Metathesis polymerization of exo,exo-, endo,exo- and endo,endo-5,6-dimethylbicyclo[2.2.1]hept-2-enes; microstructure of the polymers and their hydrogenated products

Polymers of exo,exo-, endo,exo, and endo,endo-5,6-dimethylbicyclo[2.2.1]hept-2-ene monomers were prepared using a selection of eight metathesis catalysts and their structures examined by ¹³C NMR spectroscopy. Tacticities could be determined for the polymers of the endo, endo and endo,exo monomers and for all three hydrogenated polymers. RuCl₃ gave hightrans atactic polymers while ReCl₅ gave high-cis syndiotactic polymers, but WCl₆/Bu₄Sn gave a high-cis atactic polymer of the endo,endo monomer. The endo,exo monomer was unusual in giving polymers of relatively low cis content (fraction of cis double bonds σ_c ≤ 0,3), and with strong exo,endo (XN) bias except in the case of RuCl₃. The parallel with the head, tail (HT) biased polymers of 1-methylbicyclo[2.2.1]hept-2-ene is noted. Polymers of the exo,exo and endo,endo monomers have a blocky cis/trans double bond distribution at moderate cis content. The results are discussed in terms of a mechanism involving propagation by metal-carbene, metal-carbene-olefin and metallacyclobutane complexes.     

NMR Characterization of Carbazole‐Substituted Norbornene Comonomer 9‐(Bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) and Poly(ethylene‐co‐BHMCZ) Copolymer

Carbazole‐substituted norbornene comonomer 9‐(bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) can be copolymerized with ethylene using the [Ph₂C(Ind)(Cp)ZrCl₂] catalyst and methylaluminoxane (MAO) cocatalyst system. The microstructures of BHMCZ comonomer and of ethylene–BHMCZ copolymer containing 4.6 mol‐% BHMCZ units in the chain were characterized by one‐dimensional ¹³C DEPT and two‐dimensional homonuclear ¹H‐¹H COSY and heteronuclear ¹H‐¹³C HXCO NMR spectroscopy. The BHMCZ comonomer appears as endo and exo stereoisomers, which were identified on the basis of chemical shifts, signal multiplicities, and coupling in the 2D NMR spectra. The NMR information on the BHMCZ isomers was used to assist in the determination of the chemical shifts and microstructure of ethylene–BHMCZ copolymer. The NMR analysis of ethylene–BHMCZ copolymer indicated that exo‐BHMCZ polymerizes with ethylene slightly more readily than does endo‐BHMCZ under the polymerization conditions employed.

Isolated segments of exo(2)‐exo(5)‐exo(6) and endo(2)‐exo(5)‐exo(6) ethylene‐BHMCZ copolymer showing carbon atom numbering.     

1H NMR study of the kinetics of metathesis polymerization of 5- and 5,6-methoxycarbonyl derivatives of bicyclo[2.2.1]-hept-2-ene,initiated by

The ring-opening metathesis polymerization of 5-endo-methoxycarbonyl ( 1 ), 5-exo-methoxy-carbonyl ( 2 ), 5,6-endo,endo-bis(methoxycarbonyl) ( 3 ), 5,6-exo,exo-bis(methoxycarbonyl) ( 4 ) and 5,6-endo,exo-bis(methoxycarbonyl) ( 5 ) derivatives of norbornene, initiated by the tungsten cyclopentylidene complex , have been followed by ¹H NMR in situ at 290 – 320 K. The initial metal-carbene adduct P ₁ is usually distinguishable from the subsequent adducts P _n(n > 1). Initiation is generally faster than or as fast as propagation. The propagation rate constants for the monosubstituted derivatives 1 and 2 are two to four times greater than those for the 5,6-disubstituted derivatives 3 – 5 . Arrhenius parameters were determined for the propagation reactions of 1 and 3 .     

Endo/Exo Reactivity Ratios in Living Vinyl Addition Polymerization of Substituted Norbornenes

Substituted norbornenes may be enchained by vinyl addition polymerization (VAP), through the norbornene double bond. Such monomers are generally prepared by Diels–Alder cycloaddition of cyclopentadiene and the corresponding olefin, which leads to a mixture of endo and exo stereoisomers with potentially very different reactivity, but these differences have not previously been quantified (e.g., as copolymerization reactivity ratios r_endo and r_exo). A living Pd‐based VAP initiator is employed and the consumption of endo and exo monomers to high conversions is measured to determine r_endo and r_exo; since the polymerization is living, the products are gradient copolymers. For norbornenes bearing n‐butyl, norbornyl, or methylhexafluoroisopropanol substituents, r_exo = 1–4, and r_exo r_endo = 0.2–0.8, indicating only moderate deviations from ideal copolymerization behavior. By contrast, for norbornene bearing a pentamethyldisiloxane substituent, r_endo is indistinguishable from zero, indicating that the endo isomer is effectively incapable of homopropagation. However, since the polymerization is living, propagation resumes (and chain extension proceeds) when additional exo monomer is charged.     

