Dynamic viscoelastic behavior of cholesteric liquid crystalline side-chain copolymers

Summary The rheological behavior of the cholesteric side-chain copolysiloxane whose two kinds of mesogenic groups consist of cholesteryl units and biphenyl benzoate units was investigated for three different compositions: 31:69, 35:65, 37:63 (in mol%). On the frequency dependence diagram of G′ for the copolymers at various temperatures, G′ decreases with decreasing frequency. The slope of G′ in a higher frequency region at lower temperatures (110°–130°C) is similar to that in the flow region of amorphous polymer melts. However, the slope of G′ in a lower frequency region at higher temperatures (140°–160°C) is relatively small, and the G′ curves in this region can not be superposed on to a single master curve. This deviation seems to be due to change in stability of the domain structure of the cholesteric phase. Furthermore, on the temperature dependence curve of G′, G′ showed a maximum near T _c1 . This maximum of G′ curve seems to be caused by molecular organization of a blue phase.     

A new approach to anisotropic conductive networks

A liquid-crystalline bifunctional monomer with two different reactive moieties was prepared by esterification of 4-(6-(acryloyloxy)hexyloxy)benzoic acid and 4-[11-(3-thienyl)undecyloxy]-4′-hydroxybiphenyl. A mesogenic side-chain polyacrylate containing a thienyl moiety at the extremity of its side chain was obtained by radical polymerization of the monomer. The subsequent reaction of the thienyl moiety with FeCl₃ leads to the formation of an anisotropic network with a poly(thiophene) unit. Received: 17 January 1997/Accepted: 5 March 1997     

Binders for higher-solids coatings. IV. Liquid–crystalline acrylic lacquers

A previously reported synthetic procedure was used to graft oligo-p-hydroxybenzoic acid (oligo-PHBA) to COOH-functional acrylic copolymers. Most of the products were side-chain LC copolymers. Length of the mesogenic oligo-PHBA groups averaged up to five aromatic rings per group. Because these long mesogenic groups have a strong tendency to form LC domains, it was possible to prepare LC side-chain copolymers having as little as 5 mol % of mesogenic monomer. Thus this synthetic procedure provides a versatile route for exploration of the properties of LC copolymers having relatively few but especially effective mesogenic groups. The potential utility of such LC copolymers as binders for nonbake coatings was assessed. Variables studied were molecular weight and T_g of the acrylic copolymer backbone, number and average length of oligo-PHBA segments, and the presence or absence of a flexible spacer between the acrylic backbone and the PHBA segments. Optimum LC copolymers have moderate (15,000–30,000) M_n, low (?10°C) backbone T_g, and low (5–7.5 mol %) population of long (5 PHBA units) oligo-PHBA units. Such copolymers have two major advantages as coatings binders: They form concentrated, stable, low-viscosity dispersions in common solvents, a very desirable characteristic for application. Coating films have excellent adhesion to metal, and they have an extraordinary combination of hardness (H–2H) and impact resistance (> 80 in. Ib). These properties are key indicators of coating performance and indicate that LC copolymers have excellent potential for use as binders for nonbake coatings. Other properties remain to be investigated.     

Cirality induction in liquid crystalline side-chain polyethers prepared by copolymerization of oxiranes with mesogenic and non mesogenic groups

Copolymers prepared by anionic initiation from racemic or optically active styrene oxide and a racemic oxirane bearing cyanobiphenyl mesogenic group in the side chain are liquid crystalline when the content of the mesogenic monomer exceeds 60 mole %. Copolymers prepared from a mesogenic oxirane with a short spacer and racemic styrene oxide exhibit a nematic phase, while those prepared with optically active styrene oxide exhibit a cholesteric phase, thus indicating a transfer of chirality from the main chain towards the mesophase. Such a transfer of chirality is no more observed in the case of a copolymer prepared from a mesogenic oxirane with a long spacer. Received: 18 October 1996/Revised: 18 November 1996/Accepted: 20 November 1996     

Dynamics of the Kerr effect in the isotropic phase of comb-shaped nematic polymers

The equilibrium Kerr effect and its dynamics are investigated in isotropic melts of the comb-shaped LC polymer poly(4-[(4′-cyano-1,1′-biphenyl-4-yl)oxy]butyl-2-acrylate) and its copolymers with acrylic acid or methyl methacrylate and isotropic melts of the LC ionomer containing rubidium ions in a wide temperature range. A sharp change in the temperature dependence of relaxation times for the induced macroscopic orientational order is found for the LC copolymers and the LC ionomer in the temperature range 10–15 K higher than the temperature of the nematic-isotropic phase transition. In contrast, the phenomena caused by the small-scale dynamics, such as electric conductivity and dipole relaxation, are approximated by the conventional Arrhenius type dependence, and the equilibrium electrooptical properties of the copolymers are well characterized via the Landau-De Gennes model. The nonclassical behavior of macroscopic relaxation times may be associated with temperature variations in the contribution of main polymer chains to the orientation macroscopic dynamics of the melt, in which the decisive role is played by side mesogenic groups.     

