Controlled stereochemistry of polyamides derived from cis/trans‐1,4‐cyclohexanedicarboxylic acid

A series of copolyamides 12.y was synthesized either with y = 6, or 1,4‐cyclohexanedicarboxylic acid (1,4‐CHDA) residue, or a mixture of both. The influence of the synthetic route of 1,4‐CHDA containing polyamides on the obtained cis–trans ratio of the incorporated 1,4‐CHDA was investigated. The use of acid chlorides provided a synthetic route with full control of the cis–trans ratio of the 1,4‐CHDA residue during synthesis, whereas synthesis at elevated pressure and temperature caused isomerization. The content and cis–trans ratio of 1,4‐CHDA in the copolyamides were determined by solution ¹³C NMR spectroscopy. Increasing the degree of partial substitution of the adipic acid by 1,4‐CHDA resulted in an increase in T_m, even for low molar precentages of 1,4‐CHDA. This phenomenon points to isomorphous crystallization of both the 12.6 and 12.CHDA repeating units. The mps of the synthesized polyamides were independent of the initial cis–trans ratio of 1,4‐CHDA, provided that the samples were annealed at 300 °C before DSC analysis. The polyamides exhibited a different melting pattern depending on the 1,4‐CHDA content. At a low a 1,4‐CHDA content a net exothermic recrystallization occurred during melting, whereas at higher contents of 1,4‐CHDA this recrystallization occurs to a lesser extent, and two separate melting areas are observed. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 833–840, 2001     

Cocrystallization phenomena in piperazine‐based copolyamides as examined by differential scanning calorimetry,wide‐angle X‐ray diffraction,and solid‐state NMR

Copolyamides 2.14/piperazine.14 with variable built‐in ratios of 1,2‐ethylenediamine (1,2‐EDA) and piperazine (pip) were synthesized by solution polycondensation. The built‐in ratio of both diamine comonomers was determined with solution ¹³C NMR analysis. The gradual replacement of 1,2‐EDA units by cycloaliphatic pip units in polyamide 2.14 resulted in a progressively decreased melting (T_m) and crystallization temperature of the obtained copolyamides. Apparently, the T_m raising effect of the incorporation of rigid cycloaliphatic moieties is overruled by the simultaneous T_m reduction caused by a decreasing hydrogen‐bond density. Indications for cocrystallization of 2.14 and pip.14 repeating units were obtained by the thermal analysis of copolyamides 2.14/pip.14 and of a blend of both homopolyamides. A preliminary wide‐angle X‐ray diffraction study pointed to the same conclusion. Solid‐state NMR spectroscopy was used to investigate the influence of the composition on the percentage of the rigid phase of the copolyamides and delivered additional indications for cocrystallization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2082–2094, 2003     

Poly(1,4‐cyclohexylenedimethylene 1,4‐cyclohexanedicarboxylate): Influence of stereochemistry of 1,4‐cyclohexylene units on the thermal properties

A series of poly(1,4‐cyclohexylenedimethylene 1,4‐cyclohexanedicarboxylate) (PCCD) samples, characterized by different cis/trans ratio of the 1,4‐cyclohexanedicarbonyl unit, have been synthesized and analyzed by thermogravimetry (TGA), calorimetry (DSC), and X‐ray diffraction (WAXD). The thermal stability results are good and are not affected by the stereochemistry of the 1,4‐cyclohexylene units. On the other hand, the thermal transitions are notably influenced by the cis/trans content. With the increment of the trans content the polymer changes from completely amorphous to semicrystalline material. T_g, T_m, and crystallinity increase. These results suggest that the trans configuration induces a better chain packing and higher symmetry, improving the crystallizability of the samples. The effect of the molecular structure on the thermal properties is analyzed by using a statistical approach. From the effective correlations found between stereochemistry of the C₆ rings and transition temperatures it is possible to extrapolate that the configuration of 1,4‐cyclohexylene ring deriving from 1,4‐cyclohexanedicarboxylic acid or dimethyl 1,4‐cyclohexanedicarboxylate results to be the main element responsible for the thermal properties. This is due to the high rigidity of the 1,4‐cyclohexanedicarbonyl unit with respect to 1,4‐cyclohexanedimethyleneoxy unit, deriving from the diol. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 619–630, 2008     

