Polymer-solvent interactions in mixed solvents, 1. Isotactic,syndiotactic and atactic poly(methacrylic acid) in water/2-chloroethanol mixtures

The viscosimetric behaviour and the preferential solvation of syndiotactic, isotactic, and atactic poly(methacrylic acid), [poly(1-carboxy-1-methylethylene)] are studied in water/2-chloroethanol mixtures. The experimental results show that the preferential solvation of the polymer is strongly dependent on its local conformation. In the case of the syndiotactic sample, a close correlation has been established between the compact structure ? coil conformational transition and the variation of the preferential and absolute solvation of the polymer by 2-chloroethanol, asserting the importance of hydrophobic interactions in the stabilization of the compact structure. Experimental data concerning the isotactic sample suggest the existence of an “inverse compact structure” in 2-chloroethanol-rich mixtures.     

Poly-(α-methyl benzyl methacrylate). Preparation and preliminary observations

Poly-(α-methyl benzyl methacrylate) (PMBMA) polymers were prepared in isotactic, syndiotactic, and atactic forms using both optically active and racemic monomers. The isotactic material was prepared by anionic polymerization in a hydrocarbon solvent at a low temperature (～?60°C), the syndiotactic and atactic polymers were synthesized by ultraviolet initiated free radical polymerization at –65 and 32°C, respectively. From the proton magnetic resonance spectrum, it could be determined that the isotactic polymer was of high stereochemical purity. The syndiotactic material was less pure, and the atactic polymer was largely syndiotactic. Racemic and optically active α-methyl benzyl pivalates were prepared to serve as monomeric analogues of the polymer. The optical activity of the isotactic polymer in dioxane is one-third greater than that of the monomeric analogue at 5890 Å; the syndiotactic polymer is slightly less optically active than the monomeric analogue, and the atactic polymer is between the syndio- and iso-polymers but much nearer the syndio material. The enhancement or decrease of the optical activity is associated with the orientation correlation of successive chain segments, the specific chemical structure of the optically active group, and on solvent-polymer interactions. The orientation correlations persist over a short range only.     

Polymer-solvent interactions in mixed solvents, 3. Poly(methacrylic acid) and poly(sodium methacrylate) in water-dioxane mixtures

The preferential solvation of poly(methacrylic acid) and poly(sodium methacrylate) in waterdioxane mixtures was investigated by means of specific refractive index increment measurements on dialysed and undialysed solutions. The correlation with the solvent-induced conformational transition of poly(methacrylic acid) was also studied. Potentiometric titrations indicate that this transition occurs at around 25–30 vol.-% of dioxane. Comparison with previous results on poly(acrylic acid) and poly(sodium acrylate) in the same solvent system and on poly(methacrylic acid) in water-2-chloroethanol mixtures, shows differences in the mode of solvation of the compact conformation. It is suggested that this may be dependent on the existence of water-organic solvent specific interactions such as the formation of a water-dioxane hydrogen-bonded complex.     

Polymer-solvent interactions in mixed solvents, 5. Ionized ethyl,butyl, and hexyl vinyl ether-maleic acid alternating copolymers in water/2-chloroethanol mixtures

Viscosity and preferential solvation measurements were carried out on ionized maleic acidethyl, -butyl, and -hexyl vinyl ether alternating copolymers (i-MA/EVE, i-MA/BVE, and i-MA/HVE, respectively) in water-2-chloroethanol mixtures. i-MA/EVE and i-MA/BVE are completely coiled and their preferential and absolute solvation by water and 2-chloroethanol reflects their more or less hydrophilic or hydrophobic nature. For i-MA/HVE, the viscosimetric and preferential solvation measurements suggest that, in 2-chloroethanol rich mixtures, the polymer retains a hypercoiled conformation in which an important part of the hexyl side chains are screened form contact with both componenets of the solvent mixture.     

