Donor acceptor interactions in polymeric systems, 5. A polyurethane with pendant carbazolyl groups

A polyurethane having pendant carbazolyl groups separated by four methylene groups was prepared and the EDA complex formation with 2,4,7-trinitrofluorenone (TNF) was studied in chloroform. EDA complexes of the polymer and the monomer model compound are spectroscopically indistinguishable. The formation constant (K) of the polymer complex is about equal to that of the monomer model compound in the oligomeric range whereas K increases with increasing molecular weight of the polymer. This trend of polymer effect is the same for the complex formation with other acceptors such as tetracyanoethylene (TCNE) and 1,3,5-trinitrobenzene (TNB). The formation of the polymer complex is entropically favoured although the negative enthalpy change is larger for the monomer model compound. The reasons are discussed.     

Donor acceptor interactions in polymeric systems, 7. Structure matching effect in interpolymer EDA complex formation

Interpolymer EDA complex formation between polyesters bearing pendant carbazolyl groups and polyurethanes bearing pendant trinitrofluorenonyl groups was investigated in dioxane at 25°C. Complex formation depends on the degree of polycondensation (DP) as well as on structure matching of polymeric D and polymeric A. With increasing DP, the solubility of the D polymer-A polymer mixture trends to decrease. Even when the polymer complexes do not precipitate, the Ketelaar's plots do not always fall on a straight line. These phenomena were interpreted as due to higher order complex formation and/or dependence of the formation constant on the fraction of saturation. It was found that polymeric donor acceptor pairs in which the number of atoms in a repeating main chain unit are identical for D and A polymers form a stronger complex than other combinations. It was concluded that structure matching of an interacting pair is a favourable condition to form tight complexes as in the case of antigenantibody interactions.     

Polymers with pendant carbazolyl groups, 5. Photoconductive properties of some carbazole derivatives with electron donor and acceptor groups

In this paper photocurrents of N-isopropylcarbazole (NIPC) derivatives in polycarbonate hosts are reported and compared to data for a benzotriazole derivative (BTA). The carbazole moiety was substituted with both electron donor and acceptor substituents and the photoconductivity was measured as a function of concentration, electrical field, and temperature using the time-of-flight (TOF) technique. The observed increase of the effective mobility of charge carriers at low dopant concentrations upon substitution with a moderate electron acceptor is in contrast to literature data for some other materials. We interpret this increase as being due to an increase in the delocalisation radius of the transport state of the substituted carbazole molecule. The field dependence of the effective mobility shows Poole-Frenkel behaviour, which is attributed to polaron formation. Comparison of the effective mobility of the NIPC derivatives with BTA shows that the size of the molecule plays a decisive role for the absolute value of the effective mobility.     

Polymer effect on the electron-donating character of a polymeric donor, 3. Formation of charge-transfer complexes between polymer containing carbazolyl groups and three kinds of common acceptors

Charge-transfer complex formations with carbazole containing polymers are studied by using copolymer donors. Donors employed are poly(N-vinyl carbazole) (poly[1-(N-carbazolyl)ethylene]), (PVK), copolymers of N-vinyl carbazole (VK) and vinyl acetate (VAc) with various compositions, and N-ethyl carbazole (NEK). As acceptor are used p-chloranil (2,3,5,6-tetrachloro-2,5-cyclohexadiene-1,4-dione) (CA), tetracyanoethylene (ethylenetetracarbonitrile) (TCNE) and 2,4,5,7-tetranitrofluorenone (TNF). A smooth bathochromic shift in the wave length of maximum absorption λ_max was observed with increasing the VK content in copolymers when CA and TCNE were used as common acceptor. In the case with TNF, since PVK and the copolymers give too broad charge transfer absorption bands, their λ_max cannot clearly be read. In both cases with CA and TCNE, the association constant of charge-transfer complex formation K_CT was found to decrease with increasing the VK content in the copolymers, whereas in the case with TNF it increases. The thermodynamic parameters of complex formation were also discussed: ΔH and ΔS were found to decrease with increasing VK content in all cases with three common acceptors. Differences in their degrees of contribution to the free energy of the complex formation between enthalpy and entropy probably causes two types of variation of K_CT with the VK content in the copolymers. In addition, effects of acceptors and solvents on the charge-transfer complex formation were studied. A difference in λ_max between with NEK and with PVK, corresponding to the so-called polymer effect, was observed to be largest when CA was used as common acceptor and also to become larger as the dielectric constant of the solvent is increased.     

