Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups

The synthesis of side-chain liquid crystalline polysiloxanes containing either 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an S_A phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the technique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2793–2800, 1997     

Synthesis and Characterization of Polymethacrylates,Polyacrylates, and Poly(Methylsiloxane)S Containing 4-[S(-)-2-Methyl-1-Butoxy]-4′-(ω-Alkanyl-1-OXY)-α-Methylstilbene Side Groups

Abstract

The synthesis and characterization of polymethacrylates, polyacrylates, and poly(methylsiloxane)s containing 4-[S(-)-2-methyl-1-butoxy]-4′-(ω-alkanyl-1-oxy)-α-methylstilbene side groups with ω-alkanyl from 11-undecanyl to 2-ethyl are presented. According to both differential scanning calorimetry and thermal optical polarized microscopy analyses, the poly(methylsiloxane)s containing 1-octyl and 1-hexyl as ω-alkanyl groups exhibit enantiotropic S _A and S _C* mesophases. All other polymers display only an enantiotropic S _A mesophase.     

Molecular engineering of liquid crystal polymers by living polymerization. II. Living cationic polymerization of 11-[(4-cyano-4′-biphenyl) oxy] undecanyl vinyl ether and the mesomorphic behavior of the resulting polymers

The synthesis and living cationic polymerization of 11-[(4-cyano-4′-biphenyl)oxy]-undecanyl vinyl ether ( 6 – 11 ) are described. The mesomorphic phase behavior of poly( 6 – 11 ) with different degrees of polymerization was compared to that of 6 – 11 and of 11-[(4-cyano-4′-biphenyl) oxy] undecanyl ethyl ether ( 8 – 11 ) which is the model compound of the monomeric structural unit of poly( 6 – 11 ). 6 – 11 displays a monotropic S_A and a monotropic nematic mesophase while 8 – 11 an enantiotropic S_A mesophase. Poly( 6 – 11 ) with low degrees of polymerization exhibits an enantiotropic S_A mesophase. Poly( 6 – 8 ) with high degrees of polymerization displays an enantiotropic S_X (i. e., an unidentified smectic phase) and an enantiotropic S_C mesophase. These results demonstrate that the transformation of the nematic mesophase of the monomer into a smectic mesophase after polymerization, occurs at the level of monomeric structural unit.     

New Stereoselective GC Phases: Immobilized Chiral Polysiloxanes with (S)-(–)-t-Leucine Derivatives as Selectors

New chiral polysiloxanes have been prepared as stationary phases for gas chromatography, with (S)-(–)-t-leucine-t-butylamide, (S)-(–)-t-leucine-(S)-(–)-1-phenylethylamide, (S)-(–)-t-leucine-(S)-(–)-1-(α-naphthyl)ethylamide, (S)-(–)-t-leucine-(R)-( + )-1-phenylethylamide, and (S)-(–)-t-leucine-(R)-( + )-1-(α-naphthyl)ethylamide as selectors. Immobilization is achieved by radical-induced cross-linking with 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V₄) and dicumyl peroxide (DCUP) as cross-linking reagents and cured at 170°C. Under these conditions, racemization of (S)-(–)-t-leucine is less than 4.5% (R) for 1 h curing, while for polysiloxanes with the conventional (S)-(–)-valine selectors about 20% of R-enantiomers are formed by racemization. In the presence of 5% (w/w) V₄ and 6% of DCUP with regard to the phases, 70–80% immobilization is achieved; without V₄, the degree of immobilization is about 50% for both the (S)-(–)-t-leucine and (S)-(–)-valine selectors. As the size of the amide moieties of the selectors increases from t-butyl to 1-(α-naphthyl)ethyl, the degree of immobilization decreases. If the curing time is prolonged to 2 h, the extent of racemization increases. The selectivity factors achieved for amino acid enantiomers and similar pharmaceuticals are generally higher than those obtained with the corresponding non-immobilized Chirasil-Val phases.     

