13C NMR spectra of tactic and atactic hydrogenated ring-opened polymers of enantiomeric and racemic endo,exo-5,6-dimethylnorbornene

Polymers 1 of the title monomer, prepared using well-defined molybdenum carbene complexes as catalysts, have been hydrogenated and the structures of the resultant polymers 2 examined by ¹³C NMR spectroscopy. The hydrogenated polymer made from the all-cis isotactic polymer of (±)-monomer showed a single set of ¹³C NMR lines as expected for an NX sequence of endo (N) and exo (X) substituents. The hydrogenated polymer made from a cis isotactic polymer of (±)-monomer showed additional fine structure arising from the random incorporation of both enantiomers in the isotactic polymer chain: four equal lines for C-9 (orientational triad sensitivity), two equal lines for C-3, C-4, C-5, and C-1 (dyad sensitivity), but single lines for C-8, C-2, C-7 and C-6 (insensitive to the relative orientation of adjacent repeating units). The hydrogenated polymer made from a trans atactic polymer of (±)-monomer showed fine structure due to the presence of both m and r dyads. That made from a trans atactic polymer of (±)-monomer contains 16 possible triad sequences and gave a more complicated spectrum. A complete assignment was made for the first three polymers and a partial assignment for the fourth. Polymers made using non-carbene catalysts were also examined. Hydrogenation of an all-trans precursor made from (±)-monomer using RuCl₃ as catalyst gave an atactic polymer, confirming previous observations. Hydrogenation of a 61% cis, cis/trans blocky precursor, made from (±)-monomer using OsCl₃/PhCCH as catalyst, gave a syndiotactic-biased stereoblocky polymer, indicating a c/r, t/m correlation in the precursor polymer.     

Stereospecific polymerization of higher α-olefins with the solvay type catalyst TiCl3/Cp2Ti(CH3)2

Polymerizations of higher α-olefins (C₁₀–C₂₀) were carried out at 40°C in heptane, using the following three catalysts which differ in the isospecificity for propene polymerization: Solvay type TiCl₃/Cp₂TiMe₂((A) highly isospecific), Solvay type TiCl₃/AlEt₃((B) isospecific) and TiCl₃.3Py/MgCl₂/AlEt₃((C) aspecific). The isospecificity of the catalysts was found to decrease in the following order: (A) ? (B) ? (C), which agrees well with the results obtained in propene polymerization. The crystallinity of these polymers is discussed in brief.     

A convenient method for the preparation of a highyl active MgCl2-supported TiCl3 catalyst for the polymerization of propylene

A highly dispersed MgCl₂-supported TiCl₃ catalyst was conveniently prepared by treating the complex of TiCl₃ · 3 C₅H₅N with AlEt₂Cl in the presence of MgCl₂. The catalyst combined with AlEt₃ showed a very high activity for the polymerization of propylene, and gave a polymer with considerably high isotacticity. The catalyst displayed a sharp ESR signal with a g-value of 1,94, which is identical with that of the ground H-grade TiCl₃.     

Ring-opening metathesis polymerization of endo- and exo-5-methoxymethylbicyclo[2.2.1]hept-2-ene; microstructure of the polymers

The title monomers 1 and 2 were polymerized by Ru-, Ir-, Mo-, W- and Re-based metathesis catalysts to yield polymers with cis contents ranging from 10% to at least 90% for 1 and 23–60% for 2 . Assignments of the ¹³C NMR spectra were made. No significant head-tail bias was observed in either polymer. A high-trans polymer made from the optically active endo monomer ((?)- 1 ) was atactic, while high-cis polymers could be either atactic or biased towards syndiotactic, depending on the catalyst.     

