Well-defined crosslinked materials via ring opening metathesis polymerisation

The work reported here is part of our ongoing programme of work directed. towards the synthesis and characterisation of polymeric materials via ROMP-RIM and ROMP-RTM. It describes the synthesis and characterisation of well-defined linear and crosslinked polymeric materials via ROMP-RTM. The process involves in-mould polymerisation of monofunctional imidonorbornene monomers, with different alkyl side chain lengths, to give a range of linear polymers. The process also involves in-mould copolymerisation of monofunctional imidonorbornene monomers, with different alkyl side chain lengths and difunctional monomers with different alkylene spacer lengths, to produce well-defined crosslinked polymers. The glass transition temperature (T_g) of the linear polymers was found to depend on the length of the alkyl side chain. For the crosslinked materials the results show that as the percentage of the difunctional, crosslinking unit, is increased (1, 5 and 10 molar percentage of the difunctional monomer) the glass transition shifts to a higher temperature, the height of the tanδ peak decreases and the plateau shear modulus above T_g increases. These results are as expected for an increase in the crosslink density of a polymer.     

The mass spectra of carboxylic acids—V: Carboxyl-carboxyl interaction in the fragmentation of some cycloalkene-1,2-dicarboxylic acids

The fragmentation mechanisms of the six isomeric cyclohexene-1,2-dicarboxylic acids are discussed. Only the 1-cyclohexene acid, by virtue of the major sequential losses of H₂O and CO₂ from the molecular ion, is readily distinguishable from its isomers, all of whose mass spectra are closely similar. In contrast to cis and trans cyclohexane-1,2-dicarboxylic acids, whose mass spectra were markedly different, the cis and trans cyclohexene-1,2-dicarboxylic acids fragment in a similar fashion. The mass spectra of 1-cyclopentene-1,2-dicarboxylic acid and 1-cyclobutene-1,2-dicarboxylic acid also exhibit a strong carboxyl-carboxyl interaction; the fragmentation behaviour of the 1-cyclopenteneacid is, however, more complex than that of the 1-cyclohexene and 1-cyclobutene acids.     

Biobased poly(2,5‐furandimethylene succinate‐co‐butylene succinate) crosslinked by reversible Diels–Alder reaction

We synthesized biobased poly(2,5‐furandimethylene succinate‐co‐butylene succinate) [P(FS‐co‐BS)] copolymers by polycondensation of 2,5‐bis(hydroxymethyl)furan, 1,4‐butanediol, and succinic acid. These copolymers could be crosslinked to form network polymers by means of a reversible Diels–Alder reaction with bis‐maleimide. The thermal properties, mechanical properties, and healing abilities of the P(FS‐co‐BS)s and the network polymers were investigated. The mechanical properties of the network polymers depended on the comonomer composition of the P(FS‐co‐BS)s and the maleimide/furan ratio in the network polymers. Some of the copolymers exhibited healing ability at room temperature, and their healing efficiency was enhanced by solvent or heat. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 216–222     

The influence of N‐vinyl pyrrolidone on polymerization kinetics and thermo‐mechanical properties of crosslinked acrylate polymers

Polymerization of multifunctional acrylate monomers generates crosslinked polymers that are noted for their mechanical strength, thermal stability, and chemical resistance. A common reactive diluent to photopolymerizable formulations is N‐vinyl pyrrolidone (NVP), which is known to reduce the inhibition of free radical photopolymerization by atmospheric oxygen. In this work, the copolymerization behavior of NVP was examined in acrylate monomers with two to five functional groups. At concentrations as low as 2 wt %, NVP increases the polymerization rate in copolymerization with multifunctional acrylate monomer. The relative rate enhancement associated with adding NVP increases dramatically as the number of acrylate double bonds changes from two to five. The influence of NVP on polymerization kinetics is related to synergistic cross‐propagation between NVP and acrylate monomer, which becomes increasingly favorable with diffusion limitations. This synergy extends bimolecular termination into higher double bond conversion through reaction diffusion controlled termination. Copolymerizing concentrations of 5–30 DB% NVP with diacrylate or pentaacrylate monomer also increases Young's modulus and the glass transition temperature (T_g) in comparison to neat acrylate polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4062–4073, 2007     

