophenone)‐core micelles via mild Friedel–Crafts benzoylation of polystyrene amphiphiles

Photocrosslinkable poly(vinylbenzophenone)‐containing polymers were synthesized via a one‐step, Friedel–Crafts benzoylation of polystyrene‐containing starting materials [including polystyrene, polystyrene‐block‐poly(tert‐butyl acrylate), polystyrene‐block‐poly(ethylene oxide), polystyrene‐block‐poly(methyl methacrylate), and polystyrene‐block‐poly(n‐butyl acrylate)] with benzoyl trifluoromethanesulfonate as a benzoylation reagent. The use of this mild reagent (which required no added Lewis acid) permitted polymers with well‐defined compositions and narrow molecular weight distributions to be synthesized. Micelles formed from one of these benzoylated polymers, [polystyrene_0.25‐co‐poly(vinylbenzophenone)_0.75]₁₁₅‐block‐poly(acrylic acid)₁₄, were then fixed by the irradiation of the micelle cores with UV light. As the irradiation time was increased, the pendent benzophenone groups crosslinked with other chains in the glassy micelle cores. Dynamic light scattering, spectrofluorimetry, and Fourier transform infrared spectroscopy were all used to verify the progress of the crosslinking reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2604–2614, 2006     

Preparation and characterization of cyclic polystyrene with short poly(2‐tert‐butylbutadiene) sequences

A polystyrene‐block‐oligo(2‐tert‐butylbutadiene)‐block‐polystyrene triblock copolymer was prepared and cyclized by end‐to‐end ring closure. Ring‐shaped polystyrene‐block‐oligo(2‐tert‐butylbutadiene) was isolated from the coupling product via gel permeation chromatography (GPC) fractionation. The ring polymer was ozonized for decomposition of the oligo(2‐tert‐butylbutadiene) sequences selectively referring to the linear molecule. From GPC analysis of the decomposed products by ozonolysis, it was quantitatively confirmed that the fractionated product was 86% ring molecules. Single chain dimensions of the ring and linear molecules in a good solvent, benzene, and in a θ solvent, cyclohexane, were measured with small‐angle neutron scattering. The ratios of the radii of gyration, R_g(ring)/R_g(linear), were 0.780 in benzene and 0.789 in cyclohexane. These were compared with theoretically predicted values. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1582–1589, 2002     

Orientation of cylindrical microdomains of triblock copolymers by in situ stress–strain‐ birefringence measurements

The orientation behavior of polystyrene‐block‐hydrogenated polyisoprene‐block‐polystyrene (SEPS) with cylindrical microdomains of polystyrene (PS) dispersed in the rubbery segments was investigated by simultaneous measurements of stress and birefringence during uniaxial stretching. The stress increased sharply with strain below the yield strain and then it gradually increased. In contrast, the birefringence changed little below the yield strain, increased sharply with strain above the yield strain up to a strain of 0.5, and then gradually increased. The characteristic birefringence behavior is attributed to the form birefringence induced by the orientation and the parallel arrangement of the cylindrical microdomains associated with the orientation of the rubbery segments. The orientation function of the cylindrical microdomains f evaluated by analyzing the form birefringence agrees well with that obtained from the SAXS result. The f was almost zero below the yield strain and it increased sharply with strain up to a strain of 0.5 and then was constant above a strain of 0.5. These results suggest that the orientation of the cylindrical microdomains occur above the yield strain up to a strain of 0.5 and that the orientation does not increase above a strain of 0.5 in spite of the continuous orientation of the rubbery ethylene–propylene segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 715–723, 2009     

Synthesis of amphiphilic ABC triblock copolymers by single electron transfer nitroxide radical coupling reaction in tetrahydrofuran