Modelle und modellreaktionen für die halogenierung von cis- und trans-1.4-polybutadien. Ein beitrag zur stereochemie der „kopf-kopf-polyvinylhalogenide”︁

The all-cis and all-trans isomers of have been synthesized in order to investigate reaction models for cis- and trans-1.4-polybutadienes. The halogenation by means of pyridinium perbromide and pyridinium perchloride leads to these being model compounds for head-to-head poly(vinyl halides). Structural units with erythro configuration result from trans olefins, such with threo configuration from cis olefins. The characteristic C? X frequencies for trans and gauche positions of vicinal halogen atoms derived from infrared and RAMAN spectra are being determined: trans position ν_{C? Br} 550 to 560 cm^?1 (IR), 595–620 cm^?1 (Ra), ν_{C? Cl} 650–660 cm^?1 (IR), 670–690 cm^?1 (Ra), gauche position ν_{C? Br} 520–535 cm^?1 (IR, Ra), ν_{C? Cl} 550–560 cm^?1 and 590–610 cm^?1 (IR, Ra). On the basis of these values a local conformational analysis of the halogenated cis- and trans-1.4-polybutadienes has been made.     

Methacrylic polymers containing permanent dipole azobenzene chromophores spaced from the main chain. 13C NMR spectra and photochromic properties

Dynamics in solution and photochromic properties of radical copolymers of 4-(4-oxy-4′-cyanoazobenzene)but-1-yl methacrylate, 6-(4-oxy-4′-cyanoazobenzene)hex-1-yl methacrylate, and 8-(4-oxy-4′-cyanoazobenzene)oct-1-yl methacrylate with (–)-menthyl methacrylate were investigated. ¹³C NMR and 2D HETCOR spectroscopy allowed assignment of ¹³C NMR signals and evaluation of main chain tacticity. ¹³C T₁ relaxation times evidenced a rather limited mobility of the azobenzene chromophores when inserted in polymer macromolecules. Mobility increased with increasing the length of the polymethylene spacer that acted as a flexible joint between the aromatic chromophore and polymer backbone. Both the trans to cis photoisomerization and the cis to trans thermal isomerization processes showed a small dependence on monomer structure and chemical composition of the investigated photochromic polymers. These data seem to suggest an appreciable contribution of the in-plane inversion mechanism to both isomerization processes of the azobenzene chromophores. The absence of appreciable dichroic bands in the copolymer CD spectra and the negative results obtained in preliminary second harmonic generation measurements are discussed in terms of the polymer structural features.     

MgCl2-supported catalysts for the propylene polymerization: effects of triethers as internal donors on the activity and stereoselectivity

The effects of triethers as internal donors on the activity and stereoselectivity of MgCl₂-supported Ziegler-Natta type catalysts in the propylene polymerization were studied. In particular, we prepared and fully characterized some procatalysts of the type δ-MgCl₂/ID/TiCl₄, where ID are internal donors such as di(ethyleneglycol) diethyl ether (DEGDEE) and di(ethyleneglycol) dimethyl ether (DEGDME). By aging these procatalysts with AlEt₃ (cocatalyst) we obtained δ-MgCl₂/ID/TiCl₄/AlEt₃ catalytic systems, which were tested in the propylene polymerization in order to evaluate their catalytic performance. All polymerizations were carried out in the absence of both external donors (ED) and hydrogen. The productivity and the properties (M_w, M_n, M_w/M_n, and isotacticity index (I.I.)) of the polymers obtained were determined and the results compared with those obtained by using catalysts either lacking an internal donor or with ethyl benzoate as internal donor. The comparison pointed out that the presence of triethers lowers the productivity of the catalysts and increases their stereoselectivity. Polydispersity is also remarkably enhanced suggesting that a multiplicity of active catalytic sites characterized by different environments is present.     

Microstructure of 1,5-cyclooctadiene oligomers

¹H and ¹³C NMR spectra of 1,5-cyclooctadiene oligomers were investigated and compared with those of 1,4-polybutadiene. The oligomers were prepared with Rh₂O₇ as catalyst and fractionated by vacuum distillation or gel-permeation chromatography. It was found that each fraction consists of a mixture of steric isomers possessing cis and trans structures in different ratios. The ¹³C NMR spectra of oligomers with less than 24 carbons vary with ring size, which is explained in terms of ring strain effects. The ¹³C NMR spectra of oligomers with more than 28 carbons are identical with the spectrum of 1,4-polybutadiene. It resulted that the ratio of cis to trans structure in the oligomers decreases with increasing molecular weight from 70:30 (C₁₆) to that in the cyclooctadiene polymer (40:60).     

