N-alkyl Side Chains Research Articles

Synthesis of Piperazinephen-1-ylethylamines as Potent and Selective Antagonists of the Human Melanocortin-4 Receptor

A series of piperazinephen-1-ylehtylamines were synthesized and evaluated for their biological activity at the human melanocortin-4 receptor. This modification reduced the size and flexibility of the N-alkyl side-chain of some earlier lead compounds, while maintained the low nanomolar binding affinity. Keywords: Melanocortin, antagonist, piperazinephenylamine, synthesis

Synthesis and characterization of film-forming poly(urethaneimide) cationomers containing quaternary ammonium groups

In a recent work, we have described an original family of poly(urethaneimides) containing tertiary amine groups from a polytetramethylene oxide diol (PTMO1000), N-methyldiethanolamine (MDEA), 4,4′-methylene-bis-phenylisocyanate (MDI) and 4,4′-hexafluoroisopropylidene-bis-phthalic anhydride (6FDA). This paper reports their quaternization with various alkylating agents to give the cationic quaternary ammonium groups. An optimization of the experimental conditions led to three new families of PUI cationomers with a good structural control and high quaternization degrees. These polymers differed in the number of their cationic groups (0<x≤0.7equiv.), the type of their counter-ions X− (methyl sulfate, tosylate, triflate, chloride, bromide, iodide) and their steric hindrance by the length of their n-alkyl side chain (C1–C6). Complementary NMR techniques, including HSQC and COSY two-dimensional NMR, enabled to characterize the control of the polymer structure and to determine quantitatively the quaternization degree of the PUI cationomers. Properties in solution (solubility and viscosity) and in the solid state (film-forming ability and density) were then examined in relation with the membrane separation application targeted for these new PUI cationomers.

Silver(I) N-Heterocyclic Carbenes with Long N-Alkyl Chains

Silver(I) N-heterocyclic carbene complexes (Ag(I)−NHCs) with long N-alkyl side chains formulated as (a) ion pairs, (b) halide-bridged neutral complexes, and (c) disilver tetrahalide anion bridged tetranuclear complexes were obtained by the reaction of benzimidazolium and imidazolium halide salts with Ag2O. Interestingly, when excess Ag2O was used, Ag nanoparticles were formed along with Ag(I)−NHCs. Crystal structures of Ag(I)−NHC complexes including both long and short N-alkyl chains were determined. The diversity of the solid-state structures depended on the halide ions, chain length, carbene cores, and crystallization conditions. The Ag(I)−NHCs of long alkyl chains did not show liquid crystal properties but did so when mixed with their corresponding imidazolium salts. These organic−inorganic hybrids were good single-source precursors for silver nanomaterials.

Synthesis of a Novel Chiral Squaraine Dye and Its Unique Aggregation Behavior in Solution and in Self‐Assembled Monolayers