Mesomomorphism enhancement of modified side‐chain liquid‐crystalline polysiloxanes by copolymerization

The liquid‐crystalline (LC) monomer 4‐allyoxybenzoyloxy‐4′‐buthylbenzoyloxy‐p‐phenyl (M₁), whose LC phase appeared at lower temperatures, from 137 to 227°C, and the modified mesogenic monomer 4‐allyoxybenzoyloxy‐4′‐methyloxybenzoyloxy‐p‐biphenyl (M₂), whose LC phase appeared at higher temperatures, from 185 to 312°C, were prepared. A series of side‐chain LC polysiloxanes containing M₁ and M₂ were prepared by graft copolymerization. Their LC properties were characterized by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. The results show that the introduction of the modified mesogenic monomer M₂ into the polymeric structure caused an additional increase in the clearing point (isotropic transition temperature) of the corresponding polysiloxanes, compared with unmodified polysiloxanes, but did not significantly affect the glass‐transition temperature. Moreover, the modified polysiloxanes exhibited nematic phases as the unmodified polymer did. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1196–1201, 2005     

Compatibilization of low-density polyethylene/polystyrene blends by segmented EB(PS-block-EB) n block copolymers

Hydrogenated segmented poly[butadiene-block-(styrene-block-butadiene)_n] block copolymers, which were developed by use of a polymeric iniferter technique, were tested on their compatibilizing effectiveness for (10/90) LDPE/PS blends. They were found to be effective compatibilizers for this mixture, already giving a pronounced improvement in both tensile strength and strain of the blend at block copolymer concentrations of one percent. A concentration of five weight percent of segmented block copolymer provided a tenfold improvement in blend toughness. The effectiveness of the segmented block copolymers was found be dependent on the block copolymer composition. Block copolymer compositions of close to 50 : 50 EB : PS gave the best results. Received: 23 September 1996/Revised: 4 November 1996/Accepted: 7 November 1996     

Monomer unit sequence distribution and linkage configurations at citraconic anhydride units in the copolymers of citraconic anhydride and styrene prepared in carbon tetrachloride

The triad monomer unit sequence distribution and the cis and trans linkage configurations at the cyclic citraconic anhydride units are quantitatively determined for the copolymers of citraconic anhydride (α-methylmaleic anhydride) (CA) and styrene (ST) prepared with AIBN in CCl₄ solutions at 50 °C. Semi-alternating copolymers are obtained for most feed compositions with rigidly alternating copolymers being formed when CA in feed is more than 90%. Greater than 50% of the linkages at CA units are found to be in cis configuration in semi-alternating copolymers. This may be explained if the donor-acceptor complex formed between CA and ST participates in the copolymerization. Received: 14 November 1996/Revised: 5 March 1997/Accepted: 10 March 1997     

Thermally reactive liquid crystalline copolymers based on 11-[(4-cyano-4′-biphenyl)oxy]undecanyl vinyl ether and 2-vinyloxyethyloxy methacrylate

Summary Living cationic copolymerization of 11-[(4-cyano-4-biphenyl)oxy]undecanyl vinyl ether (6-11) with 2-vinyloxyethyloxy methacrylate (16-2) leads to reactive copolymers poly[(6-11)-co-(16-2)]X/Y (where X/Y is the mol ratio between the two monomers in copolymer) containing methacryloyl side groups. Upon thermal crosslinking via the polymerization of their methacryloyl side groups, the copolymers with X/Y=5/5 to 9/1 lead to liquid crystalline networks displaying a S_A mesophase. These results have demonstrated that a shorter spacer in the reactive bifunctional monomer 16-2 than in the mesogenic 6-11 monomer leads to networks with broader range of mesomorphism than those derived from a reactive monomer containing a spacer length equal to that of the mesogenic monomer.This paper is part 27 in the series: Molecular engineering of liquid-crystalline polymers by living polymerization. Part 26: V. Percec, Q. Zheng: Polym. Bull., previous paper in the issue     

Synthesis,characterization, and mesomorphic behavior of side-chain liquid crystalline copolysiloxane polymers I. with an oligo (ethylene oxide) unit and a cyano unit in the side chain

The syntheses and characterizations of poly [4-allyloxy-benzoic acid [4-(2-methoxy) ethoxy] biphenyl]-4-yl ester-co-4-allyloxy-[(4-cyano)-4-phenyl] carboxyl benzoate ester (poly [(MS3BDBE1)-co-(MCN)]_x/y) (where x/y represents the molar ratio of the two structural units on the side chain) were performed in this study. The molar compositions of the structural units on the copolymers side chain were characterized by¹H NMR. The transition temperatures, mesophase texture, and layer spacing (dl) of the polysiloxane polymers and copolymers were determined by differential scanning calorimetry (DSC), polarized optical microscopy, and X-ray diffraction patterns. The effects of the molar composition in the copolymers on the mesophase texture, transition temperatures, enthalpy/entropy change of mesophase/isotropic transition, dl of these copolymers were also discussed.     

