Spinning and characterization of fibers from poly(2,6-dichloro-p-phenyleneterephthalamide): a study of constitutional isomerism and solid-state arrangements by comparison between simulation and experiment

Fibers of three constitutionally isomeric rigid-rod polymers, produced by polycondensation of 2,6-dichloro-p-phenylenediamine and terephthaloyl dichloride, were spun from nematic solutions and characterized by wide-angle X-ray diffraction (WAXD) measurements and mechanical tests. A post-spin heat treatment was employed to improve the low degrees of orientation and crystallinity that the untreated fibers showed. The dominating crystal structure of constitutionally ordered head-to-head/tail-to-tail fibers seems to be very similar to “Modification II” of the fibers from poly(p-phenyleneterephthalamide) (PPTA), but the fibers do not suffer a comparable structural transformation upon heat treatment. Influences of the constitutional regularity in the chains on the crystal structure, structural order and mechanical properties of the fibers could be observed. Both the observed crystal structure and the experimentally determined mechanical properties agree well with the results of detailed atomistic modeling predictions.     

Ordering of liquid crystalline solutions of rigid-rod aramids using mechanical shearing and electric-field poling

2′,5′-Diamino-4-(dimethylamino)-4′-nitrostilbene was polymerized with terephthaloyl dichloride and 2,6-difluoroterephthaloyl dichloride in a low-temperature solution polycondensation to give two novel, fully aromatic rigid-rod polyamides. Nematic solutions of these polymers were processed into fibers and films that were characterized by wide-angle X-ray diffraction measurements. A post-spin annealing process was employed to enhance the chain orientation in the fibers. The dominating crystal structure was found to be similar to “modification II” of the fibers from poly(p-phenyleneterephthalamide), but the fibers do not suffer a comparable structural transformation upon heat treatment. A corona-discharge poling process gave rise to a remarkable gain in average chain orientation in the films. Again the crystal structure was found to be similar to “modification II”. The aramids investigated in this work represent a new approach to the design of liquid-crystalline rigid-rod polymers, where different mechanisms of orientation can be combined. In the nematic phase, the rigid-rod molecules form highly oriented domains that can be oriented using mechanical processes such as shearing. In addition the stilbene units that are fixed in the polymer backbone with their dipole moments oriented transverse to the main chain can be oriented in an electric field. The combination of both orientation mechanisms seems to cause a synergistic effect, probably since each affects different levels of the polymer microstructure in the solid.     

An investigation of novel approaches in order to provide crosslinked fully aromatic polyamide chains

Two different, novel approaches to crosslink fully aromatic, rigid‐rod aramid chains were studied. First, the new rigid‐rod aramid poly[1,4‐phenylen‐2,5‐bis(prop‐2‐ynyloxy)‐terephthalamide] with an inherent viscosity of η_inh = 2.74 dL/g was synthesized by low temperature polycondensation of p‐phenylendiamine and 2,5‐bis(prop‐2‐ynyloxy)‐terephthaloylchloride. The pendant alkinyl moieties allowed thermally induced crosslinking at temperatures higher than 200°C. No weight loss was found due to this treatment, but curing gave rise to the formation of stable radicals. However, no fiber spinning experiments were carried out using this material due to the insufficient stability of the polymer chains against degradation when being dissolved in sulfuric acid. Furthermore, fibers of a rigid rod polyamide containing pyrimidine moieties, produced by polycondensation of bis‐silylated 2,5‐diaminoprimidine and terephthaloyl dichloride, were spun from nematic solutions. Fibers were crosslinked by complexation with nickel(II)‐ions in the swollen state. Both crosslinked and non‐crosslinked, otherwise identically processed samples, were characterized by wide‐angle X‐ray‐diffraction (WAXD) measurements and mechanical tests. A post‐spin heat treatment was employed to improve the low degrees of orientation and crystallinity that the untreated fibers in general showed. The dominating crystal structures of both fiber samples are similar to “Modification II” of the well characterized fibers from poly(p‐phenylene‐terephthalamide) (PPTA). The number and size of the morphological defects in the crosslinked fibers was significantly higher than in the non‐crosslinked samples. The influence of the annealing on the mechanical fiber properties and the molecular order in the fibers was investigated. The values of all mechanical parameters were considerably lower in the case of the crosslinked fibers, probably due to the collapse of the entire supramolecular order and fiber morphology.     