Highly Active Single‐Site Catalysts for the 1,4‐cis Polymerization of Butadiene from Allylneodymium(III) Chlorides and Trialkylaluminiums – A Contribution to the Activation of Tris(allyl)neodymium(III) and the Further Elucidation of the Structure‐Activity Relationship

To further elucidate the structure‐reactivity relationship in the allylneodymium complex‐catalyzed 1,4‐cis polymerization of butadiene, the following catalyst systems are investigated in toluene more thoroughly: Nd(C₃H₅)₂Cl·1,4‐dioxane, Nd(C₃H₅)Cl₂·2.5 tetrahydrofuran (THF)/5–30 AlMe₃ and preformed Nd(C₃H₄R)₃ in combination with 2 Ph₃CCl, 2 Ph₃CCl/5 AlEt₃; 2 AlMe₂Cl, 2 AlMe₂Cl/30 AlMe₃; 2 AlEt₂Cl and 2 AlEt₂Cl/10 AlEt₃. From the catalytic activity, cis selectivity, polydispersity, degree of polymerization as a function of conversion, as well as the comparison of theoretical and experimental chain length and kinetic analysis, essential conclusions can be drawn concerning the formation reaction and structure of the real catalyst complex and the course of the polymerization reaction. For the combinations of Nd(C₃H₄R)₃ with 2 AlMe₂Cl/30 AlMe₃, 2AlEt₂Cl and 2 AlEt₂Cl/10AlEt₃, the rate law r_P = k_P[Nd][BD]² is derived with the values for k_P of 3.4 (at 35°C), 2.0 and 1.5 L²/(mol²·s¹) (at 50°C), respectively. In each case the formation of a η³‐butenyl bis(η⁴‐butadiene)neodymium(III) complex [Nd(η³‐C₃H₄R)(η⁴‐C₄H₆)₂(ClAlR′₂C₃H₄R)₂] (R′ = Me, Et) is assumed. The insertion reaction proceeds according to the π‐allyl insertion mechanism, and the high cis‐selectivity in accordance with the anti‐cis and syn‐trans correlation is a consequence of the preferential η⁴‐cis coordination of butadiene.     

Functionalized monomers, 3. An investigation of initiation systems used in the anionic and complex-coordination polymerization of oxirane groups in 4-vinylphenyloxirane

The effect of various types of alkoxides and of a complex coordination initiator based on Et₂Al? O? AlEt₂, of the polarity of the medium and of the temperature on the rate of polymerization of 4-vinylphenyloxirane ( 1 ) and on the structure of the resulting polymers was studied as part of the investigation of the activity of the oxirane ring in the structure of ( 1 ) under the conditions of anionic polymerization. In a nonpolar medium the activity of the initiators increases in the series sodium methoxide < potassium tert-butoxide < Et₂Al? O? AlEt₂. The complex Et₂Al? O? AlEt₂ preferentially initiates the polymerization of 1 via the oxirane cycles, giving rise to soluble polymers, the structure of which, determined on the basis of their ¹³C NMR spectra, corresponds to that of polyethers substituted with 4-vinylphenyl groups. In the presence of aluminium isopropoxide the polymerization of 1 via the vinyl groups proceeded with the formation of a solution of a polymer which becomes insoluble after the termination of polymerization. Copolymerization of 1 with phenyloxirane, initiated with the complex Et₂Al? O? AlEt₂, yields soluble copolymers containing a fraction of monomeric units of 1 , higher than that of 1 in the feed.     