Polyamides of 2,5-bis(amino methyl) 1,4-dioxane and dicarboxylic acids

Novel polyamides of 2,5-bis(amino methyl) 1,4-dioxane (cis/trans-BAMD) with adipic/sebacic acids and of 2,5-bis(carboxy methyl)/2,5-bis(carboxy) 1,4-dioxane with 1,6-hexane diamine have been prepared. Because of the slightly higher conformational flexibility of the 1,4-dioxane ring in comparison with that of the cyclohexane ring, the BAMD polyamides have lower T_g and T_m than the corresponding 1,4-bis(amino methyl) cyclohexane (BAMC) polyamides. The symmetry of the trans-dioxane moiety permits high crystallinity in the trans-BAMD polymers. The crystallinity T_g and T_m of the trans polymers are decreased with the incorporation of the cis-dioxane moiety which lacks a plane of symmetry. Because of the hydrophilic nature of the dioxane ring, t-BAMD-6 has good moisture-regain properties, yet is melt processable (T_m = 292°C).     

Thermodynamic and Mechanistic Insights into Translesion DNA Synthesis Catalyzed by Y‐Family DNA Polymerase Across a Bulky Double‐Base Lesion of an Antitumor Platinum Drug

To determine how the Y‐family translesion DNA polymerase η (Polη) processes lesions remains fundamental to understanding the molecular origins of the mutagenic translesion bypass. We utilized model systems employing a DNA double‐base lesion derived from 1,2‐GG intrastrand cross‐links of a new antitumor Pt^II complex containing a bulky carrier ligand, namely [PtCl₂(cis‐1,4‐dach)] (DACH=diaminocyclohexane). The catalytic efficiency of Polη for the insertion of correct dCTP, with respect to the other incorrect nucleotides, opposite the 1,2‐GG cross‐link was markedly reduced by the DACH carrier ligand. This reduced efficiency of Polη to incorporate the correct dCTP could be due to a more extensive DNA unstacking and deformation of the minor groove induced in the DNA by the cross‐link of bulky [PtCl₂(cis‐1,4‐dach)]. The major products of the bypass of this double‐base lesion produced by [PtCl₂(cis‐1,4‐dach)] by Polη resulted from misincorporation of dATP opposite the platinated G residues. The results of the present work support the thesis that this misincorporation could be due to sterical effects of the bulkier 1,4‐DACH ligand hindering the formation of the Polη–DNA–incoming nucleotide complex. Calorimetric analysis suggested that thermodynamic factors may contribute to the forces that governed enhanced incorporation of the incorrect dATP by Polη as well.     

Gas permeability and selectivity of hexafluoroisopropylidene aromatic isophthalic copolyamides

The synthesis, thermal, and gas transport properties of poly(hexafluoroisopropylidene isophthalamide), HFA/ISO homopolymer, and HFA/TERT‐co‐HFA/ISO copolyamides with different poly(hexafluoroisopropilydene‐5‐t‐butylisophthalamide), HFA/TERT, ratios are reported. The results indicate that the glass transition temperatures of the copolyamides increase as the concentration of HFA/TERT in the polyamide increases. The gas permeability coefficients in the polyamides and copolyamides are independent of pressure or decrease slightly particularly with CO₂, N₂, and CH₄. It was seen that HFA/TERT is 2–6 times more permeable than HFA/ISO, depending on the gas being considered. This was assigned to the presence of the bulky lateral substituent, t‐butyl group in HFA/TERT and HFA/TERT‐co‐HFA/ISO copolyamides. This substituent increases fractional free‐volume, as expected. Therefore, the gas permeability and diffusion coefficients generally increase with increasing fractional free‐volume. The experimental results for the gas permeability and permselectivity for the copolyamides was well represented by a logarithmic mixing rule of the homopolyamides permeability coefficients and their volume fraction. The selectivity of gas pairs, such as O₂/N₂, CO₂/CH₄, and N₂/CH₄ decreased slightly with the addition of HFA/TERT. The temperature dependence of permeability for homopolyamides and copolyamides can be described by an Arrhenius type equation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2625–2638, 2005     

Preparation and properties of new random and block copolyamides derived from 1,3-bis(3-aminopropyl)tetramethyldisiloxane,aromatic diamines,and isophthaloyl chloride

Random and block disiloxane-containing copolyamides were prepared through one- and two-step procedures, respectively, by the low temperature solution polycondensation in chloroform containing triethylamine hydrochloride starting from 1,3-bis(3-aminopropyl)tetramethyldisiloxane, an aromatic diamine [3,4'-diaminodiphenyl ether (ODA) or m-phenylenediamine], and isophthaloyl chloride. The random copolyamides exhibited composition-dependent single glass transition temperature (T_g), and gave transparent and tough films by solution casting or hot pressing. The ODA-based block copolyamides had two T_g's, and the solvent-cast transparent films exhibited microphase separated morphology. The block copolymers gave better quality films than the single-phase random copolymers. © 1992 John Wiley & Sons, Inc.     