Synthèse et réactions photochimiques d'homopolymères et de copolymères de la p-vinylbenzophénone et du vinylferrocène

Poly(p-vinylbenzophenone), (poly[1-(4-benzoylphenyl)ethylene]), (PVB) has been synthesized for the first time directly from its monomer p-vinylbenzophenone (VB) the preparation of which was improved. In a second step, copolymers containing blocks of photosensitive VB units separated by isolated quenching vinylferrocene (VF) units have been prepared. PVB and the VB-VF copolymers were irradiated in the presence of isopropyl alcohol in benzene solutions. The benzophenone groups inserted in these macromolecular chains obey the same reaction scheme as the photoreduction of the small molecule of benzophenone. However, recombination of the radicals located along the polymeric chain leads to intra- and intermolecular reactions changing drastically the macromolecular morphology by the formation of cycles and networks and by chain scissions. The quantum yields of the photochemical transformations were measured, but they could not be related quantitatively to morphological parameters. In all cases the ferrocene group inhibits strongly the photochemical reaction.     

Polymere und Copolymere mit p-Vinyl-α.α-diphenyläthylen-Grundbausteinen

p-Vinyl-α.α-diphenylethylene (pNDPÄ) was polymerized radically in bulk at 80°C and copolymerized with styrene. The resulting polymers and copolymers had relatively low degrees of polymerization (ranging from 10 to 100). The polymerization took place primarily via the vinyl group and to a lower extend via the vinyliden group. The unsaturated side group enabled subsequent crosslinking reactions with these polymers. Copolymers with pVDPÄ-groups having higher molecular weights were obtained by GRIGNARD reaction of p-vinyl benzophenone/styrene copolymers with methyl magnesium iodide. These copolymers yielded the corresponding macromolecular polyanions upon treatment with naphthalene sodium in tetrahydrofuran; the latter were able to start graft-copolymerization of acrylonitrile, methylmethacrylate, and styrene; when using styrene, living side chains were formed. It was shown by dissolution experiments that no ungrafted backbone polymer and no free homopolymers were present in the graft-copolymers with acrylonitrile and methylmethacrylate.     

Thermal properties of poly(butylene isophthalate) and its copolyesters with poly(butylene adipate)

The thermal properties of uniformly random poly(butylene adipate/isophthalate) copolyesters of various composition and different molecular weight were investigated by means of differential scanning calorimetry. All copolymers were partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. The heat of fusion of 100% crystalline poly(butylene isophthalate), estimated by different methods, was found to fall within the range 22–25 kJ · mol^?1. Completely amorphous samples, obtained by rapid quenching from the melt, showed a monotonic decrease of the glass transition temperature T_g and a monotonic increase of the heat capacity increment ΔC_p with increasing butylene adipate content in the copolymers. The T_g-composition dependence was found to be well fitted by the Couchman equation with no excess enthalpy correction.     

Electrochemical studies of some three component copolymers in nonaqueous media

Some three-component copolymers have been prepared by condensing formaldehyde with each of the following groups of monomeric species: (i) sulfanilic acid + p-toluidine + p-bromoaniline; (ii) p-aminobenzoic acid + p-toluidine + p-bromoaniline; (iii) sulfanilic acid p-aminobenzoic acid + p-bromoaniline. The composition of the copolymers has been deduced from electrometric titration studies in nonaqueous media, and Br content of the copolymers. Differentiation of acidic functional groups and the degree of polymerization of the copolymers could be obtained from their titration curves.     

Regenerated Silk Fibroin Nanofibrous Matrices Treated with 75% Ethanol Vapor for Tissue-Engineering Applications

As an excellent biocompatible and biodegradable protein polymer, silk fibroin (SF) has found wide applications, particularly serving as therapeutic agent for tissue-engineering applications, on which both post-spin treatment and sterilization processing are crucial to drug-loaded matrices. To find a safe, effective and appropriate post-spin treatment and sterilization approach for drug-loaded biomaterial matrices is one of the major problems in the field of tissue engineering at present. In this work, a simple, safe and effective approach skillfully integrating post-spin treatment with sterilization processing was developed to drug-loaded SF nanofibrous matrices. Electrospun SF nanofibrous matrices from its aqueous solution were post-treated with 75% ethanol vapor. ¹³C-NMR and WAXD analysis demonstrated that such post-spin treatment rendered the structure of SF nanofibrous matrices transform from the silk I form to the silk II form. Furthermore, biological assays suggested that as-treated SF nanofibrous matrices significantly promoted the development of murine connective tissue fibroblasts. Skillfully integrated with novel sterilization processing, 75% ethanol vapor treatment could be a potential approach to designing and fabricating diverse drug-loaded SF nanofibrous matrices serving as therapeutic agents for tissue-engineering applications in that it can effectively protect the drug from losing compared with traditional post-spin treatment and sterilization processing.     

