Polybutadiène hydroxytéléchélique, 7. Cinétique de polycondensation en solution et en masse du polybutadiène hydroxytéléchélique avec le méthylène-4,4′ di(isocyanate de phényle) en l'absence de catalyseur. Etude par 1H NMR et 13C NMR

Quantitative determinations by ¹³C NMR performed with insoluble polyurethanes allow to study the kinetics of the polymerization in bulk between hydroxytelechelic polybutadiene G 1000 and 4,4′-methylene diphenylisocyanate (MDI). Comparisons have been made with (G 1000 + MDI) polymerization and (monoalcohol or G 1000 + phenyl isocyanate) model reactions in toluene. With [NCO]/[OH] = 1 and T ? 60°C, in solution as well as in bulk, conversions are not complete. Because of the presence of gels, part of the reactive functions have been found to be trapped. For kinetic tests, only the first stage of the polymerization (conversion < 70%) may be taken into account. In bulk, the two alcohol functions are equally reactive, whereas in toluene, the hydroxylated 1,4 ends of the polybutadiene chains are more reactive. As evidenced for model reactions in the foregoing paper of this series, the kinetics fit better with the 3rd order than with the 2nd order equation. Nevertheless, at higher temperatures, the 2nd order may be used. The autocatalysis phenomenon found effective for model reactions is negligible in polymerization. All kinetic constants and activation parameters calculated must be considered to be apparent ones only.     

Hydroxytelechelic polybutadiene, 10. Molecular weight and functionality distribution of a radically obtained hydroxytelechelic polybutadiene studied by GPC and 1H NMR

Hydroxytelechelic polybutadiene (HTPB) Arco-R45M® obtained by free-radical-initiated polymerization of butadiene was fractionated by preparative gel permeation chromatography (GPC) using styragel and silicagel as column material. The fractions separated were extensively studied by vapour pressure osmometry (VPO), GPC, and ¹H NMR. Commercially available non-hydroxylated polystyrene and polybutadiene standards cannot be utilized for the proper direct determination of the molecular weight of HTPB by means of GPC. Both high and low hydroxyl functionalities were found for high- and low-molecular-weight HTPB. The analytical results are discussed in terms of the polymerization mechanism.     

Hydroxytelechelic polybutadiene, 9. Kinetics of reactions in solution and in bulk between radically obtained hydroxytelechelic polybutadiene and propyl and phenyl isocyanate studied by 1H NMR

The kinetics of the reactions of radically obtained hydroxytelechelic polybutadiene (Arco R45M) with propyl isocyanate and phenyl isocyanate were studied by ¹H NMR at high field. The reactivities of the three alcohol functions of Arco R45M were found to be different. The three individual reactions follow a 3rd order law and are accelerated by autocatalysis. There is competition between (OH, OH) auto-association and (free OH + isocyanate) reactions. As a consequence, rate constants are strongly affected by (OH, OH) association phenomena.     

Hydroxytelechelic polybutadiene, 13. Microstructure,hydroxyl functionality and mechanisms of the radical polymerization of butadiene by H2O2

The mechanism of the radical polymerization of butadiene with H₂O₂ has been clarified by indepth examination of very low M?_n hydroxytelechelic polybutadiene (HTPB) synthesized with high concentration of H₂O₂. For the well-known R45M®-HTPB^1,2, only primary alcohol functions were found, and most of them originate from initiation steps (termination mechanisms only proceed by coupling of macroradicals); in low M?_n HTPB (HTPB-C), the presence of a secondary alcohol function suggests termination reactions by coupling between macroradicals and primary hydroxyl radicals. Being more branched, HTPB-C has a larger hydroxyl content, and also a larger amount of epoxidized 1,4-units. Finally, some lower alcohols, utilized for homogenizing H₂O₂ with butadiene, are also transfer agents giving rise to ether groups.     