The substituent effect on mesomorphic properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy)benzoates and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates

Abstract

The thermal properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy) benzo-ates (1) and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates (2) have been examined, where R = hydrogen, halogens, alkyl and alkoxy groups. The derivatives of compound 1 incorporating hydrogen, halogens, methoxy and nitro groups show a smectic A phase having a bilayer arrangement, and the others with a long alkoxy group show the S_A phase with the monolayer arrangement. The derivatives of compound 2 incorporating halogens, and the nitro group show the S_A phase with the monolayer arrangement. The alkoxy derivatives show a smectic C phase as well as the nematic phase. The nitro group at the lateral position tends to increase the ratio of the S_A-N transition temperature to the N-I. The effect of the nitro group on the smectic properties has been discussed in terms of the structural and electrostatic nature of the nitro group.     

Cyclosiloxane-based liquid-crystalline elastomers containing fluorinated mesogens and chiral crosslinking groups

A series of chiral fluorinated liquid-crystalline elastomers (LCEs) IP-VIP are prepared by 4-cyano-3-fluorophenyl 4′-(undec-10-enoyloxy)biphenyl-4-carboxylate, isosorbide bis(4-allyloxybenzoate) and 2,4,6,8-tetramethylcyclotetrasiloxane via Pt-catalyzed hydrosilylation. The chiral crosslinking moieties increase from IP to IVP. The elastomers IP, IIP, and IIIP containing low content of chiral crosslinking moieties display S_C ^* liquid-crystalline phase, but IVP, VP, and VIP do not show S_C ^* phase except for N^* mesophase. The mesophase is testified according to typical diffractogram measured by X-ray diffraction (XRD) analysis. The layer spacings of the LCEs decrease from IP (d-spacing of 34.2 Å) to VIP (d-spacing of 31.6 Å) with increase of chiral crosslinking groups in the polymers systems. Moreover, the optical properties are performed by ultraviolet–visible–near-infrared spectrophotometry. VP and VIP containing the most chiral crosslinking moieties display maximum reflection in near infrared spectra in the measurement of optical properties, while IP, IIP, IIIP, and IVP do not show obvious maximum reflection. It is interesting that a specific reflection of circularly polarized light appears along with a changing mesophase due to high enough concentration of chiral crosslinking dopants for VP and VIP. All these results suggest that the chiral crosslinking moieties exert influence on the structures of these kinds of LCEs.     

Synthesis and characterization of liquid crystalline copolymethacrylates,copolyacrylates, and copolysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers as side-groups

The synthesis of methacrylates and acrylates containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers attached to the polymerizable group through flexible spacers containing 11, 8, 6, 3, and respectively 2 methylenic units is described. The radical copolymerization of a 1/2 or 2/1 mole ratio of the two constitutional isomeric monomers led to thermotropic side-chain liquid crystalline polymers in all cases. The synthesis of copolysiloxanes based on the same constitutional isomeric mesogens as side groups, and flexible spacers containing 11, 8, 6, 5, and respectively 3 methylenic units is also described. All polymers were characterized by differential scanning calorimetry and optical polarization microscopy. The polymers containing 11 methylenic units in the spacer exhibit S_c mesomorphism, while the other polymers are nematic. Copolymethacrylates do not undergo side-chain crystallization. Only the copolyacrylate containing 11 methylenic units in the spacer exhibits side-chain crystallization. All the copolysiloxanes display side-chain crystallization. The number of melting transitions seen for these polymers decreases with increasing spacer length. Copolysiloxanes containing dissimilar spacer length were also prepared. Only the copolymer synthesized with highly dissimilar spacer lengths, i.e., containing 3 and 11 methylenic units, does not undergo side-chain crystallization. These results have demonstrated that while the type of mesophase is dictated only by the spacer length, the degree of decoupling of the motion of the side-groups from the motion of the main chain is strongly dependent on the nature of the polymer backbone. For the same mesogenic unit and spacer length, the thermal stability of the mesophase is also dictated by the nature of the polymer backbone. The use of constitutional isomers of mesogenic units as side groups in liquid crystalline polymers provides at least qualitative information on the degree of decoupling of the side groups from the polymer main chain.     