Donor acceptor interactions in polymeric systems, 2. Polyesters from N-[5,5-bis(hydroxymethyl)hexyl]carbazole

Polyesters with a pendant 9-carbazolyl group were prepared by polycondensation of 9-[5,5-bis(hydroxymethyl)hexyl]carbazole ( 1a ) with diethyl malonate, dimethyl terephthalate, and adipoyl chloride. Charge transfer complex formation of these polyesters and their monomeric model compound with 2,4,7-trinitrofluorenone (TNF) was investigated by means of absorption spectroscopy in 1,2-dichloroethane. Stability constants (K) of the polymeric systems were always larger than that of the monomeric system in the following order: polymer 3c (with the terephthaloyl unit) > polymer 3a (with the malonyl unit) ≈ polymer 3b (with the adipoyl unit) > 9-[5,5-bis-(acetoxymethyl)hexyl]carbazole ( 2b ). From the measurements of monomer and excimer emission in dilute solutions, interactions between the 9-carbazolyl groups are discussed for the polymers and the monomeric model compound. For the polymer 3c (containing the terephthaloyl unit), exciplex formation between the 9-carbazolyl group and the terephthaloyl group was demonstrated. Polymer effects on K are discussed based on the structural information obtained from fluorescence measurements.     

Donor acceptor interactions in polymeric systems, 3. Oligoesters from 9-[1,1-bis(hydroxymethyl)ethyl]carbazole

Oligoesters having a 9-carbazolyl group attached to the main chain were prepared by oligocondensation of 9-[1,1-bis(hydroxymethyl)ethyl]carbazole ( 2a ) with diethyl malonate, dimethyl terephthalate, and diethyl 2-(carbazol-9-yl)-2-methylmalonate ( 1 ). Charge transfer complex formation of these oligoesters and their monomeric model compound with 2,4,7-trinitrofluorenone was investigated by means of absorption spectroscopy. The stability constants (K) of the oligomeric systems were always larger than those of the monomeric systems. The magnitude of K was found to be in the following order:

• oligo[oxy-(2-carbazol-9-yl-2-methyl)trimethyleneoxy-(2-carbazol-9-yl-2-methyl)-malonyl] ( 3c ) ? oligo[oxy-(2-carbazol-9-yl-2-methyl)trimethyleneoxymalonyl] ( 3a ) ≈ oligo[oxy-(2-carbazol-9-yl-2-methyl)trimethyleneoxyterephthaloyl] ( 3b ) >9-[1,1-bis-(acetoxymethyl)ethyl]carbazole ( 2b ).

Fluorescence spectroscopy of these carbazolyl derivatives in dilute solutions indicate the environmental difference of chromophors.     

Polymerization initiated by an electron donor-acceptor complex. Part III. Polymerization of methyl methacrylate initiated in the systems containing polymer electron donor,acceptor, and carbon tetrachloride

The polymerization of methyl methacrylate can be easily initiated in systems containing poly-2-vinylpyridine (polymer electron donor), liquid sulfur dioxide (acceptor), and carbon tetrachloride. The various types of polymer electron donors and acceptors which range widely in their electron affinity were also examined. The addition of DPPH causes the retardation; a decrease in the poly-2-vinylpyridine concentration or an increase in the monomer concentration leads to a higher molecular weight of poly-MMA. The values of k_p/√k_t obtained under the various polymerization conditions are satisfactorily consistent with the literature values, suggesting that the polymerization proceeds through free radical intermediates.     

