Microstructure Induced Rigidity of Polysiloxane Yielding Hierarchical Self‐Assembly of Alkyl Side Chains

The influence of a backbone microstructure on the side chain crystallization of a comb‐like polymer is analyzed systematically using a tailor‐made random versus block siloxane copolymer system. While the side alkyl chains of the random siloxane undergo a stepwise order–disorder (OD) transition to form well‐ordered orthorhombic structure at low temperature, the packing structure of the alkyl chains pertaining to the block siloxane maintains their original hexagonal lattice up to a temperature of as low as 173 K. The unit lattice ordering of side alkyl chains in the random siloxane polymer is also accompanied by a major restructuring of the backbone conformation ultimately losing out long range ordered structure in the solid state. The OD transitions of side alkyl chains and their dynamic relationship with the backbone conformation are established unambiguously by a combination of temperature dependent small‐angle X‐ray and wide‐angle X‐ray scattering techniques. The observed conformational variations in random versus block polymers are explicitly discussed in terms of molecular chain mobility and theory of macromolecular chain conformation.     

Rigid rod polymers with flexible side chains, 4. Synthesis,structure and phase behaviour of polyimides prepared from pyromellitic anhydride and 2,5-di-n-alkoxy-1,4-phenylene diisocyantes

A series of rigid rod polyimides 1a–f derived from pyromellitic anhydride (PMDA) and 2,5-di-n-alkoxy-1,4-phenylenediamine containing flexible alkoxy side chains with 4 to 16 carbon atoms was prepared by solution polycondensation. As demonstrated by model experiments full conversion to the imide structure is achieved by reaction of PMDA with 2,5-dialkoxyphenylene diisocyanate, the latter compound being blocked by imidazole. The best solvent for the polycondensation, found in the course of the model reaction, is 1,3-dimethyl-2-oxo-perhydro-pyrimidine together with 4-dimethylaminopyridine as an accelerator. Wide-angle X-ray diffractograms showed that all polyimides under consideration here are highly crystalline at room temperature. The occurrence of a sharp reflection at the region of low angles together with its higher orders demonstrates the presence of a layered structure. The layer spacing was found to increase linearly with the length of the alkyl side chains. Polyimides bearing long side chains (n ≥ 10) exhibit two broad endotherms in the DSC analysis. As is revealed by wide-angle X-ray analysis the first transition is related to a disordering process of the side chains. The second transition leads to a layered high-temperature phase akin to the modification (B) found in a recent study of a similar rigid polyester bearing flexible side chains.     

Langmuir-Blodgett mono- and multilayers of preformed poly(octadecyl methacrylate)s, 1. Surface-area isotherms of atactic and isotactic poly(octadecyl methacrylate)s and transfer into multilayers

In order to elucidate some of the parameters controlling the transfer of compressed monomolecular layers of preformed poly(octadecyl methacrylate)s (PODMA) onto substrates by the so-called Langmuir-Blodgett technique, an investigation was undertaken of PODMA's of different tacticity and different molecular weights. For the preparation of multilayered structures it was necessary to decrease the interaction between the side chains. This could be accomplished by introducing side chain inhomogeneities especially in the form of comonomers with shorter alkyl side chains. The transferability of a monolayer could be correlated with features in the pressure-area diagrams, as there is a liquid-analogous state formed when shorter alkyl chains are introduced; moreover a partial “melting” with lowering of the collaps pressure of the layer is seen. It appeared that with isotactic PODMA regular Y-type transfer

1 Y-Type transfer: During one dipping and withdrawing cycle, two layers are transferred. Z-Type transfer: Only during withdrawing one layer is transferred.

took place, whereas with the atactic polymers at the beginning a Z-type transfer occurred , gradually changing into a Y-type transfer. Applying the concept of decreasing interaction of the side chains it was possible to prepare multilayers of isotactic and atactic PODMA's.     