Stereochemistry of Macrocyclization of cis-4-Cyclohexene-1,2-dicarboxylic Acid with Dihalogen Derivatives

Stereochemistry of [2+2]- and [1+1]-macrocylization of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane, 1,3-dichloro-2-propanol, and 1,5-dichloro-3-oxapentane was studied. The reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane according to the [2+2]-cyclization scheme gave a mixture of stereoisomeric macroheterocycles with cis,syn,cis- and cis,anti,cis-junction of the polyether and cyclohexene rings. In the reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,5-dichloro-3-oxapentane, a mixture of crown compounds with cis,anti,cis- and cis-junction of the polyether and cyclohexene rings was obtained. The structure of the products was established on the basis of their chemical transformations and spectral data.     

Fluorocarbon polymers with alternating oxyalkylene and oxysilylene units

Linear polymers were prepared by the condensation of bis(dimethylamino)dimethylsilane and 1,4-bis(dimethylaminodimethylsily)benzene with fluorocarbon diols. 1,5-Dihydroxy-3-methyl-1,1,5,5-tetrakis(trifluoromethyl)-2-pentene, the cis addition product of hexafluoroacetone and isobutylene, with the silylbenzene monomer gave a polymer that cured at room temperature to a rubber exhibiting a glass transition temperature of 0°C, low swelling in hydrocarbons, and excellent resistance to hydrolytic, oxidative, and thermal degradation, retaining its flexibility after exposure to air for 3 hr at 305°C. The polymers obtained by condensing 1,5-dihydroxy-1,1,5,5-tetrakis(trifluoromethyl)-2-pentene, the trans addition product of hexafluoroacetone and propylene, with the silylbenzene and the silane monomers had glass transition temperatures of ?12 and ?50°C respectively, and greater resistance to swelling in hydrocarbons.     

A generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers

A generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers has been developed, which takes into account the influences of end groups, branching, and crosslinking, and their functionality distribution. DiBenedetto's theory was found to correctly characterize the influence of crosslinks on the glass temperature. Normalized to constant crosslink functionality, the crosslink constant is a universal parameter suggesting that the entropic theory of glasses is applicable to crosslinked systems. Data on linear polymers and networks from the crosslinking of polymer chains, vinyl/divinyl-copolymers and step-growth polymers, such as polyurethanes, amine-cured epoxies, or inorganic glasses, are presented.     

The mass spectra of carboxylic acids·IV: Carboxyl-carboxyl interaction in some cycloalkane 1,2 dicarboxylic acids and its relationship with molecular geometry

The interaction of the carboxyl groups in the fragmentation of the molecular ions of trans cyclohexane-1,2-dicarboxylic acid and cis cyclobutane-1,2-dicarboxylic acid serves to distinguish these acids from their cis and trans isomers respectively. This ‘ortho effect’ can be related to the geometrical arrangement of the carboxyl groups in the ground-state molecules.     

Synthesis and characterization of biocompatible and biodegradable polymers

New polyesters were synthesized using Krebs cycle acids. Poly(1, 4-butanediol dilactate succinate)(PBDS) and poly(1, 4-butanediol dilactate 2-acetoxy succinate)(PBDAS) were prepared by the polycondensation of 1, 4-butanediol dilactate with succinic anhydride and 2-acetoxy succinic acid, respectively. Poly(1, 4-butanediol succinate)(PBS) was also synthesized from 1, 4-butanediol and succinic anhydride. PBS/PBDS and PBS/PBDAS blends were prepared by the method of solvent casting. The effects of crystallization time and temperature onto melting behavior of PBS/PBDS and PBS/PBDAS blends were investigated by differential scanning calorimetry. The compatibility of each blend system was discussed using equilibrium melting point depressions. The biodegradation behavior was studied using PBS, PBDS, and PBDAS as the sole carbon source by Aspergillus niger. The molecular weights of the polymers which were obtained from GPC analysis decreased after degradation in five weeks.     