Polymerization of Butadiene with V(acac)3‐Methylaluminoxane Catalyst

Full Paper: Polymerization of butadiene (Bd) with V(acac)₃‐methylaluminoxane (MAO) catalyst was investigated. The microstructure of the polymer was found to depend strongly on the polymerization conditions. High polymerization temperature and high MAO/V(acac)₃ mole ratios were preferential to produce cis‐1,4 structure. Two kinds of active species were presumed from the GPC measurement of the polymers; one gives a high molecular weight polymer bearing high cis‐1,4 content, another affords a low molecular weight polymer with high trans‐1,4 content. A Solvent effect was observed. A polymer consisting of mainly trans‐1,4 unit was produced in CH₂Cl₂ in contrast to toluene and n‐heptane in which polymers consisting of mainly cis‐1,4 structure were observed. The addition of ethyl benzoate, triethylamine, chloranil, and tetracyanoquinodimethane to the V(acac)₃‐MAO catalyst gave an influence to not only the activity for the polymerization but also the microstructure of the polymer.     

Polymerization of 5-vinyl-2-norbornene with TiCl3 and alkylaluminium catalysts

The polymerization of 5-vinyl-2-norbornene (VNB) with TiCl₃-alkylaluminium catalysts proceeded selectively via the vinyl group; the vinylene group in the bicyclic ring did not participate in the polymerization. The rate of polymerization of VNB was slow due to the steric effect of the side chain, but effects of the types of TiCl₃ and alkylaluminiums on the polymerization were observed. Hydrogen-activated TiCl₃ plus Al(C₂H₅)₃ revealed the highest catalytic activities among the catalysts examined. The monomer-isomerization copolymerization of VNB and trans-2-butene with TiCl₃/Al(i-C₄H₉)₃ afforded a copolymer consisting of VNB and 1-butene units. The rate of copolymerization of VNB and 1-butene was larger than the monomer-isomerization copolymerization of VNB and trans-2-butene. Copolymers rich in VNB units were produced easily by monomerisomerization copolymerization of VNB and trans-2-butene.     

Stereospecific polymerization of cis,cis-1,4-dideuterio-1,3-butadiene to trans-1,4 or cis-1,4 polymers

cis,cis-1,4-Dideuterio-1,3-butadiene ( 1 ) was polymerized by various catalyst systems {Al(C₂H₅)₃? VCl₃, Al(C₂H₅)₂ Cl? VO(acac)₂, Al(C₂H₅)₃? TiI₄, Al(C₂H₅)₂ Cl? Co(acac)₂, (π-allyl)NiOCOCl₃, (π-allyl)NiI} to polymers having a trans-1,4 or a cis-1,4 structure. Degradative oxidation of the polymers gave a mixture of racemic and meso 2,3-dideuteriosuccinic acid ( 2 ), in a ratio dependent on the particular catalyst used. The polymers obtained with the catalyst systems Al(C₂H₅)₃? VCl₃ and Al(C₂H₅)₂Cl? Co(acac)₂ gave oxidation products with a high percentage of the racemic form of 2 (85–92%), which is indicative of a threo structure of the polymers. IR examination of the polymers obtained by the cobalt or vanadium system showed them to possess a regular structure (presence of the so-called regularity bands). The results are interpreted on the basis of a cis-addition of the monomer. The factors that determine the stereospecificity in the polymerization of 1 are discussed and possible schemes for the formation of the stereoregular polymers are examined.     

On the properties and thermal conversion of ladder polymers with conjugated bonds

The cationic polymerization of vinylacetylenes can be implemented using an excess of catalysts, such as BF₃O(C₂H₅)₂, SnCl₄, H₂SO₄, CCl₃COOH, CF₃COOH (20–50 mol per 100 mol monomer). This is due to the formation of a charge-transfer complex between the catalyst and the polymer obtained, which was confirmed by UV, ESR and IR spectra. Polymers with conjugated ladder sequences in the chain (LP) ( 4 ) were prepared using vinylacetylene ( 1a ), 1-hexen-3-yne ( 1b ), 2-methyl-1,5-hexadiene-3-yne ( 3a ), 2-methyl-5-hexen-3-yn-2-ol ( 3b ) or 5-methoxy-5-methyl-1-hexen-3-yne ( 3c ). The polymers obtained (molar mass = 2000–7000) are pale yellow to pale brown powders which display properties characteristic of polymers with conjugated bonds, i.e. thermal stability in vacuum and air, continuous absorption in UV and near visible regions, broad fluorescence spectra, electric conductivity and ESR signals. The effect of heat treatment in vacuum and air on the structure and some electrophysical properties of LPs was studied by IR, luminescence, ESR and mass-spectroscopy and also by TGA, DTA, and X-ray diffraction analyses. The heat treatment in the temperature range of 150–400°C gives rise to a complete cyclization accompanied by a partial degradation and leads to the formation of polycondensed aromatic structures and to a sharp increase of electroconductivity up to 1.10^?5Ω^?1cm^?1 and to an increase of the concentration of paramagnetic particles up to 1.10²⁰ spin/g at an ESR signal width in vacuum of 0,4 gauss (0,4.10^?4 tesla).     