Hydroxytelechelic polybutadiene, 11. Kinetics of dibutyltin dilaurate-catalyzed addition reaction between a hydroxytelechelic polybutadiene and propyl isocyanate

Complexations of 1-octanol (O) and propyl isocyanate (PI) by dibutyltin dilaurate (DBSnDL) were examined by 350 MHz ¹H NMR. Whereas the 1:1 O/DBSnDL complex was easily evidenced, the behaviour of the mixture (1 PI + 1 DBSnDL) suggested slow formation of (a) relatively stable coordination compounds(s). The three alcohol functions of the hydroxytelechelic polybutadiene Arco-R45M® were found to be equally catalyzed by DBSnDL in the addition with PI in toluene and in the bulk. Linear relationships between initial reaction rates and catalyst concentrations were found only for mole ratios [DBSnDL]/[Arco-R45M]® < 0,06 and 0,1 in dilute solution and in bulk, respectively. (Acro-R45M® + PI) additions catalyzed by DBSnDL follow 3rd-order kinetics. The activation enthalpies and entropies calculated from kinetic data show that, compared to spontaneous addition, catalyzed reaction rates are less sensitive to temperature. Negative activation entropies suggest the existence of relatively stable transition states.     

Suspension polymerization of 2-hydroxyethyl methacrylate in the presence of polymeric diluents: a novel route to spherical highly porous beads for biomedical applications

Spherical, highly porous beads of poly(2-hydroxyethyl methacrylate) (PHEMA) cross-linked with ethylene glycol dimethacrylate (EGDM) were prepared by suspension polymerization of HEMA in concentrated NaCl solutions in presence of toluene, poly(methyl methacrylate) (PMMA) in toluene, and poly(tetramethylene glycol) (PTMG). Magnesium hydroxide prepared in situ in the dispersion medium gave the best stabilization effect for the monomer droplets. In the presence of PTMG, beads having nearly 1.0 mm in diameter could be prepared, while toluene alone as the diluent produced beads of very small size. Removal of PMMA or PTMG from the beads after polymerization using suitable solvents gave rise to highly porous PHEMA microspsheres. Polymerization in the presence of PTMG produced microspsheres with better spherical geometry as compared to those generated in the presence of PMMA. The effect of various factors such as NaCl concentration, concentration of Mg(OH)2, and the concentration of PMMA or PTMG in the monomer phase on the stability of the suspension and the particle size distribution was investigated.     

The effect of a polyurethane coating incorporating both a thrombin inhibitor and nitric oxide on hemocompatibility in extracorporeal circulation

Nitric oxide (NO) releasing (NORel) materials have been extensively investigated to create localized increases in NO concentration by the proton driven diazeniumdiolate-containing polymer coatings and demonstrated to improve extracorporeal circulation (ECC) hemocompatibility. In this work, the NORel polymeric coating composed of a diazeniumdiolated dibutylhexanediamine (DBHD-N₂O₂)-containing hydrophobic Elast-eon™ (E2As) polyurethane was combined with a direct thrombin inhibitor, argatroban (AG), and evaluated in a 4 h rabbit thrombogenicity model without systemic anticoagulation. In addition, the immobilizing of argatroban to E2As polymer was achieved by either a polyethylene glycol-containing (PEGDI) or hexane methylene (HMDI) diisocyanate linker. The combined polymer film was coated on the inner walls of ECC circuits to yield significantly reduced ECC thrombus formation compared to argatroban alone ECC control after 4 h blood exposure (0.6 ± 0.1 AG/HMDI/NORel vs 1.7 ± 0.2 cm² AG/HMDI control). Platelet count (2.8 ± 0.3 AG/HMDI/NORel vs 1.9 ± 0.1 × 10⁸/ml AG/HMDI control) and plasma fibrinogen levels were preserved after 4 h blood exposure with both the NORel/argatroban combination and the AG/HMDI control group compared to baseline. Platelet function as measured by aggregometry remained near normal in both the AG/HMDI/NORel (63 ± 5%) and AG/HMDI control (58 ± 7%) groups after 3 h compared to baseline (77 ± 1%). Platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry also remained near baseline levels after 4 h on ECC to ex vivo collagen stimulation (16 ± 3 AG/HMDI/NORel vs 11 ± 2 MFI baseline). These results suggest that the combined AG/HMDI/NORel polymer coating preserves platelets in blood exposure to ECCs to a better degree than AG/PEGDI/NORel, NORel alone or AG alone. These combined antithrombin, NO-mediated antiplatelet effects were shown to improve thromboresistance of the AG/HMDI/NORel polymer-coated ECCs and move potential nonthrombogenic polymers closer to mimicking vascular endothelium.     