Bacteriophage attachment to the somatic antigen of salmonella: effect of o-specific structures in leaky R mutants and s, t1 hybrids

The phage adsorption ability and serological specificity of different Salmonella strains having either complete or leaky mutations in their lipopolysaccharide (LPS) synthesis were compared, together with their genotype and sugar composition, to provide a set of standards relating these parameters to LPS structure. Strains that had T1-specific side chains in their LPS, both with or without O side chains, were examined to learn more about the organization of these two side chains in the LPS and a possible competition between them. It was found that (i) adsorption of O-specific antibodies was a very sensitive test for the presence of even very small amounts of O-specific structures, (ii) that phage P22 adsorption was dependent on the presence of a nearly complete O side chain complement, and both long and numerous O side chains were required, and (iii) that the adsorption of the phages FO (Felix O-1), 6SR, and Br2, which attach to structures in the LPS core, was a sensitive indicator of any defect in O-antigen synthesis, and well developed O side chains blocked their attachment efficiently. Semirough (SR) strains with only one O-specific repeating unit per side chain adsorbed FO efficiently, whereas the access of the 6SR and Br2 phages to their receptors was blocked. Strains with T1 side chains adsorbed the FO and 6SR phages efficiently, whereas the adsorption of the Br2 phage was blocked to a large extent. The phage adsorption of four S, T1 strains (with both O and T1 side chains) showed that, as the amount of O side chain material increased, there was a reduction of the adsorption of phages in the following order: 6SR, Br2, and FO. P22 attachment appeared with the increase of O side chains. The LPS composition of these strains revealed a 10-fold reduction of the O-specific structures compared to the smooth parent strain, whereas the amount of T1-specific material was the same as in T1 strains. The short O side chains of a SR, T1 strain were, however, not reduced in number, suggesting that the apparent competition between O and T1 side chains may not be a competition for available sites in the LPS.     

L‐Tyrosine Ester‐Mediated Photosensitized Charge Separation – Length Effects of Alkyl Side Chains in Polymers and Alkyl Groups in L‐Tyrosine Esters

The ruthenium(II) complex‐ and viologen‐containing partially quaternized poly(1‐vinylimidazole)s with a butyl (C₄RuVQPIm), an octyl (C₈RuVQPIm), a dodecyl (C₁₂RuVQPIm), and hexadecyl (C₁₆RuVQPIm) as alkyl side chains have been prepared. The length‐effects of the alkyl side chain in the polymers and the alkyl groups in the L ‐tyrosine esters on the L ‐tyrosine‐ester‐mediated intra‐polymer photosensitized charge‐separation reactions have been investigated in methanol. The L ‐tyrosine esters with a hexyl (C₆Tyr), an octyl (C₈Tyr), and a dodecyl (C₁₂Tyr) group were used. The luminescence intensities decreased with the addition of the L ‐tyrosine esters, and they significantly depended on the length of the alkyl side chains on the polymers, C₁₂RuVQPIm showed the smallest luminescence intensity. In contrast, the luminescence intensity of C₄RuVQPIm depended on the length of the alkyl groups in the L ‐tyrosine esters, but not for C_nRuVQPIms (n ≥ 8). These results were explained by a difference in the microdomain structure formed by the polymer structure between C₄RuVQPIm and other polymers. During the photosensitized charge separation, the reaction proceeded through a mediated process, using L ‐tyrosine esters, and a direct process (without L ‐tyrosine esters). The initial rate of the viologen radical formation was influenced by both the alkyl side chains on the polymers and alkyl groups in the L ‐tyrosine esters, particularly; particularly influenced was the back reaction in the mediated process.     

Synthesis and antithrombogenicity of polyetherurethaneurea containing quaternary ammonium groups in the side chains and of the polymer/heparin complex

Novel polyetherurethaneureas containing tertiary amino groups in the side chains (PAEUU) were synthesized, quaternized with different alkyl halides (Q-PAEUU), and heparinized (H-PAEUU). The antithrombogenicity of PAEUU in vitro was improved by quaternization, and further by heparinization. The excellent antithrombogenicity of H-PAEUU was controlled by the kind of quaternizing agent through the polar effect of quaternizing agent on the water content and through the steric effect of quaternizing agent on the heparin content of H-PAEUU. The antithrombogenicity of H-PAEUU was found to be affected by the water content more strongly than by the heparin content. H-PAEUUs containing tertiary amino groups in the main chain, which were synthesized previously, showed a little better short-term antithrombogenicity than the present H-PAEUUs containing tertiary amino groups in the side chains. Since ammonium groups in the side chains of Q-PAEUU impose little steric hindrance against the heparin adsorption, the release of heparin from the side chains of H-PAEUU was slower but lasted longer than that from the main chain. Therefore, the present H-PAEUU is expected to be a long-term antithrombogenic material.     