Synthesis of water-soluble biologically active phenol (or catechol) containing copolymers of N-vinyl-2-pyrrolidone

Water-soluble N-vinyl-2-pyrrolidone (VP) copolymers containing phenol (or catechol) groups in the side chains were synthesized by reactions of copolymers of VP and crotonic acid (CA) with p-aminophenol and by reaction of p-nitrophenyl ester groups containing VP-CA copolymers with dopamine. It was established that phenol (or catechol) containing multiunit VP copolymers (which were characterized by GPC, viscometry, UV, IR and ¹H NMR spectroscopy) exhibit immunostimulating activity. In addition, the phenol-containing copolymers exhibit antitumor activity. The VP-CA-p-crotonoylaminophenol terpolymer can be used as a macromolecular carrier in the synthesis of a carcinogen-polymer antigen: a polymeric azo derivative of ß-naphthylamine.     

Preparation of Polyisobutene‐graft‐Poly(methyl methacrylate) and Polyisobutene‐graft‐Polystyrene with Different Compositions and Side Chain Architectures through Atom Transfer Radical Polymerization (ATRP)

Polyisobutene‐graft‐poly(methyl methacrylate) and polyisobutene‐graft‐polystyrene with controlled compositions and side chain architectures were prepared through atom transfer radical polymerization (ATRP). Poly[isobutene‐co‐(p‐methylstyrene)‐co‐(p‐bromomethylstyrene)] (PIB) was used as a macroinitiator in the presence of CuCl or CuBr as a catalyst and dNbpy as a ligand. The compositions were controlled by the conversion of the monomer with polymerization time. The molecular weight distributions of the side chains were controlled through ATRP in the presence/absence of a halogen exchange reaction. DSC and DMA measurements showed that graft copolymers have two glass transition temperatures suggesting microphase separated behavior, which was also confirmed by SAXS measurements. The phase and dynamic mechanical behaviors were strongly affected by the compositions and/or the side chain architectures. The properties of the graft copolymers were controlled in a wide range leading to toughened glassy polymers or elastomers.     

On the copolymerization of acrylonitrile with styrene in the presence of Lewis acid, 3. Photoinitiated copolymerization

The rate of the acrylonitrile (AN)-styrene (St) copolymerization (R_p) photoinitiated (λ=365 nm) by the St? AN? ZnCl₂ complex at 30°C is proportional to the square root of the intensity of radiation. The limiting viscosity number [η] of alternating copolymers increases with the intensity of radiation. The 1/[η] vs. R_p relationship for the St? AN copolymers is similar as has been found for the initiation of copolymerization by thermal decomposition of 2,2-azoisobutyronitrile. Provided benzophenone combined with 2-propanol is used as a photosensitizer, the rate of the St? AN copolymerization in acetone—at constant concentrations of both comonomers, zinc chloride, and benzophenone—decreases with 2-propanol concentration in the reaction mixture. If benzophenone alone (e.g. without 2-propanol) is used as a photosensitizer under equal conditions, the observed values of the rate of copolymerization are lower in comparison with the system where the ternary molecular complex is empolyed as a photosensitizer. Moreover, R_p decreases with increasing concentration of benzophenone in the system. These findings are interpreted as a result of the termination reactions of ketyl radicals (hydroxydiphenylmethyl radicals) with macroradicals of copolymer.     

Kinetic and structural studies of the copolymerization of the cleavable bismaleimide p-maleimidobenzoic anhydride and styrene

The polymerization of a bismaleimide-styrene system was studied by using a model compound, p-maleimidobenzoic anhydride, that can be split by simple hydrolysis. Compared to known divinyl systems, a decreased reactivity of the pendant double bonds is observed, probably as a result of cyclization and the steric excluded volume effect. The use of a solvent causes an additional shift of the gel point towards higher conversion. Hydrolysis of gelled material affords soluble p-maleimidobenzoic acid-alt-styrene copolymers. Compared to a linear system, methyl p-maleimidobenzoate and styrene, the primary chains obtained by hydrolysis show an increased polydispersity, probably due to retardation of bimolecular termination of the free radicals that are attached to the polymer network (gel effect).     