Controlled-release of drugs from cross-linked polymers containing cubane as a crosslinking agent

Two anti-inflammatory drugs, indomethacin and aspirin together with cubane-1, 4-dicarboxylic acid (CDA) were covalently linked with 2-hydroxyethyl methacrylate (HEMA). The drug-linked HEMA (indomethacin-linked HEMA) is abbreviated as HI, aspirin-linked HEMA as HA and cubane-1, 4-dicarboxylic acid (CDA) linked to two HEMA group is the cross-linking agent (CA). A difunctional spacer group was introduced between the drugs and acrylic moiety of the monomer through a hydrolyzable ester linkage. Free radical cross-linking polymerization of the monomers with drug effect was carried out in dioxane solution at various CA ratios, using AIBN as initiator in the temperature range 60-70°C. The compositions of the cross-linked three-dimensional polymers were determined by FT-IR spectroscopy. The glass transition temperature (Tg) of the network polymers was determined calorimetrically. The hydrolysis of drug-polymer conjugates was carried out in cellophane membrane dialysis bags containing an aqueous buffer solution (pH 8 and pH 1) at 37°C. Detection of the hydrolysis product by UV spectroscopy shows that the drugs were released by hydrolysis of the ester bond located between the drug and spacer group.     

Conformational properties of structurally rigid polyamides. I. Conformation of polyamides and model diamides derived from optically active cyclic 1,2-dicarboxylic acids

The conformational equilibria of piperidine diamides derived from five cyclic 1,2-dicarboxylic acids (I–V) have been investigated by dipole moment measurements and a priori conformational energy estimates. Since these diamides represent the building blocks of the polyamides derived from the above cyclic diacids and piperazine or trans-2,5-dimethylpiperazine, the results obtained in the study of the models have been used to investigate the conformation of the polymers. The overall evidence suggests that cyclopentane, cyclohexane, and bicyclooctane piperazine polymers behave as rigid rods in which the structural units possess approximately the same conformational preference exhibited by the respective model diamides.     

Effect of the molecular mobility of epoxy amine crosslinked polymers on their relaxation and physicomechanical characteristics

The results on molecular mobility in epoxy amine crosslinked polymers at segmental (α process) and local (β process) levels are analyzed. The effect of intrachain and interchain rigidities on the above processes is considered, where the intrachain rigidity is measured with the use of flexibilizing agents and the interchain rigidity is dependent on the intermolecular-interaction intensity, which is governed by the introduction of plasticizing agents. Both modes of molecular mobility in the crosslinked polymers show a cooperative character that controls the dissipation energy of the corresponding relaxation process. The correlation between the above processes and the elastic, strength, and relaxation characteristics of the epoxy amine crosslinked polymers is studied. Molecular mobility is shown to exert an inverse effect on the relaxation and dissipative characteristics of the network polymers.     

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.     

The dissimilarity between the electron-impact and photochemical or thermal behaviour of some methyl cyclobut-3-ene-1,2-dicarboxylates and muconates

Comparison of the mass spectral behaviour of the dimethyl esters of the epimeric (cis- and trans-) cyclobut-3-ene-1,2-dicarboxylic acids and the isomeric muconates (cis, cis-, cis, trans- and trans, trans-) and some substituted analogues shows that no correlation exists between the electron-impact-induced fragmentation and the predicted photochemical or thermal transformations in these systems. The comparison involved fragmentation patterns (supported by deuterium labelling), metastable transitions, and also kinetic energy release in the field free region.     

