Vinyl Chloride Copolymerization. Penultimate Effects with Conjugated Comonomer

A kinetic study of the radical copolymerization of vinyl chloride with acrylonitrile, methyl methacrylate, or styrene, using the chromatographic method, shows that penultimate effects are observed in all cases, chiefly for the acrylonitrile case (r_cc = 0.03, r_ac = 3.0). The conjugated monomer induces a stronger penultimate effect than the unconjugated vinyl chloride; this effect might be correlated with the e values of the Q-e scheme. A strong antepenultimate effect is observed on the styrene ended radicals (r_sss = 3.0, r_css = 20.0, r_scs = 18.5, r_ccs = 2.7), which might be related to a steric effect.     

The characteristics of lanthanide coordination catalysts and the cis-polydienes prepared therewith

The stereoregularity of polydienes is almost the same in regard to the individual elements of the lanthanide series, whereas the activity of the Ln catalysts in diene polymerization varies from one to the other within the series. The latter may be attributed to the difference in the number of electrons that occupy the 4f orbitals. It has been proved that the polymerization of dienes with Ln catalysts under certain conditions proceeds by a “living polymer” mechanism. With regard to the polymerization of butadiene, the most active catalyst is a Nd³⁺species a new binary system of NdCl₃-3ROH + AlR₃ has been discovered. The cis- 1,4 content in polybutadiene is about 97% and the 1,2 content, less than 1%. For the polymerization of isoprene with a Nd³⁺ catalyst system, the effects of ligand and alkyl groups in AIR₃ on cis-1,4 content (ca. 95%) in polyisoprene can be neglected. For the copolymerization of butadiene and isoprene, the cis-1,4 contents of these two monomeric units in the copolymer are greater than 95% the reactivity ratios r₁ and r₂ are determined. and the T_g's of the copolymers of various compositions deviate slightly from the calculated values for random copolymers. A linear relationship exists between the yield strength from the stress-strain curve of Ln-polvbutadiene and its [n] This relationship is verified by Ln-polyisoprene and natural rubber but different slopes are obtained     

Copolymerization of oxetane with 3,3-dimethyloxetane-I. Reactivity parameters and microstructure of the copolymers

The copolymerization of 3,3-dimethyloxetane and oxetane has been studied in methylene chloride at 20°, with triethyloxonium tetrafluoroborate as initiator. The copolymerization reactivity parameters are r_DMOx = 0.95 and r_Ox = 1.19. By means of 300 MHz ¹H-NMR spectroscopy, the microstructure of the copolymers could be analyzed in terms of triad abundances. The observed values are in good agreement with the values calculated from the reactivity parameters thus showing the absence of penultimate effects and of re-distribution of the structural units in the copolymers. The results demonstrate that Ox is more reactive than DMOx to either of the two growing species in the copolymerization.     

Polymerization and copolymerization of 2-phthalimidomethyl 1,3-butadiene. I. Preliminary studies of free radical polymerization and polymerizations initiated by various transition metal allyl complexes

2-Phthalimidomethyl 1,3-butadiene was homopolymerized and copolymerized with butadiene by free radical initiators; r₁ and r₂ were close to 1. All the attempts to polymerize 2PMB anionically have been unsuccessful. Preliminary studies of various η³-allylic catalysts showed that η³-allyl M₀(CO)₃OOCCF₃ initiates the polymerization of butadiene and is not sensitive to N-methyl phthalimide (NMP); neither does it initiate the copolymerization of butadiene and 2PMB. On the other hand, a catalyst that results from the reaction of allyl trifluoroacetate with nickel tetracarbonyl is efficient for the copolymerization of butadiene and 2PMB. η³-Allyl nickel trifluoroacetate was prepared in heptane or benzene and used in benzene or methylene chloride. In all cases it initiated the copolymerization of butadiene with 2PMB     

Random copolymer of butadiene and propylene prepared with TiCl4–Et3Al–phosgene catalyst

The copolymerization of butadiene and propylene was investigated. It was found that the catalyst system of TiCl₄–Et₃Al–COCl₂ yields a random copolymer of high molecular weight with a small amount of gel polymer above room temperature. Tetrachloroethylene was a good solvent for the production of high polymer containing a high proportion of propylene units in high yield. The fractionation and the analysis of degradation experiments of copolymer indicate that the copolymer is of random distribution of propylene units in the copolymer. However, the monomer reactivity ratios, r_BD = 6.36 and r_Pr = 0.42, suggest some degree of blocked character. The properties of the copolymer were superior to those of cis-1,4–polybutadiene, especially in resistance to thermal aging.     

