Grafting copolymerization of vinyl monomers on polyimide macroinitiators by the method of atom transfer radical polymerization

Graft copolymers with the main polyimide chain and side chains of poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl methacrylate), poly(tert-butyl methacrylate), polystyrene, and polystyrene-block-poly(methyl methacrylate) were synthesized by atom transfer radical polymerization on the multicenter polyimide macroinitiators in the presence of the halide complexes of univalent copper with nitrogen-containing ligands. Polymerization of metha-crylates is most efficiently developed on the polyimide macroinitiators. The obtained graft copolymers initiate the secondary polymerization (“post-polymerization”) of methyl methacrylate. The conditions of detachment of side chains of graft polymethacrylates that do not involve the ester groups of their monomeric units were found. The molecular mass characteristics of the graft copolymers and isolated polymers, being the detached side chains of the copolymers, were determined. The detached side chains of different chemical structures have low values of the polydispersity index. The procedure developed was used for the preparation of new graft polyimides with side chains of poly-4-nitro-4′-[N-methylacryloyloxyethyl-N′-ethyl]amino-azobenzene that cause the nonlinear optical properties and with the side chains of poly(N,N-dimethylaminoethyl methacrylate) that cause the thermosensitive properties of the copolymers.     

Dielectric relaxations and electrical conductivities of poly(alkyl methacrylates) under high pressure

Dielectric properties of four methacrylate polymers (methyl, ethyl, n-butyl and n-octyl) were studied in the frequency range 0.0001 cps–300 kcps at temperatures above and below the glass transition temperature and at various pressures up to 2500 atm. At temperatures well above T_g a single relaxation peak (α′ peak) was observed in the case of the higher n-alkyl methacrylates. However, this peak was split into two peaks, α and β, with decrease in temperature or increase in pressure. The molecular motions corresponding to the α and the β relaxation processes are the micro-Brownian motions of amorphous main chains and of flexible side chains, respectively. From the temperature and the pressure dependence of the average dielectric relaxation time of these polymers the single relaxation process (the α′ process) was attributed to the micro-Brownian motion of the main chain coupled with that of the side chain. The effects of temperature and pressure on the d.c. conductivity of these polymers were also studied.     

Linear and branched alkyl substituted octakis(dimethylsiloxy)octasilsesquioxanes: WAXS and thermal properties

A series of octakis(dimethylsiloxy)octasilsesquioxanes bearing linear and branched alkyl substituents has been prepared in high yield by Pt-catalyzed hydrosilylation of alkenes with octakis(hydrodimethylsiloxy)octasilsesquioxane, chain length varying between C3 and C8 for the straight-chain derivatives and between C5 and C7 for the branched-chain derivatives. On the basis of a WAXS study, we showed that the linear derivatives are amorphous and that the interdigitation of alkyl chains between neighboring POSS molecules increases as the alkyl chain length increases from propyl to octyl. The thermal behavior of these compounds was studied by DSC, polarized optical microscopy and TGA in nitrogen and air atmosphere. The derivatives with shorter n-alkyl chains from C3 to C6 crystallize below 0 °C whereas the derivatives with longer n-alkyl chains (C7 and C8) can be regarded as amorphous glasses with a T_g around –100 °C. The morphology and thermal properties change considerably with branching of the alkyl chain. Melting points above ambient temperature were found for the iso-hexyl and iso-heptyl POSS derivatives whereas the iso-pentyl POSS derivative is liquid at 25 °C. From the values of the heat of fusion as well as entropy of fusion, it was concluded that packing of the side groups in the crystal structure increases as the size of the branched alkyl group increases. TGA evidenced a negative effect of the branching of the alkyl chain on the thermal stability in air.     

High-performance fullerene-free polymer solar cells with solution-processed conjugated polymers as anode interfacial layer