Squaraine dyes have been studied extensively in the last few decades due to their advantageous optical properties that enable applications including imaging technologies and photoconducting devices, photovoltaics and non-linear optics, and sensing and photodynamic therapy. The isolated squaraine chromophore exhibits an intense and narrow absorption band in the long-wavelength range of the visible spectrum. Furthermore, the dye displays a pronounced tendency to form Hand J-type aggregates in different homogenous and heterogeneous media. In order to harness the beneficial opto-electronic characteristics of this unique class of chromophores for the construction of improved devices, control over their aggregation behavior is absolutely critical since it influences electronand energy-transport processes. Since chirality has been used as a guiding element to direct self-assembly processes, we investigated the influence of introducing a chiral bias to squaraine aggregation. Here, we present our initial results on the synthesis of a novel chiral squaraine dye and the investigation of its unique aggregation behavior in aqueous solution and on a solid substrate. Condensation of electron-rich aromatics with squaric acid in an azeotropic solvent mixture such as toluene/1-butanol provides a simple access to squaraines. Highly activated N,N-dialkylated 3,5-dihydroxyanilines are conveniently generated in situ by condensation of secondary amines with 1,3,5trihydroxybenzene (phloroglucinol), and subsequent reaction with squaric acid in the same pot leads to formation of bis(4-dialkylamino-2,6-dihydroxyphenyl)squaraines, which offer the advantages of much higher intrinsic fluorescence quantum yields, increased relative chemical stability, and stronger aggregation tendency than their non-hydroxylated analogues. Such a two-step, one-pot procedure can also be applied to the synthesis of polysquaraines, useful for cation sensing. Since secondary amines are mandatory to avoid squaramide formation, the natural amino acid L-proline is an obvious choice for a chiral building block. Preliminary experiments indicated that an ester linkage to the side chain was not stable during the squaraine condensation step due to transesterification and therefore, initial reduction to L-prolinol, and attachment of the side chains via ether linkages was pursued. Our route (Scheme 1) involves preparation of the alkylated L-prolinol followed by the two-step, one-pot procedure to access chiral squaraine 1 carrying nonpolar, linear n-alkyl side chains. This synthesis takes advantage of the enhanced nucleophilicity of aromatics possessing cyclic, i.e., pyrrolidino, rather than acyclic secondary amine substituents. Compound 1 showed a characteristic sharp (full width at half maximum, FWHM ∼ 20 nm) and intense (molar absorption e ∼ 300 000 M cm) absorption band centered around 640 nm that is indicative of the presence of mostly monomeric, i.e., non-aggregated, squaraine chromophores. Significant variation of solvent polarity, from cyclohexane to chloroform to acetonitrile, led to negligible bathochromic shifts (637→ 638→ 642 nm). Emission measurements revealed sharp fluorescence spectra with relatively small Stokes shifts (Dkmax ∼ 17 nm) and high fluorescence quantum yields (Uf ∼ 0.85), illustrating the rigidified character of the chromophore due to intramolecular hydrogen bonding. Due to the hydrophobic nature of the squaraine moiety and the unique quality of water to promote aggregation as a consequence of the operating hydrophobic effect, solvent titration experiments involving a systematic variation of the water content in acetonitrile solution were carried out (Fig. 1). The UV-vis spectra (Fig. 1, top) clearly show that aggregation is induced above a critical water concentration of ∼ 10 vol.-%. Above this threshold value, the monomer band initially rapidly decreases, and, at ∼ 18 vol.-% water content, aggregate bands start to emerge. At 30 vol.-% water content, the monomer band is greatly reduced to ∼ 10 % of its initial intensity, and both blueand red-shifted bands at 555 and 761 nm, respectively, were observed. The corresponding C O M M U N IC A IO N S

Phase Transition and Conformational Variation of N-Alkylated Branched Poly(ethyleneimine) Comblike Polymer

A series of branched poly(ethyleneimine) (PEI) derived polymers with different lengths of n-alkyl side chains, denoted as PEI(n)Cs (n = 12, 14, 16, 18, 20, number of carbon atoms in alkyl side group), have been prepared by a N-alkylation method, and systematically characterized by differential scanning calorimertry (DSC) and wide-angle X-ray diffraction (WAXD) as well as Fourier transform infrared spectroscopy (FTIR). The side chains grafted on these comblike polymers are long enough to form crystalline phase composed of paraffin-like crystallites. The crystallization of the side chains forces the branched poly(ethyleneimine) molecules to pack into layered structure, between which the crystallites are located. The melting temperatures of the side chain crystallites increase from −12.36 to +51.49 °C with increasing the length of the side chains from n = 12 to n = 20, which are a little bit lower than the corresponding pristine n-alkanes. PEI18C was taken as an example in this work for the investigation of phase transition and conformational variation of the side chains with temperature changing. With temperature increasing, the crystalline phase of the side chains undergoes a phase transition process from orthorhombic to hexagonal form and then from hexagonal to melt state. Similarly, increasing temperature leads to the regular trans sequences of the orthorhombic phase transforming to conformationally disordered trans sequences of the hexagonal phase and then to the gauche conformational state (melt state) at higher temperature. The above-described experimental phenomena for both crystalline transition and conformational structure variation are reversible as temperature decreases. Combining the transformations of the crystalline phase and the conformational structure, it is confirmed that hexagonal phase exists as an intermediate phase in the process of temperature variation.

