Synthesis,characterization and photoreaction of side-chain liquid-crystalline polymers comprising cinnamoyl biphenyl mesogen

Liquid-crystalline (meth)acrylate monomers and polymers having mesogenic groups based on 4-alkyloxy-4′-cinnamoylbiphenyl (m = 2, 6) were synthesized. The methacrylate monomers 4c, d were polymerized by free radical polymerization. Under the same conditions, the acrylate monomers 4a, b gave unidentified polymers in very low yield. To synthesize the acrylate polymer, the acrylate monomer having 4-alkyloxy-4′-hydroxybiphenyl (m = 2, 6) was polymerized followed by the esterification of the hydroxy group using cinnamoyl chloride. All synthesized polymers having mesogenic moieties showed liquid-crystalline phases in the high temperature range between 140°C and 245°C. The difference of aggregation of the cinnamoyl biphenyl mesogen among the polymers was studied by UV-VIS spectroscopy at various temperatures. The photoreaction was performed in both solution and thin film. The [2+2] cycloaddition reaction preferentially occurred in the thin film although both [2+2] cycloaddition and photo-Fries reactions could occur in the solution.     

Preparation of the precursors of new tannin-like polymers with potential biological effects

New acrylate based polymers, with the potential to be converted to polyphenolic polymers — poly[2-(4-benzyloxyphenyl)ethyl acrylate] ( 4 ) and poly[3-(4-benzyloxy-3-methoxyphenyl)propyl acrylate] ( 9 ) — were prepared from the corresponding monomers 3 and 8 by free-radical polymeri- zation, initiated by 2,2′-azoisobutyronitrile (AIBN). The acrylate monomers, 2-(4-benzyloxy- pheny1)ethyl acrylate (3) and 3-(4-benzyloxy-3-methoxyphenyl)propy1 acrylate (8), were synthes- ized from acryloyl chloride and the corresponding alcohols — 2-(4-benzyloxyphenyl)ethanol(2) and 3-(4-benzyloxy-3-methoxyphenyl)- 1 -propano1 (7), respectively. The monomer 7 was prepared from 3-(4-benzyloxy-3-methoxyphenyl)-1-propene (6) by hydroboration/oxidation and 6 was obtained from eugenol(4-allyl-2-methoxyphenol) as the starting material. The compounds were characterized by ¹H NMR, ¹³C NMR, FTIR, and elemental analyses. The molecular weight of the synthesized polymers was determined by gel-permeation chromatography (GPC).     

Synthesis and characterization of isomeric biphenyl-containing poly(aryl ether bisketone)s, 3. Polymers derived from 3,4′-bis(4-fluorobenzoyl)biphenyl and bisphenols

A series of high-molecular-weight amorphous and semicrystalline poly(aryl ether bisketone)s were prepared from bisphenols and 3,4′-bis(4-fluorobenzoyl)biphenyl via nucleophilic aromatic substitution reactions. Model compound studies were carried out with several substituted monohydric phenols, 3,4′-bis(4-fluorobenzoyl)biphenyl and 3,4′-bis(4-Chlorobenzoyl)biphenyl. The dihalo-substituted aromatic ketones were synthesized by the reaction of 3,4′-biphenyldicarboxylic acid with thionyl chloride, followed by Friedel-Crafts acylation with the appropriate aryl halide. The required dicarboxylic acid was prepared starting from 4-bromotoluene and 3-methylcyclohexanone. Potassium carbonate mediated reaction of the monomers in dimethylacetamide or diphenyl sulfone gave high-molecular-weight polymers in excellent yield. The glass transition temperatures of the polymers are in the 170 to 190°C range. In addition, the polymers exhibit excellent thermal stability, as evidenced by both dynamic and isothermal thermogravimetric analysis, and afford tough films by compression molding.     