Synthesis and Characterization of Poly(methylsiloxane)S Containing 4-[S(-)-2-Methyl-1 -Butoxy1-4′ -[p-(ω-alkan-l-yloxy)benzoyloxy]-α-methylstilbene Side Groups

The syntheses of poly(methylsiloxane)s containing 4-[S(-)-L-methyl-1 -butoxy] -4′-[p-(ω -alkan -1 -yloxy)benzoyloxy] -a-methylstilbene side groups containing 11-undecanyl (18), 8-octyl (19), 6-hexyl (20), and 3-propyl (21), of a poly[(50-55%)-methyl-co-(45-50%)-dimethylsiloxane] containing 4-[S(-)-2-methyl-1-butoxy]-4′-[p-(8-octan-1-yloxy)benzoyloxy]-α-methylstilbene side groups (22) and of a poly(methylsiloxane) containing a 1:1 molar ratio of 4-[S(-)-2-methyl-1 -butoxyl]-4′ -[p-(8-octan-1 -yloxy)benzoyloxy] -α-methylstilbene and 4-[S(-)-2-methyl-l -butoxyl-4′ -[p-(6-hexan-1-yloxy)-benzoyloxyl-α-methylstilbene side groups (23) are described. All polymers and copolymers were characterized by a combination of differential scanning calorimetry and thermal optical polarized microscopy techniques. 18 exhibits an enantiotropic S _A, while 19, 20, 21, and 23 display both enantiotropic s _A and S*_c mesophases. 22 exhibits only an enantiotropic s: mesophase. In addition, all polymers and copolymers exhibit sidechain crystallization. These results have demonstrated that extending the length of the rigid part of the mesogenic unit of 4-[S(-)-2-methyl-l-butoxy]-4′-(ω-alkan-l-yloxy)-α-methylstilbene to 4-[S(-)-2-methyl-l-butoxy]-4′ -[p-(ω-alkan-l -yloxy)benzoyloxy]-α-methylstilbene increases the tendency of the resulting poly(methylsiloxane)s toward polymesomorphism.     

Dielectric and switching properties of a highly tilted AFLC material (S)-(+)-4-(1-methylheptyloxycarbonyl)-2,3-difluorophenyl 4′-[3-(2,2,3,3,4,4,4-heptafluorobutoxy)prop-1-oxy]biphenyl-4-carboxylate

Thermodynamic, dielectric, optical and switching parameters of a single-phase antiferroelectric (AF) liquid crystalline material (S)-(+)-4-(1-methylheptyloxycarbonyl)-2,3-difluorophenyl 4′-[3-(2,2,3,3,4,4,4-heptafluorobutoxy)prop-1-oxy]biphenyl-4-carboxylate have been studied. These studies show wide temperature range (~97.8°C–25.3°C) of AF SmC^*_A phase in the material. The dielectric studies have been carried out in the frequency range of 1 Hz–35 MHz under planar anchoring conditions of the molecules. The dielectric spectrum of the SmC^*_A phase exhibits three relaxation modes due to the collective as well as individual molecular processes. Relaxation frequencies of these modes lie in the range of kHz–MHz regions. Relative permittivity of the material (at 10 kHz) varies from ~8.8 at 98.8°C to 9.9 at 41.0°C. Maximum tilt of the molecule in the SmC^*_A phase is ~43°C. Spontaneous polarisation, switching time and rotational viscosity have also been determined. The maximum value of P_S is ~439 nC/cm² and switching time is the order of 1–5 millisecond, whereas viscosity is moderate.     

Stereochemische Korrelationen zwischen (2R,4′R,8′R)-α-Tocopherol, (25S,26)-Dihydroxycholecalciferol, (–)-(1S,5R)-Frontalin und (–)-(R)-Linalol

Stereochemical Correlations between (2R,4′R,8′R)-α-Tocopherol, (25S,26)-Dihydroxycholecalciferol, (–)-(1S,5R)-Frontalin and (–)-(R)-Linalol The optically active C₅- and C₄-building units 1 and 2 with their hydroxy group at a asymmetric C-atom were transformed to (–)-(1S,5R)-Frontalin ( 7 ) and (–)-(3R)-Linalol ( 8 ) respectively; 1 and 2 had been used earlier in the preparation of the chroman part of (2R,4′R,8′R)-α-Tocopherol ( 6a , vitamin E), and for introduction of the side chain in (25S,26)-Dihydroxycholecalciferol ((25S)- 4 ), a natural metabolite of Vitamin D₃. The stereochemical correlations resulting from these converions fit into a coherent picture with those correlations already known from literature and they confirm our earlier stereochemical assignments. A stereochemical assignment concerning the C(25)-epimers of 25,26-Dihydroxycholecalciferol that was in contrast to our findings and that initiated the conversion of 1 and 2 to 7 resp. 8 for additional stereochemical correlations has been corrected in the meantime by the authors [26].     