Olefin terpolymerizations. III. Symmetry,sterics, and monomer structure in ansa-zirconocenium catalysis of EPDM synthesis

Ethylenebis (η⁵-fluorenyl) zirconium dichloride ( 1 ) and rac-dimethylsilylene bis (1-η⁵-in-denyl) zirconium dichloride ( 2 ) were activated with methylaluminoxane (MAO) to catalyze ethylene (E) propylene (P) copolymerizations. The former produces high MW copolymer at 20°C rich in ethylene with reactivity ratio values of r_E = 1.7 and r_P <0.01, whereas the latter produces lower MW random copolymers with r_E = 1.32 and r_p = 0.36. Ethylidene norbornene (ENB) complexes with 1/MAO but does not undergo insertion in the presence of E and P. In contrast, 2/MAO catalyzes terpolymerization incorporating 9-15 mol % of ENB with slightly lower MW and activity than the corresponding copolymerizations. In comparison, 1,4–hexadiene was incorporated by 2/MAO with much lower A and MW . Terpolymerizations were also conducted with vinylcyclohexene using both catalyst systems. The steric and electronic effects in these processes were discussed. © 1995 John Wiley & Sons, Inc.     

Structure of ascorbic acid and its biological function

Summary Only LAMMA spectra of negative ions of ascorbic acid and isoascorbic acid exhibit a deprotonated peak. In the case of the radicals Na-ascorbate and K-isoascorbate neither the positive nor the negative ion spectra show a similar peak. Only a peak at m_r/z=41 can be detected in the negative ion spectra of both of the radicals. Positive ion spectra exhibit peaks at m_r/z =63 (for Na-ASC) and at 95 (for K-Iso-ASC) in addition to the Na⁺ and K⁺ peaks in the corresponding radicals. The peaks at 41, 63, and 95 might represent Na and K complexes engulfed in the cyclic structure of the side chain. From the results obtained one can be certain, that both of the radicals are electroneutral.

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Struktur von Ascorbinsäure und ihre biologische Funktion: IV. Untersuchung der Struktur durch laser-induzierte Massenspektrometrie

Zusammenfassung Nur die LAMMA-Spektren der negativen Ionen von Ascorbinsäure und Isoascorbinsäure haben einen deprotonierten Peak. Bei den Radikalen Na-Ascorbat und K-Isoascorbat ist dieser weder bei den positiven noch bei den negativen Ionen-Spektren vorhanden. Bei beiden Radikalen kann nur bei m_r/z=41 ein Peak im negativen Ionen-Spektrum nachgewiesen werden. Die positiven Ionen-Spektren haben neben den Na⁺- und K⁺-Peaks solche bei m_r/z=63 (für Na-ASC) und 95 (für K-Iso-ASC). Die Peaks bei 41,63 und 95 stellen wahrscheinlich Na- und K-Komplexe dar, die in der cyclischen Struktur der Seitenkette eingebettet sind. Auf jeden Fall kann aus den erhaltenen Ergebnissen geschlossen werden, daß beide Radikale elektroneutral sind.

     

Solvent and kinetic penultimate unit effects in the copolymerization of acrylonitrile with itaconic acid