Viscoelasticity of crosslinked epoxy polymer in the transition region

The dynamic mechanical properties of highly crosslinked epoxyamine polymer networks with nonrandomly distributed crosslinks were investigated. The transition temperatures of these polymers can be correlated with the number of CH₂ groups between crosslink junctions in the aliphatic amine portions of the network. The steepness of the modulus-temperature curve is also a function of crosslink density. This is in contrast with the case of natural rubber crosslinked by sulfur or by electron irradiation, where the modulus-temperature curves have similar shapes although the glass transition temperature increases with the degree of crosslinking. An empirical distribution function, similar to the one used by Tobolsky for stress relaxation distributions, was used to describe the temperature dispersion of the dynamic moduli. Two parameters, h_g and h_r, are used to characterize the steepness of the dispersion curve below and above the transition temperature, respectively. It is tentatively concluded that h_g correlates with the length of the CH₂ sequences in the amine portion of the polymer. The quantity h_r may be related perhaps to the motion involving the trifunctional nitrogen junction.     

Novel polymers with a high carboxylic acid loading

Click chemistry has been used to prepare a range of novel polymers with pendant carboxylic acid side groups. Four azido carboxylic acids, either mono‐ or difunctional and aliphatic or aromatic, have been prepared and thoroughly characterized. Extensive model reactions with 1‐ethyl‐4‐hydroxybenzene, the simplest model for poly(4‐hydroxystyrene), and the four azido carboxylic acids have been conducted to establish the proper reaction conditions and provide an analytical frame for the corresponding polymers. Poly(4‐hydroxystyrene) moieties in three different polymers—poly(4‐hydroxystyrene), poly(4‐hydroxystyrene‐co‐methyl methacrylate), and poly(4‐hydroxystyrene‐b‐styrene)—have been quantitatively transformed into oxypropynes by the use of either Williamson or Mitsunobu strategies and subsequently reacted with the azido carboxylic acids. Detailed differential scanning calorimetry investigations of all the polymers in general exhibit [when poly(4‐hydroxystyrene) is a substantial part] significant changes in the glass‐transition temperature from the polar poly(4‐hydroxystyrene) (120–130 °C) to the much less polar alkyne polymers (46–60 °C). A direct correlation between the nature of the pendant groups in the derivatized polymers and the glass‐transition temperature has emerged: the aromatic carboxylic acids give high glass‐transition temperatures (90–120 °C), and the aliphatic carboxylic acids give lower glass‐transition temperatures (50–65 °C). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6360–6377, 2006     

Polyimidines: A new class of polymers. III. A comparison of isomers of polypyromellitimidines

The cis (3,3,5,5-), trans (3,3,7,7-), oxo, and thio analogs of tetraphenylpyromellitide were polymerized with 1, 6-hexane diamine, p-phenylene diamine, and p,p'-diaminodiphenyl ether under various conditions. A comparison was then made of reactivity of the isomers and of the properties of the polymers. In general the thio monomers were more soluble and reactive than the oxo. They also gave more thermally stable polymers. The cis isomers of the monomers were more soluble than the trans, but the trans were more reactive. The least stable of the 12 polymers prepared was that from the cis–oxo monomer and 1,6-hexane diamine. It gave a 10% weight loss at 300°C in air and 340°C in nitrogen by TGA. The most stable polymer was from the reaction of the cis–thio pyromellitide with p,p'-diaminodiphenyl ether, which showed 10% weight losses by TGA at 560 and 650°C in air and nitrogen, respectively. The polymers were stable in hot dilute hydrochloric acid and sodium hydroxide. They were all soluble in chloroform, dimethylformamide, and sulfuric acid. Polymers that contained sulfur were also soluble in carbon tetrachloride, benzene, xylene, and toluene. Brittle films could be cast from solution or melt-pressed.     