Structure and Mechanical Behavior of Fully Substituted Acid Starch Esters

This study deals with the evolution of structural, thermal, and mechanical properties of a series of fully substituted fatty acid starch esters (FASEs) according to side chain length (from 2 (C2) up to 16 (C16) Carbons). FASEs with C2 to C12 side chains are fully amorphous with a glass transition temperature depending on chain length while in the case of FASE with C16 side chains, a part of side chains is able to crystallize. Thermomechanical behavior depends strongly on both the alkyl chain length and crystallinity of samples. In particular, for FASE-C16, the presence of crystals leads to a brittle behavior. During stretching, no macromolecular orientation is evidenced for short-chain FASEs (<C8), whereas, for long-chain starch ester from C8 to C16 length, an orientation of starch backbone in the drawing direction is observed.     

Tetrahexylsexithiophene: crystal structure and molecular mechanics calculations

The synthesis, crystal structure and detatiled molecular mechanics calculations, including crystal packing interactions, of tetrahexylsubstituted sexithienylene are presented. Unexpectedly the molecule, which arranges in the P-1 space group, displays no herringbone arrangement, thienylenic rings are far from coplanarity and the alkylic side chains present different conformations. Molecular mechanics fully accounts for these findings. From crystal packing computations it is derived that different arrangements are unable to lower the packing energy, due to the closeness of two alkyl chains on the same side of the thienylenic backbone, which prevents interspersion of non-parallel molecules.     

Structure-activity relationships (SAR) of the 3-alkyl substituents among a series of hydroxyacetophenone leukotriene antagonists

LY171883 is an orally active antagonist of leukotriene (LT) D₄ and LTE₄. A series of related compounds varying the position and nature of the alkyl side chain were synthesized and evaluated for their ability to block LTD₄-induced contraction of guinea pig ileum. Maximal activity was obtained with n-propyl, n-butyl, and n-pentyl substituents with slightly reduced activity for longer side chains. Polar groups on the side chain substantially reduced activity. Thus, it appears that the leukotriene receptor site requires a nonpolar alkyl group of moderate size at the 3-position on this type of receptor antagonist.     

Finely Tuned Fluorescence Emission of Polydiphenylacetylene Films Obtained by Copolymerization

PDPAs containing longer (octadecyl, C18) and shorter (methyl, C1) alkyl side chains in the same backbone are synthesized. The copolymerization of C1 and C18 monomers at a range of feed ratios afford high‐molecular‐weight (M _w > 10⁶) copolymers almost quantitatively. As the content of longer alkyl chain units in the copolymers increases, the emission band in the bulk film shifts to shorter wavelengths and the emission intensity increases. The lamellar layer distance increases with increasing C18 content. The excited species with shorter lifetimes decrease gradually with increasing C18 content, whereas the longer‐lasting emission increases. Fine tuning of the FL emission of PDPAs is achieved by simple copolymerization of monomers with different alkyl side‐chain lengths.     

Crystalline and disordered state of poly(dihexylsilylene) copolymers

A systematic comparison of random copolymers, derived from poly(dihexylsilylene) (PDHS) by incorporation of monomeric units with shorter unbranched alkyl side chains, has been carried out based on calorimetry, variable temperature UV spectroscopy, and ²⁹Si MAS (magic angle spinning) solid state NMR investigations. Also, hexylmethylsilylene units and branched monomers have been copolymerized. Up to 10% comonomer with shorter linear side chains (i. e., pentyl to propyl) could be incorporated into PDHS without impeding the all-trans order of the crystalline phase. In this case, the UV absorption maximum of the crystalline low-temperature phase was affected only slightly according to the length and fraction of the comonomer side chains. A less ordered crystal structure (λ_max = 345–355 nm) was observed when the content of comonomers with shorter side chains was about 20%. Yet, all these materials form conformationally disordered mesophases. A clear disordering transition and corresponding thermochromism was not observed any more when 50% of propyl side chains were incorporated. The order of the crystalline and the mesophase is also strongly perturbed if only a small fraction (4%) of the side chains are branched at C².     