A series of conjugated polymers based on PFS derivatives with π-conjugated 5-(9H-fluoren-2-yl)-2,2′-bithiophene(fluorene-alt-bithiophene) backbones, namely PFS-3C, PFS-4C and PFS-6C, were synthesized for their use as the anode interfacial layers(AILs) in the efficient fullerene-free polymer solar cells(PSCs). Alkyl sulfonate pendants with different lengths of alkyl side chains were introduced in the three polymers in order to investigate the effect of the alkyl chain length on the anode modification. The obtained three polymers exhibited similar absorption bands and energy levels, indicating that changing the length of the alkyl side chains did not affect the optoelectronic properties of the conjugated polymers. Based on the PBDB-T:ITIC active layer, we fabricated the fullerene-free PSCs using the three polymers as the AILs. The superior performance of the fullerene-free PSC device was achieved when PFS-4C was used as the AIL, showing a power conversion efficiency(PCE) of 10.54%. The high performance of the PFS-4C-modified device could be ascribed to the high transmittance, suitable work-function(WF) and smooth surface of PFS-4C. To the best of our knowledge, the PCE obtained in the PFS-4C-modified device is among the highest PCE values in the fullerene-free PSCs at present. These results demonstrate that the PFS derivatives are promising candidates in serving as the AIL materials for high-performance fullerene-free PSCs.     

Side chain engineering and conjugation enhancement of benzodithiophene and phenanthrenequnioxaline based conjugated polymers for photovoltaic devices

A series of donor‐acceptor conjugated polymers incorporating benzodithiophene (BDT) as donor unit and phenanthrenequnioxaline as acceptor unit with different side chains have been designed and synthesized. For polymer P1 featuring the BDT unit and alkoxy chains substituted phenanthrenequnioxaline unit in the backbone, serious steric hindrance resulted in quite low molecular weight. The implementation of thiophene ring spacer in polymer P2 greatly suppressed the interannular twisting to extend the effective conjugation length and consequently gave rise to improved absorption property and device performance. In addition, utilizing the alkylthienyl side chains to replace the alkyl side chains at BDT unit in polymer P3 further enhanced the photovoltaic performance due to the increased conjugation length. For polymer P4, translating the alkoxy side chains at the phenanthrenequnioxaline ring into the alkyl side chains at thiophene linker group enhanced molecular planarity and strengthened π?π stacking. Consequently improved absorption property and increased hole mobility were achieved for polymer P4. Our results indicated that side chain engineering not only can influence the solubility of polymer but also can determine the polymer backbone planarity and hence the photovoltaic properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1915–1926     

Synthesis and functionalities of poly(N-vinylalkylamide). V. Control of a lower critical solution temperature of poly(N-vinylalkylamide)

N-vinyl-n-butyramide (NVBA), N-vinylisovaleramide (NVIVA), and N-vinyl-n-valeramide (NVVA), which are N-vinylalkylamides with different alkyl groups were synthesized and their solution behavior in a polymeric form was examined. Copolymers of N-vinylisobutyramide (NVIBA) with N-vinylacetamide (NVA), NVIBA with NVVA, and NVVA with NVA were prepared by the solution polymerization to control the LCSTs. The resultant polyNVBA showed a lower critical solution temperature (LCST) sharply at 32°C, but polyN-vinylisovaleramide (polyNVIVA) and polyN-vinyl-n-valeramide(polyNVVA) that have n-butyl and isobutyl groups, respectively, on their side chains were insoluble even in cold water. The water solubility of the resulting polymers was found to vary, depending on the molecular shapes as well as the side chain length of the alkyl groups in question. The copolymers consisting of NVVA, NVIBA, and NVA in water showed LCSTs sharply between 10 and 90°C, depending on changes in their comonomer content. It was found that the changes in LCST that are caused by the incorporation of comonomers are due to changes in the overall hydrophilicity of the polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3087–3094, 1997     

The influence of terminal chlorine on the mesomorphic properties of new thiobenzoates containing two and three benzene rings

New liquid crystalline chloro‐substituted thioesters containing two and three benzene rings have been synthesized. 4‐Chlorophenyl 4‐n‐alkoxythiobenzoates and 4‐chlorophenyl 4‐n‐alkoxybenzoyloxy‐4′‐thiobenzoates are referred to as nO.SCl and nO.OSCl, respectively, where n varies from 4 to 16 for nO.SCl, from 4 to 10 for nO.OSCl and denotes the number of carbon atoms in the alkyl chain. Their mesomorphic properties were investigated by means of polarizing optical microscopy, differential scanning calorimetry, transmittance light intensity and X‐ray diffraction measurements. The nO.SCl homologous series possesses smectic A (SmA) and nematic (N) phases for n?=?4, 5, 6 while higher homologues have only an enantiotropic SmA phase. Those from the nO.OSCl homologous series have enantiotropic N and SmA phases and higher transition temperatures. The range of the N phase decreases, and of the SmA increases, with the elongation of the alkoxy chain in the nO.OSCl homologous series. The effect on mesomorphic behaviour of terminal alkoxy chain lengthening and replacement by chlorine on the other side of the molecule is discussed.     