Chiral recognition in molecular and macromolecular pairs of (S)‐ and (R)‐1‐cyano‐2‐methylpropyl‐4′‐ {[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐ carboxylate enantiomers

(S)‐1‐Cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐ 4‐carboxylate [ (S)‐11 ] and (R)‐1‐cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐carboxylate [( R)‐11 ] enantiomers, both greater than 99% enantiomeric excess, and their corresponding homopolymers, poly[ (S)‐11 ] and poly[ (R)‐11 ], with well‐defined molecular weights and narrow molecular weight distributions were synthesized and characterized. The mesomorphic behaviors of (S)‐11 and poly[ (S)‐11 ] are identical to those of (R)‐11 and poly[ (R)‐11 ], respectively. Both (S)‐11 and (R)‐11 exhibit enantiotropic S_A, S, and S_X (unidentified smectic) phases. The corresponding homopolymers exhibit S_A and S phases. The homopolymers with a degree of polymerization (DP) less than 6 also show a crystalline phase, whereas those with a DP greater than 10 exhibit a second S_X phase. Phase diagrams were investigated for four different pairs of enantiomers, (S)‐11 /( R)‐11 , (S)‐11 /poly[ (R)‐11 ], and poly[ (S)‐11 ]/poly[ (R)‐11 ], with similar and dissimilar molecular weights. In all cases, the structural units derived from the enantiomeric components are miscible and, therefore, isomorphic in the S_A and S phases over the entire range of enantiomeric composition. Chiral molecular recognition was observed in the S_A and S_X phases of the monomers but not in the S_A phase of the polymers. In addition, a very unusual chiral molecular recognition effect was detected in the S phase of the monomers below their crystallization temperature and in the S phase of the polymers below their glass‐transition temperature. In the S phase of the monomers above the melting temperature and of the polymers above the glass‐transition temperature, nonideal solution behavior was observed. However, in the S_A phase the monomer–polymer and polymer–polymer mixtures behave as an ideal solution. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3631–3655, 2000     

Stereoselective synthesis of (1′S,3R,4R)-4-acetoxy-3-(2′-fluoro-1′-trimethylsilyloxyethyl)-2-azetidinone

A stereoselective synthesis of (1′S,3R,4R)-4-acetoxy-3-(2′-fluoro-1′-trimethylsilyloxyethyl)-2-azetidinone as a new fluorine-containing intermediate towards β-lactams, is described. The synthetic key step relies upon the dynamic kinetic resolution (DKR) of ethyl 2-benzamidomethyl-4-fluoro-3-oxo-butanoate via asymmetric transfer hydrogenation catalyzed by [Ru(η⁶-arene)(S,S)-R₂NSO₂DPEN].     

Synthesis and mesomorphic properties of 7-acyloxy-3-(4-acyloxyphenyl)-4H-1-benzopyran-4-one

A new homologous series of 7-acyloxy-3-(4-acyloxyphenyl)-4H-1-benzopyran-4-ones was synthesized and characterized by elemental analysis and spectroscopic techniques along with thermal behaviour study using differential scanning calorimetry. Texture observation was performed under the polarizing optical microscope from which the derivatives were found to exhibit different molecular organizations as exemplified by various mesophases. Whilst the compounds containing butanoyloxy and hexanoyloxy groups behave as nematogens, the other compounds with heptanoyloxy and longer side chains show a SmC phase. The octadecanoyloxy derivative was the only member showing a monotropic SmC phase. The difference in phase behaviour is discussed based on the molecular structure and the presence of a lateral dipole which can be associated with the intermolecular interaction within the mesophase.     