Layered structure and Xe sorption and diffusion properties of low-density liquid-crystalline polyesters with n-alkyl side chains

Four low-density liquid-crystalline polyesters with n-alkyl side chains, B–C n ( n is a carbon number of n-alkyl group), were synthesized from the 1,4-di-( n-alkyl ester) of 1,2,4,5-benzenetetracarboxylic acid and 4,4′-biphenol, to clarify the effect of side chain length on higher ordered structure in the solid state and gas sorption and diffusion properties of these polyesters. All the B–C n ( n=6, 10, 14, 18) samples behaved as a thermotropic liquid crystal and formed a layered structure composed of alternating rigid aromatic main chain layers and flexible n-alkyl side chain layers. In the crystal phase, the distance between the rigid aromatic main chain layers, namely the layer spacing, linearly increased with n, indicating that the conformational feature of n-alkyl side chains was trans-rich. This finding was supported from the 13C NMR chemical shift values of methylene carbons in B–C14 and B–C18. Xe sorption of B–C n was restricted to the side chain layer, which is almost a liquid-like environment, and these sorption isotherms obeyed Henry's law. The density of side chain layers was estimated from experimental values of layer spacing and density, under some speculate assumptions, but that determined individually by 129Xe NMR spectroscopy was coincidence. The estimated density of side chain layers became higher with increasing n, as well as n-alkane liquid, and closed to that of the polyethylene in rubbery state. Xe solubility coefficient corrected with the estimated side chain layer's density decreased with increasing n. On the other hand, the diffusion coefficient of Xe in B–C n increased with n, and this was supported from the NMR spectral width of the 129Xe in B–C n. These results also indicate that the main chain layers of B–C n were very dense and could not sorb Xe.

Structural study on rodlike aromatic polyimides derived by solid-state thermal and chemical imidization of poly(amic n-dodecyl ester)

Para-linked aromatic poly(amic n-dodecyl ester) (PA-12), in which long n-alkyl side chains are attached on rodlike aromatic polyamide, was prepared by polycondensation of 2,5-bis(1-dodecyloxycarbonyl)terephthaloyl chloride and 1,4-diaminobenzene. In as-cast PA-12 film, formation of layered structure with alternating main-chain-segregated and side-chain-segregated layers is suggested by X-ray diffraction measurement. PA-12 is a precursor of rodlike aromatic polyimide, poly(1,4-phenylene pyromellitimide) (PPPI). Solid-state thermal imidization and base-catalyzed chemical imidization of PA-12 film has been investigated. Although the layered structure of PA-12 was destroyed during the imidization reaction, the obtained PPPI exhibited lower density than densely packed PPPI. This result may indicate that the side chain-segregated domain was transformed to a cavity surrounded by PPPI after the imidization reaction. Chemical imidization in pyridine/toluene mixture and subsequent heating at 200 °C was the optimum condition to obtain low density PPPI.

Diffusion process of methane molecules in cylindrical channel cavities of oriented polyester with long n-alkyl side chains as studied by field-gradient 1H NMR spectroscopy

Pulse field-gradient spin-echo 1H NMR experiments on methane molecules charged into cylindrical channel cavities in the hexagonal columnar phase of oriented poly( p-biphenylene terephthalate) with long n-dodecyl side chains have been carried out in order to elucidate diffusion process of the methane molecules in the directions parallel and perpendicular to the cylindrical channel cavity axis. From these experimental results, it is found that methane molecules in the cylindrical channel cavities are not only diffusing in the direction parallel to the cylindrical channel cavity axis, but are diffusing through the wall of the cylindrical channel cavity.