Synthesis,characterisation and mesomorphic properties of ester containing aroylhydrazones and their nickel(II) complexes

A new series of mesogenic aroylhydrazone-based ligands, N-[4-(4′-alkoxy)benzoyloxybenzylidene]-N′-[4″-alkoxybenzoyl]hydrazine with either the same or different peripheral alkyl chains, and nickel(II) complexes of some of them have been synthesised. They were characterised by elemental analyses, Fourier transform infrared, proton and carbon nuclear magnetic resonance and ultraviolet-visible spectroscopy. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry and polarising optical microscopy. All the aroylhydrazones, except those with no lateral chains on either end of the molecule and where m?=?n?=?14, 16, exhibit a monotropic or enantiotropic smectic C mesophase, which are almost insensitive to the peripheral alkoxy chain length. The square planar nickel(II) complexes of the ligands show only an isotropic phase at higher temperature (>175°C) and no mesogenic nature is observed. Density functional theory calculations have been performed using the GAUSSIAN-03 program at the Becke, three-parameter, Lee–Yang–Parr level to obtain the stable electronic structure of the ligand.     

Cationic polymerization of α,β-disubstituted olefins. V. Reactivity of propenyl alkyl ethers in cationic polymerization

To elucidate the effect of the introduction of a methyl group in the β-position of a vinyl monomer, propenyl alkyl ethers were copolymerized with vinyl ethers having the same alkoxy group. Propenyl alkyl ethers with an unbranched alkoxy group (ethyl or n-butyl propenyl ether) were more reactive than the corresponding vinyl ethers. This behavior is quite different from that of β-methylstyrene derivatives. However, propenyl alkyl ethers with branched alkoxy groups at the α carbon atom (isopropyl or tert-butyl propenyl ether) were less reactive than the corresponding vinyl ethers. Also, cis- isomers were more reactive than the trans isomers, regardless of the kind of alkoxy group and the polarity of the solvent.     

Synthesis and Properties of Poly(4,8-dialkoxy-1,5-naphthalenevinylene)s

Novel conjugated materials, poly(4,8-dialkoxy-1,5-naphthalenevinylene)s (OC_n-PNV, n = 4, 6, 8, and 12), have been prepared by a method similar to the Gilch procedure. The structure, optical and thermal properties of these polymers with various alkoxy side chain lengths have been evaluated by IR, UV-Vis absorption, fluorescence emission and thermogravimetric analysis. The band gap of OC_n-PNV increases with increasing side chain length. Moreover, wavelengths of the photoluminescence (PL) emission peaks (λ_max) of OC_n-PNV solutions decrease with increasing alkoxy side chain length. This is probably due to the entanglement of long side chains that causes distortion of the conjugated main chains and thereby raises band gap of the polymer. PL λ_max's of these polymers in film state are red-shifted by 14–59 nm than those in solution state. The red-shift is due to the more chain aggregations after spin coating from solution into film state and consequently the lower band gap in the film state. Besides, the polymer with shorter side chains is more thermally stable than that with longer side chains.     

Alkoxy substituted benzodithiophene-alt-fluorobenzotriazole copolymer as donor in non-fullerene polymer solar cells

A new benzodithiophene(BDT)-alt-fluorobenzotriazole(FBTA) D-A copolymer J40 was designed and synthesized by introducing 2-octyldodecyloxy side chains on its BDT units, for expanding the family of the BDT- alt-FBTA-based copolymers and investigating the side chain effect on the photovoltaic performance of the polymer in non-fullerene polymer solar cells(PSCs).J40 exhibits complementary absorption spectra and matched electronic energy levels with the n-type organic semiconductor(n-OS)(3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-sindaceno[1,2-b:5,6-b′]dithiophene)(ITIC) acceptor, and was used as polymer donor in the non-fullerene PSCs with ITIC as acceptor. The power conversion efficiency(PCE) of the PSCs based on J40:ITIC(1:1, w/w) with thermal annealing at 120 °C for 10 min reached 6.48% with a higher open-circuit voltage(Voc) of 0.89 V. The high Voc of the PSCs is benefitted from the lower-lying highest occupied molecular orbital(HOMO) energy level of J40. Although the photovoltaic performance of the polymer J40 with alkoxy side chain is lower than that of J60 and J61 with alkylthio-thienyl conjugated side chains, the PCE of6.48% for the J40-based device is still a relatively higher photovoltaic efficiency in the non-fullerene PSCs reported so far. The results indicate that the family of the BDT-alt-FBTA-based D-A copolymers are high performance polymer donor materials for non-fullerene PSCs and the side chain engineering plays an important role in the design of high performance polymer donors in the non-fullerene PSCs.     

