Synthesis and properties of side‐chain liquid‐crystalline polysiloxanes containing hemiphasmidic mesogens

The synthesis of hemiphasmidic monomers 4‐[(3,4,5‐triethoxy)benzoyloxy]‐4′‐[(p‐allyloxy)benzoyloxy]biphenyl (M₁), 4‐[(3,5‐diethoxy)benzoyloxy]‐4′‐[(p‐allyloxy)‐benzoyloxy]biphenyl (M₂), and of the corresponding side‐chain liquid‐crystalline polysiloxanes (P₁, P₂) was carried out. For comparison, rodlike monomer 4‐[(p‐ethoxy)‐benzoyloxy]‐4′‐[(p‐allyloxy)benzoyloxy]biphenyl (M₃) and its polysiloxanes (P₃) were also prepared. The chemical structures of the monomers and polymers obtained were confirmed by FTIR and ¹H‐NMR spectra. Their mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The relationship between structures and properties was discussed. It was observed that M₁ and M₃ were enantiotropic nematic phase, M₂ was monotropic mesophase, and their poly(methylsiloxanes) (P₁–P₃) possessed a broad range enantiotropic nematic phases and high thermal stability. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 946–952, 2005     

Investigation of liquid crystalline and photocrosslinkable poly[4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamate]s

Three series of liquid‐crystalline‐cum‐photocrosslinkable polymers were synthesized from 4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamates (x = ? H, ? OCH₃ and ? CN; m = 6, 8 and 10) by free radical solution polymerization using azobisisobutyronitrile as an initiator in tetrahydrofuran at 60 °C. All the monomers and polymers were characterized using intrinsic viscosity, and FTIR, ¹H NMR and ¹³C NMR spectroscopy. The liquid crystalline behavior of these polymers was examined using a hot stage optical polarizing microscope. All the polymers exhibited liquid crystalline behavior. The hexamethylene spacer‐containing polymers exhibited grainy textures; in contrast, the octamethylene and decamethylene spacer‐containing polymers showed nematic textures. Differential scanning calorimetry data confirmed the liquid crystalline property of the polymers. Thermogravimetric analysis revealed that all the polymers were stable between 236 and 344 °C in nitrogen atmosphere and underwent degradation thereafter. As the methylene chain length increases in the polymer side‐chain, the thermal stability and char yield of the polymers decrease. The photocrosslinking property of the polymers was investigated using the technique of exposing the polymer solution to UV light and using UV spectroscopy. The crosslinking reaction proceeds via 2π–2π cycloaddition reactions of the ? CH?CH? of the pendant cinnamate ester. The polymers containing electron‐releasing substituents (? OCH₃) showed faster crosslinking than the unsubstituted polymers and those containing electron‐withdrawing substituents (? CN). Copyright © 2007 Society of Chemical Industry     

Synthesis and phase behavior of chiral side‐chain liquid‐crystalline polysiloxanes containing two mesogenic groups

The synthesis of chiral side‐chain liquid‐crystalline polysiloxanes containing both cholesteryl undecylenate (M_I) and 4‐allyloxy‐benzoyl‐4‐(S‐2‐ethylhexanoyl) p‐benzenediol bisate (M_II) mesogenic side groups was examined. The chemical structures of the obtained monomers and polymers were confirmed with Fourier transform infrared spectroscopy or ¹H‐NMR techniques. The mesomorphic properties and phase behavior of the synthesized monomers and polymers were investigated with polarizing optical microscopy, differential scanning calorimetry, and thermogravimetric analysis (TGA). Copolymers IIP–IVP revealed a smectic‐A phase, and VP and VIP revealed a smectic‐A phase and a cholesteric phase. The experimental results demonstrated that the glass‐transition temperature, the clearing‐point temperature, and the mesomorphic temperature range of IIP–VIP increased with an increase in the concentration of mesogenic M_I units. TGA showed that the temperatures at which 5% mass losses occurred were greater than 300°C for all the polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2670–2676, 2002     

Synthesis and properties of side chain cholesteric liquid‐crystalline polyacrylates containing two mesogenic groups