A series of ABC triblock copolymers, that is, polyisoprene‐block‐polystyrene‐block‐poly(ethylene oxide) (PI‐PS‐PEO), PI‐block‐poly(tert‐butyl acrylate)‐block‐PEO (PI‐PtBA‐PEO), and PI‐block‐poly(acrylic acide)‐block‐PEO (PI‐PAA‐PEO) were obtained by combination of anionic technique, atom transfer radical polymerization (ATRP), and single electron transfer nitroxide coupling (SETNRC) reaction. Anionic polymerization of isoprene followed by end capping with ethylene oxide yielded hydroxyl‐terminated PI. After esterification, PI with Br end group was used as a macroinitiator to initiate the polymerization of styrene and tBA by ATRP that was then trapped by 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) group in PEO by SETNRC reaction rapidly with high efficiency in tetrahydrofuran at room temperature. The effect of reaction time and polymer chain length on SETNRC reaction was discussed in detail. In the presence of Cu⁰/tris[2‐(dimethylamino)ethyl]amine, SETNRC between PI‐PS‐Br and PEO‐TEMPO was carried out with the efficiency of up to 91.6% in 2 h. With the increase in polymer chain length, the efficiency decreased fleetly. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of comb‐type polycarbosilanes via nucleophilic substitution reactions on the main‐chain silicon atoms

A series of comb‐type polycarbosilanes of the type [Si(CH₃)(OR)CH₂]_n {where R = (CH₂)_mR′, R′ = ? O‐p‐biphenyl? X [X = H (m = 3, 6, 8, or 11) or CN (m = 11)], and R′ = (CF₂)₇CF₃ (m = 4)} were prepared from poly(chloromethylsilylenemethylene) by reactions with the respective hydroxy‐terminated side chains in the presence of triethylamine. The product side‐chain polymers were typically greater than 90% substituted and, for R′ = ? O‐p‐biphenyl? X derivatives, they exhibited phase transitions between 27 and 150 °C involving both crystalline and liquid‐crystalline phases. The introduction of the polar p‐CN substituent to the biphenyl mesogen resulted in a substantial increase in both the isotropization temperature and the liquid‐crystalline phase range with respect to the corresponding unsubstituted biphenyl derivative. For R = (CH₂)₁₁? O‐biphenyl side chains, an analogous side‐chain liquid‐crystalline (SCLC) polysiloxane derivative of the type [Si(CH₃)(O(CH₂)₁₁? O‐biphenyl)O]_n was prepared by means of a catalytic dehydrogenation reaction. In contrast to the polycarbosilane bearing the same side chain, this polymer did not exhibit any liquid‐crystalline phases but melted directly from a crystalline phase to an isotropic liquid at 94 °C. Similar behavior was observed for the polycarbosilane with a fluorocarbon chain, for which a single transition from a crystalline phase to an isotropic liquid was observed at ?0.7 °C. The molecular structures of these polymers were characterized by means of gel permeation chromatography and high‐resolution NMR studies, and the crystalline and liquid‐crystalline phases of the SCLC polymers were identified by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 984–997, 2003     

Effect of Casting Solvent on Morphology and Physical Properties of Partially Sulfonated Polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene Copolymers

The effect of casting solvent on the morphology of sulfonated polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SSEBS) was investigated using transmission electron microscopy and small‐angle X‐ray scattering. Proton conductivities and methanol permeabilities were measured and the related impact on morphological changes is discussed. SSEBS is transformed from a well‐ordered lamellar to a disordered structure as the concentration of MeOH in MeOH/THF mixtures increases.     

Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

This article reports the synthesis and the properties of novel thermoplastic elastomers of A‐B‐A type triblock copolymer structure, where the hard segment A is poly(l ‐lactide) (PLLA) and the soft segment B is poly(ε‐caprolactone‐stat‐d ,l ‐lactide) (P(CL‐stat‐DLLA)). The P(CL‐stat‐DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature (T_g = approximately ?40 °C). Successive polymerization of l ‐lactide afforded PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLAs, which exhibited melting temperature (T_m = approximately 150 °C) for the crystalline PLLA segments and still low T_g (approximately ?30 °C) of the soft segments. The triblock copolymers showed very high elongation at break up to approximately 2800% and elastic properties. The corresponding d ‐triblock copolymers, PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLAs (PDLA = poly(d ‐lactide)) were also prepared with the same procedure using d ‐lactide in place of l ‐lactide. When the PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLA was blended with PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLA, stereocomplex crystals were formed to enhance their T_m as well as tensile properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 489–495     