Side-Chain liquid-crystalline polymers containing a siloxane spacer, 2. Effects of mesogenic groups on the thermal properties of side-chain liquid-crystalline polymers containing a disiloxane unit in the spacer

A series of side-chain Iiquid-crystalline polymers was prepared containing disiloxane units in the spacer. The polymers consist of a polymethacrylate backbone and several kinds of mesogenic side groups. For the synthesis of the desired monomers, silanol compounds carrying a mesogenic groups were prepared as the intermediates. The polymers were obtained by ordinary free-radical polymerization. As the mesogenic groups, linear-type p- or p′-substituted phenyl and biphenylyl benzoates, p- or m-substituted benzoyloxybiphenyl groups and laterally attached biphenylyl benzoate-type mesogens were chosen, and the structural effects on the thermal properties of the polymers were investigated. In the case of linear-type mesogens, only when triple-core mesogens were introduced a stable smectic mesophase was observed with a wide range of phase stability, while on mesophase was observed for the linear double-core and the laterally attached mesogens. On the other hand, a highly ordered smectic phase was observed for polymers having linear-type triple-core mesogens with p-alkoxy and m-cyano end groups. Furthermore, it was revealed that the introduction of a disiloxane unit in the spacer lowered the temperature range of the mesophase, in comparison with polymers having an alkylene spacer with the same backbone component and mesogens.     

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.     

Fluorination of polymers containing COOH/COOR groups with SF4/HF, 1. Model reactions with low molecular weight compounds

Model studies with low molecular weight compounds are performed in order to evaluate the feasibility of synthesizing fluorine-containing polymers by modification of commercially available products. The conversion of ? COOH and ? COOR into ? CF₃ moieties by means of SF₄/HF is checked with the following low molecular weight models for poly(acrylic acid) and poly(acrylic ester)s: hexanoic acid ( 1 ), ethyl hexanoate ( 2 ), 2,4-dimethylglutaric acid ( 3 ), 4-carboxypimelic acid ( 4 ) and 2,2-diethylmalonic acid ( 5 ). For the model compounds, the reaction conditions have been optimized. The desired products are obtained in high yield and in high selectivity. Therefore, this type of reaction will be applied to the modification of polymers in the next step.     

Effects of protein molecular weight on the intrinsic material properties and release kinetics of wet spun polymeric microfiber delivery systems

Wet spun microfibers have great potential for the design of multifunctional controlled release scaffolds. Understanding aspects of drug delivery and mechanical strength, specific to protein molecular weight, may aid in the optimization and development of wet spun fiber platforms. This study investigated the intrinsic material properties and release kinetics of poly(l-lactic acid) (PLLA) and poly(lactic-co-glycolic acid) (PLGA) wet spun microfibers encapsulating proteins with varying molecular weights. A cryogenic emulsion technique developed in our laboratory was used to encapsulate insulin (5.8 kDa), lysozyme (14.3 kDa) and bovine serum albumin (BSA, 66.0 kDa) within wet spun microfibers (～100 μm). Protein loading was found to significantly influence mechanical strength and drug release kinetics of PLGA and PLLA microfibers in a molecular-weight-dependent manner. BSA encapsulation resulted in the most significant decrease in strength and ductility for both PLGA and PLLA microfibers. Interestingly, BSA-loaded PLGA microfibers had a twofold increase (8 ± 2 MPa to 16 ± 1 MPa) in tensile strength and a fourfold increase (3 ± 1% to 12 ± 6%) in elongation until failure in comparison to PLLA microfibers. PLGA and PLLA microfibers exhibited prolonged protein release up to 63 days in vitro. Further analysis with the Korsmeyer–Peppas kinetic model determined that the mechanism of protein release was dependent on Fickian diffusion. These results emphasize the critical role protein molecular weight has on the properties of wet spun filaments, highlighting the importance of designing small molecular analogues to replace growth factors with large molecular weights.     

Liquid crystalline main chain polymers containing the ferrocene unit as a side group, 2. Variation of the spacer length