Vinyl polymerization initiated with the lanthanum versatate/p-chlorobenzenediazonium tetrafluoroborate system

The system of lanthanum versatate ( 1 ) and p-chlorobenzenediazonium tetrafluoroborate ( 2 ) was found to induce effectively polymerizations of electron-accepting monomers such as methyl methacrylate ( 3 ) and di-2-ethylhexyl itaconate (DEHI). The polymerization rate (R_p) was expressed by R_p = k[ 1 / 2 ]^0,44 [ 3 ]^0,65 at 50°C fixing the mole ratio of 1 and 2 at unity. The overall activation energy of the polymerization was calculated to be 37, 1 kJ · mol^?1. The spin trapping result revealed that the initiator system produces p-chloropheneyl radicals. The polymerization system of DEHI was observed to involve ESR-observable propagating polymer radicals, indicating that the polymerization initiated with the 1/2 system proceeds through radical mechanism. During the polymerization, the ESR spectrum was changed in shape, suggesting that the propagating polymer radicals interact with some species formed by the initiation reaction. Interacting polymer radicals were also observed in the polymerizations of diethyl itaconate and N-dodecylmaleimide with the 1/2 system. The polymerization systems of MMA, styrene and butyl acrylate were also found to involve ESR-observable radicals, although it is vague whether they are propagating polymer radicals or not.     

Theta-behaviour of poly(p-tert-butylstyrene)-block-poly(dimethylsiloxane)-block-poly(p-tert-butylstyrene)

The theta-behaviour of poly(p-tert-butylstyrene)-block-poly(dimethylsiloxane)-block-poly(p-tert-butylstyrene) ABA type triblock copolymers containing ca. 28% by weight tert-butylstyrene was studied in the selective solvents 1-nitropropane and 2-butanone using the phase separation method. The theta-temperatures in these solvents were found to be 157°C and 31°C, respectively. The intrinsic viscosities of the copolymers in 2-butanone (MEK) were obtained at different temperatures. The Mark-Houwink-Sakurada exponent α in MEK at 31°C is greater than 0,5, suggesting that the theta-behaviour of block copolymers is different from that of the homopolymers due to the presence of repulsive interactions between incompatible blocks.     

Poly(propylene terephthalate) Modified with 2,2‐Bis[4‐(ethylenoxy)‐1,4‐phenylene]propane terephthalate) Units: Thermal Behaviour,Crystallisation Kinetics and Morphology

Summary: The thermal behaviour of poly(propylene terephthalate) modified with 2,2‐bis[4‐(ethylenoxy)‐1,4‐phenylene]propane terephthalate) units (PPT/BHEEBT copolymers) was investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and hot‐stage optical microscopy (MO). Good thermal stability was found for each sample. The thermal analysis carried out using the DSC technique showed that the T_m of the copolymers decreased with the increment in BHEEBT unit content. This was different from the T_g which, on the contrary, increased. Wide‐angle X‐ray diffraction measurements allowed the identification of the PPT crystalline structure in each semicrystalline sample. Multiple endotherms were shown in the PPT/BHEEBT samples, due to melting and recrystallisation processes, similarly to PPT. The of the copolymers was derived from the application of the Hoffman‐Weeks' method. The isothermal crystallisation kinetics were analysed according to Avrami's treatment. The introduction of BHEEBT units was found to decrease the crystallisation rate compared to pure PPT. Values of the Avrami's exponent n close to 3 were obtained for PPT/BHEEBT6 and PPT/BHEEBT12, regardless of T_c, in agreement with a crystallisation process originating from pre‐determined nuclei and characterised by three‐dimensional spherulitic growth. As a matter of fact, for these two copolymers, space‐filling spherulites were observed through optical microscopy at all T_cs. The heat of fusion (ΔH_m) was correlated to the specific heat increment (Δc_p) for samples with different degrees of crystallinity, and the results were interpreted on the basis of the existence of an interphase, whose amount was found to depend mainly on composition, despite the thermal treatment applied to the polymer also playing an important role.

Calorimetric curves of PPT, PBHEEBT homopolymers and their random copolymers after melt quenching.     

Soluble polystyrene-block-poly(p-phenylene) block copolymers prepared from polystyrene-block-poly(1,3-cyclohexadiene) precursors. Study of the aromatization process

Polystyrene-block-poly(p-phenylene) block copolymers were prepared from polystyrene-block-poly(1,3-cyclohexadiene) (PS-PCHD) precursors. The PS-PCHD copolymers were initiated by sec-butyllithium in benzene. The aromatization of poly(1,3-cyclohexadiene) sequences was carried out by dehydrogenation with substituted quinones. Secondary reactions occur during this reaction leading to defects in the poly(p-phenylene) (PPP) sequences which limit the mean length of conjugated blocks at about 11–12 phenylene units. The defects result from the addition of hydroquinone ether groups to the chain. The influence of experimental conditions (nature of quinone, additives, temperature) on the aromatization yield and defect content is studied. The reaction with p-chloranil

1 System. name: tetrachloro-p-benzoquinone.

at 130°C gives the best results. The formation of aggregates during this reaction is observed and explains the final slow kinetics. The purified copolymers are partly aggregated into micelles with a PPP core. For a given polystyrene sequence the fraction of aggregated chains and the size of PPP core increases with the length of PPP sequences. Improvements of PPP blocks are expected by a better control of the aggregation process.     