The synthesis of side chain cholesteric liquid‐crystalline polymers containing both 4‐cholesteryl‐4'‐acryloyloxybenzoate (M_I) and 4‐methoxyphenyl‐4'‐acryloyloxybenzoate (M_II) mesogenic side groups is described. The chemical structures of the obtained monomers and polymers are confirmed by Fourier transform infrared (FTIR) spectroscopy. The phase behavior and optical properties of the synthesized monomers and polymers were investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and thermogravimetric analyses (TGA). The homopolymer IP reveals a cholesteric phase and VIIP displays a nematic phase. The copolymers IIP–VIP exhibit, respectively, cholesteric oily‐streak texture and focal‐conic texture. The fixation of the helical pitch and oily‐streak texture of the cholesteric phase is achieved by quenching, and polymer films with different reflection colors are obtained. The experimental results demonstrate that the glass transition temperature (T_g) and the melting temperature (T_m) of the copolymers IIP–VIP decrease, whereas the isotropization temperature (T_i) and the mesomorphic temperature range (ΔT) increase with increasing content of mesogenic M_II units. TGA results indicate that the temperatures at which 5% mass loss occurred (T_5wt%) of all copolymers are >245°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1936–1941, 2003     

Synthesis,structure, and phase behavior of new chiral liquid‐crystalline polysiloxanes based on mesogenic menthyl monomers

Six new chiral monomers ( M ₁ – M ₆ ), and their corresponding side chain polymers ( P ₁ – P ₆ ) containing menthyl groups were synthesized. The chemical structures of M ₁ – M ₆ were characterized with FTIR and ¹H NMR. The structure–property relationships of the monomers and polymers obtained are discussed. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. Some compounds containing menthyl groups formed mesophase when a flexible spacer was inserted between the mesogenic core and the menthyl groups by reducing the steric hindered effect. The monomers M ₁ , M ₄ , and M ₅ did not reveal mesomorphic properties because of the weaker rigid core or the longer flexible terminal groups, whereas M ₂ , M ₃ , and M ₆ all revealed cholesteric phase. Except P ₄ and P ₅ , the homopolymers P ₁ – P ₃ and P ₆ showed a smectic A phase. In addition, melting, glass transition temperature, or clearing temperature increased, and the mesophase temperature range widened with increasing the rigidity of mesogenic core or decreasing the length of the flexible spacer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and optical properties of cholesteric liquid‐crystalline oligomers displaying reversible thermochromism

A series of side‐chain liquid crystalline oligomers (P₁–P₇) have been synthesized with cyclo(methylhydrogeno)siloxane and two cholesteric liquid crystalline monomers cholesteryl 4‐(10‐undecylen‐1‐yloxy)benzoate (M₁) and cholesterol 4‐{6‐[(4‐(allyloxyl)‐benzoyl]‐hexanoxocarbonyl}‐benzoate (M₂). The chemical structures and liquid crystalline properties of the synthesized oligomers were investigated using various experimental techniques such as FTIR, ¹H‐NMR, DSC, POM, and XRD. All monomers and chiral oligomers show a cholesteric mesophase with very wide mesophase temperature ranges. They appear highly thermally stable with decomposition temperatures (T_d) at 5% weight loss greater than 300°C. The optical properties of the oligmers have been characterized by reflection spectra and optical rotation analysis. All synthesized oligomers display colors at room temperature, and show reversible thermochromism within a wide temperature range (>120°C). The λ_max values of the oligomers also nearly coincide during the first, second, and third heating cycles. The specific rotation of each oligomer is very sensitive to temperature, and the specific rotation value of P₃ smoothly changes from ?21.7° to ?0.7° when it is heated. The optical properties of the oligomers offer tremendous potential for various optical applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1321‐1327, 2013     

Synthesis,structures, and properties of side‐chain cholesteric liquid‐crystalline polysiloxanes

The synthesis of three cholesteric monomers and side‐chain liquid‐crystalline polymers was described. The structure–property relationships of monomers IM–IIIM and polymers IP–IIIP were discussed. Their phase behavior and optical properties were investigated by differential scanning calorimetry, thermogravimetric analyses (TGA), and polarizing optical microscopy. Monomers IM–IIIM exhibited cholesteric oily‐streak texture and focal‐conic texture. Polymers IIP and IIIP revealed smectic A fan‐shaped texture and cholesteric grandjean texture, respectively. Experimental results demonstrated that the selective reflection of IM–IIIM shifted to the short‐wavelength region with increasing the flexible spacer length or decreasing the rigidity of the mesogen. Polymers with a longer flexible spacer had lower glass‐transition temperatures and wider mesomorphic temperature ranges. TGA showed that the temperatures at which 5% weight loss occurred were greater than 300°C for all the polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3944–3950, 2003     