Polymer-solvent interactions in mixed solvents, 4. Ethyl- and butyl vinyl ether-maleic acid alternating copolymers in water/2-chloroethanol mixtures

Viscosity and preferential solvation measurements were carried out on maleic acid-ethyl- and -butyl vinyl ether alternating copolymers (MA-EVE and MA-BVE, respectively) in watermethanol and water-2-chloroethanol mixtures. The conformational transition of MA-BVE was found to be strongly related to the solvation of the polymer by 2-chloroethanol. Comparison of experimental results on MA-BVE, MA-EVE, and poly(methacrylic acid) (PMA) in water-2-chloroethanol mixtures indicates that the behaviour of MA-EVE is different from that of MA-BVE and PMA because it does not undergo any conformational transition.     

Stereoregularity of poly(methacryloyl chloride) and poly(methacrylic salts) prepared by photopolymerization

Poly(methacryloyl chloride) (PMACl) and poly(methacrylic tetramethylammonium salts) and poly(methacrylic tetraethyl ammonium salts) (PMAAN⁺) have been prepared by radical photopolymerization at different temperatures. The obtained molecular weights are independent of the polymerization temperature in the range studied (+24 to ?30°C) which is in agreement with a purely photochemical process. The dependence of the tacticity upon temperature was examined by means of NMR spectroscopy. Deviations from Bernoullian statistics were confirmed. PMAAN⁺ salts prepared in water are highly syndiotactic and a nearly pure syndiotactic structure is obtained at +5°C. This behavior is explained by the repulsive interactions between the carboxylate anions promoting the racemic placement. The tacticity of PMACl is comparable with that of poly(methacryloyl fluoride). The structure is less syndiotactic and much more isotactic than that of poly(methyl methacrylate). This result is interpreted by considering the electron-withdrawing character of chlorine and fluorine atoms which affects the electronic structure and polarity of the carbonyl group near to the macroradical and competes with the preferential syndiotactic placement observed with α-substituted acrylates.     

Propene polymerization in the presence of MgCl2-supported Ziegler-Natta catalysts, 4.. Effects of Lewis bases on polymer stereochemistry

The stereochemistry of polypropenes obtained in the presence of several MgCl₂-supported Ziegler-Natta catalyst systems comprising different Lewis bases has been investigated by ¹³C NMR spectroscopy, with special attention paid to the “less tactic” (heptane-soluble) fractions. These have been found to consist of “tendentially isotactic” and “tendentially syndiotactic” stereosequences, in largely variable amounts (depending on the catalyst system). The microstructure of the former is in accordance with the enantiomorphic site model, whereas that of the latter suggests a stereocontrol arising from the asymmetry of the growing chain end. In both cases, propene insertion is primary (1–2). Polymerization conditions leading to the formation of “syndiotacticrich” polymers showing syndiotactic crystallinity have been identified.     

Propylene polymerization with Ph2C(3-RCp)(Flu)ZrCl2 [R = Me,i-Pr,PhCH2, Me3Si] catalysts activated with MAO and Me2PhNH·B(C6F5)4/i-Bu3Al

Propylene polymerization was conducted with Ph₂C(R-Cp)(Flu)ZrCl₂ [R = Me, i-Pr, PhCH₂, Me₃Si] catalysts in combination with methylaluminoxane (MAO) and dimethylanilinium tetrakis(pentafluorophenyl)borate (Me₂PhNH·B(C₆F₅)₄) as cocatalyst; the dependence of the stereoregularity of poly(propylene) on cocatalysts and bulkiness of the substituents in β-position of the cyclopentadienyl ligand was studied. Methyl and i-propyl substituted metallocene catalysts produce hemi-isotactic poly(propylene). These results are in good agreement with the results of the isopropylidene bridged metallocene analogue. The benzyl substituted metallocene catalyst produces syndiotactic poly(propylene) regardless of the cocatalyst. This means that this substituent group does not affect migration insertion of propylene. Stereoregularity of poly(propylene) obtained with diphenylmethylidene(3-trimethylsilylcyclopentadienyl)(fluorenyl)zirconium dichloride (Ph₂C(Me₃SiCp)(Flu)ZrCl₂) as a catalyst was significantly influenced by the cocatalyst. Me₂PhNH· B(C₆F₅)₄/triisobutylaluminium(i-Bu₃Al) produces poly(propylene) with 65% racemic and 23% meso pentads at 40°C, whereas the MAO activated catalyst produces isotactic rich poly(propylene). Fractionation experiments indicated that Me₂PhNH·B(C₆F₅)₄/i-Bu₃Al forms two active sites, one of them being the same as that of the MAO activated catalyst, the other one producing syndiotactic rich poly(propylene).     