Thermal properties of polyamides containing 1,3–cyclohexane rings

The effect of the 1,3–cyclohexane rings in the chain backbone on thermal properties of polyamides, especially the glass-transition temperature, has been studied using polyamides based on 1,3–cyclohexanebis(methylamine). The increase in glass-transition temperature was far greater than that obtained with the analogous polymers containing m–benzene rings. However, the effects of 1,4–cyclohexane and p-benzene rings are nearly equal. Several possible causes for this difference are examined. It is concluded that restricted chain mobility due to steric hindrance of the cis-1,3–cyclohexane ring, the predominant isomer, is the most likely cause of the difference.     

Synthesis and properties of cyclic diester based aliphatic copolyesters

Melt polycondensation was used to prepare a systematic series of random and amorphous copolyesters using the following cycloaliphatic diesters: dimethyl‐1,4‐cyclohexane dicarboxylate (DMCD), dimethyl bicyclo[2.2.1]heptane‐1,4‐dicarboxylate (DMCD‐1), dimethyl bicyclo[2.2.2]octane‐1,4‐dicarboxylate (DMCD‐2), dimethyl bicyclo[3.2.2]nonane‐1,5‐dicarboxylate (DMCD‐3), 1,4‐dimethoxycarbonyl‐1,4‐dimethylcyclohexane (DMCD‐M) and the aliphatic diols: ethylene glycol (EG) and 1,4‐cyclohexane dimethanol (CHDM). The polymer compositions were determined by nuclear magnetic resonance (NMR) and the molecular weights were determined using size exclusion chromatography (SEC). The polyesters were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The copolyester based on DMCD‐2 was observed to have a higher glass transition temperature (T_g up to 115 °C) than the other copolyesters of this study. For poly[x(DMCD‐2)y(DMCD) 30(EG)70(CHDM)], T_g increases linearly with increase of DMCD‐2 mole content. DMA showed that all of the cycloaliphatic copolyesters have secondary relaxations, resulting from the conformational transitions of the cyclohexylene rings. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2162–2169, 2010     

Effect of the ortho Modification of Azobenzene on the Photoregulatory Efficiency of DNA Hybridization and the Thermal Stability of its cis Form

We synthesized various azobenzenes methylated at their ortho positions with respect to the azo bond for more effective photoregulation of DNA hybridization. Photoregulatory efficiency, evaluated from the change of T_m (ΔT_m) induced by trans–cis isomerization, was significantly improved for all ortho‐modified azobenzenes compared with non‐modified azobenzene due to the more stabilized trans form and the more destabilized cis form. Among the synthesized azobenzenes, 4‐carboxy‐2′,6′ ‐ dimethylazobenzene ( 2′,6′‐Me‐Azo ), in which two ortho positions of the distal benzene ring with respect to carboxyl group were methylated, exhibited the largest ΔT_m, whereas the newly synthesized 2,6‐Me‐Azo (4‐carboxy‐2,6‐dimethylazobenzene), which possesses two methyl groups on the two ortho positions of the other benzene ring, showed moderate improvement of ΔT_m. Both NMR spectroscopic analysis and computer modeling revealed that the two methyl groups on 2′,6′‐Me‐Azo were located near the imino protons of adjacent base pairs; these stabilized the DNA duplex by stacking interactions in the trans form and destabilized the DNA duplex by steric hindrance in the cis form. In addition, the thermal stability of cis‐ 2′,6′‐Me‐Azo was also greatly improved, but not that of cis‐ 2,6‐Me‐Azo . Solvent effects on the half‐life of the cis form demonstrated that cis‐to‐trans isomerization of all the modified azobenzenes proceeded through an inversion route. Improved thermal stability of 2′,6′‐Me‐Azo but not 2,6‐Me‐Azo in the cis form was attributed to the retardation of the inversion process due to steric hindrance between lone pair electrons of the π orbital of the nitrogen atom and the methyl group on the distal benzene ring.     