Tieftemperaturpolymerisation des cyclopentadiens mit BF3-katalysatoren

Soluble polycyclopentadienes (PCPD) were obtained by polymerizing cyclopentadiene (CPD) with BF₃-etherate(I)/water(II)-catalyst in toluene. The plot of log [η] vs. 1/T from + 20°C down to about -20°C is steeper than the plot from ?20°C down to -78°C, indicating that [η] is controlled by different processes at higher and lower temperatures than ?20°C, respectively. At fixed initial concentrations of CPD and I and at constant temperature, the yield of PCPD after a given time is controlled by the amount of water, which is present in the reaction mixture. At a molar ratio I/II < 1 no appreciable polymerization takes place at -40°C. Best yields are obtained at molar ratios from 1,5–5, at higher the yields were diminished. Whereas little amounts of I only induced very slow polymerization at -78°C in toluene, BF₃-anisol (in toluene) and BF₃-2CH₃COOH (in toluene/CH₂CL₂) proofed to be powerful catalysts. Good yields of PCPD with high molecular weight ([η] = 1.5–1.8 dl/g) could thus be obtained.     

Polyuréthannes à propriétés emulsifiantes et électrolytiques, 2. Cinétique de polycondensation en solution des alkylimino-2,2′ diéthanols avec le diisocyanate d'isophorone. Etude par 1H et 13C NMR

¹³C NMR analysis of carbamates and substituted ureas as model compounds, derived from 5-isocyanato-1,3,3-trimethylcyclohexylmethyl isocyanate (isophorone diisocyanate) (3), allowed the quantitative determination of global conversions of hydroxyl and NCO groups. The individual conversions of the two NCO groups, as observed in the polycondensations of 2,2′-methylimino- and 2,2′-dodecyliminodiethanol (1a and 1b) with 3 in toluene, were examined. The primary NCO group of 3 was found to be two times more reactive than the secondary one. The global kinetics of the polycondensations followed the 2nd and 3rd order for conversions lower than 50%. Beyond 50% of conversion, zero order kinetics were observed because of the decrease of the rate due to the steric hindrance of both cyclohexyl and alkyl residues. Alkyl radical length in 1 and hydroxyl auto-association equilibria were found to have the same effect on polycondensation as on condensation.     

Effect of styrene on the polymerization of acrylamide in inverse microemulsion

The macroviscosity of a single-phase toluene/styrene/sodium bis(2-ethylhexyl)sulfosuccinate/water/acrylamide Winsor IV inverse microemulsion prior to polymerization as a function of the volume fraction ϕ_aw, of the dispersed aqueous (water + acrylamide) phase at 20°C reaches three distinct maxima of 16, 66, and 30 mPa ·;s for ϕ_aw values 25%, 46%, and 62%, respectively. At 60°C, the viscosity maxima practically vanish and the macroviscosity of the dispersion systems is in the range of 5–7 mPa · s. The overall maximum (co)polymerization rate of acrylamide and styrene increases with increasing ϕ_aw. On the other hand, an increase of the mass ratio styrene/toluene leads (for a given ϕ_aw value) to a decrease of the overall maximum (co)polymerization rate regardless of the nature of the initiator used. This points to an effective competition between monomer in the oil phase (slow homopolymerization of styrene and/or (co)polymerization of styrene with acrylamide dissolved in the oil phase) and monomer in the water pools of inverse micelles (rapid homopolymerization of a major part of acrylamide) for initiator radicals and/or (co)oligomer radicals.     

