Lithiation of diene polymers

It was found that the metallation of diene polymers with n-butyllithium in n-heptane takes place in the presence of a tert amine, i.e. N,N,N′,N′-tetramethylethylenediamine. Butyllithium was added to the diene polymer in n-heptane in the presence of an equimolar amount of the amine, and the mixture was allowed to react at 80°C. for 60 min. under nitrogen. As a result, 27% and 9% per monomer unit for polybutadiene and polyisoprene, respectively, were metallated. The effects of the concentrations of the diene polymer, butyllithium, and the amine on the reaction were studied at 80°C., and the reaction mechanism was discussed. The overall rate of metalation was proportional to the diene polymer concentration and to the square root of the butyllithium concentration. The overall activation energies of metalation were 6.6 and 8.4 kcal./mole for polybutadiene and polyisoprene, respectively. Many kinds of polymer derivative were obtained by treating the metalated polymers with various reagents, such as carbon dioxide, Michler's ketone, trimethylchlorosilane, triphenylchlorosilane, benzaldehyde, and pyridine.     

Organometallic polymers. III. Organometallic modifications of diene polymers

A process for the chemical modification of polybutadienes and natural rubber by various metallocene compounds is described. Soluble products of up to 43% ferrocene content were obtained. The effect of substrate, metallocene, and reaction conditions on the course and extent of substitution was investigated. The glass transition temperature T_g was found to increase considerably with the degree of substitution, e.g., cis-polybutadiene substituted with ferrocene (18 mole-%) has a T_g of 30°C, as compared with ?91°C for the unsubstituted polymer.     

Bond exciton model of alkenes and diene polymers

The bond exciton model, developed originally for alkane molecules, is applied here to a range of alkene molecules and diene polymers. The necessary empirical parameters are derived by comparison of the theory with the vacuum-ultraviolet absorption spectra of ethylene and a number of alkyl-substituted ethylenes, and these values are used to predict the energies, intensities and polarizations of the lower energy allowed valence transitions of fine diene polymers. Despite its simplicity the bond exciton model is found to give results in quite reasonable agreement with the available experimental data, and suggests that considerable excitation energy transfer may occur along the main chains of certain diene polymers.     

Anionic graft copolymerization of diene polymers with vinyl monomers

A mixture of homopolymer and graft copolymer was obtained by adding the monomer at 0°C to the polylithiodiene solution. Styrene, methyl methacrylate, and acrylonitrile were used as the monomers. Polylithiodienes were prepared by the metalation of diene polymers, i.e., polybutadiene or polyisoprene, with the use of n-butyllithium in the presence of a tertiary amine (N,N,N′,N′-tetramethylethylenediamine) in n-heptane. The graft copolymers were separated by solvent extraction and were confirmed by turbidimetric titration and elementary analysis. Oxidation of the polybutadiene–styrene grafts revealed that the molecular weight of the side chains was the same as the molecular weight of the free polystyrene formed. The grafting efficiency and grafting percentage were studied for polybutadiene–styrene graft copolymers prepared under various conditions.     

Experimental branching results for diene polymers by use of gel-permeation chromatography

Branching analyses in styrene–butadiene rubbers and polybutadiene rubbers have revealed large differences in branching between rubbers polymerized in different ways. The functionalities of several star-branched solution-polymerized styrene–butadiene rubbers were calculated and compared to their expected structures. Emulsion-polymerized polybutadiene rubber and a series of solution-polymerized polybutadienes made with different catalysts had different degrees of random branching, and evidence is presented indicating that the different available catalyst systems provide some latitude in making rubbers of different branching contents. Random branching analyses on a series of emulsion-polymerized styrene–butadiene rubbers revealed the dependency of branching on molecular weight and molecular weight distribution. The influence of polymerization temperature on the branching of emulsion-polymerized styrene–butadiene rubber was also studied.     

Acyclic diene metathesis (ADMET) depolymerization of functionalized furan-based polymers

Acyclic dience metathesis (ADMET) depolymerization of functionalized furan-based polymers prepared via aqueous ring-opening polymerization of 7-oxanobornenes has been investigated. Results indicate that while very high molecular weight poly [exo-N-methyl-7-oxabicyclo [2.2.1] hept-2,5-diene-2,3-dicarboximide] can be depolymerized to oligomers with ease, poly [2,3-dicarbomethoxy-7-oxabicyclo [2.2.1] hept-2,5-diene] is more resistant to depolymerization under similar conditions. This difference may be due to differential interaction of the carbonyls in the side chains with the metal atom of the catalyst in the proposed metallacyclobutane intermediate. ADMET depolymerization of poly [2,3-bis (trifluoromethyl)-7-oxabicyclo [2.2.1] hept-2,5-diene] was feasible, however, the extent of depolymerization was decreased due to the use of a coordinating solvent (THF) used during the depolymerization process. © 1994 John Wiley & Sons, Inc.     