Cellular effects of deoxynojirimycin analogues: uptake, retention and inhibition of glycosphingolipid biosynthesis.

Deoxynojirimycin (DNJ) analogues are inhibitors of ceramide glucosyltransferase (CGT), which catalyses the first step in the glucosphingolipid (GSL) biosynthetic pathway. We have synthesized a series of DNJ analogues to study the contribution of N-alk(en)yl side chains (C4, C9 or C18) to the behaviour of these analogues in cultured HL60 cells. When cells were treated for 16 h at non-cytotoxic concentrations of inhibitor, a 40-50% decrease in GSL levels was measured by HPLC analysis of GSL-derived oligosaccharides following ceramide glycanase digestion of GSL and 2-aminobenzamide labelling of the released oligosaccharides. Using a novel technique for short-term [14C]galactose labelling of cellular GSL, we used compound inhibition of GSL biosynthesis as a marker for compound uptake into cells. Surprisingly, the uptake of all three of the DNJ analogues was extremely rapid and was not dependent upon the length of the N-alk(en)yl moiety. Compound uptake occurred in less than 1 min, as shown by the complete inhibition of GSL labelling in cells treated with all the DNJ analogues. Greatly increased cellular retention of N-cis-13-octadecenyl-DNJ was observed relative to the shorter-chain compounds, N-butyl-DNJ and N-nonyl-DNJ, as indicated by complete inhibition of CGT 24 h after removal of inhibitor from the culture medium. The present study further characterizes the properties of N-alk(en)ylated DNJs, and demonstrates that increasing the length of the side chain is a simple way of improving imino sugar retention and therefore inhibitory efficacy for CGT in cultured cells.

Effects of bisphosphonates on the growth of Entamoeba histolytica and Plasmodium species in vitro and in vivo.

The effects of a series of 102 bisphosphonates on the inhibition of growth of Entamoeba histolytica and Plasmodium falciparum in vitro have been determined, and selected compounds were further investigated for their in vivo activity. Forty-seven compounds tested were active (IC(50) < 200 microM) versus E. histolytica growth in vitro. The most active compounds (IC(50) approximately 4-9 microM) were nitrogen-containing bisphosphonates with relatively large aromatic side chains. Simple n-alkyl-1-hydroxy-1,1-bisphosphonates, known inhibitors of the enzyme farnesylpyrophosphate (FPP) synthase, were also active, with optimal activity being found with C9-C10 side chains. However, numerous other nitrogen-containing bisphosphonates known to be potent FPP synthase inhibitors, such as risedronate or pamidronate, had little or no activity. Several pyridine-derived bisphosphonates were quite active (IC(50) approximately 10-20 microM), and this activity was shown to correlate with the basicity of the aromatic group, with activity decreasing with increasing pK(a) values. The activities of all compounds were tested versus a human nasopharyngeal carcinoma (KB) cell line to enable an estimate of the therapeutic index (TI). Five bisphosphonates were selected and then screened for their ability to delay the development of amebic liver abscess formation in an E. histolytica infected hamster model. Two compounds were found to decrease liver abscess formation at 10 mg/kg ip with little or no effect on normal liver mass. With P. falciparum, 35 compounds had IC(50) values <200 microM in an in vitro assay. The most active compounds were also simple n-alkyl-1-hydroxy-1,1-bisphosphonates, having IC(50) values around 1 microM. Five compounds were again selected for in vivo investigation in a Plasmodium berghei ANKA BALB/c mouse suppressive test. The most active compound, a C9 n-alkyl side chain containing bisphosphonate, caused an 80% reduction in parasitemia with no overt toxicity. Taken together, these results show that bisphosphonates appear to be useful lead compounds for the development of novel antiamebic and antimalarial drugs.

Lithium diisopropylamide-mediated lithiations of imines: insights into highly structure-dependent rates and selectivities.