New soluble azophenol polymers prepared by oxidative polycondensation

New azophenol polymers (P₁, P₂ and P₃) were synthesised by the oxidative polycondensation (OP) reaction of three different azophenol monomers in aqueous alkaline medium with NaOCl as the oxidant. The monomers and the polymers were characterised by elemental analyses, and UV‐visible, Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopic studies, which revealed that the polymers synthesised by OP are composed of oxyphenylene (C? O? C) and phenylene (C? C) units. The polymers obtained are soluble in dimethylformamide and dimethylsulfoxide. Average molecular weights of the polymers were determined by gel permeation chromatography. Additionally, P₂ and P₃ are soluble in water and methanol. On the basis of thermogravimetric analyses, 5 and 50% weight‐loss temperatures of the polymers were found to be 218, 700 (P₁), 263, 609 (P₂) and 100, 809 °C (P₃), respectively, suggesting a high thermal stability. Thermal analyses using differential scanning calorimetry revealed that the azophenol polymers are highly amorphous, and melting peaks were not observed in the heating cycles. This suggests that all the polymers are highly amorphous. The azophenol polymers show a reversible trans–cis–trans isomerisation process. These properties of the polymer could be promising for their technological usage. Copyright © 2007 Society of Chemical Industry     

The Effect of the Structural Elements on the Properties of Side Chain Mesomorphic Polymers

The thermal properties of mesomorphic polymers depend on the relative amounts of the different structural elements (hard core, flexible chains, main chain) of the polymer. Literature data are compared with the conclusions obtained from the three-component thermodynamic model of side chain mesomorphic polymers. The effects of the different soft elements (main chain, spacer and p-alkyl or alkoxy chain) depend first of all on the length of the spacer and its interaction with the main chain. The thermal properties of the polymer can be well regulated by varying the different structural elements of the homo- and co-polymers. The glass transition temperature (T_g) of the polymer can be reduced by building O and N atoms into the main chain and/or by binding the side chains on 3rd, 4th, etc. atoms of the main chain. The T_g can be further reduced by increasing the length of the spacer. If the spacers are long enough, the layer type structures are favored, with p-alkoxy chains behaving also as a plasticizer of the main chain. The clearing point can be influenced by copolymerization of monomers with different hard cores. The three-component thermodynamic model of side-chain mesomorphic polymers well explains the effect of different structural elements on the structure and properties of these polymers.     

Side‐chain copolymers containing smectic monomer and chiral reagent—Synthesis and characterization

A series of new chiral side‐chain liquid‐crystalline polymers were prepared containing smectic‐nematic monomer and nonmesogenic chiral monomer. All polymers were synthesized by graft polymerization using polymethylhydrosiloxane as backbone. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analyses, and X‐ray diffraction measurements. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared, proton nuclear magnetic resonance spectra (¹H NMR). M₁ showed smectic (S_B, S_C) and nematic phase on the heating and the cooling cycle. Polymers P₀–P₂ were in chiral smectic A phase, while P₃–P₅ were in cholesteric phase, P₆ has bad LC properties, and P₇ has no LC properties. Experimental results demonstrated that nonmesogenic chiral moiety and LC mesogenic with long carbochain offered the possibility of application because of its lower glass transition temperature, and the glass transition temperatures and isotropization temperatures and the ranges of the mesophase temperature reduced with increasing the contents of chiral agent. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of side‐chain liquid‐crystalline polyacrylates containing azobenzene moieties