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     

Miniemulsion polymerization of styrene using well-defined cationic amphiphilic comblike copolymers as the sole stabilizer

Well-defined, positively charged, amphiphilic copolymers containing long alkyl side chains were used as stabilizers in the miniemulsion polymerization of styrene. The copolymers were prepared by controlled free-radical copolymerization of styrene and vinyl benzyl chloride using either the reversible addition-fragmentation chain transfer method or TEMPO-mediated polymerization. The benzyl chloride moities were modified by two different long alkyl chain tertiary amines (N,N-dimethyldodecyl amine and N,N-dimethylhexadecyl amine) to yield the amphiphilic copolymers with vinylbenzyl dimethyl alkyl ammonium chloride units. Owing to their high structural quality, only a small amount of these copolymers was required to stabilize the latex particles (0.5–2 wt% vs styrene). Moreover, in the absence of any hydrophobic agent, the amphiphilic comblike copolymer preserved the colloidal stability of both the initial liquid miniemulsion and the final latex. Ill-defined, analogous copolymers were synthesized by conventional free-radical polymerization and in comparison, exhibited poor stabilization properties.     

Mesomorphic molecular materials. Influence of chain length on the structural properties of octa-alkyl substituted phthalocyanines

Phthalocyanines R, PcM (R = alkyl, M = H, Ni, Cu) substituted with alkyl chains have been synthesized and their liquid crystalline properties studied by differential scanning calorimetry and X-ray diffraction at small angles. The influence of the chain length on the mesomorphic properties has been determined. A model is proposed to rationalize the structural modifications induced by varying the nature of the connecting link between the macrocycle and the side chains (alkyl, alkoxymethyl, alkoxy).     

Phase structures and transition behaviors in polymers containing rigid rodlike backbones with flexible side chains. V. Methylene side‐chain effects on structure and molecular motion in a series of polyimides

A series of organo‐soluble hairy‐rod polyimides was recently synthesized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and di[n‐alkyl]‐4,4′‐diamino‐6,6′‐dibromo‐2,2′‐biphenyldicarboxylate with side chains of varying lengths (the numbers of methylene units), BACBP(n). Dynamic mechanical (DM) results reveal two cooperative relaxation processes for BACBPs(n > 10), which correspond to the two (low‐ and high‐) transition temperatures observed in differential scanning calorimetry (DSC). For BACBPs(n < 10), although two DM relaxation processes can be observed, the low‐temperature relaxation peak shifts into a medium temperature region that is difficult to observe in DSC experiments. Measurements indicate that the density of BACBP(n)s decreases with increasing numbers of methylene units. A discontinuity in the rate of density change can be seen at BACBP(10). Variable temperature solid‐state nuclear magnetic resonance experiments were also carried out to determine the molecular origins of each of the observed DM relaxation processes. The low‐ [for BACBPs(n > 10)] and possibly the medium‐ [for BACBPs(n < 10)] temperature relaxations are associated with the onset of motion in the side chains, and the high‐temperature relaxation is associated with motion in the backbones. Wide‐angle X‐ray diffraction analysis indicates that the lateral packing periodicity of the backbones in the unoriented polyimides changes its relationship with the side‐chain length at around 10 methylene units. In the oriented films of these polyimides, furthermore, those having the long side chains [BACBPs(n > 10)] adopt monoclinic unit cells, whereas those having the short side chains [BACBPs(n ≤ 10)] possess hexagonal unit cells. The drastic temperature difference between the low‐ and medium‐relaxation processes observed in DM experiments may be explained because of a change in the lateral packing arising from the variation of the side‐chain length. The limited mobility afforded the BACBPs(n ≤ 10) is a result of their more ordered conformation and interdigitation between the neighboring side chains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1633–1646, 1999     

Ionic hexagonal columnar metallomesogens derived from tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine

A series of transition metal (Ni, Cu, Pd) complexes derived from macrocyclic tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine (TAAB) was synthesized and their mesomorphic properties studied by differential scanning calorimetry, polarized optical microscopy and X-ray powder diffraction (XRD). These compounds have eight alkoxy side chains attached around the central molecular core and form disc-like molecules. All the derivatives exhibited columnar mesophases over a wide range of temperature. The mesomorphic behaviour was found to be dependent on the incorporated metal and the carbon length of the alkoxy side chains. The clearing temperatures decreased in the order M = Ni > Pd > Cu; this decrease was probably due to the size of the metal ions. Some derivatives with shorter side chains (n = 10, 12) were room temperature liquid crystals. All compounds were found to exhibit hexagonal columnar (Col_h) phases which were confirmed by powder XRD.     