Structure and content of dicyclopentadiene in ethylene-propylene-dicyclopentadiene terpolymers

With the aid of model compounds – derivatives of endo- and exo-dicyclopentadiene – it has been established that:

• (a) the 9,10-double bond (the double bond in the norbornane-ring) is involved in the polymerization of dicyclopentadiene with ethylene and propylene;
• (b) dicyclopentadiene, present in the polymerization mixture in the endo-configuration, occurs in the exo-configuration in the polymer chain. The same model compounds enable the DCPD-content of ethylene-propylene-DCPD terpolymers to be determined by infrared-spectroscopic methods. Use is made of the 3045 cm^?1 band, which is characteristic of endo-cyclic double bonds in five-membered rings.

     

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.     

How to Fight Kinetics in Complex Radical Polymerization Processes: Theoretical Case Study of Poly(divinyl ether‐alt‐maleic anhydride)

Products of free‐radical polymerization (FRP) are usually not regulated on the molecular scale, consisting of blocks obtained through the fastest kinetic scheme pathways. The side or kinetically restricted products can be a source of impurities in a complex FRP case, or possess new properties if isolated solely. FRP synthesis of poly(divinyl ether‐alt‐maleic anhydride), known as “DIVEMA”, serves as a polymerization example with such kinetic and thermodynamic complexities. Uncertainty in factors regulating polymer structure is a challenge in advancement “DIVEMA” derivatives toward medical practice. In‐depth investigation via quantum‐chemical and molecular mechanics methods unveils mechanistic aspects of polymer stereoisomerism and confirms possible isolation of thermodynamically or kinetically controlled products on a large data set. Strategies toward regulation of 5‐exo/6‐endo cycloisomerism are theorized and then studied via microkinetic modeling. Thermodynamically controlled products can be isolated utilizing lower monomer concentrations, in range of 10^?3 to 10^?1 m , and/or application of a complexing agent that is better to realize via solvents, capable of formation π‐ and σ‐radical complexes. Change of electrophilic monomer is proposed as an approach for designing more molecularscale adjustable copolymerization processes. Methodology, obtained results, and conclusions for “DIVEMA” can be valuable to control other FRP processes on the molecular scale, unlocking polymers with improved or new functionalities.     

The ring-opening metathesis polymerization of (±)-5-endo-methoxynorborn-2-ene. Microstructure of the polymers

The title monomer (±)-5-endo-methoxynorborn-2-ene ((±)-5-endo-methoxybicyclo[2.2.1]-hept-2-ene, 1 ) was polymerized by Ru-, W-, Ir-, Re- and Mo-based metathesis catalysts to yield polymers with cis contents ranging from 10% to 48%. An assignment of the ¹³C NMR spectra was made. No significant head-tail bias was observed and no splitting due to tacticity could be positively identified.     

Polynorbornene Dicarboximides with Cyclic Pendant Groups: Synthesis and Gas Transport Properties

Summary: The synthesis of new N‐cyclopentyl‐exo,endo‐norbornene‐5,6‐dicarboximide (CpNDI) ( 3a ) and N‐cyclohexyl‐exo,endo‐norbornene‐5,6‐dicarboximide (ChNDI) ( 3b ) monomers was carried out. From these monomers, two polynorbornene dicarboximides with cyclopentyl and cyclohexyl pendant groups, poly(exo,endo‐N‐cyclopentyl norbornene‐5,6‐dicarboximide) (PCpNDI) and poly(exo,endo‐N‐cyclohexyl norbonene‐5,6‐dicarboximide) (PChNDI), respectively, were synthesized by ring opening metathesis polymerization (ROMP). PCpNDI, which bears a cyclic pentyl moiety, shows a higher T_g and mechanical properties compared to PChNDI. A comparison of density, fractional free volume, and gas permeability coefficients of the synthesized polynorbornenes shows that PCpNDI presents a slightly higher density and lower fractional free volume than PChNDI. It was also found that gas permeability coefficients for PCpNDI are lower than those of PChNDI. In all cases, the selectivity followed the usual trade‐off found in other glassy polymers: as gas permeability coefficients increase selectivity decreases.

Poly(exo,endo‐N‐cyclopentyl norbornene‐5,6‐dicarboximide) (PCpNDI) was synthesized here by ROMP.     