Syntheses of novel liquid‐crystalline polymers containing azobenzene moieties were performed by a convenient route with an acrylate backbone. The azobenzenes were key intermediates of the monomers, and side‐chain liquid‐crystalline polymers were prepared, that is, poly[α‐{4‐[(4‐acetylphenyl)azo]phenoxy}alkyloxy]acrylates, for which the spacer length was 3 or 11 methylene units. In addition, poly[3‐{4‐[(3,5‐dimethylphenyl)azo]phenoxy}propyloxy]acrylate was prepared with a spacer length of 3 methylene units. The structures of the precursors, monomers, and polymers were characterized with Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR techniques. The polymers were obtained by conventional free‐radical polymerization with 2,2′‐azobisisobutyronitrile as an initiator. The phase‐transition temperatures of the polymers were studied with differential scanning calorimetry, and the phase structures were evaluated with a polarizing optical microscopy technique. The results showed that two of the monomers and their corresponding polymers exhibited nematic liquid‐crystalline behavior, and one of the monomers and its corresponding polymer showed smectic liquid‐crystalline behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2653–2661, 2002     

Synthesis and characterization of chiral smectic side‐chain liquid crystalline polysiloxanes and ionomers containing sulfonic acid groups

The synthesis of new chiral smectic A (S_A) side‐chain liquid crystalline polysiloxanes (LCPs) and ionomers (LCIs) containing 4‐allyloxy‐benzoyl‐4‐(S‐2‐ethylhexanoyl) p‐benzenediol bisate (ABB) as mesogenic units and 4‐[[4‐(2‐propenyloxy)phenyl]azo]benzenesulfonic acid (AABS) as nonmesogenic units is presented. The chemical structures of the monomers and polymers are confirmed by FTIR spectroscopy or ¹H–NMR. Differential scanning calorimetry (DSC), optical polarizing microscopy, and X‐ray diffraction measurements reveal that all the polymers P_I–P_IV and ionomers P_V–P_VI exhibit S_A texture. The results seem to demonstrate that the tendency toward the S_A‐phase region increases with increasing sulfonic acid concentration, and the thermal stability of the S_A phase is determined by the flexibility of the polymer backbones and the interactions of sulfonic acid groups. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2335–2340, 2001     

Accelerated controlled radical polymerization of methacrylates

BACKGROUND: Nitroxide adducts 1,1‐ditertbutyl‐1‐(1‐methyl‐1‐cyanoethoxy)‐amine (AIBN/DBN), 1,1‐ditertbutyl‐1‐(benzoylperoxy)‐amine (BPO/DBN) and 2,2,6,6,‐tetramethyl‐4‐oxo‐1‐(1‐methyl‐1‐cyanoethoxy)‐piperidine (AIBN/4‐OXO‐TEMPO) were prepared and evaluated as stabilized unimolecular initiators for controlled radical polymerization of methacrylate monomers using sulfuric acid as an accelerating additive. Their effectiveness was evaluated from polymerization rates, molecular weight control and dispersity (D) of the polymers. Thermal stabilities of the polymers were also examined. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Polymerization was accomplished at 70 and 130 °C in 5 min to 144 h. The value of D of poly(methyl methacrylate) (PMMA) was 1.05–1.22. The glass transition temperature (T_g) for PMMA was 122–127 °C. The activity of the chain ends was established by chain extension and controlled polymerization was established by plotting M_n versus monomer conversion. First‐order kinetics in monomer consumption was established and an electron paramagnetic resonance study was conducted. Decomposition temperature (T_d) for PMMA was 360–380 °C, for poly(TEGDMA) was 300–380 °C and for poly(EBPADMA) was 360–440 °C. Photoinitiation without additive yielded no polymer. Thermal initiation by AIBN/4‐OXO‐TEMPO was the fastest. CONCLUSIONS: The initiators are applicable in low‐temperature additive‐enhanced controlled polymerization of methacylates and dimethacrylates, producing polymers with excellent attributes and a low value of D. Copyright © 2008 Society of Chemical Industry     

Europium‐containing cholesteric liquid crystalline polymers in the side chain

Europium‐containing cholesteric liquid crystalline polymers were graft copolymerized using poly(methylhydrogeno)siloxane, cholesteryl 4‐(allyloxy)benzoate (M₁), cholesteryl acrylate (M₂), and a europium complexes monomer (M₃). The chemical structures of the monomers were characterized by Fourier transform infrared and ¹H‐nuclear magnetic resonance. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermo gravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. With an increase of europium complexes units in the polymers, the glass transition temperature (T_g) did not change significantly; the isotropic temperature (T_i) and mesophase temperature range (ΔT) decreased. All polymers showed typical cholesteric Grandjean textures, which was confirmed by X‐ray diffraction. The temperatures at which 5% weight loss occurred (T_d) were greater than 300°C for the polymers. The introduction of europium complexes units did not change the liquid crystalline state of polymer systems; on the contrary, the polymers were enabled with the significant luminescent properties. With Eu³⁺ ion contents ranging between 0 and 1.5 mol %, luminescent intensity of polymers gradually increased and luminescent lifetimes were longer than 0.45 ms for the polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40866.     