Ferrocene-containing polymers synthesized by acyclic diene metathesis (ADMET) polymerization

Herein we reported that ferrocene-containing polymers could be synthesized via acyclic diene metathesis(ADMET) polymerization of ferrocene-containing bis-styryl monomers. The all-trans-configured vinylene bonds of stilbene segment were proven by means of 13C-NMR, 1H-NMR, MALDI-TOF mass spectrometry and FTIR. Poly(1) showed maxima for absorption at 320 nm and emission at 430 nm which are structurally very similar to trans-stilbene, but 24 and 16 nm red shifted respectively. CIE chromaticity diagram shows that emission color could be adjusted by controlling the molecular weight. The polymer showed excellent solubility in common organic solvents and good thermal stability evidenced by TGA and DSC. The results of CV suggested the polymer possessed noninteracting metal centers which was confirmed by a reversible one-electron redox wave observed for the polymer.     

Cyclo- and cyclized diene polymers. XII. Cationic polymerization of isoprene

Polymerization of isoprene with Lewis acids in n-heptane is a process leading to a quasiequilibrium which is characterized by very low conversions. Polymerization rates in aromatic solvents are much higher due to extensive chain transfer with solvent with regeneration of the original active centers. The rate of monomer disappearance in benzene or toluene when aluminum bromide is the catalyst is second order with respect to monomer concentration. The reaction order with respect to the catalyst depends on the reaction conditions; at constant monomer concentration it is approximately one. Polymerization rates in halogenated solvents with the use of syringe techniques are much higher than those in aromatic solvents. Polymers obtained with various cationic catalysts ranged from oils to white powders having molecular weights up to more than 100,000 depending on reaction conditions. All polymers exhibited infrared spectra characteristic of cyclopolydienes, and the content of linear structures usually did not exceed 20%, irrespective of the nature of the catalyst or solvent. In solvents of higher polarity, such as o-dichlorobenzene, more linear structures were detected. Among residual linear forms the trans-1,4 addition was found to prevail. Residual unsaturation in polymers did not exceed 30%.     

Aggregation behaviour below the gelation threshold for metal-olefin coordination in diene polymers

This study focuses on aggregation below the gelation threshold in ternary solutions containing diene polymers, atactic 1,2-polybutadiene (PBu) or 3,4-polyisoprene (PI), and an inorganic salt, bis(acetonitrile) dichloropalladium(II). Upon mixing, effective coordination crosslinks are formed because the acetonitrile ligands of the palladium salt are displaced by olefinic pendant groups of the polymers. In all cases, the aggregation kinetics correlate with PdCl₂ concentration because the polymer concentration is 100 times greater than the salt concentration. Aggregation is the process that occurs prior to gelation as the transition-metal salt forms a coordination bridge between two different polymer chains. Differential analysis of the initial aggregation rate on the basis of light scattering data at 45° relative to the incident throughput beam reveals that the ‘true’ order of the coordination reaction is close to unity. This suggests that coordination crosslinking is diffusion-controlled in the early stages of aggregation. Half-life analysis of viscous solutions yields an overall reaction order of 1.6 for aggregation of polybutadiene and palladium chloride in tetrahydorfuran (THF). Scaling analysis of the weight-average molecular weight dependence of the root-mean-square size of isolated scattering particles yields an effective exponent of 0.7 for polymer/metal-salt complexes at infinite dilution. This experimental scaling law agrees with literature values for cross-linked polymer networks. In all cases, the size of the aggregates increases at higher PdCl₂ concentration. For polybutadiene/PdCl₂ mixtures in THF or toluene below the gelation threshold, the light-scattering-detected average aggregation number (AN = M_{w, complex}/M_{w, pure polymer} via Zimm-plot intercepts) for low-viscosity solutions is 2, while AN ∼ 9 for viscous THF solutions. In contrast, low aggregation numbers (AN ∼ 2) were calculated for viscous ternary mixtures of 3,4-polyisoprene and PdCl₂ in THF.     

Anionic polymerization initiators containing protected functional groups and functionally terminated diene polymers

Organolithium reagents substituted with hydroxyl-carrying mixed acetals (i.e., tetra-hydropyranyl and α-ethoxyethyl ethers) have been prepared in high yields and used to polymerize 1,3-butadiene to various acetal-terminated polybutadiene polymers. A method is described for converting acetal-containing polymers into hydroxyl-containing polymers. The polybutadienes have been characterized with regard to endgroup types, quantitative functionalities, molecular weights, molecular weight distributions, and microstructures. Dihydroxyl terminated polymers are prepared anionically in the absence of gel. Such materials are more suitable from the standpoint of f (OH) and M?_w/M?_n for chain extension studies than are prepolymers prepared by radical methods.     