Polymerizable dendrimers. Synthesis of a symmetrically branched methacryl derivative bearing eight ester groups

The synthesis of chiral acryl and methacryl derivatives containing four ester groups, tetramethyl 5-((meth)acryloylamino)isophthalamido-di-2L -succinate ( 2a and 2b ), was done by condensation of 5-(N-acryloylamino)isophthalic acid ( 1a ) or 5-(N-methacrylamino)isophthalic acid ( 1b ) with L -aspartic acid dimethyl ester in a mole ratio of 1:2. In a similar way, a methacryl monomer bearing eight ester groups, octamethyl 5,5′-[5-(methacryloylamino)-isophthalamido]bis(isophthalamido)tetra-2L -succinate ( 6b ), was obtained using the Z-protected intermediate tetramethyl 5-(benzyloxycarbonylamino)isophthalamido-di-2L -succinate ( 4 ). The monomers were homopolymerized radically with AIBN as initiator, yielding optically active polymers and oligomers ( 2a ′, 2b ′ and 6b ′) with branched side groups and degree of polymerization P _n between 2 and 23, depending on the architecture of the monomers.     

Liquid-crystalline polyacrylates containing biphenyl and chiral terminal groups in the side chain, 1. Influence of the spacer length on the liquid-crystal behavior

Three acrylate monomers having mesogenic moieties based on 4-(n)-alkyloxy-4′-(2-chloro-propanoyloxy)biphenyl (n = 6, 8 or 10) have been synthesized. There is no evidence for liquid-crystal properties in any of the three new monomers. The corresponding polymers have been prepared by free-radical polymerization. Their liquid-crystal behavior has been investigated by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. On cooling from the isotropic liquid, smectic A (S_A), smectic B (S_B) and crystalline phases (probably crystal-like S_E phases) have been evidenced. It should be noted that the chlorine atoms in the chiral groups do impose a local ordering of the mesogenic side groups.     

(Meth)acrylate monomer-induced cytotoxicity and intracellular Ca(2+) mobilization in human salivary gland carcinoma cells and human gingival fibroblast cells related to monomer hydrophobicity

To elucidate a possible link between the cytotoxicity and Ca(2+) mobilization by (meth)acrylates, we investigated the cell survival of and change in [Ca(2+)](i) in human salivary gland (HSG) cells (salivary gland carcinoma cell line) and human gingival fibroblasts (HGF) cells treated separately with 9 (meth)acrylate monomers used in dentistry. The cell survival was determined by the MTT method, and the [Ca(2+)](i) changes after the stimulation with the (meth)acrylate monomers were measured in floating indo-1/AM-loaded cells in Ca(2+)-free medium. For both HSG and HGF cells, the cytotoxicity of the monomers was approximately proportional to their hydrophobicity (logP). No increase in [Ca(2+)](i) was found with hydrophilic monomers, even with 10mm stimulation. [Ca(2+)](i) elevation by hydrophobic monomers occurred in a dose- and hydrophobic-dependent manner. The [Ca(2+)](i) change in HSG cells appeared as twin peaks, i.e., an initial sharp peak followed by a delayed broad one; whereas with the HGF cells only a single broad peak was seen, possibly dependent on their membrane quality. Pretreatment with n-butanol or methylmethacrylate enhanced the butylmethacrylate-induced [Ca(2+)](i) elevation, suggesting the [Ca(2+)](i) elevation by (meth)acrylate may be related to monomer hydrophobicity and cell type. The causal link between the cytotoxicity and [Ca(2+)](i) mobilization of monomers is discussed.     

Preparation and characterization of aromatic polyamides from 4,4′-(2,6-naphthylenedioxy)dibenzoic acid and aromatic diamines

A new aromatic dicarboxylic acid, 4,4′-(2,6-naphthylenedioxy)dibenzoic acid ( 3 ), was synthesized by the fluoro-displacement reaction of p-fluorobenzonitrile with 2,6-naphthalenediol in the presence of potassium carbonate, followed by alkaline hydrolysis. A series of aromatic polyamides having inherent viscosities of 1.30–2.19 dL/g were prepared by the triphenyl phosphite activated polycondensation from the diacid 3 with sixteen aromatic diamines. Most of the resulting polymers were noncrystalline and readily soluble in a variety of polar solvents such as N,N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP). Except for those polymers derived from p-phenylenediamine, benzidine, and 4,4′-bis(p-aminophenoxy)biphenyl, transparent, tough, and flexible films were cast from the DMAc or NMP solutions. The films had tensile strengths ranging from 70 to 91 MPa, elongations at break from 6 to 50%, and initial moduli from 1.35 to 2.32 GPa. The polyamides exhibit glass transition temperatures in the range of 178–300°C. Almost all polymers are stable up to 400°C, with 10% weight loss being recorded above 500°C, in air and nitrogen atmosphere.     