Hyaluronic acid and sulfated hyaluronic acid in aqueous solution: effect of the sulfation on the protonation and complex formation with Cu2+ and Zn2+ ions

The behaviour of hyaluronic acid (Hyal) and sulfated hyaluronic acid (HyalS) in aqueous solution was investigated in terms of protonation and complex formation by thermodynamic and spectroscopic techniques. The presence of the scarcely protonable sulfate groups in the polymer chain provided the HyalS molecule with a more rigid structure in aqueous solution, allowing this polysaccharide to remain in the stretched conformation even after neutralisation of the carboxylate moieties. The presence of the sulfate groups also increases the basic character of the COO^– group. Both Hyal and HyalS were able to form complexes with Cu²⁺ and Zn²⁺ ions in aqueous solution. The metal ion has a preferential binding site on these polysaccharides, providing a precise stoichiometry for the metal ion complex. The sulfate groups were not directly involved in the coordination of the metal ion, and the stoichiometry of the complex species is not affected by the presence of these groups. However, by increasing the negative charge on the polymer chain, the sulfate groups are responsible for the electrostatic attraction of the metal ion.     

Copolymer statistics during esterification of syndiotactic poly(methacrylic acid) with diazotoluene and diazodiphenylmethane

Syndiotactic poly(methacrylic acid) has been partially esterified with diazotoluene or diazodiphenylmethane in extension of work carried out with diazomethane¹. The sequence statistics of the resulting cosyndiotactic benzyl methacrylate–methacrylic acid and diphenylmethyl methacrylate–methacrylic acid copolymers have been studied with ¹H-NMR spectroscopy, by relating the triad probabilities obtained by employing different NMR solvents. For both types of copolymers BERNOULLI an triad statistics were found within accuracy of the NMR measurements. Therefore, these polymer analogous reactions, like the reaction of diazomethane with syndiotactic poly(methacrylic acid)¹, are not influenced by a kinetic neighboring group effect, despite the greater space requirement of the two diazoalkanes when compared to diazomethane. The copolymers possess therefore a simple, and defined configurational and compositional structure which cannot be obtained at present by the copolymerization of monomers. The polyelectrolyte character of the copolymers could be eliminated without altering the configurational and compositional statistics by complete esterification with a second diazoalkane. Thus the diphenylmethyl methacrylate–methacrylic acid copolymers were converted with diazomethane to diphenylmethyl methacrylate–methyl methacrylate copolymers and with diazotoluene to diphenylmethyl methacrylate–benzyl methacrylate copolymers. Furthermore, it appears that the reaction with syndiotactic poly(methacrylic acid) may also be utilized to prepare defined cosyndiotactic copolymers composed of three or four different types of monomeric units by successive partial esterification with different diazoalkanes.     

Light scattering and viscosity studies of poly(2-vinylpyridine 1-oxide) in some organic solvents at 25°C

Light scattering in 2-propanol and viscosity measurements in six good solvents were carried out at 25°C for fourteen fractions of poly(2-vinylpyridine 1-oxide) (P2VPO) with molar mass of (1,3–34,4) · 10⁴ g · mol^?1, which were synthesized by oxidizing poly(2-vinylpyridine) with H₂O₂. The numerical values of the Mark-Houwink-Sakurada constants K′ and a and of the parameters K and B from the plots of Kamide-Kawai, Kurata-Stockmayer and Inagaki-Ptitsyn as well as Stockmayer-Fixman, were determined as well. The averaged characteristic ratio C∞ and steric factor σ for this polymer are 8,58 and 2,07, evaluated from K in each solvent except benzyl alcohol with the last plot. The value in benzyl alcohol is rather large and clearly shows the solvent dependence in K. Comparing this average value with those of similar polymers, it is concluded that the P2VPO chain acquires a compact coil structure. The solvent power was found to increase in the following sequence: chloroform < 2-propanol < 1-propanol < methanol ≤ 1-butanol < benzyl alcohol, as judged from the B values.     