Low glass transition temperature fluorocarbon ether bibenzoxazole polymers

Fluorocarbon ether bis(o-aminophenol) monomers were prepared by a multistep synthetic route based on the copper-promoted coupling of 4-iodophenyl acetate with 1,8-diiodoperfluoro-3,6-dioxaoctane, 1,11-diiodoperfluoro-3,9-dioxaundecane, 1,14-diiodoperfluoro-5,10-dimethyl-3,-6,9,12-tetraoxatetradecane, and 1,17-diiodoperfluoro-3,6,9,15-tetraoxaheptadecane. Acetic acidpromoted polycyclocondensations of the monomers with long-chain fluorocarbon ether-diimidate esters and -dithioimidate esters led to linear fluorocarbon ether-bibenzoxazole polymers soluble in 1,1,1,3,3,3-hexafluoroisopropanol and 1,1,2-trichloro-1,2,2-trifluoroethane. Polymer structures were verified by elemental and infrared spectral analysis. The polymers were rubbery gums and could be obtained in the inherent viscosity range of 0.20–0.79 dlg^?1. Selection of monomers governed the glass transition temperatures of the resultant polymers. As expected, the polymers exhibited lower glass transition temperatures with increased fluorocarbon ether content, a minimum value of ?58°C being achieved. None of the polymers exhibited crystalline melt temperatures. Based on thermogravimetric analysis data, the thermooxidative stability of the polymers tended to decrease with increased fluorocarbon ether content. Onset of breakdown during thermogravimetric analysis in air occurred in the 350–400°C range. Isothermal aging of the polymers in air indicated good thermooxidative stability at 260°C; only 5% weight loss was recorded after 200 hr.     

Prediction of the glass transition temperature of polymers: A model based on the principle of corresponding states

The application of corresponding state principles to describe the properties of polymers is implicit in many of the fundamental studies of polymeric behavior. The seminal works of Prigogine, Hildebrand, Eyring, Flory, Gibbs, and DiMarzio in which multidimensional lattice representations and refined statistical mechanical approaches have been used are the basis for much of today's understanding of the thermodynamic behavior of polymers and their solutions. In this work the lattice energy of a polymer is defined in terms of reduced molecular parameters, and it is assumed that all polymers with the same functional form for their lattice energies will be in corresponding states. A reduced second order transition temperature is defined relative to a characteristic temperature T* = s?*/2kv* c, where the molecular parameters refer to the properties of the repeating segments of the polymer chain. Equations are derived that express the effects of molecular weight, plasticization, degree of crosslinking, and copolymerization on the second order (i.e., glass) transition temperature. In their limits, the equations are shown to reduce in form to equations derivable from free volume theory. They are also used to analyze successfully a variety of glass transition temperature data available in the literature on homogeneous uncrosslinked and crosslinked polymers, plasticized polymers, and random copolymers.     

Synthesis and characterization of poly(arylene ether sulfone)s with trans‐1,4‐cyclohexylene ring containing ester linkages

trans‐1,4‐Cyclohexylene ring containing acid chloride monomers were incorporated into poly(arylene ether sulfone) (PAES) backbones to study their effect on mechanical and thermal properties. The trans‐1,4‐cyclohexylene ring containing acid chloride monomers were synthesized and characterized by NMR and high‐resolution mass spectrum. trans‐1,4‐Cyclohexylene containing PAESs were synthesized from the acid chloride monomers and hydroxyl terminated polysulfone oligomers with a pseudo‐interfacial method and a solution method. These PAESs, with trans‐1,4‐cyclohexylene ring containing ester linkages, were fully characterized by NMR, thermogravimetric analysis, differential scanning calorimetry (DSC), size exclusion chromatography, and dynamic mechanical analysis (DMA). The tensile properties were also evaluated. The polymers made with the pseudo‐interfacial method had relatively low molecular weights when compared to the solution method where much higher molecular weight polymers were obtained. Crystallinity was promoted in the low molecular weight biphenol‐based PAES samples with the pseudo‐interfacial method. The crystallinity was confirmed by both the DSC and the wide angle X‐ray diffraction results. The tensile test results of the high molecular weight polymers suggested that incorporation of the trans‐1,4‐cyclohexylene ring containing linkage slightly improved the ultimate elongations while maintaining the Young's moduli. The trans‐1,4‐cyclohexylene ring containing PAESs also showed higher sub‐T_g relaxations in DMA when compared with their terephthaloyl containing analog. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011