Influence of monofunctional reactants on the physical properties of dimer acid‐based polyamides

Dimer acid‐based polyamides were synthesized by condensation polymerization in the absence and presence of monofunctional reactants. Acetic acid, oleic acid and propyl amine were used as monofunctional reactants. The influences of the equivalent percentage (E%) and type of monofunctional reactant on the physical properties of dimer acid‐based polyamides such as glass transition temperature (T_g), melting point (T_m), heat of fusion (ΔH), degree of polymerization (DP), number average molecular weight (M_n), and kinematic viscosity were investigated. The molecular weight and viscosity of dimer acid‐based polyamides decreased with the increase in equivalent percentage of monofunctional reactant. Differential scanning calorimetry (DSC) studies showed that acetic acid and propyl amine had higher effect on the thermal properties of polyamides than that of oleic acid. In the case of polyamides prepared in the presence of acetic acid, the values of T_g, T_m, and ΔH of the polyamides increased remarkably with the increase in acetic acid content. On the contrary, propyl amine had a decreasing effect on the values of T_g, T_m, and ΔH of the polyamides. Incorporation of oleic acid into the polymer structure had no significant effect on the values of T_g and T_m of the dimer acid‐based polyamides. Copyright © 2006 John Wiley & Sons, Ltd.     

Cis/trans copolyamides of 1,4-bisaminomethylcyclohexane

Copolyamides prepared from cis- and trans-1,4-bisaminomethylcyclohexane with adipic, sebacic, and dodecanoic acids showed a decrease in melting point with increasing cis diamine content and increasing chain length of the diacid. Most unusual was the fact that the glass transition temperature of these copolymers were essentially independent of diamine isomer content. The existence of an intermediate conformation for some of the cyclohexane rings such as the “twistmer” is suggested to account for this discrepancy. The T_g, T_c, and T_m all decreased with increasing chain length of the diacid. The thermal stability as exemplified by the polysebacamides, was independent of diamine isomer content.     

Thermotropic copolyamides from polyethyleneglycol bis(4-carboxyphenyl)ethers with different oxyethylene units

Copolymerizations of polyethyleneglycol bis(4-carboxyphenyl)ethers (PEG_n) with different n values were found to significantly lower the anisotropic transition temperature (T_m) of the copolymers produced, and the thermotropic copolyamides of thermally more stable nematic phases were obtained. The effect was investigated in terms of PEG_m/PEG_n molar ratios, the number of oxyethylene units, and the even—odd character of the flexible segment. Several modes of copolymerization were carried out to investigate the effect of monomer (PEG_n sequence on T_m. By these copolymerizations thermally stable copolyamides even from p-phenylenic diamines such as methyl-p-phenylenediamine and p-phenylenediamine were obtained. © 1993 John Wiley & Sons, Inc.     

Solid‐state NMR studies of cis‐1,4‐polyisoprene crosslinked with dicumyl peroxide in the presence of triallyl cyanurate

The network of dicumyl peroxide (DCP)/triallyl cyanurate (TAC) crosslinked cis‐1,4‐polyisoprene was studied by solid‐state NMR techniques such as direct‐polarization (DP), cross‐polarization (CP), and proton T₂ experiments. Line broadening and cis/trans isomerization of mobile carbons were observed in the DP experiments. The information on rigid carbons of network structures was observed with the CP technique. Motional heterogeneity was examined by proton T₂ relaxation experiments. Decreases in long T₂ (T_2L) values from the mobile non‐network structures and short T₂ (T_2S) values from the rigid network structures were observed with an increase in peroxide or coagent concentration. The percentage of T_2S in T₂ relaxation, which is related to network density, was observed to increase with peroxide and coagent addition. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1417–1423, 2000     

Synthesis and Properties of Novel Aromatic Copolyamides Containing Phthalazinone Moiety

A series of novel aromatic copolyamides were synthesized by the direct polycondensation of 2‐(4‐carboxyphenyl)‐4‐[4‐(4‐carboxyphenoxyl)phenyl]‐phthalazinone (1), terephthalic acid (TPA), and four commercial diamines. The inherent viscosities of the polyamides were between 0.79～1.56 dL/g. Introduction of the non‐coplanar phthalazinone segments into the main chains remarkably decreased the crystallinity and improved the solubility of the copolyamides. When the percentage of 1 in the diacid monomers was above 50%, the copolymers were soluble in aprotic polar solvents, such as N‐methyl‐pyrrolidinone and N,N‐dimethylacetamide. The copolyamides showed high thermal properties associated with the glass transition temperatures in the range of 276～337°C and 10% wt loss temperatures in nitrogen over 496°C. Some polymer films cast from NMP solution had tensile strengths up to 123.4 MPa, initial moduli up to 2.10 GPa, and elongation at break values up to 9.6%.     