Polymerisationsauslösung mit substituierten ethanen, 2. Trennung der Oligomeren aus Methylmethacrylat und 1,1,2,2-Tetraphenyl-1,2-diphenoxyethan

The telechelics 1 from methyl methacrylate and 1,1,2,2-tetraphenyl-1,2-diphenoxyethane, can be separated by adsorption chromatography. The structure of the dimers and trimers was identified by ¹H NMR-spectroscopy. The free radical oligomerization is a process in which the syndiotactic structure is favoured above the isotactic one.     

HR-NMR study of formation and structure of the stereocomplex of poly(methyl methacrylate) in solution

From high-resolution NMR spectra of mixtures of solutions of isotactic and syndiotactic poly(methyl methacrylate), the content p of the associated stereocomplex was determined. From the values of p, the minimum length of associated syndiotactic sequences was found to be ca. 10 monomeric units in aromatic solvents and ca. 3 such units in CCl₄ and CD₃CN. In the associated stereocomplex the ratio of monomeric units in isotactic and syndiotactic sequences is (iso/syndio) = 1:1,5; the process of dissociation of the stereocomplex with increasing temperature is reminiscent of the melting of microcrystallites. The melting point of associated segments in a given solvent increases with the length of the associated sequences.     

Reactive groups on polymer coated electrodes, 7. New electrogenerated electroactive polythiophenes with different protected carboxyl groups

By the protection of the carboxyl group of 3-thiopheneacetic acid with differently substituted benzyl groups a series of new thiophene derivatives were synthesized. While 3-thiopheneacetic acid is not electropolymerizable, the new obtained monomers can be easily electrooxidized to form stable electroactive polymers. The electrochemical characterizations show that the substitution of the benzyl groups exerts little effect on the electropolymerization process and that the obtained polymers exhibit the typical properties of polythiophene derivatives, e. g., redox behavior and electrochromism. SEM studies show that all synthesized monomers possess a very good film formability and the resulting polymers exhibit a rather compact and homogeneous morphology on the Pt electrodes also containing scattered particles. Using p-nitrobenzyl-protected polymer as an illustrative example, it was demonstrated that the used protecting group can be easily split off in the solid state and the desired reactive carboxyl group can be produced on the polymer surface. Therefor, through the protection of the carboxyl group, the electropolymerization and the following removal of the protecting group, a new type of polymer matrix material with reactive carboxyl groups was simply prepared by using commercially available 3-thiopheneacetic acid monomer.     

Determination of the Crystal Structure of Syndiotactic 3,4‐Poly(2‐methyl‐1,3‐butadiene) by Molecular Mechanics and X‐Ray Diffraction

Summary: The crystal structure of syndiotactic 3,4‐poly(2‐methyl‐1,3‐butadiene) has been determined by the joint use of molecular mechanics and X‐ray diffraction. Molecular mechanics calculations have been performed both on the isolated chain and on the crystal by the use of various force fields. The energy minimizations predict a model of the crystal structure. The calculated X‐ray powder diffraction pattern is in good agreement with the experimental one. This model has been refined in order to obtain the best agreement with all the experimental data. The space group is Pbcm and the parameters of the unit cell are a = 6.6 Å, b = 13.2 Å, c = 5.27 Å. The presence of defects in the crystal has been taken into account. Analogies and differences with the crystal structure of syndiotactic 1,2‐poly(1,3‐butadiene) are discussed.

X‐ray fiber diffraction pattern of syndiotactic 3,4‐poly(2‐methyl‐1,3‐butadiene).     