Production of poly[(ethylene glycol dimethacrylate)-co-acrylamide] based hydrogel beads by suspension copolymerization

Poly(EGDMA/AAm) copolymer beads, in the size range of 25–170 μm, were produced by suspension copolymerizations of the respective monomers, i. e., ethylene glycol dimethacrylate (EGDMA) and acrylamide (AAm), in aqueous media, with or without using toluene as the diluent. Poly(vinyl alcohol) and benzoyl peroxide were used as the stabilizer and the initiator. The beads were characterized by optical microscopy, FTIR-DRS, and elemental analysis. Swellabilities in aqueous media were obtained. Dry state porosities were calculated from densities measured pycnometrically. In the polymerization without toluene, nonswellable and nonporous microbeads were obtained, with AAm incorporation up to 9.55%. Including toluene in the polymerization recipe resulted in larger, swellable (with swelling ratios of 10–16%) and microporous (with dry state porosities of 0.020–0.080) beads with higher AAm incorporations (up to 29.9%) and high polymerization yields up to 96%.     

A study on grafting and characterization of HMDI-modified calcium hydrogenphosphate

It is known that the organic molecules can provide an effective means to manipulate the surface properties of the biodegradable ceramic. There are two ways to modify the surface of the biodegradable ceramic by organic molecules. The first one is through surface adsorption but organic molecules will easily be washed out in the physiological environment. The second approach is to graft organic molecules through covalent bond to the hydroxyl groups that are available on the surface of the ceramics. Isocyanate group has been reported as a coupling agent for hydroxyapatite and organic molecule. The studies showed that the isocyanate could react with hydroxyl groups of hydroxyapatite and form a covalent bond between isocyanate and hydroxyapatite. In the study, hexamethylene diisocyanate (HMDI) was used as coupling agent and calcium hydrogenphosphate (CaHPO4, CHP) was the candidate ceramic. CHP will react with HMDI at the temperature of 20 degrees C, 30 degrees C, 40 degrees C, 50 degrees C, 60 degrees C, and 70 degrees C for 4h. Dibutyltin dilaurate and hydroquinone were used as catalyst and inhibitor, respectively. The effect of reaction temperature on the grafted yield will be described. The linkage between CHP and HMDI will be characterized by DTA, TGA, FTIR, XRD, and 31P, 13C liquid state NMR. From the results, we successfully modified the surface of CHP with coupling agent of HMDI. The grafted yield of HMDI on CHP was increasing with the reaction temperature. The best temperature for CHP modified by HMDI is around 50 degrees C. The linkage between HMDI and the surface of CHP is a urethane linkage as CHP-O-CO-NH-(CH2)6-N=C=O. After further treatment, the terminal group of CHP treated with HMDI (MCHP) will be converted into a primary amine group as the formula of CHP-O-CO-NH-(CH2)6-NH2. If reaction temperature is 60 degrees C, long extension chain will occur with a urea linkage between the isocyanate groups as the formula of CHP-O-CO-NH-(CH2)6-(NH-CO-NH-(CH2)6)n-NH2. At reaction temperature higher than 60 degrees C, the HMDI will become prepolymerized forms in solution. The prepolymerized forms such as allophanate, biuret, uretidione and urea linkage will turn the solution into gel type mixture, which will lead to low grafted yield of HMDI on CHP. When MCHP prepared at the temperature 20 degrees C, there is no evidence of long extension but the grafted yield is the lowest only 0.9 wt% around.     

Synthesis of block copolymers containing polybutyramide blocks

Several methods were employed to synthesize block copolymers of a polyamide and polystyrene (or polyisoprene). The polystyrenes (or polydienes) were obtained anionically and were fitted with terminal acyllactam functions. In a second step the acyllactam groups were used as promoters for the polymerization of the corresponding lactam. The best results were obtained when the functionalization was carried out with toluene diisocyanate, followed immediately by protonation by means of the lactam itself. This method yields, the highest degrees of functionalization and low coupling rates; the subsequent polymerization of the lactam in the bulk leads to block copolymers which were characterized as such; they were found to contain only small amounts of homopolystyrene, easy to remove.     