Functional monomers and polymers, 118. Asymmetric syntheses of 2-alkylcyclohexanones using chiral polymers containing aminobornanol moieties

Cis-endo-3-amino-endo-2-bornanol ( 5 ) and exo-5-amino-endo-2-bornanol ( 2 ) (prepared from endo-2-hydroxy-5-bornanone ( 1 )) were reacted with chloromethylated polystyrene. With the resulting chiral polymers 4 and 6 asymmetric syntheses of 2-alkyl-cyclohexanones were carried out. These reactions showed a high enantioselectivity particularly with the chiral polymer 6 , which suggests a specific restricted transition state to be important for the asymmetric alkylation reaction.     

On the mechanism of polymerization of methyl substituted 7-oxabicyclo-[2.2.1]-heptanes

The polymerization of endo- and exo-2-methyl-7-oxabicyclo-[2.2.1]-heptane with phosphorus pentafluoride catalyst in methylene dichloride and nitrobenzene has been found to proceed with increasing yield and molecular weight with decreasing temperature in the range +25°C to ?30°C, but at ?78°C there was no polymerization. The ring-opening appears to proceed exclusively through nucleophilic attack at C-1 in the alkyloxonium ion, leading to only one type of structural unit in each type of polymer. The polymers of the exo-2-methyl isomer are completely soluble in THF, whilst those of the endo-2-methyl isomer are insoluble. The solubility appears to be connected with flexibility of the chain molecule associated with the possibility for interconversion between different chair conformations for the cyclohexane ring-structures. By ring-closure of 2.6-dimethylcyclohexane-(1.4)-diol two isomers have been prepared and identified. The endo,exo-2.6-dimethyl-7-oxabicyclo-[2.2.1]-heptane gives insoluble, highly crystalline polymers with phosphorus pentafluoride catalyst in methylene dichloride. The failure of the corresponding exo,exo-2.6-dimethyl isomer to polymerize under identical conditions is explained by conformational analysis.     

The ring-opening metathesis polymerization of (±)-endo-bicyclo[2.2.1]hept-5-en-2-yl acetate; microstructure of the polymer

The monomer (±)-endo-bicyclo[2.2.1]hept-5-en-2-yl acetate ( 1 ) was polymerized by Re-, W-, Mo- and Ru-based metathesis catalysts to yield polymers with cis double bond contents ranging from 76% to 16%. A complete assignment was made of the lines in the ¹³C NMR spectra. No significant head-tail bias was observed and no splittings due to tacticity were detected.     

Transition-metal-catalyzed vinyl addition polymerizations of norbornene derivatives with ester groups

Norbornene derivatives containing ester substituents were submitted to Pd(II)-catalyzed vinyl addition polymerization. The transition metal catalyst was found to tolerate the ester functionality. However, the rate of polymerization was reduced in comparison to the polymerization of norbornene. The polymerization of the pure exo-isomers produced substantially higher yields than reactions of monomers containing a high proportion of the corresponding endo-isomer. By varying the ester substituent, amorphous polymers with glass transition temperatures over the range of ?40 to 268°C were synthesized. An approximately linear relationship of molecular weight to monomer conversion was established, and the non-uniformity remained narrow (M?_w/M?_n ≈ 1,15 – 1,25) until high conversions for several of the exo-isomers studied. This indicates that both chain transfer and chain termination are rare.     

Preparation of block copolymers by ring-opening polymerization of cycloalkenes initiated by a tungstencyclopentylidene complex

The possibility of making block copolymers at room temperature from the monomer pairs 2a,b/1, 4/1, 5/1 and 5/3 (1 = norbornene = bicyclo[2.2.1]hept-2-ene; 2a,b = anti- and syn-7-methylbicyclo[2.2.1]hept-2-ene; 4 = methyl endo-bicyclo[2.2.1]hept-5-ene-2-carboxylate; 5 = endo-bicyclo[2.2.1]hept-5-ene-2-carbonitrile; 3 = 1,5-cyclooctadiene) was explored using as initiator of metathesis polymerization in CD₂Cl₂. The reactions of successive small amounts of the monomers with the catalyst were first followed by ¹H NMR to determine the rate of the reaction and the stability of the metal-carbene propagating species. AB and ABA type block copolymers were prepared on this basis and analysed by GPC. An increase in molecular weight after each addition was observed in most cases. Secondary metathesis reactions of double bonds in the polymer chains appear to be significant only for blocks formed from 3 .     

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.     