Synthesis of polystyrene-polysiloxane side-chain liquid crystalline block copolymers

The synthesis of a new liquid crystalline block copolymer consisting of a polystyrene block and a side-chain liquid crystalline siloxane block is reported. The synthetic approach described is based on the anionic polymerization of styrene and cyclic trimethyltrivinyltrisiloxane monomers, followed by functionalization of the siloxane block with side chain mesogens. The siloxane block has a T_g well below 25°C and is designed to exhibit a chiral smectic C^* phase at room temperature. These block copolymers are the first side-chain liquid crystalline block copolymers which contain both a high T_g glassy block and a low T_g liquid crystalline block.     

Structural arrangement of crystalline/amorphous phases of polyethylene‐block‐polystyrene copolymer as induced by orientation techniques

A polyethylene‐block‐polystyrene copolymer film having a bicontinuous crystalline/amorphous phases was tensile‐drawn under various conditions for the structural arrangement of these phases. The prepared film could be drawn below the melting temperature of the polyethylene component, with the highest drawability obtained at 60°C. However, the initial bicontinuous structure was gradually destroyed with increasing strain because the drawing temperature was lower than the glass‐transition temperature of the polystyrene component. Correspondingly, a necking phenomenon was clearly recognizable when samples were drawn. In contrast, drawing near the melting temperature of the polyethylene component produced less orientation of both the crystalline and amorphous phases, resulting in homogeneous deformation with lower drawing stress. These results indicated that the modification of the lower ductility of the polystyrene component was key to the effective structural arrangement of both phases by tensile drawing. Here, a solvent‐swelling technique was applied to improve polystyrene deformability even below its glass‐transition temperature. Tensile drawing after such a treatment successfully induced the orientation of both the crystalline and amorphous phases while retaining their initial continuities. A change in the deformation type from necking to homogeneous deformation was also confirmed for the stress–strain behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1731–1737, 2006     

Synthesis and self‐assembly of diblock copolymers bearing 2‐nitrobenzyl photocleavable side groups

The light‐responsive behavior in solution and in thin films of block copolymers bearing 2‐nitrobenzyl photocleavable esters as side groups is discussed in this article. The polymers were synthesized by grafting 2‐nitrobenzyl moieties onto poly(acrylic acid)‐block‐polystyrene (PAA‐b‐PS) precursor polymers, leading to poly(2‐nitrobenzyl acrylate‐random‐acrylic acid)‐block‐polystyrene (P(NBA‐r‐AA)‐b‐PS) block copolymers. The UV irradiation of the block copolymers in a selective solvent for PS led to the formation of micelles that were used to trap hydrophilic molecules inside their core (light‐induced encapsulation). In addition, thin films consisting of light‐responsive P(NBA‐r‐AA) cylinders surrounded by a PS matrix were achieved by the self‐assembly of P(NBA‐r‐AA)‐b‐PS copolymers onto silicon substrates. Exposing these films to UV irradiation generates nanostructured materials containing carboxylic acids inside the cylindrical nanodomains. The availability of these chemical functions was demonstrated by reacting them with a functional fluorescent dye. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thermal monitoring of morphology in triblock terpolymers with crystallizable blocks

The bulk morphology of poly(1,4‐butadiene)–block–polystyrene–block–poly (ethylene oxide) (PB‐b‐PS‐b‐PEO) and polyethylene–block–polystyrene–block–poly (ethylene oxide) (PE‐b‐PS‐b‐PEO) triblock terpolymers is analyzed under a thermal protocol. This allows the investigation of the morphology during the occurrence of thermal transitions, such as crystallization and melting, which is a neat way of studying the competition between microphase separation and crystallization for the morphology formation. Only one of the studied systems presented a morphological transition upon melting of the PEO and the PE blocks, attributed to the crystallization of the PE block in finite interconnected domains. All the other systems presented no morphological transitions during the thermal scan. The results prove that the crystallization only disrupt the microphases generated in the molten state under very specific circumstances for these block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3197–3206, 2007     