Synthesis and Characterization of New Acrylate and Methacrylate Monomers with Pendant Pyridine Groups

To overcome some drawbacks of polyvinylpyridines, new monomers of acrylate and methacrylate type with pendant pyridine groups i.e., 4‐(3‐methacryloylpropyl)pyridine 1a and 4‐(3‐acryloylpropyl)pyridine 1b were successfully prepared, although it turned out to be challenging work to synthesize the acrylate monomer 1b . First polymerization studies showed that the new monomers could be polymerized easily by atom transfer radical polymerization (ATRP). The new polymers show excellent characteristics, such as very good solubility, low glass‐transition temperature, and easy quaternization.

Design and structure of new monomers 1a and 1b .     

High Glass‐Transition Temperature Acrylate Polymers Derived from Biomasses,Syringaldehyde, and Vanillin

The contribution reports a unique type of lignin‐based (meth)acrylate polymers which are derived from syringaldehyde and vanillin and show high glass transition temperature (T_g). The four (meth)acrylate monomers undergo free radical polymerization and yield the corresponding polymers in high yield (>80 wt%). The obtained polymers display relatively higher thermostability. Especially, the polymers demonstrate remarkably high glass transition temperature (T_g), well exemplified by syringaldehyde‐derived polymers which show a T_g up to 180 °C. This type of polymers can be applied as novel high temperature‐resistant plastics and even heat‐resistant additives for other general polymers.

     

Poly(crown ether)s with rubidium cation selectivity

Polymers having both crown ether moieties as cation binding sites and cinnamoyl moieties as photodimerizable pendant groups were prepared by cationic polymerization of 2-vinyloxyethyl 3-(2,3-benzo-1,4,7,10,13-pentaoxacyclopentadecen-4′-yl)acrylate ( 1 ) or 2 -vinyloxyethyl 3-(2,3-benzo-1,4,7,10,13,16-hexaoxacyclooctadecen-4′-yl)acrylate ( 2 ). The copolymer 3a was also prepared from 1 and 2 . On irradiation with UV light, the cinnamoyl moieties of the polymers undergo dimerization in solution. The cation binding properties were investigated by using a fluorescent probe, 8-anilino-1-naphthalenesulfonate. The cation binding ability of the photoreacted polymers was found to be higher than that of the original polymers. A significant template effect of alkali metal chlorides during photodimerization reaction on the cation binding ability was observed. The copolymers 4a , prepared by irradiation with template cations, show a remarkable rubidium cation selectivity, which is not observed for polymers with only 15-crown-5 or 18-crown-6 moieties.     

Syntheses and Characterization of Luminescent Polymers Containing Rhenium(I) Pyridinyl‐Carbonyl Complexes

The syntheses of methacrylate‐ and styrene‐based monomers containing substituted pyridine ligands are reported. The preparation of the corresponding homopolymers has been performed by free radical polymerization by using 2,2′‐azoisobutyronitrile (AIBN) at 60 °C. The high molecular weights, up to 119 000 g · mol^?1, and low glass transition (T_g) values (< ?43 °C) have been obtained by the copolymerization reaction with butyl acrylate. The free metal homopolymer and copolymer were subsequently metalated by reaction with Re[phen(CO)₃(acetone)]⁺. All polymer materials have been characterized by conventional experimental techniques, such as gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). UV‐Vis and fluorescence spectroscopy have been used to investigate the optical and photophysical properties of the polymers in solid‐state films and in solution. ¹H NMR spectra confirmed the structure of the synthesized polymers and contributed to the estimate of the monomer sequences in the copolymer chains. Time‐resolved and emission‐quenching experiments in diluted solutions and on the solid films suggest application of the polymeric materials as oxygen sensors. The morphological aspects of some polymers containing a low amount of rhenium metal complexes have been investigated by scanning electron microscopy (SEM).