Lithium diisopropylamide-mediated lithiations of N-alkyl ketimines derived from cyclohexanones reveal that simple substitutions on the N-alkyl side chain and the 2-position of the cyclohexyl moiety afford a 60,000-fold range of rates. Detailed rate studies implicate monosolvated monomers at the rate-limiting transition structures in all instances. Comparisons of experimentally derived regioselectivities and rates, taken in conjunction with density functional theory computational studies, reveal a number of factors that influence reactivities including: (a) axial versus equatorial disposition of the proton on the cyclohexane ring, (b) syn versus anti orientation of the lithiation relative to the N-alkyl group, (c) the presence or absence of a potentially chelating methoxy moiety on the N-alkyl group, (d) the presence of a 2-methyl substituent at the geminal or distal alpha-carbon, and (e) branching in the N-alkyl group. The isolated contributions are not large, yet they display a strong and predictable additivity leading to a kinetic resolution of imines derived from racemic 2-methylcyclohexanone.

Charge-Induced Microphase Separation in Polyelectrolyte Hydrogels with Associating Hydrophobic Side Chains: Small-Angle Neutron Scattering Study

The structure of amphiphilic hydrogels of copolymers of acrylic acid and n-alkylacrylate swollen by D2O was studied by small-angle neutron scattering (SANS). For most of the uncharged gels, a scattering peak is observed. It is attributed to the correlation between hydrophobic domains formed by self-assembled n-alkyl side chains. From the SANS data, the aggregation number of the hydrophobic domains was derived. It increases with increasing length of hydrophobic groups and also as a result of absorption of hydrophobic additives that are solubilized inside hydrophobic domains. The most important observation of this work consists of the fact that the introduction of charged groups into the gel leads to microphase separation with the formation of hydrophobic regions including several densely packed hydrophobic domains that alternate with hydrophilic regions swollen by water where most of the charged repeat units and counterions are located. The size of the hydrophobic regions decreases with increasing charge c...

Structure and dynamics of rodlike polyester with long n-alkyl side chains over a wide range of temperatures by solid state 13C NMR

Solid state 13C NMR experiments on poly( p-biphenylene terephthalate) with long n-dodecyl side chains have been carried out over a wide range of temperatures, in order to elucidate conformational and dynamical behavior of the polyester in the crystalline state and thermotropic liquid crystalline state. From these experimental results, it is found that at temperatures from room temperature to 80 °C the n-alkyl side chains take both of the immobile and the mobile regions, and at temperatures above 120 °C take only the mobile region. In the immobile region the n-alkyl side chains are in the all-trans zigzag conformation and in the mobile state are undergoing fast exchange between the trans and gauche conformations. On the other hand, the terephthalate moiety of the main chain undergoes rotational motion after the melt of n-alkyl side chains as the temperature is increased.

Correlation between sonochemistry of surfactant solutions and human leukemia cell killing by ultrasound and porphyrins.

The synergistic effect of ultrasound and drugs on cells is known as sonodynamic therapy. The use of sonodynamic therapy for the potential clinical treatment of certain tumors is promising, however, the mechanism of sonodynamic therapy could be due to either sonomechanical and/or sonochemical effects on the cells. The aim of the current study is to determine the importance of the sonochemical mechanism for sonodynamic therapy. Sonochemical effects arise from the formation of radical species following collapse of cavitation bubbles. The synergistic effect of ultrasound (47 kHz) and analogues of a gallium-porphyrin derivative (ATX-70) on cytolysis of Human leukemia cells (HL-525 and HL-60) suspended in a cell culture medium were studied. Organic surfactants preferentially accumulate and subsequently decompose at the gas/solution interface of cavitation bubbles, producing secondary radicals that can diffuse to the bulk solution. The gallium porphyrin analogues used in the current study possess two n-alkyl side chains (ATX-C(x), where x = number of carbon atoms, ranging from x = 2 to x = 12). By varying the n-alkyl chain length, thereby modifying the surfactant properties of the ATX-C(x) derivatives, cell killing in relation to the accumulation of ATX-C(x) derivatives at the gas/solution interface of cavitation bubbles was determined. Following sonolysis in the presence of ATX-C(x), a strong correlation for the yield of carbon-centered radicals and cell killing was observed. These results support the hypothesis that a sonochemical mechanism is responsible for the synergistic effect of ultrasound and ATX-C(x) on HL-525 and HL-60 cells.