Copolymerization of acrylonitrile (AN) with itaconic acid (IA) in dimethylformamide (DMF) and DMF/water mixture was investigated at enhanced concentrations of the latter. Analysis of the copolymer composition revealed the existence of a marked penultimate unit effect with respect to radicals terminated in AN. The reactivity of IA was considerably less than that of AN, manifested as a negative reactivity ratio for the former. The r_IA values ranging from −0.28 to −0.50 and r_AN values ranging from 0.53 to 0.70, were obtained by Kelen-Tudo's (KT) and extended KT methods. The penultimate reactivity ratios were determined by both linear and non-linear methods. The values ranged from r₁=0.009 to 0.01, r₁^′=0.0015 to 0.0043, r₂=0.54 to 0.69 and r₂^′=0.9 to 1.03. The reactivity of AN radical towards IA decreased about twofold when the latter formed the penultimate group. The penultimate model explained an acceptable rational feed-copolymer composition profile for the whole composition range. Addition of water decreased the reactivity of IA slightly. IA caused a decrease in the apparent copolymerization rate in agreement with the observed trends in the reactivity ratios; presence of water caused a further decrease in the rate of polymerization. A statistical prediction of monomer sequences based on reactivity ratios implied that IA existed as a lone monomer unit between the long sequences of AN units.     

Thermal degradation of copolymers of butadiene and acrylonitrile

Ten copolymers of butadiene and acrylonitrile have been prepared covering the composition range 100-25 mole % butadiene; reactivity ratios are r_butadiene = 0?50, r_{acrylonitrile} = 0?07. The thermal analysis techniques (TVA, TGA and DSC) have been applied to determine the general features of the thermal degradation of these copolymers. The fractions of products comprising permanent gases, products volatile at 20°, chain fragment material and residue have been separated and analysed. The constituent parts of the overall reaction have been discussed and the whole represented in the form of an integrated reaction mechanism.     

Introduction of unsaturated pendant groups to polyethylene by γ-ray irradiation under a 1,3-butadiene atmosphere

Ultra-high-molecular-weight polyethylene (Mˉ _v: 5 × 10⁶, 100-times elongated film) was irradiated with γ-rays under a 1,3-butadiene atmosphere at room temperature. Electron paramagnetic resonance (EPR) measurements indicated that the radicals formed on the polyethylene substrate during the irradiation were short-lived. EPR, Fourier transform IR spectroscopy, solid-state NMR, and differential scanning calorimetry of the as-irradiated materials indicated that butadiene molecules were covalently bound to the polyethylene chains as pendant groups bearing trans-vinylene and vinyl functions in a ratio of 3:1. Some crosslinks among the pendants, or between pendants and the main chains were produced. The number of unsaturated pendants introduced (including bridges) per carbon atom of the polyethylene main chain was dependent on the irradiation dose and the butadiene pressure, and was 0.096 butadiene units for 10 kGy irradiation under a 304 kPa butadiene atmosphere. The unsaturated pendants or bridges on the polyethylene chain thus introduced may be good targets to functionalize polyethylene by covalent modification. Received: 22 February 1999 Accepted in revised form: 30 June 1999     

Free-Radical Copolymerization of Methyl Methacrylate and a-Methacrylophenone. II. Sequence Distribution through13 C-[1H] NMR Spectroscopy

Sequence distribution in methyl methacrylate (A)-methacrylo-phenone (B) copolymers obtained by free-radical copolymerization at 60°C has been studied by ^l3C-[¹H] NMR spectroscopy. Quantitative analysis of the resonance patterns of the quaternary carbon atom of A units and of the α -CH₃ carbon atoms of A and B units has been carried out, considering both compositional and configurational effects. All the kinetic and structural data may be readily taken into account by a scheme in which copolymerization obeys a penultimate unit model characterized by the four reactivity ratios r., = 1.77 ± 0.02, r = 2.30 ± 0.10, r_BB = 0.058 ± 0.01, r_AB = 0.325 ± 0.03. The stereochemistry of the cross-propagation steps may be described by a single cotacticity parameter: a = σ_AB = σ_BA ? 0.40. Its relatively high value probably arises from the great steric hindrance and the high polarizability of the aromatic keto group of methacrylo-phenone.     