Synthesis of biodegradable polyesteramides with pendant functional groups

Morpholine-2,5-dione derivatives having substituents with benzyl-protected carboxylic acid, benzyloxycarbonyl-protected amine and p-methoxy-protected thiol groups, respectively, were prepared in 29–58% yield by cyclization of the corresponding N-[(2RS)-bromopropionyl]-L -amino acids. Polyesteramides with protected pendant functional groups were obtained by ring-opening copolymerization of either ?-caprolactone or DL -lactide with morpholine-2,5-dione derivatives having protected functional substituents. The copolymerizations were carried out in the bulk at 130°C using stannous octoate as an initiator and using low mole fractions (0,05, 0,10 and 0,20) of morpholine-2,5-dione derivatives in the feed. The molecular weight of the resulting copolymers ranged from 1,4 to 8,3 · 10⁴. The ring-opening homopolymerization of morpho-line-2,5-dione derivatives with protected functional substituents was not successful. Polyesteramides with either pendant carboxylic acid groups or pendant amine groups were prepared by catalytic hydrogenation of the corresponding protected copolymers. Treatment of copolymers having pendant p-methoxybenzyl-protected thiol groups with trifluoromethanesulfonic acid resulted not only in the removal of the p-methoxybenzyl group but also in severe degradation of the copolymers, due to acidolysis of main-chain ester bonds.     

Cell–tissue interactions in osteoarthritic human hip joint articular cartilage

Volume and morphology of chondrocytes in osteoarthritic human hip joint articular cartilage were characterized, and their relationship to tissue structure and function was determined. Human osteochondral articular cartilage samples (n?=?16) were obtained from the femoral heads of nine patients undergoing total hip arthroplasty due to osteoarthritis (OA). Superficial chondrocytes (N?=?65) were imaged in situ with a confocal laser scanning microscope at 37?°C. This was followed by the determination of the mechanical properties of the tissue samples, depth-wise characterization of cell morphology (height, width; N?=?385) as well as structure and composition of the tissues using light microscopy, digital densitometry, Fourier transform infrared microspectroscopy and polarized light microscopy. Significant correlations were found between the cell volume and the orientation angle associated with the collagen fibers (r?=?0.320, p?=?0.009) as well as between the cell volume and the initial dynamic modulus of the tissue (r?=??0.305, p?=?0.013). Furthermore, the depth-dependent chondrocyte aspect ratio (height/width) correlated significantly with the orientation angle of the collagen fibers and with the tissue’s proteoglycan content (r?=?0.261 and r?=?0.228, respectively, p?相似文献   

Generation of Hydroxyl Radicals from Polymer Containing Reducing Sugar Branches in the Presence of Hydrogen Peroxide

The generation of hydroxyl radicals from poly(6‐O‐vinyladipoyl‐D ‐glucose) [poly(VAG)] in the presence of hydrogen peroxide was detected by oxidation of p‐nitrosodimethylaniline (p‐NDA). Several hydroxyl radical scavengers inhibited the reaction, but inhibition by superoxide dismutase (SOD) was low. This suggests that hydroxyl radicals from Harber‐Weiss reaction made relatively small contributions to this reaction, and that the enediol moiety of reducing sugar branches in poly(VAG) reacted with hydrogen peroxide to produce hydroxyl radicals. The polymer degraded to a low molecular weight material after reaction with hydrogen peroxide.     

Styrene/p-methoxystyrene random copolymers. Part III. Some remarks on dilute solution properties

Styrene/p-methoxystyrene random copolymers of three different compositions and poly(p-methoxystyrene) have been examined by viscosity measurements in some solvents (including good and Θ solvents) at different temperatures. Current theories have been applied to evaluate the FLORY constant K_Θ; the values obtained for the copolymers are quite different from the “ideal” values and are independent on the temperature. The measurements in Θ solvents suggest that the conformations of the copolymers differ sometimes from the GAUSSian coil conformation.