Preferential solvation of poly(acrylic acid) and its sodium salt in water/dioxane mixtures: A comparison with poly(α-L-glutamic acid)

The preferential solvation of poly(acrylic acid) and its sodium salt in water/dioxane mixtures was studied. The comparison with results previously obtained on poly(χ-L -glutamic acid) indicates the preferential solvation of the latter polymer by dioxane is due to the existence of the peptide group in the polymer. The viscosimetric behavior of poly(acrylic acid) in water/dioxane mixtures is interpreted by the existence of water-dioxane complexes with a definite stoechiometry.     

1-Butene polymerization in the presence of MgCl2-supported Ziegler-Natta catalysts: polymer microstructure in relation to polymerization mechanism

1-Butene polymerization in the presence of MgCl₂-supported Ziegler-Natta catalyst systems was investigated under conditions such as to obtain polymer samples containing high amounts of (prevailingly) syndiotactic sequences. These were found in part to be linked to (prevailingly) isotactic sequences in stereoblock macromolecules. More clearly than in the case of the corresponding propene polymers, the spectroscopic characterization of the poly(1-butene) samples proved that the syndiospecificity in such systems is dictated by the asymmetry of the last inserted monomer unit.     

The behaviour of poly(methacrylic acid) and poly(2-hydroxyethyl methacrylate) in water/2-chloroethanol mixtures

The viscosimetric behaviour and the preferential solvation of poly(methacrylic acid), (PMA, poly(1-carboxy-1-methylethylene)) and poly(2-hydroxyethyl methacrylate), (PHEMA, poly[1-(2-hydroxyethoxycarbonyl)-1-methylethylene]) in water/2-chloroethanol mixtures were studied. The system PHEMA/water/2-chloroethanol is a typical polymer/solvent/precipitant system in which 2-chloroethanol is preferentially solvated in the whole range of solubility. On the contrary, the system PMA/water/2-chloroethanol is a typical cosolvent system which exhibits the so-called inverse adsorption. This difference is attributed to the more hydrophilic character of the carbonyl group in PMA.     

Polymere ester von Säuren des phosphors, 5. Ringöffnende polymerisation des 2-phenoxy-1,3,2-dioxaphospholan durch Michaelis-Arbuzov-reaktion

2-Phenoxy-1,3,2-dioxaphospholane ( 14 ) was polymerized by benzyl halogenides at temperatures between 120 and 200°C. It was found that the main chain consists predominantly of unexpected ethylene 1,2-ethanediphosphonate units 7 ; only about 10% of the monomer was incorporated as the expected 2-hydroxyethanephosphonate structure. An insertion mechanism, proposed by Harwood and Patel for the analogous polymerization of 2-phenyl-1,3,2-dioxaphospholane, does not agree with our experimental results. A hypothesis is developed involving a two step addition process, which exclusively occurs at the chain end. Alternating, one monomer molecule is added by a normal Michaelis-Arbuzov-reaction, and then a second molecule is added followed by an intermediate 1,2-shift of the endstanding halogen cryptoanion. With benzyl bromide as initiator, the growing end shows alternating the sequences CPOCCBr (2-bromoethyl ester) and COPCCBr (2-bromoethanephosphonate).     

Dimethylsiloxane-ethylene oxide block copolymers, 2. Preliminary results on dilute solution properties

The dilute solution properties of poly(ethylene oxide)-polydimethylsiloxane-poly(ethylene oxide) (POE-PDMS-POE) triblock copolymers, of a POE-PDMS segmented block copolymer and of a grafted PDMS-g-(POE-co-POP) copolymer are investigated by means of viscosity, light scattering and small angle neutron scattering. The experiments indicate that the copolymers are molecularly dispersed or aggregated, depending on the properties of the solvents. A rather compact conformation is deduced from the viscosity measurements. Negative A₂-values are observed in preferential solvents for one of the segments, a positiv A₂-value in a common solvent for both segments forming the block copolymer.