Mechanism of ring-opening polymerization of 1-methylbicyclo[2.2.1]hept-2-ene using metathesis catalysts

Polymers of the title monomer have been made using 24 different metathesis catalysts, based on Nb, Mo, W, Re, Ru, Os and Ir compounds. Their structure, determined by ¹³C NMR spectroscopy, varies from all-cis (ReCl₅) to all-trans (RuCl₃, OsCl₃) and from fully biased (head-tail) to unbiased. The bias stems partly from an inability to from head-head dyads containing cis double bonds and partly from the dipolar interaction between the propagating metal-carbene complex and the monomer in forming the [2 + 2] transition state. Arguments are presented to show that the formation of biased polymers proceeds largely through a metal carbene species in which the last-added monomeric unit has its methyl group adjacent to the metal centre (P_H). In high-cis polymers the sequences of three double bonds are such as to indicate that a kinetic distinction must be made between species in which the previous double bond formed was cis or trans (P_Hc or P_Ht), consistent with the observation that high-cis polymers of related monomers have a blocky cis/trans distribution.     

A UV/visible spectroscopic study of water-soluble conjugated polyenes prepared via the ring-opening metathesis polymerization reaction

A series of water-soluble conjugated polyenes, based on the poly(furanylvinylene) structure, have been prepared from readily available starting materials using ring-opening metathesis polymerization followed by dehydrogenation of the resulting polymer. ¹³C NMR analysis of the precursor polymers shows that the stereochemistry of the main-chain double bonds varies from 93% trans to 10% trans and is retained in the water-soluble derivatives, allowing different degrees of extended conjugation. This is reflected in the UV/vis spectra of the materials. The polymers may be cast into films from aqueous solution, and the UV/vis spectra exhibit vibrational fine structure indicative of conformational rigidity; significantly this fine structure is retained on redissolving the high-trans but not the high-cis films. The absorption maximum of the visible spectrum shows a stronger pH dependence in the high-cis polymers than in the high-trans, and this is interpreted in terms of the different modes of hydrogen bonding which cis and trans units can adopt.     

Cationic polymerization of α·β-disubstituted olefins. Part XI. Polymerization of 2-chloroethyl propenyl ether catalyzed by BF3·O(C2H5)2

2-Chloroethyl propenyl ether (CEPE) was synthesized, and its cationic polymerizability by BF₃·O(C₂H₅)₂ and the steric structure of the resulting polymer were studied. In the polymerization in toluene at ?78°C, the rate of consumption of monomers decreased in the following order: cis-CEPE > 2-chloroethyl vinyl ether > trans-CEPE. The steric structure of the β-methyl group of the resulting polymer was determined quantitatively on the basis of the NMR spectrum of the β-methyl protons decoupled from β-methine protons. In the polymerization of CEPE in toluene at ?78°C, the polymer obtained from trans-CEPE was rich in threo-meso structure whilst cis-CEPE gave a polymer containing almost the same amount of threo-meso and erythro-meso structures. With methylene chloride as solvent, the amount of threo-meso structure increased and that of erythro-meso structure decreased for the polymer obtained from cis-CEPE. The steric structure of the polymer obtained from trans-CEPE was independent of the nature of the solvent used. The effect of polymerization temperature on the steric structure of the polymers was also investigated.     