Densely grafted polyisocyanides synthesized by two types of polymerization techniques

A series of novel polyisocyanide‐graft‐polystyrenes and polyisocyanide‐graft‐[polystyrene‐block‐poly(butyl acrylate)]s were synthesized through the grafting‐through and grafting‐from routes with two types of living polymerization techniques: polymerization with the Pd–Pt μ‐ethynediyl dinuclear complex as the initiator and catalyst for the polyisocyanide backbone and atom transfer radical polymerization for the grafted side chain. Through the introduction of a chiral center at the side chain of the polyisocyanide backbone, helical grafted and graft block polyisocyanides were prepared through the grafting‐from method. All of the obtained polymers exhibited polydispersities in the range of 1.07–1.41. This might have been the first time grafted polyisocyanides were prepared, especially helical grafted polyisocyanides, through the operation of two living polymerization techniques. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1871–1880, 2003     

Synthesis of Well‐Defined Polybenzamide‐block‐Polystyrene by Combination of Chain‐Growth Condensation Polymerization and RAFT Polymerization

Well‐defined diblock copolymers composed of poly(N‐octylbenzamide) and polystyrene were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene with a polyamide chain transfer agent (CTA) prepared via chain‐growth condensation polymerization. Synthesis of a dithioester‐type macro‐CTA possessing the polyamide segment as an activating group was unsatisfactory due to side reactions and incomplete introduction of the benzyl dithiocarbonyl unit. On the other hand, a dithiobenzoate‐CTA containing poly(N‐octylbenzamide) as a radical leaving group was easily synthesized, and the RAFT polymerization of styrene with this CTA afforded poly(N‐octylbenzamide)‐block‐polystyrene with controlled molecular weight and narrow polydispersity.

     

Synthesis of densely grafted comblike copolymers

Densely grafted copolymers were synthesized using the “grafting from” approach via the combination of reversible addition‐fragment chain transfer polymerization (RAFT) and atom transfer radical polymerization (ATRP). First, a novel functional monomer, 2,3‐di(2‐bromoisobutyryloxy)ethyl acrylate (DBPPA), with two initiating groups for ATRP was synthesized. It was then polymerized via RAFT polymerization to give macroinitiators for ATRP with controlled molecular weights and narrow molecular weight distributions. Last, ATRP of styrene was carried out using poly(DBPPA)s as macroinitiators to prepare comblike poly(DBPPA)‐graft‐polystyrenes carrying double branches in each repeating unit of backbone via “grafting from” approach. Furthermore, poly(DBPPA)‐graft‐[polystyrene‐block‐poly(t‐BA)]s and their hydrolyzed products poly(DBPPA)‐graft‐[polystyrene‐block‐poly(acrylic acid)]s were also successfully prepared. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 362–372, 2008     

High‐molecular‐weight side‐chain liquid‐crystalline polyethers based on 4′‐cyanobiphenyl‐4‐oxy mesogenic groups

A set of poly[ω‐(4′‐cyano‐4‐biphenyloxy)alkyl‐1‐glycidylether]s were synthesized by the chemical modification of the corresponding poly(ω‐bromoalkyl‐1‐glycidylether)s with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl. New high‐molecular‐weight side‐chain liquid‐crystalline polymers were obtained with excellent yield and almost quantitative degree of modification. All side‐chain liquid‐crystalline polymers were rubbers soluble in tetrahydrofuran. The characterization by ¹H and ¹³C NMR revealed no changes in the regioregular isotactic microstructure of the starting polymer and the absence of undesirable side reactions such as deshydrobromination. The liquid crystalline behavior was analyzed by DSC and polarized optical microscopy, and mesophase assignments were confirmed by X‐ray diffraction. Polymers that had alkyl spacers with n = 2 and 4 were nematic, those that had spacers with n = 6 and 8 were nematic cybotactic, and those that had longer spacers (n = 10 and 12) were smectic C and showed some crystallization of the side alkyl chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3002–3012, 2004     