Sulfur‐Containing Polyesters, 9. The Synthesis and Characterization of New Diphenylmethane‐Derivative Thiopolyester Diols and Their Use for the Preparation of Thermoplastic Polyurethanes

The new linear thiopolyester diols (PEs) containing sulfur in the main chain were prepared by melt polymerization of newly obtained diphenylmethane‐4,4′‐bis(methylthiopropionic acid) with excess of 1,4‐butanediol, 1,5‐pentanediol, and 1,6‐hexanediol. All these PEs (M̄_n of ≈2 000) were converted to thiopoly(ester‐urethane)s (PEUs) by addition reaction with hexamethylene diisocyanate (HDI) or 4,4′‐diphenylmethane diisocyanate (MDI) which was carried out in melt at a ratio of NCO/OH = 1 or 1.05. The resulting thermoplastic PEUs were elastomeric products, completely amorphous from MDI, with glass transition temperatures ranging from –22 to –8°C. Segmented PEUs (hard segment content ≈53–60 wt.‐%) prepared by using PEs, HDI or MDI, and bis[4‐(6′‐hydroxyhexylthio)phenyl] ether as chain extender were elastomeric materials, particularly those from MDI, with tensile strength of 9.4–12.7 MPa. All the polymers were thermally stable up to 200–270°C. The structures of the polymers were determined by Fourier transform infrared, ¹H NMR, and X‐ray analysis.     

Untersuchungen zur Thermolyse und zur Sauerstoff-Stabilität der 4π + 2π-Diels-Alder Addukte des Styrols

The 4π + 2π-Diels-Alder cycloadduct 1 involved in the spontaneous polymerization of styrene was investigated under conditions, where bimolecular reactions with styrene leading to a consumption of 1 can be neglected. For this reason 1 was (a) submitted to thermolysis in an inert solvent (toluene) at different temperatures (90, 100 and 110°C) and (b) oxidized with an excess of oxygen in styrene at room temperature. The reactions were followed spectrometrically at the wavelength λ = 325 nm and analyzed in terms of a first order reaction. The results show strong evidence for the involvement of two diastereomers ( 1a and 1b ) of different reactivity. This is in qualitative and quantitative agreement with the two isomers' concept, which had been deduced previously from kinetic analysis of the formation of 1 during the thermal polymerization of styrene. Rate constants and activation energies as well as possible reaction pathways are given.     

Kinetics of isoprene polymerization in the presence of 2-ethylhexylsodium and its mixtures with 2-ethylhexyllithium in hydrocarbon solvents

The anionic polymerization of isoprene with 2-ethylhexylsodium soluble in hydrocarbons in the absence of electron donor additives has been studied. The kinetics of the propagation reaction is shown to strongly depend on the solvent used. In toluene, the reaction order in initiator appears to be fractional, its value being dependent on the initiator concentration, while in heptane the first order is known to be followed. For polymerization in toluene, a scheme is suggested where monomeric and tetrameric active species are supposed to take part in propagation. With a non-linear regression fit, apparent constants in the equation describing this scheme were evaluated. The kinetics of isoprene polymerization with the mixed 2-ethylhexylsodium/2-ethylhexyllithium initiator, as well as UV spectra of the living polymers obtained, were also studied. Formation of complex active species is suggested.     

Polyuréthannes à propriétés émulsifiantes et électrolytiques, 1. Cinétique de condensation des alkylimino-2,2′ diéthanols et de leurs dérivés sulfobétaïniques avec divers monoisocyanates

This work deals with model reactions allowing the synthesis of low-molecular-weight polyurethanes with electrolytic and emulsifier properties. The kinetics of addition reactions of 2,2′-alkyliminodiethanols (3a – c) and their ammonium sulfonate derivatives 5 and 6 with propyl (8a) and cyclohexyl isocyanate (8b) were studied in DMSO and in the bulk. The tertiary amino groups of 3 exhibit catalytic effects, whereas the ammonium sulfonate internal salts inhibit the reaction. 8a is 2 – 3 times more reactive than 8b and the addition rates decrease with increasing R. Autoassociations (OH ··· OH) should mainly be intramolecular because of the proximity of the alcohol groups. In bulk the 8a + 3 additions apparently follow second order kinetics. On the other hand, the third order law must be taken into account with 8b . In contrast, in DMSO, due to the strong (solvent, ? OH and/or ? NCO) complexations, the kinetics do neither follow the simple second order, nor the third order law. By the use of two successive second order kinetics, diols were found more reactive than their monoalcohol-monocarbamate derivatives. However, the difference in reactivity decreases with increasing reaction temperatures. Sulfobetaine units may be inserted into the polyurethane chains if diols with ammonium sulfonate groups are used as comonomer, but their weak reactivity must be taken into account.     