Novel butadiene-isobutene copolymers obtained by means of coordination catalysts: Synthesis and physico-chemical characterization

The synthesis of novel butadiene (B)-isobutene (I) copolymers, prepared with coordination catalysts, is reported and discussed. The best results were obtained by using at ?40°C ternary systems, based on TiCl₄, (i-C₄H₉)₃Al or (i-C₄H₉)₂AlH, and benzophenone or acetophenone, previously aged at ?78 °C. The formation of the novel B–I copolymers was accompanied by polybutadiene (cis- and trans-1,4-units were prevalent) and, sometimes by cationic I–B copolymer. The new copolymers, after isolation, underwent thorough spectroscopic investigations. IR analysis yielded the microstructure of B units: trans-1,4=55%, cis-1,4=31%, and 1,2=14%. ¹H NMR spectroscopy showed that I unit is present only in alternating triad BIB and ruled out the presence of any I homosequence. The study, by ¹³C NMR, of both the original and hydrogenated copolymer evidenced that only trans-1,4-B is linked to I units and hence the copolymer structure is described by IBI and IB_nI (where n≥2) sequences. A copolymer containing 30% of I showed the following mole fractions of triads centered on B: F_IBI=0,158; F_BBI+IBB=0,382; and F_BBB=0,462. The mechanistic implications of the copolymer structure are discussed.     

Study of the mechanism of propagation and transfer reactions in the polymerization of olefins by Ziegler-Natta catalysts, 1. Determination of the number of propagation centers and the rate constant

The number of propagation centers (C_p) and the propagation rate constant (K_p) in the polymerization of ethylene and propene in the presence of heterogeneous TiCl₃ derived Ziegler-Natta catalysts of different composition were determined using the method of quenching the polymerization by radioactive carbon monoxide (¹⁴CO). The values of K_p, (1,2±0,3)·10⁴ l mol^?1 s^?1 at 75°C for ethylene and (90±20) l mol^?1 s^?1 at 70°C for propene polymerization, significantly exceed those ones obtained by use of tritium tagged alcohols as quenching agents. Further, for the polymerization of olefins in the presence of TiCl₃ based catalysts, the influence of catalyst composition, polymerization conditions, and monomer nature on C_p and K_p was studied.     

Conformational stability and force field of polyphosphazenes: MNDO calculations,vibrational spectra and normal coordinate analyses of [NP(R)2]n (R = Cl,OCH2CF3, OC6H5)

Raman and Fourier-transform Raman spectra (1500 ? 100 cm^?1) of (PCl₂N)_n (PDCP) were recorded in the solid phase and in solution at room temperature. Raman (3 500 ? 100 cm^?1) and infrared (4 000 ? 200 cm^?1) spectra of [P(OCH₂CF₃)₂N]_n (PDFP) and [P(OC₆H₅)₂N]_n (PDPP) were recorded in the solid phase and at different temperatures (in the case of Raman spectroscopy). The conformation of the isolated macromolecule PDCP is assumed to be analogous to the geometry of the Cl₂(O)PN(PCl₂N)₆PCl₃ oligomer optimized by the use of MNDO (modified neglect of diatomic overlap) calculations. The optimized cis-trans conformation is in good agreement with the X-ray experimental data concerning the polymer. The calculated low energy barriers around the PN bond along the chain axis can explain the flexibility of the phosphazene backbone and the elastomeric properties of the polymers. The MNDO calculation of the harmonic force field of Cl₂(O)PN(PCl₂N)₆PCl₃ is in reasonable agreement with the experimental values for (PCl₂N)_n in solution as well as in the amorphous phase. The normal coordinate analyses of (PCl₂N)_n were undertaken according to several structural hypotheses using a force field derived from linear short-chain molecules. The Raman spectra of PDCP in solution or in the amorphous phase are in reasonable agreement with the vibrational frequencies calculated for a planar cis-trans macromolecule and have a striking resemblance with those of linear short-chain analogs Cl₂(O)PN(PCl₂N)_n PCl₃ (n = 1,2). The Raman and infrared spectra of the substituted polymers PDFP and PDPP are dominated by the characteristic features of the chain substituents.