Kinetic parameters and geometry of the transition state of acyl radical decarbonylation

Experimental data on acyl radical decomposition reactions (RC^·O → R^· + CO, where R = alkyl or aryl) are analyzed in terms of the intersecting parabolas method. Kinetic parameters characterizing these reactions are calculated. The transition state of methyl radical addition to CO at the C atoms is calculated using the DFT method. A semiempirical algorithm is constructed for calculating the transition state geometry for the decomposition of acyl radicals and for the reverse reactions of R^· addition to CO. Kinetic parameters (activation energy and rate constant) and geometry (interatomic distances in the transition state) are calculated for 18 decomposition reactions of structurally different acyl radicals. A linear correlation between the interatomic distance r ^#(C…C) (or r ^#(C…O)) in the transition state the enthalpy of the reaction (δH _e) is established for acyl decomposition reactions (at br _e = const). A comparative analysis of the enthalpies, activation energies, and interatomic distances in the transition state is carried out for the decomposition and formation of acyl, carboxyl, and formyl radicals.     

Facile synthesis of blocky styrene(1,3)‐butadiene copolymers having stereoregular monomeric sequences

Half titanocenes (CpCH₂CH₂O)TiCl₂ 1 and (CpCH₂CH₂ OCH₃)TiCl₃ 2 , activated by methylaluminoxane are tested in styrene–1,3‐butadiene copolymerization. The titanocene 1 is able to copolymerize styrene and 1,3‐butadiene, with a facile procedure, to give products with high molecular weight. The analysis of microstructure by ¹³C‐NMR reveals that the styrene homosequences in copolymers are in syndiotactic arrangement, while the butadiene homosequences are, prevailingly, in 1,4‐cis configuration, according with behavior of 1 in the homopolymerizations of styrene and 1,3‐butadiene, respectively. The reactivity ratios of copolymerization are estimated by diad composition analysis. All obtained copolymers have r₁ × r₂ values much larger than 1, indicating blocky nature of homosequences. The structural characterization by wide‐angle X‐ray powder diffraction and differential scanning calorimetry indicates that all copolymers are crystalline, with T_m varying from 171 to 239 °C, depending on the styrene content. The titanocene 2 did not succeed in styrene–1,3‐butadiene copolymerization, giving rise to a blend of homopolymers. Compounds 1 and 2 were also tested in the polymerization of several conjugated dienes, and the obtained results were very useful to rationalize the behavior of both catalysts in the copolymerization of styrene and butadiene. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 815–822, 2010     

Organometallic polymers. XIV. Copolymerization of vinylcyclopentadienyl manganese tricarbonyl and vinylferrocene with N-vinyl-2-pyrrolidone

N-Vinyl-2-pyrrolidone(I) has been copolymerized with vinylferrocene(II) and vinylcyclopentadienyl manganese tricarbonyl(III) in degassed benzene solutions with the use of azobisisobutyronitrile (AIBN) as the initiator. The polymerizations proceed smoothly, and the relative reactivity ratios were determined as r₁ = 0.66, r₂ = 0.40 (for copolymerization of I with II, M₁ defined as II) and r₁ = 0.14 and r₂ = 0.09 (for copolymerization of I with III, M₁ defined as III). These copolymers were soluble in benzene, THF, chloroform, CCl₄, and DMF. Molecular weights were determined by viscosity and gel-permeation chromatography studies (universal calibration technique.) The copolymers exhibited values of M?_n between 5 × 10³ and 10 × 10³ and M?_w between 7 × 10³ and 17 × 10³ with M?_w/M?_n < 2. Upon heating to 260°C under N₂, copolymers of III underwent gas evolution and weight loss. The weight loss was enhanced at 300°C, and the polymers became in creasingly insoluble. Copolymers of vinylferrocene were oxidized to polyferricinium salts upon treatment with dichlorodicyanoquinone (DDQ) or o-chloranil (o-CA) in benzene. Each unit of quinone incorporated into the polysalts had been reduced to its radical anion. The ratio of ferrocene to ferricinium units in the polysalts was determined. The polysalts did not melt at 360°C and were readily soluble only in DMF.     

Structure and reactivity in cationic polymerization of butadiene derivatives. IV. 1-alkoxybutadienes

The reactivity of trans-1-alkoxybutadienes in cationic homopolymerization and copolymerizations and structure of the polymers produced were investigated. 1-Ethoxybutadiene is polymerized easily at ?78°C by various acidic catalysis. The reactivity of 1-ethoxybutadiene was similar to that of ethyl vinyl ether. The polymers produced possessed molecular weights of several thousands, and were composed of 70–95% 1,4 structure and 5–30% 3,4 structure. In the copolymerization of ethyl vinyl ether (M₁) with 1-ethoxybutadiene at ?78°C in toluene by boron trifluoride diethyl etherate, r₁ = 1.15, r₂ = 2.62. From the Hammett plot of the relative reactivities of alkoxybutadienes (alkoxy: CH₃O, C₂H₅O, i-C₃H₇O), the reaction constant _p^* was determined to be ?2.9. Results of the present study were compared with those of various butadiene derivatives.     