Four new ω-ferrocenylalkyl diethyl malonates with varying length of the alkyl group from 4 to 10 methylene units were incorporated via Ti(OiPr)₄-catalyzed copolymerization into smectic liquid crystalline main-chain polymers in contents of about 10 mol-%. As mesogenic unit 4,4′-bis(6-hydroxyhexyloxy)azoxybenzene was used as diol component and diethyl phenyl malonate as diester component. Polymer analogous oxidation of the ferrocene units leads to liquid crystalline ionomers, which also form smectic phases. The ferrocene containing polymers were investigated in the oxidized and non-oxidized state of the ferrocene unit. Differential scanning calorimetry (DSC) data show a shift towards higher phase transition temperatures after oxidation, which is in agreement with the behaviour of classical ionomers. Small angle X-ray scattering (SAXS) experiments show an excess scattering to small angles, which is a hint for dispersed particles in the polymer matrix (ionic clusters). In one polymer series the ferrocene content was varied. Increasing the ferrocene content changes the type of the LC phase from smectic A to nematic presumably because of the bulkiness of the neutral ferrocene group. It is, however, possible to restore the smectic A phase by an oxidation of the ferrocene units to ferrocenium ions. This is a result of microphase separation in ionic domains and non-ionic domains, which supports the formation of layered structures.     

Kinetics of complex formation of tetracyanoethylene with poly-N-vinyl carbazole and polynaphthyl methacrylate and the corresponding low molecular weight donors

The complex formation of tetracyanoethylene with poly-N-vinyl carbazole, polynaphthyl methacrylate and the corresponding low molecular weight analogues, N-ethylcarbazole and naphthyl methacrylate resp., in chloroform solution proceeds at a considerable rate and is accompanied by change in the absorption spectra in the visible region. The rates of donor-acceptor complex formation in mole ratios of 1 : 1 at room temperature are studied by means of spectrophotometric “stopped-flow” technique. The apparent rate constants of complex formation for all complexes are of the order of 10⁴l · mole^?1 · sec^?1. Their values do not depend on the molecular weight of the donors. The apparent rate constants of the formation of tetracyanoethylene complexes of poly-N-vinyl carbazole and N-ethylcarbazole are slightly greater than those of polynaphthyl methacrylate and naphthyl methacrylate, which shows that the rate of complex formation is influenced by the electron donating capacity of the complex forming units.     

Nematic elastomers, 1. Effect of the spacer length on the mechanical coupling between network anisotropy and nematic order

The influence of the spacer length was investigated for the correlation between the network anisotropy and the order parameter of the mesogenic units. Stress-optical measurements show that a closer coupling of the mesogenic moieties to the polymer backbone results in an increased interaction between the mechanical field and the mesogenic groups. The correlation between the phase transformation temperature T_NI and the mechanical stress σ is represented using both, our experimental measurements and the derivation from the Landau-de Gennes (LDG) formulation. From our results, it is possible, for the first time, to estimate the cross-coupling coefficient U between the order parameter and the strain of a nematic elastomer. The analysis of the elastic properties of the elastomers suggests that non-linear coefficients might become important to obtain quantitative agreement between theory and experiment.     

Relationship between axial length of the emmetropic eye and the age, body height, and body weight of schoolchildren.

This report assesses the relationship of axial length of emmetropic (without refractive error) eyes to age, height, and weight in 1,600 Croatian schoolchildren. Axial eye lengths were determined by an ultrasonic eye biometry (A scan). Axial length of both eyes increases with age, height, and weight but shows a closer correlation to height and weight than to age. Boys have a significantly longer axial eye length than girls (P < 0.01). Boys or girls of similar or nearing body height and body weight and with emmetropic eyes have close linear measures of anatomic eye structures within their sex, regardless their age. Body height demonstrates the closest correlation to the growth and development of the emmetropic eye.     

Thermotropic polyesters, 6. New approach to the synthesis of segmented liquid-crystalline polymers with an increased with an increased length of mesogenic and flexible elements

A new approach to the synthesis of segmented liquid-crystalline (LC) polymers with an increased length of both mesogenic and flexible moieties is suggested. It consists in the preparation of intermediate polymeric compounds on the basis of aliphatic diols and a “triade” type complex monomer, 4,4′-(oxalyldioxy)dibenzoyl dichloride ( 6 ), whose central oxalyl unit plays the role of a bifunctional protective group and proves to be the structural element of the main chain of the intermediate polymer. The chemodegradation of the latter to bifunctional alkylene bis(4-hydroxybenzoate)s ( 3 ), which differ from the initial complex monomer, is achieved by selective removal of the oxalyl protective group. The desired LC polymers may be synthesized on the basis of such hydroxy-bifunctional compounds 3 and another triade type monomer carrying two acyl chloride functions, 4,4′-(terephthaloyldioxy)dibenzoyl dichloride. The features of each stage of the synthesis are discussed. Special attentional is paid to the selectivity of hydrolysis procedure of the intermediate polymers. A series of segmented LC polyesters containing five or seven 1,4-phenylene units in the mesogenic group are synthesized, their thermal properties are compared with the properties of LC polymers described earlier.     