Photoinduced Reversible Solid‐to‐Liquid Transitions for Photoswitchable Materials

Heating and cooling can induce reversible solid‐to‐liquid transitions of matter. In contrast, athermal photochemical processes can induce reversible solid‐to‐liquid transitions of some newly developed azobenzene compounds. Azobenzene is photoswitchable. UV light induces trans‐to‐cis isomerization; visible light or heat induces cis‐to‐trans isomerization. Trans and cis isomers usually have different melting points (T_m) or glass transition temperatures (T_g). If T_m or T_g of an azobenzene compound in trans and cis forms are above and below room temperature, respectively, light may induce reversible solid‐to‐liquid transitions. In this Review, we introduce azobenzene compounds that exhibit photoinduced reversible solid‐to‐liquid transitions, discuss the mechanisms and design principles, and show their potential applications in healable coatings, adhesives, transfer printing, lithography, actuators, fuels, and gas separation. Finally, we discuss remaining challenges in this field.     

Evaluating the Thermal Hazard of Double-Base Propellant SQ-2 by Using Microcalorimetry Method

The thermal decomposition behavior of double‐base rocket propellant SQ‐2 was studied by a Calvet microcalorimeter at four different heating rates. The kinetic and thermodynamic parameters were obtained from the analysis of the heat flow curves. The critical temperature of thermal explosion (T_b), the self acceleration decomposition temperature (T_SADT), the adiabatic decomposition temperature rise (ΔT_ad), the time‐to‐explosion of adiabatic system (t), critical temperature of hot‐spot initiation (T_cr), critical thermal explosion ambient temperature (T_acr), safety degree (SD) and thermal explosive probability (P_TE) were presented to evaluate the thermal hazard of SQ‐2.     

Isomorphous replacement in nylon 6 by 4-aminomethylcyclohexanecarboxylic acid

It was desired to determine the effect of geometric configuration on the ability of 4-aminomethylcyclohexanecarboxylic acid (AMCC) to “isomorphously” replace ε-aminocaproic acid residues in nylon 6. However, we found that cis-AMCC isomerized to the more thermodynamically stable trans isomer during copolymerization with caprolactam (CL) and also during homopolymerization. A 20/80 cis/trans ratio of AMCC residues was found in the 50:50 copolyamides regardless of whether a high-cis (72/28) or high-trans (15/85) AMCC was used. Powder x-ray diagrams showed similar interplanar spacings for the copolyamides made from both high-cis and high-trans AMCC. The x-ray study also showed that the nylon 6 lattice can accommodate less than 30 mole-% AMCC residues before a new structure appears. DTA and TGA data of the CL:AMCC copolyamide showed that AMCC raised the melting point, T_g, T_c, and stability of nylon 6.     

Thermotropic copolyamides from triethylene glycol bis(4-carboxyphenyl) ether and o-tolidine modified by kinking monomers

Copolymers of triethylene glycol bis(4-carboxyphenylether) (PEG₃), 4,4′-diamino-3,3′-dimethylbiphenyl (o-tolidine, OT), and several kinking comonomers of dicarboxylic acids and diamines were prepared to investigate which of the comonomers is more effective to lower melting points (T_ms) and clearing temperatures (T_is) of the resulting thermotropic copolyamides. In general, diamine modifiers were more effective than dicarboxylic acid ones even having the same chemical structures. All of diamines examined depressed their transition temperatures linearly with the modifier content whereas the dicarboxylic acid modifiers yielded copolymers having different profiles. m-Aminobenzoic acid, another type of comonomer producing the polyamide of the AB structure, was also examined. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 363–368, 1999     

Structure–property relationships in polyamides containing cyclohexylene or phenylene structures

Polyamides were prepared from linear, aliphatic dicarboxylic acids of six to twelve carbon atoms with 1,4-cyclohexanebis(methylamine), 1,4-cyclohexanebis (ethylamine), p-xylylenediamine, and p-phenylenebis(ethylamine). Melting points, glass transition temperatures, densities, and moisture regains were compared for the polymers to determine the relative effect of the cyclohexylene and phenylene linkages. While polyamides containing the trans-cyclohexylene group possessed higher glass transition temperatures than their aromatic counterparts, melting behavior was not as consistent. The odd-even rule, which states that polyamides with an even number of methylene linkages between the ring and the functional group melt higher than those with an odd number of such linkages, was violated in the cycloaliphatic systems. The T_g of ring-containing polyamide fibers was not dependent solely upon ring concentration, but was influenced by the molecular fit of the ringed intermediate in the polymer chains. Molecular fit appears to affect the T_g and melting point of alicyclic polyamides to a greater extent than the aromatic analogs. Differences in T_g, both within and among the polymer series, was not explained by either density or the degree of crystallinity.