Intramolecular Photoreaction of Thio-barbiturates with an Alkenyl or a Benzyl Group in Their N-Alkyl Side Chain. Regio-selective Synthesis of Ring-fused Pyrimidine Derivatives through Photocyclization of Mono- and Dithiobarbiturates

Upon irradiation, thiobarbiturates with an alkenyl (4,5) or a benzyl (14,15,21) group in their N-alkyl side chain give bi- and tri-cyclic fused pyrirnidine derivatives through regioselective [2+2] photocycloaddition or Norrish type II reaction, respectively.

CRHR 1 Receptor binding and lipophilicity of pyrrolopyrimidines, potential nonpeptide corticotropin-releasing hormone type 1 receptor antagonists

A series of compounds related to N-butyl- N-ethyl[2,5,6-trimethyl-7-(2,4,6-trimethylphenyl)pyrrolo[2,3- d]pyrimidin-4-yl]amine ( 1, antalarmin, Fig. 1) have been prepared and evaluated for their CRHR 1 binding affinity as the initial step in the development of selective high affinity hydrophilic nonpeptide corticotropin-releasing hormone type 1 receptor (CRHR 1) antagonists. Calculated log P (Clog P) values were used to evaluate the rank order of hydrophilicity for these analogues. Introducing oxygenated functionalities (δ-hydroxy or bis-β-ethereal) into 1 gave more hydrophilic compounds, which had good affinity for the receptor. Introducing an amino group or shortening the alkyl side chain was detrimental to CRHR 1 affinity. The alcohol 4-[ethyl[2,5,6-trimethyl-7-(2,4,6-trimethylphenyl)pyrrolo[2,3- d]pyrimidin-4-yl]amino]butan-1-ol ( 3), bearing a terminal hydroxyl group on an N-alkyl side-chain, showed the highest CRHR 1 binding affinity among these compounds ( K i=0.68 nM), and is one of the highest affinity CRHR 1 ligands known. Compounds 3– 5, and 8, which are likely to be less lipophilic than 1, have high CRHR 1 affinity and may be valuable probes to further study the CRH system.

Structure and mobility of a series of poly(alkyl l-glutamate)s studied by VT 13C CPMAS NMR spectroscopy

VT CPMAS NMR measurements were carried out for a series of poly(alkyl l-glutamate)s (PALG) which have n-alkyl side chains with carbon numbers ranging from 2 to 12 in order to investigate the structure and mobility of the main and the side chains. From the temperature dependencies of the peak intensities for the PALGs, the relative mobilities of the main and side chains are discussed. For PG-2 and PG-4, the molecular motions of both the main and side chains are not very fast. From the amount ratio between the main and side chains, the main chain dominates the entire mobility of the polymer. As the side chain length increases, the side chain motion is drastically activated by a temperature change. In addition, the main chain motion is induced by the side chain motion. For PALGs with long alkyl side chains, the mobilities of the polymers are governed by the structure and mobility of the side chain.

Supramolecular staircase via self-assembly of disklike molecules at the solid-liquid interface.