Synthesis of Well-Defined Block Copolymers of Hyperbranched Polyamide and Polystyrene and Their Micelle-to-Vesicle Transformation in Organic Solvents

Well-defined block copolymers consisting of hyperbranched polyamide (HBPA) and polystyrene (PSt) are synthesized, and their self-assembled structures in solutions are investigated. Atom transfer radical polymerization (ATRP) of styrene initiated from an HBPA macroinitiator, prepared by the chain-growth condensation polymerization of an AB₂ monomer, followed by introduction of an ATRP initiator unit at the focal point, gives the desired block copolymers, PSt-b-HBPAs, with well-defined molecular weight and narrow molecular weight distribution. The block copolymer (PSt/HBPA = 84/16) undergoes self-assembly in toluene to form spherical micelles (≈10–20 nm), but upon addition of methanol to the toluene solution (toluene/methanol = 0.97/0.03), the morphology changes to vesicles. Further addition of methanol (toluene/methanol = 0.90/0.10) leads to an increase in vesicle size (200–300 nm) and the morphology further transforms from vesicles to large aggregates (>100 nm) at toluene/methanol = 0.80/0.20. In the case of PSt-b-HBPA with shorter PSt segments (PSt/HBPA = 76/24 and 60/40), spherical micelles are formed in toluene, but the micelle morphology remains unchanged when 10 wt% methanol is added, though large aggregates (>100 nm) are still formed in toluene/methanol = 0.80/0.20. Interestingly, the morphological transformations of linear/hyperbranched block copolymers are different from those of their double linear block copolymer counterparts.     

Metal compounds in free radical processes, 4. polymerization of vinyl monomers initiated by the system nickel(II) chloride/N,N-dimethylaniline

The system nickel(II) chloride (NiCl₂)/N,N-dimethylaniline (DMA) initiates the polymerization of methyl methacrylate and acrylonitrile. The thermal polymerization of styrene is not affected. From the polymerization and copolymerization studies as well as from spectral measurements in the UV and visible region it is concluded that this polymerization exhibits free radical character. Neither NiCl₂ nor DMA used separately initiate the polymerization. The initiating species are assumed to be formed as a result of interaction between the vinyl monomer/NiCl₂ complex {e.g. in the case of MMA, [Ni(CH₃OH)_6–x(MMA)_x]²⁺2Cl^?, ( 2 )} and DMA. Possible causes for the different initiating efficiency of the system NiCl₂/DMA for various vinyl monomers are also discussed.     

Block copolymers polybutadiene/poly(benzyl-L-glutamate) and polybutadiene/poly(N5-hydroxypropylglutamine) preparation and structural study by X-ray and electron microscopy

AB block copolymers with an amorphous polybutadiene block and a polypeptide block were prepared. The method of synthesis consists in the preparation of a polybutadiene block by anionic polymerization followed by a chemical modification of its living end introducing a primary amine group which is able to intiate the polymerization of the N-carboxy anhydride (NCA) of the chosen amino acid. By this way the block copolymers polybutadiene/poly(γ-benzyl L-glutamate) ( 14a ) were prepared, in which the poly(γ-benzyl-L -glutamate) block could be transformed into a poly(N⁵-hydroxypropyl-L -glutamine) block by reaction with 3-amino-1-propanol leading to the block copolymers polybutadiene/poly(N⁵-hydroxypropylglutamine) ( 14b ). By using X-ray diffraction and electron microscopy it could be shown that the block copolymers 14a and 14b exhibit mesophases in different solvents and it was established that the structure of the mesophases is lamellar. Each sheet of the lamellar structure consists of the superposition of two layers: one formed by the polybutadiene chains in a more or less random coil conformation; the other formed by the polypeptide chains in an α-helix conformation, arranged in an hexagonal array and folded.