Phase transition in swollen gels

Summary The dynamic mechanical behaviour of 4% aqueous solutions and networks of poly (N, N-diethylacrylamide) and copolymers of diethylacrylamide with sodium methacrylate (MNa) (molar ratio x_MNA=0–0.05) swollen in water was measured in the temperature range 20–80 °C. With increasing temperature, at T_c polymer chains collapse from random coil to more compact globular conformations. While in the region of coil conformations (T > T_c) the mechanical behaviour of solutions has a liquid-like character (the loss modulus G″ is higher than the storage modulus G′ for a constant frequency ω=1 Hz), in the region of globular conformations (T > T_c) a heterogeneous physical network is built in solutions, and the mechanical behaviour has a solid-like character (G′ > G″). In networks the collapse is reflected in an increase of storage modulus G′; the magnitude of this increase decreases with ionization. The dependence of the loss modulus G″ on the temperature of solutions and networks allows us to conclude that the magnitude of losses in the collapsed state is affected rather by x_MNa (the modulus G″ increases with increasing ionization) than by the heterogeneous structure of the samples.     

Synthesis of triblock and random copolymers of 4-acetoxystyrene and styrene by living atom transfer radical polymerization

Triblock copolymers containing polystyrene (PSt) and poly(4-acetoxystyrene) (PAcOSt) segments have been prepared by atom transfer radical polymerization (ATRP). In the first step one of the two monomers was polymerized in bulk using the initiating system α,α′-dibromo-p-xylene/CuBr/2,2′-bipyridine (1/1/3). Subsequently the resulting telechelic polymers with active bromo end group structures were used as macroinitiators for the polymerization of the second monomer under ATRP conditions. This process gave PAcOSt-PSt-PAcOSt and PSt-PAcOSt-PSt triblock copolymers with predetermined molecular weights and narrow molecular weight distributions. Polymerization of a mixture of equal molar amounts of the two monomers yielded a random copolymer with narrow molecular weight distribution. Received: 25 June 1997/Revised: 25 August 1997/Accepted: 8 September 1997     

Homopolymer of 4-chloro-3-methyl Phenyl Methacrylate and its Copolymers with Butyl Methacrylate: Synthesis, Characterization, Reactivity Ratios and Antimicrobial Activity

The methacrylate monomer 4-chloro-3‐methyl phenyl methacrylate (CMPM) was synthesized by reacting 4-chloro-3‐methyl phenol with methacryloyl chloride. The homopolymer and various copolymers of CMPM with n-butyl methacrylate were synthesized by free-radical polymerization in toluene at 70°C using 2,2′-azobis(isobutyronitrile) as the initiator. The CMPM monomer was characterized by Fourier transform IR and ¹H-NMR studies. The copolymers were characterized by IR spectroscopy. The molecular weights (M _n and M _w) and the polydispersity index were obtained from gel permeation chromatography. The solubility and intrinsic viscosity of the homopolymer and the copolymers are also discussed here. The copolymer composition obtained from UV spectra led to the determination of reactivity ratios employing Fineman-Ross and Kelen-Tudos linearization methods. Thermogravimetric analyses of the homopolymer and the copolymers were carried out under a nitrogen atmosphere. The homopolymer and the copolymers prepared were tested for their antimicrobial activity against bacteria, fungi and yeasts.     

Effects of phenyl-s-triazine moieties on thermal stability and degradation behavior of aromatic polyether sulfones

The effect of the incorporation of phenyl-s-triazine units into the main chain of phthalazinone-based polyether sulfones on initial decomposition temperature, activation energy, thermal-mechanical property and possible degradation mechanism has been investigated. To this purpose, decomposition of poly(phthalazinone ether sulfone phenyl-s-triazine) copolymers (PPESPs) of different monomer compositions have been studied by utilizing thermogravimetry and differential scanning calorimetry. Non-isothermal experiments under nitrogen were performed, and the apparent activation energy (E _a) was calculated by isoconversional and conversional methods including the methods of Flynn-Wall-Ozawa, Friedman and Kissinger. In the conversion range (5–30%) studied, solid-state decomposition process of PPESPs is found to be a mechanism involving phase boundary controlled reaction (E _a: 189–201 kJ mol⁻¹) except that phenyl-s-triazine-rich copolymers exhibit a mechanism involving three-dimensional diffusion (E _a: 196–225 kJ mol⁻¹) in terms of Coats–Redfern method. The phenyl-s-triazine-rich copolymers display much higher E _a and slighter mechanical property-change compared to sulfone-rich copolymers and generic aromatic polyether sulfone, suggesting strong stabilizing effect of the phenyl-s-triazine moieties.     