One of the Re complex‐containing copolymers synthesized here.     

Synthesis and Gas Permeation Properties of Spirobischromane‐Based Polymers of Intrinsic Microporosity

Polymers of intrinsic microporosity (PIMs) possess molecular structures composed of fused rings with linear units linked together by a site of contortion so that the macromolecular structure is both rigid and highly non‐linear. For PIM‐1, which has previously demonstrated encouraging gas permeability data, the site of contortion is provided by the monomer 5,5′,6,6′‐tetrahydroxy‐3,3,3′,3′‐tetramethyl‐1,1′‐spirobisindane. Here we describe the synthesis and properties of a PIM derived from the structurally related 6,6′,7,7′‐tetrahydroxy‐4,4,4′,4′‐tetramethyl‐2,2′‐spirobischromane and copolymers prepared from combination of this monomer with other PIM‐forming biscatechol monomers, including the highly rigid monomer 9,10‐dimethyl‐9,10‐ethano‐9,10‐dihydro‐2,3,6,7‐tetrahydroxyanthracene. Generally, the polymers display good solubility in organic solvents and have high average molecular masses ( ) in the range 80 000–200 000 g · mol^?1 and, therefore, are able to form robust, solvent‐cast films. Gas permeability and selectivity for He, H₂, N₂, O₂, CO₂, and CH₄ were measured for the polymers and compared to the values previously obtained for PIM‐1. The spirobischromane‐based polymers demonstrate enhanced selectivity for a number of gas pairs but with significantly lower values for permeability. The solubility coefficient for CO₂ of two of the copolymers exceed even that of PIM‐1, which previously demonstrated the highest value for a membrane‐forming polymer. Therefore, these polymers might be useful for gas or vapor separations relying on solubility selectivity.

     

Preparation of ordered and crosslinked films from liquid crystalline p-vinylphenoxy-based monomers

The synthesis of the following monofunctional and bifunctional liquid crystalline p-vinylphenoxy-based monomers is described: 4-methoxyphenyl 4-[11-(4-vinylphenoxy)-undecyloxy]benzoate ( 1 ), 4-cyanophenyl 4-[11-(4-vinylphenoxy)undecyloxy]benzoate ( 2 ) and 3-(4-vinylphenoxy)propyl 4-{4-[11-(4-vinylphenoxy)undecyloxy]benzoyloxy}benzoate ( 3 ). Both free radical and cationic polymerization of the monofunctional monomers 1 and 2 yielded side-chain liquid crystalline polymers exhibiting smectic A mesomorphism. The polymers exhibited high molar masses (M _n = 40000 – 100000 g/mol) and relatively narrow molar mass distributions (M _w/M _n between 1.5 and 3). Ordered thin films were prepared by in-situ photopolymerization of monomers 1 , 2 and 3 oriented in their nematic mesophases. Thin films of a thermally stabilized ordered side-chain liquid crystalline polymer were prepared by copolymerization of the monofunctional monomer 1 and the bifunctional monomer 3 , the latter present in low concentration. The films regained orientation when cooled down from temperatures above the isotropization point (137°C) as evidenced by polarized FT-Raman measurements.     

Stable Free Radical Polymerization Kinetics of Alkyl Acrylate Monomers Using in situ FTIR Spectroscopy: Influence of Hydroxyl‐Containing Monomers and Additives

Summary: The homopolymerization and copolymerization of various alkyl acrylate monomers was studied under stable free radical polymerization (SFRP) conditions using in situ FTIR spectroscopy to monitor polymerization kinetics. The IR absorbance corresponding to the C? H deformation of the monomer (968 cm^?1) was measured to determine monomer conversion in real‐time fashion. The monomer disappearance profiles were subsequently converted to pseudo‐first order kinetic plots. Altering the alkyl ester chain length and configuration did not reveal a significant trend in the resulting polymerization kinetics. However, addition of 2‐hydroxyethyl acrylate (HEA) to a polymerization of n‐butyl acrylate (nBA) substantially accelerated the rate of total monomer conversion, increasing the observed rate constant almost two times. ¹H NMR spectroscopy also showed that the resulting HEA/nBA copolymers were enriched with the HEA monomer. Moreover, a similar but enhanced effect was also observed upon the addition of small amounts of dodecanol to an n‐butyl acrylate homopolymerization resulting in more than a doubling of the observed rate constant.