Copolymerization of ethylene with 5‐vinyl‐2‐norbornene in the presence of the Ph2C(Flu)(Cp)ZrCl2 /MAO catalyst

Cycloolefin copolymer, poly[(ethylene)‐co‐(5‐vinyl‐2‐norbornene)], was synthetized using the MAO activated ansa‐metallocene Ph₂C(Flu)(Cp)ZrCl₂ as a catalyst. Formation of mostly isolated 5‐vinyl‐2‐norbornene sequences was confirmed by NMR analysis. Comonomer incorporated selectively via cyclic double bond. No selectivity towards the reactivity of the particular isomer of 5‐vinyl‐2‐norbornene (5‐endo : 5‐exo) was observed. The molar mass was found to decrease when the comonomer concentration in product increased. At low comonomer incorporation levels copolymers were insoluble, cross‐linked elastomers. With high comonomer concentration in reaction medium copolymers were amorphous determined by means of DSC and X‐ray diffraction and the vinyl group of the comonomer remained unreacted for further modification.     

1,3,5-Triphenylhexahydro-1,3,5-triazine – active intermediate and precursor in the novel synthesis of benzoxazine monomers and oligomers

The benzoxazine monomer synthesis via 1,3,5-trialkyl(aryl)hexahydro-1,3,5-triazine intermediate is followed by ¹H NMR, FT-IR, and SEC. A model compound, 1,3,5-triphenylhexahydro-1,3,5-triazine, is synthesized independently and its reaction with bisphenol-A and paraformaldehyde in stoichiometric amounts is also followed by ¹H NMR. Additional model compounds, 1,3,5-trimethyl(ethyl)hexahydro-1,3,5-triazine, are used instead of a primary amine to synthesize bifunctional benzoxazine monomers, bis(3,4-dihydro-2H-3-methyl(ethyl)-1,3-benzoxazinyl)isopropane, via novel solventless reaction with bisphenol-A in the presence of paraformaldehyde. The mechanism of this reaction is proposed.     

Enthalpy of polymerisation of 7-oxabicyclo[2.2.1]heptane,and exo- and endo-2-methyl-7-oxabicyclo[2.2.1]heptane

The enthalpies of combustion of poly(oxy-1,4-cyclohexylene) formed from 7-oxabicyclo[2.2.1]heptane ( 1 ) and of its derivatives formed from exo- and endo-3-methyl-7-oxabicyclo[2.2.1]heptane ( 2a and 2b ) have been measured. From literature values for the enthalpies of combustion of the liquid monomers, the enthalpies of polymerisation have been derived: ?ΔH(1→c)=44,3±1,9, 49,7±2,6, and 45.4±3,1 kJ mol^?1, respectively. The results indicate a minimum strain energy in these polymers of ca. 15 kJ mol^?1. The estimated entropies of polymerisation yield ceiling temperatures of 320, 240, 200°C respectively for the three bicyclic ethers.—The reasons for the discrepancy between our present ?ΔH(1→c) for the endo compound and that previously reported², are explained.     

Saccharide polymers, 2. Synthesis and polymerization of exo-glucal derivatives

Unsaturated glucopyranose derivatives such as 1,2,3,4-tetra-O-acetyl-6-desoxy-β-D -xylo-hex-5-enopyranose (3) and 1,2,3,4-tetra-O-benzoyl-6-desoxy-β-D -xylo-hex-5-enopyranose (6) , briefly called “Ac-exo-glucal (3) ” and “Bz-exo-glucal (6) ”, were synthesized. These exo-cyclic sugar vinyl ethers were investigated in polymerization reactions. The corresponding “saccharide polymers”, homo- and copolymers, were synthesized under free radical conditions. The structures and the compositions of the soluble “saccharide polymers” were established by elemental analysis, ¹H and ¹³C NMR, and FTIR spectroscopy. Characterization of the polymers, like molecular weights and optical rotations are reported. Saccharide polymers with different sugar content and low as well as high molecular weights were obtained.     

Anionic polymerization of exo-3,4,5-trithiatetracyclo[5.5.1.O2,6.O8,12]tridec-10-ene (dicyclopentadiene trisulfide)

The anionic polymerization of exo-3,4,5-trithiatetracyclo[5.5.1.O^2,6.O^8,12]tridec-10-ene ( 1 ) in bulk and/or in aromatic solvents (benzene, toluene) was studied. The polymerization was initiated with sodium benzenethiolate (sodium cation complexed with dibenzo-18-crown-6). Polymers with high-molecular weights were obtained (M _n ≈ 10⁵, osmometrically). The polymerization was found to be living and reversible; the equilibrium monomer concentration increases with the temperature. The ceilling temperature was estimated as 167°C. The thermodynamic data of the polymerization in toluene was determined and compared with those of the polymerization of exo-3,4,5-trithiatricyclo[5.2.O^2,6]decane. The standard enthalpy ΔH = ?(6,6 ± 0,6)kJ · mol ¹ and entropy ΔS = ?(29,3 ± 2,1)J · mol ¹ · K ¹ of the polymerization of 1 were evaluated from the temperature dependence of the equilibrium monomer concentration, determined dilatometrically.