The antioxidant reactivity of sorbitylfurfural towards potential harmful radicals,studied by radiation chemistry techniques

Ionising radiations, employed in a broad range of dose-rate, together with a complex non-linear computation of reaction mechanisms, allow the determination of boundary values of rate constants concerning sorbitylfurfural (SF) reactivity towards a wide series of oxidant and/or virtually harmful radicals. SF reacts with some radicals (H, SO₄^-˙, CO₃^-˙, Br₂^-˙, CH₃˙), produced with both pulse and stationary radiolysis in neutral aqueous solution, having electrophilic and/or oxidative behaviour. The rate constants range from diffusional (k = (7-9) × 10⁹ M^-1 s^-1) to relatively low values (k = 2 × 10⁵ M^-1 s^-1). The possibility to observe these reactions, by means of radiolytical techniques, is heavily influenced by dose-rate. A relation between the radical E⁰_NHE and their reactivity with SF is hinted.     

Styrene/1,3‐butadiene copolymerization by C2‐symmetric group 4 metallocenes based catalysts

C₂‐symmetric group 4 metallocenes based catalysts (rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]ZrCl₂ (1) , rac‐[CH₂(1‐indenyl)₂]ZrCl₂ (2) and rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]TiCl₂ (3) ) are able to copolymerize styrene and 1,3‐butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by ¹³C NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain‐end happens prevailingly with 1,4‐trans configuration. In the butadiene homosequences, using zirconocene‐based catalysts, the 1,4‐trans arrangement is favored over 1,4‐cis, but the latter is prevailing in the presence of titanocene (3) . Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r₁ × r₂ = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene–butadiene copolymers (r₁ × r₂ = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (n_s = 16, in the copolymer at highest styrene molar fraction). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1476–1487, 2008     

The distance distribution of radical—paramagnetic ion pairs studied by the electron spin echo method. Spatial regularities of radical diffusion in glassy alcohols

Applications of the electron spin echo (ESE) technique to determine the distance distribution function for radical-ion pairs stabilized in solids are described. The ESE signal intensity depends on the ion spin-lattice relaxation time T₁, thus on temperature, as well as on the function n(r),n(r) can be determined up to a distance of 50 A. At r < 10 - 20 A it is possible to estimate the portion of radicals stabilized at these distances in the vicinity of a paramegnetic ion. The photochemical reaction Fe³⁺ + R₂CH(OH)→Fe²⁺ +_R₂C(OH) + H⁺ has been studied in glassy methanol and isopropanol. The pair distribution function n(r) has been obtained at 17 < r < 26 A. Its changes induced by radical diffusion have been studied. The portion of radicals stabilized at distance r < 17 A was about 80% for both alcohols.     

EPR studies of mechanically induced bond rupture in elastomers

Electron paramagnetic resonance (EPR) spectroscopy was used to compute the surface bond rupture density in polyurethane and to determine the phase experiencing fracture in styrene-butadiene block copolymers when these elastomers are subjected to mechanical degradation by grinding. The polyurethane grinding was done at temperatures above and below the glass transition T_g; 0.155 × 10¹³ radicals/cm² of fracture surface area were formed above the T_g and 4.42 × 10¹³ radicals/cm² for grinding below the T_g. These values are essentially equal to those found earlier for spherulitic polymers. In all cases the fracture appears able to progress along preferential paths so as to rupture significantly fewer molecular chains than one would expect on the basis of calculations of the number of chains passing through each square centimeter of cross section. Comparison of EPR spectra formed by grinding styrene-butadiene copolymer with those of styrene and butadiene above indicated that at cryogenic temperature, the fracture in the copolymer takes place in the butadiene phase.