Synthesis and characterization of chiral side‐chain liquid‐crystalline polymer containing menthol ester

The synthesis of new chiral side‐chain liquid‐crystalline polysiloxanes containing p‐(allyoxy)benzoxy‐p‐chlorophenyl (ABCH) as mesogenic units and undecylenic acid menthol ester (UM) as chiral nonmesogenic units is presented. The chemical structures of monomers and polymers are confirmed by IR spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) are used to measure thermal properties of those polymers. Mesogenic properties are characterized by polarized optical microscope (POM), DSC, and small‐angle X‐ray diffraction. Analytic results revealed that polymers P₀–P₆ are thermotropic liquid‐crystalline polymers with low glass transition; Polymers P₂–P₆ exhibit chiral smectic liquid‐crystalline properties with marble texture, optical rotation, and a sharp reflection at low angles in X‐ray diffraction; polymers P₀, P₁ only exhibit smectic liquid‐crystalline properties without chirality; and P₇ only exhibits chirality without liquid‐crystalline properties. All the polymers exhibit good thermal stability with temperature of 5% mass loss over 297°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2845–2851, 2003     

Influence of the comonomers (styrene and methyl acrylate) on the rate of photocrosslinking of 4‐{[‐3‐(4‐hydroxybenzylidene)‐2‐oxocyclohexylidene]methyl}‐ phenyl acrylate

[2,6‐Bis(4‐hydroxybenzylidene)cyclohexanone] (HBC) was prepared by reacting cyclohexanone and p‐hydroxybenzaldehyde in the presence of acid catalyst. Acrylated derivative of HBC, 4‐{[‐3‐(4‐hydroxybenzylidene)‐2‐oxocyclohexylidene]methyl}phenyl acrylate (HBA), was prepared by reacting HBC with acryloyl chloride in the presence of triethylamine. Copolymers of HBA with styrene (S) and methyl acrylate (MA) of different feed compositions were carried out by solution polymerization technique by using benzoyl peroxide (BPO) under nitrogen atmosphere. All monomers and polymers were characterized by using IR and NMR techniques. Reactivity ratios of the monomers present in the polymer chain were evolved by using Finnman–Ross (FR), Kelen–Tudos (KT), and extended Kelen–Tudos (ex‐KT) methods. Average values of reactivity were achieved by the following three methods: r₁ (S) = 2.36 ± 0.45 and r₂ (HBA) = 0.8 ± 0.31 for poly(S‐co‐HBA); r₁ = 1.62 ± 0.06 (MA); and r₂ = 0.12 ± 0.07 (HBA) for poly(MA‐co‐HBA). The photocrosslinking property of the polymers was done by using UV absorption spectroscopic technique. The rate of photocrosslinking was enhanced compared to that of the homopolymers, when the HBA was copolymerized with S and MA. Thermal stability and molecular weights (M_w and M_n) were determined for the polymer samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2494–2503, 2004     

New thermochromic liquid–crystalline polymer: Synthesis and phase behavior

A series of new thermochromic side‐chain liquid–crystalline polymers were prepared. The chemical structures of the resulting monomers and polymers were characterized by element analyses, FTIR, ¹H‐NMR, and ¹³C‐NMR. Their mesogenic properties were investigated by differential scanning calorimetry, thermogravimetric analyses, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the content of dye groups on phase behavior of the polymers was discussed. The polymers P₁–P₃ showed smectic phase, and P₄–P₇ revealed cholesteric phase. The polymers containing less than 30 mol % of the dye groups showed good solubility, reversible phase transition, wider mesophase temperature ranges, and higher thermal stability. Experimental results demonstrated that the clearing temperature and mesophase temperature ranges decreased with increasing the concentration of the dye groups. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 329–335, 2005     