Resonance forms associated with the DEPN nitroxide and stabilization resulting from hydrogen bonding.     

Reactivity of N-alkylated cyclic iminoether salts having vinyl groups, 4. Radical polymerization and copolymerization of 3-methyl-2-vinyl-5,6-dihydro-4H-1,3-oxazinium trifluoromethanesulfonate

Radical homopolymerization and copolymerizations of a new ionic monomer, 3-methyl-2-vinyl-5,6-dihydro-4H-1,3-oxazinium trifluoromethanesulfonate ( 2c ), were studied. The homopolymerization was initiated with 2,2′-azoisobutyronitrile or benzoyl peroxide in acetonitrile to produce a polymer, poly[1-(3-methyl-5,6-dihydro-4H-1,3-oxazinium-2-yl)ethylene] ( 3c ), with a relatively low solution viscosity ([η] ≈ 0,2). The monomer was found to be copolymerizable with both electron-rich (styrene and butyl vinyl ether) and electron-deficient monomers [methyl methacrylate (MMA)]. For the copolymerization of the monomer and MMA the reactivity ratios r₁ = 0,31 and r₂ = 0,37 (MMA) were determined. From these values the Q and e values were calculated to be 3,7 and 1,9, respectively. The e-value is one of the highest among vinyl monomers reported thus far, which is consistent with the anionic polymerizability of monomer 2c .     

Novel High Temperature Polypyrrolones with Asymmetric Biphenyl Moieties in the Main Chain: Synthesis and Characterization

Summary: Two novel polypyrrolones (PPys) with asymmetric biphenyl moieties in the main chains have been synthesized from 2,3,3′,4′‐biphenyl tetracarboxylic dianhydride (a‐BPDA) and two aromatic tetra‐amines: 3,3′,4,4′‐tetra‐amino biphenyl (TABP) and 3,3′,4,4′‐tetra‐amino diphenyl ether (TADPE) respectively, via soluble poly(amide amino acid) (PAAA) precursors, followed by thermal cyclization at elevated temperatures. The polymerization and curing conditions were studied and confirmed. Asymmetric biphenyl structures endowed the polymers with good combined properties. For example, flexible and tough PPy films with acceptable mechanical properties were obtained. Tensile strengths of higher than 70 MPa and elongations at break of higher than 6% were achieved. The PPy films with a final curing temperature of 350 °C exhibited good thermal stability and the 10% weight loss temperatures were 610.3 °C for PPy‐I, and 607.8 °C for PPy‐II. The residual weight ratios at 700 °C were higher than 80%. In addition, the PPy films showed good dielectric properties with dielectric breakdown strengths of higher than 100 V · µm⁻¹ and dielectric constants of 3.64 for PPy‐I and 3.53 for PPy‐II.

Chemical structures of polypyrrolones with asymmetric biphenyl moieties.     

Polyimides with cyclohexyl-substituted indan groups in the main chain

A diamine monomer containing the 1,3-biscyclohexyl-1-methylindan group was prepared, starting from cyclohexyl phenyl ketone in four steps. This monomer was reacted with six different dianhydrides (pyromellitic dianhydride, 3,4:3′,4′-biphenyltetracarboxylic dianhydride, 3,4:3′,4′-benzophenonetetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, 4,4′-sulfonyldiphthalic anhydride, 4,4′-perfluoroisopropylidenediphthalic anhydride) to give the corresponding polyimides via the poly(amic acid) precursors and thermal imidization. All of these polyimides were soluble at least in N-methyl-2-pyrrolidone (NMP) at elevated temperatures, some were soluble in NMP and chlorinated hydrocarbons even at room temperature. The polymers were characterized by nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and dynamic thermogravimetry. All polyimides proved to be amorphous with glass transition temperatures in the range between 261°C and 295°C depending on the nature of the dianhydride moiety. Their decomposition proceeds in two steps, starting at 400°C probably with loss of the cyclohexyl substituents.     