Super impact strength of blends prepared from regular HIPS and poly(butyl acrylate)‐block‐poly(styrene) obtained by RAFT polymerization

S‐allyl‐4‐methyldithiobenzoate was synthesized and used as a chain transfer agent for the RAFT polymerization of butyl acrylate to produce a functionalized acrylic rubber. A solution of 8 wt% of this functionalized rubber was prepared in styrene and polymerized to generate a material called acrylic rubber‐modified polystyrene (AMP) constituted by well‐dispersed particles of poly(butyl acrylate)‐block‐poly(styrene) into a polystyrene matrix. Impact strength of injection‐molded samples of AMP was measured and compared with the general purpose polystyrene (GPPS) and the high impact polystyrene (HIPS). AMP itself showed an impact strength value similar to GPPS; however, when AMP was blended with conventional HIPS, the resulting material exhibited an improvement of 76–91% as compared to HIPS by itself, without affecting negatively tensile properties. Transmission electron microscopy analysis revealed both kinds of dispersed phases, i.e. the typical salami particles of polybutadiene coming from HIPS (size: 0.5–2 µ) and small particles from poly(butyl acrylate)‐block‐poly(styrene) (size: ～50 nm). We clearly showed that such a bimodality of the particle size distribution caused the positive synergistic effect on impact strength. Copyright © 2011 John Wiley & Sons, Ltd.     

Formation of triblock copolymers via a tandem enhanced spin capturing—nitroxide‐mediated polymerization reaction sequence

The preparation of ABA‐type block copolymers via tandem enhanced spin capturing polymerization (ESCP) and nitroxide‐mediated polymerization (NMP) processes is explored in‐depth. Midchain alkoxyamine functional polystyrenes (M_n = 6200, 12,500 and 19,900 g mol^?1) were chain extended with styrene as well as tert‐butyl acrylate at elevated temperature NMP conditions (T = 110 °C) generating a tandem ESCP‐NMP sequence. Although the chain extensions and thus the block copolymer formation processes function well (yielding in the case of the chain extension with styrene number average molecular weights of up to 20,800 g mol^?1 (PDI = 1.22) when the 6200 g mol^?1 precursor is used and up to 67,500 g mol^?1 (PDI = 1.36) when the 19,900 g mol^?1 precursor is used and 21,600 g mol^?1 (PDI = 1.17) as well as 37,100 g mol^?1 (PDI = 1.21) for the tert‐butyl acrylate chain extensions for the 6200 and 12,500 g mol^?1 precursors, respectively), it is also evident that the efficiency of the block copolymer formation process decreases with an increasing chain length of the ESCP precursor macromolecules (i.e., for the 19,900 g mol^?1 ESCP precursor no efficient chain extension with tert‐butyl acrylate can be observed). For the polystyrene‐block‐tert‐butyl acrylate‐block‐polystyrene polymers, the molecular weights were determined via triple detection SEC using light scattering and small‐angle X‐ray scattering. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Lithium‐Salt‐Containing High‐Molecular‐Weight Polystyrene‐block‐Polyethylene Oxide Block Copolymer Films

Ionic conductivity in relation to the morphology of lithium‐doped high‐molecular‐weight polystyrene‐block‐polyethylene oxide (PS‐b‐PEO) diblock copolymer films was investigated as solid‐state membranes for lithium‐ion batteries. The tendency of the polyethylene (PEO) block to crystallize was highly suppressed by increasing both the salt‐doping level and the temperature. The PEO crystallites completely vanished at a salt‐doping ratio of Li/EO>0.08, at which the PEO segments were hindered from entering the crystalline unit of the PEO chain. A kinetically trapped lamella morphology of PS‐b‐PEO was observed, due to PEO crystallization. The increase in the lamella spacing with increasing salt concentration was attributed to the conformation of the PEO chain rather than the volume contribution of the salt or the previously reported increase in the effective interaction parameter. Upon loading the salt, the PEO chains changed from a compact/highly folded conformation to an amorphous/expanded‐like conformation. The ionic conductivity was enhanced by amorphization of PEO and thereby the mobility of the PEO blocks increased upon increasing the salt‐doping level.