Effect of the length of the carbochain on the phase behavior of side‐chain cholesteric liquid‐crystalline elastomers

In this study, we prepared two series of new side‐chain cholesteric liquid‐crystalline elastomers (PI and PII) derived from the same chiral bisolefinic crosslinking units and different nematic liquid‐crystalline monomers. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared and ¹H‐NMR spectroscopy. The phase behavior properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. The effect of the length of the carbochain on the phase behavior of the elastomers was investigated. The polymers of the PI and PII series showed similar properties. Polymer P₁ showed a nematic phase, P₂–P₇ showed a cholesteric phase, and P₄–P₇, with more than 6 mol % of the chiral crosslinking agent, exhibited a selective reflection of light. The elastomers containing less than 15 mol % of the crosslinking units displayed elasticity, a reversible phase transition with wide mesophase temperature ranges, and a high thermal stability. The experimental results demonstrate that the glass‐transition temperatures first decreased and then increased; the isotropization temperatures and the mesophase temperature ranges decreased with increasing content of crosslinking agent. However, because of the different lengths of the carbochain, the glass‐transition temperatures and phase‐transition temperatures of the PI series were higher than those of the PII series, and the PI and PII elastomers had their own special optical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1204–1210, 2005     

Evolution of molecular weight and molecular weight distribution in ab initio styrene emulsion polymerizations using series of rigid rodlike cationic amphiphiles as surfactants

The emulsion polymerization of styrene is carried out using a series of unconventional rigid rodlike cationic surfactants (1‐[ω‐(4′‐methoxy‐4‐biphenylyloxy)alkyl]pyridinium bromides, PCX) of different lengths. The evolution of the molecular weight (M) and molecular weight distribution of the polymers is analyzed to obtain information about the chain stopping mechanism. Our results indicate that the M is strongly dependent on the initial surfactant concentration and is not dependent on the alkyl chain length. The Clay and Gilbert model [ln P(M) versus M plots] yields a concave‐up region at low molecular weights and a linear region that extends to high values. The slope of the linear region, which is related to the rate coefficient of the chain transfer to the monomer versus the propagation rate coefficient ratio, decreases as the PCX concentration increases. This behavior indicates that as the PCX concentration increases the chain transfer to monomer becomes the dominant chain stopping mechanism. On the other hand, the ln P(M) versus M plots of polymer samples taken at low and high conversions show differences in slope, particularly at low PCX concentration. It is likely that at low conversion the chain transfer to monomer competes with other chain stopping mechanisms that could be associated with a coagulative nucleation process. The formation of a high molecular weight fraction at low conversion supports this explanation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1513–1523, 2002; DOI 10.1002/app.10489     

Influence of molecular structure on the nematic-nematic transition in polyethers based on 1-(4-hydroxyphenyl)-2-(2-R-4-hydroxyphenyl)ethane where R=CH3 and Cl,and flexible spacers with an odd number of methylene units

In a previous paper (reference 1b) we reported that flexible main chain liquid crystalline copolymers based on various molar ratios between the flexible mesogenic groups 1-(4-hydroxyphenyl)-2-(2-R-4-hydroxyphenyl)ethane (RBPE) where R=F, Cl, CH₃ and several different molar ratios between flexible spacers containing odd numbers of methylenic units, i.e. 5, 7, and 9 display two enantiotropic uniaxial nematic mesophases. The homopolymers RBPE-X (where R=-CH₃ and-Cl) and X=number of methylenic units in the flexible spacer, i.e. X=5, 7, 9, 11, and 13) display also two nematic (n ₁ , n ₂ ) mesophases which are however, monotropic or virtual. This paper will discuss the dependence of the phase transition temperatures between these two nematic mesophases (Tn ₁ n ₂ ), the isotropization temperature (Tin ₁ ), and of their associated thermodynamic parameters of the MBPE-X (M=CH₃) and C1BPE-X homopolyethers as a function of spacer length X. These results will be compared with the predictions of the only available theory which predicts the existence of two uniaxial nematic mesophases in flexible main chain liquid crystalline polymers (reference 6).