An Unexpected Asymmetric Reduction of 4-(1-Nitro-2-oxocyclododecyl)butan-2-one. Determination of the absolute configuration of (‒)-15-hexadecanolide

Reduction of the carbonyl group in the side chain of 4-(1-nitro-2-oxocyclododecyl)butan-2-one ( 3 ) with organoboron complexes are influenced by the chiral center, in 4-position with respect to the carbonyl C-atom, to which the NO₂ group is attached, a rare type for an asymmetric reduction. Independent of the (R)- or (S)-configuration of the Alpine-Hydride, (+)- 3 is reduced only to the (15S)-nitrolactone (+)- 5 and, after subsequent transformations, to (+)-(-S)-15-hexadecanolide ((+)- 1 ), enantiomer of the naturally occurring (?)- 1 .     

Molecular engineering of liquid crystalline polymers by “living” polymerization. XXXII. Synthesis and “living” cationic polymerization of 3-fluoro-4′-(ω-vinyloxyalkoxy)-4-biphenylyl (2r,3s)-2-fluoro-3-methylpentanoate with undecanyl and octyl alkyl groups

The synthesis and “living” cationic polymerization of 3-fluoro-4′-(11-vinyloxyundecany-loxy)-4-biphenylyl (2R,3S)-2-fluoro-3-methylpentanoate ( 12-11 ) and 3-fluoro-4′-(8-vi-nyloxyoctyloxy)-4-biphenylyl (2R,3S)-2-fluoro-3-methylpentanoate ( 12-8 ) are presented. Poly ( 12-11 )s and poly ( 12-8 )s with degrees of polymerization from 4.0 to 16.5 and poly-dispersities ≤ 1.13 have been synthesized and characterized by differential scanning cal-orimetry (DSC) and thermal optical polarized microscopy. Over the entire range of molecular weights poly ( 12-11 )s and poly ( 12-8 )s exhibit an enantiotropic S_A and an unidentified S_X phase. In addition, regardless of its molecular weight, poly ( 12-8 ) exhibits a S^*_c phase in between the S_A and S_x phases. Poly ( 12-11 ) and poly ( 12-8 ) show lower transition tem-peratures and broader temperature ranges of all their mesophases as compared to the corresponding polymers without a fluorine atom on the biphenyl group. The role of the connecting group between the biphenyl and chiral group of the mesogenic unit on the phase behavior of these polymers is also discussed. Copolymers of 12-8 with (2R,3S)-2-fluoro-3-methylpentyl 4′-(11-vinyloxyundecanyloxy)biphenyl-4-carboxylate ( 13-11 ) {i.e., poly-[( 12-8 )-co-( 13-11 )] (X/Y), where X/Y represents the molar ratio of monomer 12-8 to monomer 13-11 } with DP of ca. 11 and polydispersities lower than 1.23 were also syn-thesized and characterized. Their S_A and S^*_c mesophases exhibit continuous dependences of composition and this support the assignment of the mesophases exhibited by poly ( 12-8 ). © 1995 John Wiley & Sons, Inc.     

Effect of the variation of swallow-tailed groups on the mesomorphic and electro-optical properties of chiral compounds derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid

Three homologous series of chiral swallow-tailed compounds, alkyl (S)-2-{6-[4-(4′-alkoxyphenyl)benzoyloxy]-2-naphthyl}propionates, (S)HNP(p,n,q) derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid in conjugation with a variety of swallow-tailed groups, attached to the external side of the chiral centre, have been synthesized and their mesomorphic and electro-optical properties studied. Both (S)HNP(p,1,2) and (S)HNP(p,1,3) exhibited an enantiotropic antiferroelectric SmC*_A phase. This implys that the swallow-tailed groups in the molecules favour zigzag pairing of the molecules in the smectic phase. The maximum P _S values of compounds (S)HNP(p,1,2) in the antiferroelectric phase were measured in the range 21–30 nC cm^-2; those of compounds (S)HNP(p,1,3) were in the range 15–23 nC cm^-2, indicating that these chiral compounds possess low polarity. The electro-optical response of the compounds in the antiferroelectric SmC*_A phase displayed thresholdless V-shaped switching.     