Phase behaviour of amphiphilic side-chain polymers

The present study describes the phase behaviour of a low-molar-mass 1,3-diol with a linear alkyl chain in aqueous solution. From the combined results of differential scanning calorimetry and optical polarizing microscopy a phase diagram was constructed. The low-molar-mass diol forms a lamellar mesophase only in the presence of water. The influence of the linkage of the amphiphilic molecule to different polymer backbones on the stability of the mesophase was investigated. It is evident that amphiphilic side-chain polymers show a distinct stabilization of the mesophase. Moreover, comparison between the polyacrylate, polymethacrylate and polysiloxane indicates a strong influence of the main-chain flexibility on the stability of the liquid-crystalline phase. The type of the liquid-crystalline phase of the side-chain polyacrylate in the water-saturated state was identified by X-ray investigations as lamellar. The hydration behaviour of the polymers was investigated by ²H-N.M.R. and isopiestic measurements.     

Phase behaviour of amphiphilic side-chain polymers

The present study describes the phase behaviour of a low-molar-mass 1,3-diol with a linear alkyl chain in aqueous solution. From the combined results of differential scanning calorimetry and optical polarizing microscopy a phase diagram was constructed. The low-molar-mass diol forms a lamellar mesophase only in the presence of water. The influence of the linkage of the amphiphilic molecule to different polymer backbones on the stability of the mesophase was investigated. It is evident that amphiphilic side-chain polymers show a distinct stabilization of the mesophase. Moreover, comparison between the polyacrylate, polymethacrylate and polysiloxane indicates a strong influence of the main-chain flexibility on the stability of the liquid-crystalline phase. The type of the liquid-crystalline phase of the side-chain polyacrylate in the water-saturated state was identified by X-ray investigations as lamellar. The hydration behaviour of the polymers was investigated by ²H-N.M.R. and isopiestic measurements.     

Synergistic mechanical response in blends of diene polymers and their complexes with palladium chloride

The mechanical properties of atactic 1,2-polybutadiene and 3, 4-polyisoprene can be modified significantly with the addition of bis(acetonitrile)dichloropalladium(II). These weak rubbery polymers are transformed into glassy materials when the salt concentration is ≅ 4 mol %, in the absence of high-temperature annealing. Stress-strain measurements and Fourier transform infrared (FTIR) spectra for blends of cis-polybutadiene and PdCl₂, without high-temperature annealing, suggest that π-complexes form between palladium and the olefinic groups within the backbone of the polymer. These solid complexes cannot be dissolved in the original solvent (tetrahydrofuran), nor can they be disrupted by triphenylphosphine. Young's modulus of the cis-polymer is enhanced by a factor of 50 when the salt concentration is 4 mol %, and the fracture strain is approximately 300%. An exothermic process centered at ≅ 250°C accompanied by minimal weight loss suggests that PdCl₂ could trigger high-temperature dimerization reactions of the carbon–carbon double bonds in the backbone of the cis-polymer. High-temperature annealing effects on the stress-strain response of cis-polybutadiene with 4 mol % PdCl₂ are consistent with the data from calorimetry, suggesting that catalytically induced chemical crosslinking is operative at high temperatures. This latter claim is verified by infrared spectroscopy at ambient and elevated temperatures. Hence, bis(acetonitrile)dichloropalladium(II) coordinates to and catalyzes dimerization reactions of olefinic groups when they are present in the main chain or the sidegroup. This square-planar transition-metal salt also enhances the high-strain mechanical response of commercial styrene-butadiene-styrene triblock copolymers (Kraton^TM D series). Reactive blending and compatibilization with transition-metal salts are attractive strategies to modify the mechanical properties of commercially important diene-based polymers that contain unsaturation in the main chain or the sidegroup. © 1996 John Wiley & Sons, Inc.     

Stereocontrol of diene polymers by topochemical polymerization of substituted benzyl muconates and their crystallization properties

We report the stereocontrol of diene polymers by the topochemical polymerization of alkoxy-substituted benzyl muconates in the solid state. A monomer stacking structure is controlled by the weak intermolecular interactions in the monomer crystals, depending on the structure and position of the alkoxy-substituent. The translational and alternating types of molecular stacking structures in a column provide diisotactic and disyndiotactic polymers, respectively, by the solid-state polymerization under UV and γ-ray irradiation. On the other hand, the meso and racemo structures of the resulting polymers are determined by the molecular symmetry of the used muconate monomers. The various substituted benzyl ester polymers are transformed into the same ethyl ester polymers with the four types of tacticities. The structure and crystallization behavior of the substituted benzyl ester polymers as well as the ethyl ester polymers have been revealed in detail. We clarify the effects of the tacticity on the crystallization property of the stereoregular polymuconates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4952–4965, 2006     

Influence of a diene impurity on the molecular structure of phosphate-containing polymers with medical applications

We have demonstrated that the unacknowledged presence of almost 30% diene impurity in some commercial phosphate monomers had not only a significant effect on the molecular structure (topology) of a series of synthesized polymers but the instability of the ester functionalities during these polymerizations resulted in unexpectedly complex co-polymer chemistry.     