Preparation and thermal properties of semi-rigid homo- and copoly(imide-carbonate)s based on 4,4′-oxydiphthalimide

New aromatic-aliphatic semi-rigid homo- and copoly(imide-carbonate)s 7 containing the 4,4′-oxydiphthalimide ring system were prepared by melt polycondensation of N,N′-bis(6-hydroxyhexyl)-4,4′-oxydiphthalimide ( 4 ) and/or 6,6′-(4,4′-biphenyldiyldioxy)dihexanol ( 5 ) with hexamethylene diphenyl dicarbonate in the presence of zinc acetate, and their thermal and mesomorphic properties were evaluated. The assigned structures of the monomer and the polymers were identified by Fourier-transform infrared and ¹³C nuclear magnetic resonance spectroscopy and elemental analyses. Differential scanning calorimetry measurements, observation of the texture by means of a polarizing microscope equipped with a hot stage and powder X-ray analyses at various temperatures demonstrated that only the biphenyl moiety-rich polymers from nematic phases, but the 4,4′-oxydiphthalimide moiety-rich polymers exhibit no liquid-crystalline melts. It was suggested that the mesogenic character of the 4,4′-oxydiphthalimide ring system is low. The glass transition temperature steps decrease with the biphenyl moiety content. Thermogravimetry/differential thermal analysis (TG-DTA) measurements indicated that the polymers are thermostable up to 300°C in air.     

Liquid crystalline poly(β-aminoester)s containing different mesogenic groups

Four series of new poly(β-aminoester)s based on different mesogenic units and amino spacers were prepared and their properties examined. The polymers were obtained by a Michael-type polyaddition reaction of the diamines piperazine ( 5a ), 2-methylpiperazine ( 5b ), N,N′-dimethylhexamethylenediamine ( 5c ), and 4,4′-trimethylenedipiperidine ( 5d ) to diacrylates containing the anisotropic group, trans-4,4′-vinylenedi-p-phenylene diacrylate ( 1 ), 4-(4-acryloyloxybenzylideneamino)phenyl acrylate ( 2 ), 4,4′-diphenylylene diacrylate ( 3 ), and 4,4′-azoxydi-p-phenylene diacrylate ( 4 ). The mesophase behaviour of the resulting polymers 6–9 was strongly influenced by the nature of both the anisotropic and spacer groups. The 4,4′-azoxydi-p-phenylene unit appeared to be the most efficient in promoting liquid crystal properties, whereas no mesophases could be observed in polymers incorporating the 4,4′-biphenylylene unit. Doping of poly(β-aminoester)s, based on 4,4′-azoxydi-p-phenylene units, with a low-molar-mass cholesterogen allowed to obtain cholesteric structures extending over wide ranges of temperature. The molecular weight of the polymers was found to play a role in determining thermotropic mesomorphism by affecting the melting temperature of the polymer. In this context, some non-macromolecular model compounds were analyzed in respect of their thermal behaviour.     

Functional monomers and polymers, 109. Asymmetric inclusion polymerization of (E)- and (Z)-2-methyl-1,3-pentadiene in apocholic acid canals

Asymmetric inclusion polymerization of the prochiral monomers (E)- and (Z)-2-methyl-1,3-pentadiene (3a and 3b) , in apocholic acid (2) canals was performed under various conditions to find out the factors controlling the asymmetric induction during the polymerization. Ozonolysis of the resulting polymers and subsequent transformation of the resulting 2-methyl-4-oxovaleric acid (4) into its 2,4-dinitrophenylhydrazone revealed the predominant formation of the (R)-absolute configuration. The optical yield was high in the initial stage of the polymerization and decreased gradually as the polymerization proceeds. To obtain a high optical yield the polymerization was performed at low temperature applying a 1:1 mole ratio monomer/apocholic acid, and an irradiation dose < 1 Mrad. The optical yield amounted to 36% at maximum, which is the highest value obtained so far in the asymmetric polymerization of 1,3-pentadiene derivatives using canal complexes or other known methods.