Synthesis of dirhodium(II) tetrakis[methyl 1-(3-phenylpropanoyl)-2-oxaimidazolidine-4(S)-carboxylate], Rh2(4S-MPPIM)4

The large-scale synthesis with greatly improved yields of methyl 1-(3-phenylpropanoyl)-2-oxaimidazolidine-4(S)-carboxylate and the chiral dirhodium(II) carboxamidate derived from it, Rh₂(4S-MPPIM)₄, is described. The key step in the overall synthesis is the Hofmann rearrangement of Boc-protected l-asparagine, the procedure for which has been modified to achieve near quantitative yield.     

Synthesis and characterization of side-chain liquid crystalline polysiloxanes containing 4-alkanyloxyphenyl trans-4-alkylcyclohexanoate side groups

The synthesis and characterization of nine polysiloxanes containing 4-alkanyloxyphenyl trans-4-alkylcyclohexane side groups are described. Six monomers which contain a pentenyloxy of a hexenyloxy flexible spacer display a nematic mesophase, while the other three monomers which contain an undecenyloxy flexible spacer display nematic, smetic A and smectic E mesophases. All synthesized polymers present two smectic mesophases except one containing 4-hexanyloxyphenyl trans-4-n-butylcyclohexanoate side groups presents one smectic mesophase and one containing 4-undecanyloxyphenyl trans-4-n-pentylcyclohexanoate side groups presents three smectic mesophases. Trans-cis isomerization of mesogens and side chain crystallization did not occur for any of the synthesized polymers.     

Synthesis of aromatic polyethers by Scholl reaction. V. Synthesis and polymerization of 1,3-bis[4-(1-naphthoxy) benzoyl]benzene, 1,4-bis[4-(1-naphthoxy)benzoyl]benzene,bis[4-(1-naphthoxy)phenyl]methane, 1,3-bis[4-(1-naphthoxy) phenylmethyl]benzene,and 1,4-bis-[4-(1-naphthoxy)phenylmethyl]benzene

This article describes the synthesis and the cation-radical polymerization (Scholl reaction) of 1,3-bis[4-(1-naphthoxy) benzoyl] benzene ( 6 ) and 1,4-bis[4-(1-naphthoxy) benzoyl]- benzene ( 7 ) initiated by FeCI₃. This polymerization produced poly(ether ether ketone ketone)s (PEEKK) of number average molecular weight (M?_n) up to 5400 g/mol. The synthesis of bis[4-(1-naphthoxy) phenyl] methane ( 8 ), 1,3-bis[4-(1-napthoxy) phenylmethyl] benzene ( 9 ), and 1,4-bis[4-(1-naphthoxy) phenylmethyl] benzene ( 10 ) are also described. Polyethers of M?_n up to 15400 g/mol at a FeCl₃/monomer molar ratio of 2/1 were obtained. An increased polymerizability of the monomers 9 and 10 containing two CH₂ groups versus that of the corresponding monomers containing two carbonyl groups ( 6 and 7 ) was observed. This enhanced polymerizability was explained based on the increased nucleophilicity of monomers 9 and 10 .     

Structure determination of a bis[4-(di-n-butylamino)phenyl](pyridin-3-yl)borane tetramer highlighting a unique geometric conformation of the core 16-membered ring

The tetramer of bis(4-di-n-butylaminophenyl)(pyridin-3-yl)borane [systematic name: 2λ⁴,4λ⁴,6λ⁴,8λ⁴-tetrabora-1,3,5,7(1,3)-tetrapyridinacyclooctaphane-1¹,3¹,5¹,7¹-tetrakis(ylium)], C₁₃₂H₁₉₂B₄N₁₂, was synthesized unexpectedly and crystallized. Its structure contains an unusual 16-membered ring core made up of four (pyridin-3-yl)borane groups. The ring adopts a conformation with pseudo-S₄ symmetry that is very different from the two other reported examples of this ring system. Density functional theory (DFT) computations indicate that the stability of the three reported ring conformations is dependent on the substituents on the B atoms, and that the pseudo-S₄ geometry observed in the bis(4-dibutylaminophenyl)(pyridin-3-yl)borane tetramer becomes significantly more stable when phenyl or 2,6-dimethylphenyl groups are attached to the boron centers.