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO2–CaO nanocomposite

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO₂–CaO nanocomposite were investigated using dimethyldiethoxysilane (DMDES) and tetraethoxysilane (TEOS), which could produce two and four siloxane linkages, respectively, after a sol–gel reaction. Methyl methacrylate was co-polymerized with 3-(trimethoxysilyl)propyl methacrylate and then co-condensed with DMDES (specimen D) and TEOS (specimen T), respectively, with calcium nitrate tetrahydrate under acidic conditions. The fracture toughness of specimen D was much improved compared to that of specimen T, whereas its fracture strength, hardness, and apatite-forming ability in simulated body fluid (SBF) were slightly decreased. The improved fracture toughness of specimen D without losing apatite-forming ability was explained by the decrease of siloxane linkage numbers and the introduction of alkyl groups in silica structure because covalently bonded siloxane linkages produce hard and brittle fracture behavior in the nanocomposite while the alkyl groups help to make the silica as linear chain structure. The practical implication of these results is that this new nanocomposite can be applied to the filler materials for bone cement and dental composite resin because of its good bioactivity and improved mechanical properties.     

Cationic polymerization of bis(1-alkylvinyl)benzenes and related monomers, 5. New thermostable polyindanes

The cationic cyclopolymerization of six monomers of the type “1,4-bis(alk-2-en-2-yl)benzene” is described. The length of the unsaturated chains of the monomers ranges from 3 (propenyl) to 8 (octenyl) carbon atoms. The polymerization yields polyindanes containing different isomeric indane structure elements, which have alkyl substituents ranging from methyl to hexyl groups. The number of carbon atoms in the alkyl side chains greatly influences the glass transition temperature T_g, which is depressed from 246°C (methyl-substituted polyindane) to 26°C (hexyl-substituted polyindane). Thermal stability is also affected, though far less than T_g: the temperature, at which the material has lost 2% of its original weight is lowered from 420°C to 340°C. The polyindanes are soluble in a number of organic solvents. Their degree of polymerization is limited by a side reaction which provides non-reactive end groups. Thus, the number-average molar masses obtained are between 2800 and 4300 g/mol.     

Glass transition temperatures of comb-like polymers. Poly(ethylene oxide)-polyacrylates and -polymethacrylates

A series of twelve poly(ethylene oxide) (PEO)-polyacrylates and -polymethacrylates with PEO side chains, ranging in molecular weight from 164 to 1000, was studied by differential scanning calorimetry in order to analyse the behaviour of the glass transition temperature. It is shown that the glass transition temperature T_g first decreases with increasing side-chain length to attain a constant value corresponding to the T_g of linear PEO. Contrary to the n-alkyl homologous polymers, the influence of the side-chain crystallization is weak and only appears for long side chains (number-average molecular weight M?_n > 450). The proposed reason is the higher content of amorphous side-chain units between the backbone and the crystallites in PEO as compared to alkyl chains. A relation predicting variations of T_g in comb-like polymers with the length of the side chains is proposed. This relation, based on variation of the T_g of the side chain with its length, fits the experimental results for n-alkyl and PEO side-chain polyacrylates and polymethacrylates using only one parameter characterizing the nature of the side chain.     

Fluorophobic Effect Driven Self‐Organization of Semifluorinated Alkyl Chain Substituted Conjugated Polymer

This paper reports on the effect of a semifluorinated alkyl side chain for achieving a self‐organized nanostructure to facilitate the efficient charge carrier transport. So far, semifluorinated alkyl side chains have rarely been introduced into semiconducting polymers, despite their interesting properties such as hydrophobicity, thermal stability, and solvent resistance, as well as self‐organization. Herein, this study synthesizes the semifluorinated alkyl chain introduced poly(3‐dodecylthiophene), SFA‐P3DT, and demonstrates that self‐organization of SFA‐P3DT is intensely induced in nonfluorous solvent by the so‐called fluorophobic effect, resulting in the formation of nanofibrillar structure. In presence of the semifluorinated alkyl side chain, organic thin film transistor (OTFT) devices exhibit the improved charge carrier mobility than that of poly(3‐dodecylthiophene) with hydrocarbon alkyl chain. Moreover, higher charge carrier mobility can be obtained from the nonfluorous solvent, in comparison to the fluorous solvent, confirming the crucial role of fluorophobic effect. These observations suggest that the introduction of semifluorinated alkyl chains into a conjugated polymer may enhance the performance of OTFTs through the development of a well‐ordered nanostructure via self‐organization by fluorophobic effect, which, in turn, facilitates the efficient charge carrier transport.