Syntheses and reaction of functional polymers. XXXIX. Syntheses of poly-N-acrylyl-2-oxazolidone and complex formation of phenol,methyl bromide and halogens with polymers containing 2-oxazolidone groups

N-Acrylyl-2-oxazolidone was synthesized by the reaction of N-sodium-2-oxazolidone with acrylyl chloride. N-Acrylyl-2-oxazolidone (M₁) was polymerized and copolymerized with styrene (M₂) by free radical initiator. The monomer reactivity ratios, r₁ (= 0.24) and r₂ (= 1.35) were determined by the method of FINEMAN and ROSS, and the ALFREY-PRICE Q (= 0.37) and e (= 0.367) values were estimated. These polymers were soluble in dimethylformamide and dimethylsulfoxide, but insoluble in common organic solvents. They formed complexes with phenol, halogens and methyl bromide. Further, the bonding characters in the complexes of various polymers containing 2-oxazolidone moiety and phenols, methyl bromide and halogens were investigated.     

Enzymes in polymer chemistry, 6. Lipase-catalyzed acylation of comb-like methacrylic polymers containing OH groups in the side chains

The enzymatically catalyzed acylation of poly[N-(2-hydroxypropyl)-11-methacryloylaminoundecanamide-co-styrene] and the corresponding monomer was performed in the presence of a lipase, with vinyl acetate, phenyl acetate, 4-fluorophenyl acetate and phenyl stearate as acylating agents. The kinetics of the enzymatically catalyzed reaction was followed by ¹H NMR spectroscopy and correlated with sterical and chemical effects. The reactivity of monomer towards acylation is higher than that of the copolymer, and that of the copolymer depends on copolymer composition, pointing at steric and hydrophobic effects.     

Studies on the phase separation of polyetherimide-modified epoxy resin, 2. Effect of molecular weight of PEI on the structure formation

The effect of molecular weight on the structure formation of polyetherimide modified epoxy system was studied. Using time-resolved light scattering (TRLS) and scanning electron microscopy (SEM), the process of phase separation and the morphology of the blends were investigated. As the curing reaction proceeds, the phase separation occurs first in the large molecular weight polyetherimide (PEI) modified epoxy resin and the time of occurrence of phase separation is increased with the decrease of the inherent viscosity of PEI. Because of the different viscosity of the blends, the blends display varied morphologies from a PEI particle dispersion to co-continuous phases. Changing of the PEI molecular weight may be another possible route to control the morphology of the PEI modified epoxy resins.     

New catalytic systems for the fixation of carbon dioxide, 2. Synthesis of high molecular weight epichlorohydrin/carbon dioxide copolymer with rare earth phosphonates/triisobutyl-aluminium systems

Copolymerization of carbon dioxide with epichlorohydrin to synthesize high molecular weight chlorine-containing poly(carbonate-ether) with RE(P₂₀₄)₃? Al[CH₂CH(CH₃)₂]₃ (with RE = La, Eu, Gd, Dy, Ho, Nd, Er, Yb, Lu, Y; P₂₀₄ = (RO)₂POO? , R = CH₃(CH₂)₃CH(C₂H₅)CH₂? ) as a catalyst was carried out for the first time. The most favorable conditions for the copolymerization were: CO₂ aged Y(P₂₀₄)₃? Al[CH₂CH(CH₃)₂]₃ as catalyst; mole ratio Al/Y = 8; reaction time 24 h; temperature 60–70°C; concentration [Y] = 3,31 · 10^?2 mol/L; 1,4-dioxane as solvent. The highest yield, intrinsic viscosity [η] and CO₂ content of the copolymer obtained reached 3 945 g per mole of rare earth element, [η] = 1,49 dL/g and f(CO₂) = 30 mol-%, respectively. Results from differential thermal analysis/thermogravimetry showed that the copolymer has high thermal stability and decomposes at 320°C.