A series of soluble hexabenzocoronene (HBC) derivatives with pendant optically active (S)-3,7-dimethyloctanyl and (R,S)-3,7-dimethyloctanyl (mixture of stereoisomers) hydrocarbon side chains with and without a phenylene spacer were assembled into differently ordered arrays at the interface between a solution and the basal plane of highly oriented pyrolytic graphite (HOPG). Molecularly resolved scanning tunneling microscopy (STM) images revealed that all derivatives self-assemble into oriented crystals in quasi-two dimensions. However, while for the alkyl-substituted HBCs (1,4) all of the single aromatic cores within a monolayer exhibit the same contrast in the STM, the single aromatic cores with a phenylene group between the alkyl side chains and the aromatic core (2a,2b,3) exhibit different contrasts within a monolayer. For the disks carrying racemic branched or n-alkyl side chains (2b,3) a random distribution of the two different contrasts within the 2D-crystal is observed, while the optically active phenylene-alkyl-substituted HBC (2a) exhibits a periodical distribution of three contrasts within the monolayer. We attribute the different contrasts of the aromatic cores in the presence of the phenylene groups to a loss of the planarity of the whole molecule and different conformations, which allow the conjugated disks to attain different equilibrium positions above the surface of HOPG. In the case of the optically active side chains a regular superstructure with three distinctly different positions such as in a staircase is attained. The self-assembly processes are governed by the interplay of intramolecular as well as intermolecular and interfacial interactions. In the present case, the interactions may induce both the molecules to acquire well distinct positions along the z axis and to adopt different conformations. The reported results open new avenues of exploration. For instance, the different couplings of conjugated molecules with the substrate at different separations can be investigated by means of scanning tunneling spectroscopy (STS). Furthermore, experiments on the STM tip-induced switching of single molecules embedded in a monolayer appear feasible.

Structure property relationships in linear and cross-linked poly(imidonorbornenes) prepared using ring opening metathesis polymerisation (ROMP)

The production and properties of a new family of materials synthesised via ring opening metathesis polymerisation (ROMP) is described. The monomers offer potential alternatives to dicyclopentadiene (DCPD) for either reaction injection moulding (RIM) or resin transfer moulding (RTM) use and provide new materials with an extended range of properties vis-à-vis poly(DCPD). Improvements include lower monomer odour together with control of both the reaction rate and the crosslinking reaction. A series of monofunctional imidonorbornene monomers, with different N-alkyl side chains, were polymerised to give a range of linear polymers, and, by copolymerisation with difunctional monomers with different N, N′-alkylene spacer lengths, a range of crosslinked materials. Processing conditions were established which gave over 95% conversion of the monomer for the linear materials, and over 95% gel fraction for the crosslinked materials. For the crosslinked materials, a value of the monomer:initiator ratio was established which gave homogeneously cured materials. The glass transition temperature ( T g) of the linear polymers was found to depend on the length of the alkyl side chain, while a sub T g, β relaxation was observed, the position of which was independent of the side chain length. For the crosslinked polymers, the molecular weight between crosslinks was found to be lower than expected at low percentage loading of the crosslinking unit, and this was attributed to the contribution of physical crosslinks. At higher percentage loading of the crosslinking unit, the molecular weight between crosslinks was higher than expected, suggesting that under these conditions not all the crosslinking units were fully bound into the network, i.e. bound at both ends. Mechanical properties of the various materials were measured using the three-point bend geometry. Of particular interest were the high values of yield strength and toughness of the crosslinked polymers, which are comparable to known ‘high toughness’ materials, such as polycarbonate.

Wettability of Maleimide Copolymer Films: Effect of the Chain Length of n-Alkyl Side Groups on the Solid Surface Tension

We report bulk and surface properties of maleimide copolymers with two different backbones, poly(propene-alt-N-(n-alkyl)maleimides) (PAlkMI) and poly(styrene-alt-N-(n-alkyl) maleimides) (SAlkMI), with different lengths of n-alkyl side chains (methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, and dodecyl). The contact angle and solid surface tension results suggest that, for the longer side chains, the surface properties are dominated by the side chains. Indeed, the surface tension of the two types of copolymers with length of the side chain above C = 6 are essentially equal, indicating complete shielding of the polar backbone chain. For the two copolymers containing dodecyl side chains, the solid surface tension is similar to that of solid surfaces consisting exclusively of CH3 groups. Apparently, these side groups are long enough to allow arrangement in the configuration of the lowest surface free energy possible for alkyl chains. For the short side chain copolymers the styrene compounds are more hydro...