     

Optical anisotropy of comb-like macromolecules of lateral and semilateral structure

Maxwell effect and Kerr effect techniques were used to study the intramoleculare axial ordering of anisotropic side groups of an isolated macromolecule in solution. Three comb-like polymers with a methacrylic main chain were investigated. The side chains contain aliphatic spacers separating the mesogenic fragments R from the backbone. R contains two or three phenylene rings with ester linking groups and cyano end groups. Fragments R are attached to the side chains, by the end or middle-point, through the para- or ortho-phenylene ring. The main-chain conformation in solution was identified to assess the hydrodynamic data using the Gaussian coil approximation. The optical anisotropy of the macromolecule segment was determined and related to the monomer unit structure. The specific Kerr constant obtained in diluted benzene solution of polymer was compared with those of low molecular weight analogues of the polymer mesogenic groups. The mobility and intramolecular ordering of the mesogenic groups in the isolated macromolecules are discussed. These properties are compared with those of comb-like polymers with another type of attachment of mesogenic groups, and with another (siloxane) chemical structure of the backbone chain. The differences in restrictions of side-chain mobility due to the backbone linkage in different types of comb-like polymers are also discussed.     

Azo-dyes as labels and as photoisomerizable units in chiral polyisocyanates

Polyisocyanates (nylon 1) with azochromophores in the side chains were prepared for the first time. For this purpose we have synthesized two new azo dyes containing isocyanato groups. The monomers were copolymerized with alkyl isocyanates to prepare chiral dye-containing polyisocyanates. Optical rotatory dispersion and circular dichroism measurements support the helical polymer structure with predominantly one twist sense (due to the chiral side chains, P and M helices are diastereomeric). The completely reversible photochemical isomerization (trans to cis) of the azochromophores reaches high conversions (about 80%), but does not change the conformation of the main chain.     

13C NMR studies of thermotropic liquid crystalline poly(γ-alkylaryl L-glutamate)s

The molecular motions of three kinds of poly(γ-alkylaryl L -glutamate)s ( 1 – 3 ) having a phenylene or a biphenylylene group and alkyl groups with various length, containing 6 to 22 carbon atoms, were investigated by means of ¹³C NMR spectroscopy as a function of temperature. The observed range of temperature covers the “crystal-to-liquid-crystal” phase transition temperature, T_m. It was found that these phase transitions are caused by an increase of the motions of aromatic or alkyl groups in the side chain, depending on the samples, and that the motion of main chains of polymers 1 – 3 with α-helical conformation does not occur on the NMR time scale at least up to 160°C. The degree of the mobility of the alkyl chain in the side chain of 1 – 3 depends on their length above T_m.     

Side Chain Influence on the Mechanical Properties and Water Uptake of Confined Comb‐Shaped Cationic Polymer Thin Films

Water uptake is measured for ≈100 nm and ≈60 μm thick quaternized comb‐shaped poly(2,6‐dimethyl‐1,4‐phenylene oxide) (QA‐PPO) polymers with 0, 6, 10, and 16 carbon alkyl side chains to probe the influence of thin film confinement. The thin film modulus is measured to probe the effect of side chain length on the thin film modulus and the ensuing water uptake. Increasing the alkyl side chain length results in increased modulus, decreased swelling strain, and decreased water uptake due to the lengthening of the n‐alkyl side chains. Confinement effects on the comb‐shaped QA‐PPO water uptake are expressed through increased water uptake in the thin film compared to the bulk membrane. The thin films also exhibit a different water sorption mechanism consistent with two types of water compared to the bulk membranes that exhibit a single type of water sorption.

     

X-ray structural studies of various octyl-substituted polythiophenes

The structure of poly(octylthiophene)s and alternating octylthiophene-thiophene-copolymers with a varying degree of intrachain regularity was studied by means of X-ray diffraction and optical absorption measurements. Although these polymers show a varying degree of crystallinity, evidence is found that they all tend to pack as relatively straight parallel chains. The lateral packing distance depends strongly on the regularity and the relative amount of alkyl side chains. Generally poly(thiophene)s with a larger relative amount and higher stereoregularity of the octyl side chains tend to pack more ordered. On the other hand, a large conjugation length (high degree of chain planarity), as revealed by optical absorption spectroscopy, and a crystalline packing of the polymer chains are not found to be interdependent. For the polymer with highest degree of crystallinity two surprisingly different crystalline structures were found for the two versions with different regularity, viz. poly(3-octylthiophene) and poly(3,3′-dioctyl-2,2′ bithiophene). For the latter we find evidence of a polymer chain twist between adjacent head-to-head coupled thiophene rings, and we propose a structural model for its crystalline packing. Our new model can explain previously measured differences in spectroscopic and transport-related properties for these two stoichiometrically identical polymers.