Phase behavior in HIQ40 liquid crystalline polymers

The thermotropic copolyester consisting of 40 mol%p-hydroxybenzoic acid and 30 mol% isophthalic acid/30 mol% hydroquinone (HIQ40), prepared by two different synthetic routes (acidolysis or phenylester) was studied by differential scanning calorimetry and X-ray diffraction. All these samples show a glass transition temperature in the range of 125–141°C, dependent on the sample thermal history. A crystal to nematic transition is observed between 300 and 375°C. The samples prepared by the acidolysis route, when compared to those producedvia the phenylester reaction, have higher crystallinity which is due to the formation of IA/HQ crystals. The crystallinity can be increased significantly (as much as twice) by annealing the polymers at 300°C. The heat of fusion (X N, crystal to nematic) of the annealed acidolysis samples is also higher than that of the polymers prepared by the phenylester process. The nematic to isotropic (N I) transitions are broad, exhibiting no definite clearing points. Several mesogenic transitions as suggested by X-ray studies and two crystallization peaks were found for all samples studied. This may be an indication that the samples consist of two, distinct polymeric compositions or that there are two crystal forms. Furthermore, since the intensity ratio of the two crystallization peaks changes as a function of annealing, it is clear that the chemical/physical state of the polymer depends on the thermal history of the samples. Attempts to prepare amorphous HIQ40 and nematic HIQ40 glass by quenching from the isotropic state (480°C and 400°C, respectively) were unsuccessful, however, it can be prepared by precipitation of the acidolysis polymer from solution.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthday     

Phase behavior of PCBM blends with different conjugated polymers

In this work the phase behavior of [6,6]-phenyl C(61)-butyric acid methyl ester (PCBM) blends with different poly(phenylene vinylene) (PPV) samples is investigated by means of standard and modulated temperature differential scanning calorimetry (DSC and MTDSC) and rapid heat-cool calorimetry (RHC). The PPV conjugated polymers include poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene) (MDMO-PPV), High T(g)-PPV which is a copolymer, and poly((2-methoxy-5-phenethoxy)-1,4-phenylene vinylene) (MPE-PPV). Comparisons of these PPV:PCBM blends with regioregular poly(3-hexyl thiophene) (P3HT):PCBM blends are made to see the different component miscibilities among different blends. The occurrence of liquid-liquid phase separation in the molten state of MDMO-PPV:PCBM and High T(g)-PPV:PCBM blends is indicated by the coexistence of double glass transitions for blends with a PCBM weight fraction of around 80 wt%. This is in contrast to the P3HT:PCBM blends where no phase separation is observed. Due to its high cooling rate (about 2000 K min(-1)), RHC proves to be a useful tool to investigate the phase separation in PPV:PCBM blends through the glass transition of these crystallizable blends. P3HT is found to have much higher thermal stability than the PPV samples.     

Characterization of diene polymers. I. Infrared and NMR studies: Nonadditive behavior of characteristic infrared bands

Extinction coefficients of the characteristic infrared bands due to isomeric structural units were measured for polybutadiene and polyisoprene in CS₂ or CCl₄ solutions and were compared with the isomer composition determined by NMR. The NMR signal assignments were made on the basis of the spectra of deutero derivatives of the polymers. In the case of polyisoprene, linear relations were obtained between the extinction coefficients and the isomer contents determined by NMR for the absorption bands at 1385 cm^?1 (characteristic of trans-1,4 units), 1376 cm^?1 (cis-1,4 units), and 889 cm^?1 (3,4 units). However, for the absorption bands at 840 cm^?1 (characteristic of cis-1,4 and trans-1,4 units), isomerized polyisoprenes did not give such a linear relationship. In polybutadiene, the extinction coefficient for the atactic 1,2 units was found to be lower than that of the syndiotactic 1,2 unit. These experimental facts lead to the conclusion that additivity of the extinction coefficients does not always hold for diene polymers. The deviation from the linear relation may be associated with regular sequences of one isomeric conformation in the chain.     

Cyclo- and cyclized diene polymers. XIII. γ-Ray-initiated polymerization of 1,3-dienes

The γ-ray-initiated polymerization of butadiene, isoprene, and 2,3-dimethylbutadiene-1,3 was carried out at temperatures of 20°C. and ?78°C. Polymers of butadiene and isoprene with mixed linear and cyclic structure were proved to result from the polymerization at ?78°C. A monocyclic structure was found for the 2,3-dimethylbutadiene-1,3 polymers initiated either at ?78°C. or in the thiourea canal complex at 20°C.