Dichloro­(4,4′‐dialkyl‐2,2′‐bipyridine‐κ2N,N′)platinum(II), where alkyl is pentyl and heptyl

Dichloro­(4,4′‐dipentyl‐2,2′‐bipyridine‐κ²N,N′)platinum(II), [PtCl₂(C₂₀H₂₈N₂)], adopts a discrete π–π stacking structure, where the alkyl chains are located in a random manner. In contrast, dichloro­(4,4′‐diheptyl‐2,2′‐bipyridine‐κ²N,N′)platinum(II), [PtCl₂(C₂₄H₃₆N₂)], forms a layer structure comprised of alkyl chain layers and paired coordination sites, as observed for analogous complexes with longer alkyl chains.     

Mesogenic Unsymmetric dimers containing cholesteryl ester and tolane moieties

Among unsymmetric oligomesogens, chiral dimers formed by connecting a cholesteryl ester fragment with various aromatic mesogenic cores through a polymethylene spacer have been attracting much attention due to their remarkable thermal behaviour. In particular, dimers containing a diphenylacetylene segment having an alkoxy chain have shown interesting mesomorphic behaviour. In view of this a new series of unsymmetric dimers consisting of a diphenylacetylene moiety having an alkyl chain and a cholesteryl ester unit joined through a paraffinic spacer have been synthesized and their liquid crystalline properties characterized. The lengths of the central methylene spacer (C₃, C₄, C₅ and C₇) as well as that of the alkyl chain (n-butyl, n-pentyl, n-hexyl and n-heptyl) have been varied to establish structure–property relationships. These investigations have revealed that all the dimers exhibit smectic A, twist grain boundary and chiral neamtic (N*) phases with the exception of one of the dimers for which only the N* phase was observed. Some differences in the mesomorphic properties of the unsymmetric dimers containing odd or even parity methylene spacers have been observed. The majority of dimers having an even (C₄) parity paraffinic spacer show a blue phase while the dimers with odd (C₃, C₅ and C₇) parity spacers exhibit the chiral smectic (SmC*) phase. In some cases, the SmC* phase exists well below (?60°C) and above room temperature.     

N-Boc-Protected α-Amino Acids by 1,3-Migratory Nitrene C(sp3)−H Insertion

N-Boc-protected α-amino acids are synthesized in two steps from linear or branched carboxylic acid feedstocks. In the first step, the carboxylic acid is coupled with tert-butyl aminocarbonate (BocNHOH) to generate azanyl ester (acyloxycarbamate) RCO₂NHBoc. In the second step, this azanyl ester undergoes a stereocontrolled iron-catalyzed 1,3-nitrogen migration to generate the N-Boc-protected non-racemic α-amino acid. This straightforward protocol is applicable to the catalytic asymmetric synthesis of α-monosubstituted α-amino acids with aryl, alkenyl, and alkyl side chains. Furthermore, α,α-disubstituted α-amino acids are accessible in an enantioconvergent fashion from racemic carboxylic acids. The new method is also advantageous for the synthesis of α-deuterated α-amino acids. N-Boc-protected α-amino acids synthesized using this two-step protocol are ready-to-use building blocks.     

Structural and spectroscopic characterization of Cu(salen) complexes bearing long alkoxy chains

Cu(II) salen (salen?=?N,N′-ethylene-bis(salicylideneimine)) complexes bearing alkoxy chains of C₁₂ (1) and C₁₀ (2) in the salicylidene moieties were synthesized and subsequently characterized by several independent methods: single crystal X-ray diffraction, infrared spectroscopy, mass spectrometry, and UV-Vis spectroscopy. The solid state structures show that the spatial orientation and packing of the complexes are not affected by the alkyl chain length but by a coordinated solvent molecule, as demonstrated by the structure of 1 having methanol in an axial position.