Violation of the power-law dynamic mechanical behaviour at the gel point threshold in non-stoichiometric epoxide systems

Summary The dynamic mechanical behaviour of fully cured off-stoichiometric epoxy systems prepared from poly(oxypropylene)diamine (Jeff D-400) or -triamine (Jeff T-403) and diglycidyl ether of Bisphenol A (DGEBA) with initial ratios of reactive amine (NH₂) and epoxide (E) groups, r _H= (2[NH₂])/[E] ranging from 2.4 to 4.3 was investigated in the gelation threshold region. The evolution of the dynamic behaviour of two stoichiometric samples with r _H= 1 with reaction time, t _r , was also studied. The critical ratios for gelation, r ^c _H, of fully cured samples were determined from extraction experiments (r ^c _H= 2.54 for Jeff D-400/DGEBA and r ^c _H= 4.15 for Jeff T-403/DGEBA systems, respectively). For both stoichiometric critical gel (CG) structures obtained by changing the curing time t _r , a power-law rheological behaviour (G′∼ G″∼ωⁿ, G′ and G″ are the storage and loss moduli, respectively, ω is angular frequency and n is a critical exponent) with the loss tangent, tan δ= G″/G′ independent of frequency, was found. On the other hand, both CG off-stoichiometric systems with r ^c _H ratios show a small dependence of tan δ on ω, so that the critical power-law behaviour is not exactly obeyed. More complex CG structure in these samples, formed due to differences in the structure growth process, was suggested to account for violation of the power-law behaviour. Received: 4 December 1998/Accepted: 10 March 1999     

Synthesis and properties of novel poly(aryl ether ketone)s containing imide linkages in the main chains

A new monomer containing imide linkages, bis[4-(p-phenoxybenzoyl)-1,2-benzenedioyl]-N,N,N′,N′-4,4′-diaminodiphenyl ether (BPBDADPE), was prepared by the Friedel–Crafts reaction of bis(4-chloroformyl-1,2-benzenedioyl)-N,N,N′,N′-4,4′-diaminodiphenyl ether (BCBDADPE) with diphenyl ether (DPE). Novel poly(aryl ether ketone)s containing imide linkages in the main chains (PEK-I) were synthesized by electrophilic Friedel–Crafts solution copolycondensation of terephthaloyl chloride (TPC) with a mixture of DPE and BPBDADPE. The polymers were characterized by different physico-chemical techniques. The polymers with 10–40 mol% BPBDADPE are semicrystalline and had increased T _gs over commercially available poly(ether ether ketone) (PEEK) and poly(ether ketone ketone) (PEKK) (70/30) due to the incorporation of imide linkages in the main chains. The polymers IV and V with 30–40 mol% BPBDADPE had not only high T _gs of 182–183 °C, but also moderate T _ms of 341–343 °C, having good potential for melt processing and exhibited high thermal stability and good resistance to common organic solvents.     

Synthesis of side chain liquid crystalline poly(vinyl ether)s containing 2,2′-dimethyl-4-methoxy-4′-[undecanyloxy-4-benzoyl]ester biphenyl side group

The synthesis and characterization of 2,2′-dimethyl-4-methoxy-[(11-vinyloxy)undecanyloxy-4-benzoyl]ester biphenyl (7), its cationic polymerization to side chain liquid crystalline polymers with relative number average degrees of polymerization (DP) of 2, 8 and 19 are presented. The mesogenic vinyl ether monomer displays an inverse monotropic nematic phase. The oligomers with DP = 2 and DP = 8 display an enantiotropic nematic, while the polymer with DP = 19 exhibits an inverse monotropic smectic A and an enantiotropic nematic phase. All the liquid crystalline polymers display only liquid crystalline phases and do not undergo side chain crystallization even though eleven methylenic units are used as the flexible spacer. Received: 28 February 1997/Accepted: 23 May 1997     

Synthesis and thermal transitional properties of side-chain liquid crystalline polyacrylates containing para-nitroazobenzene as mesogenic groups

The synthesis and characterization of side-chain liquid crystalline (LC) polyacrylates containing para-nitroazobenzene (Pn) as mesogenic groups were described. Homopolymers with 3 and 4 carbon atoms in the spacers were non-LC polymer; for homopolymers with 6 carbon atoms in the spacer, nematic LC behavior was observed. Copolymers with acrylic acid as one componenet exhibited an S_Ad phase according to the WAXD results which showed the d/l of 1.4–1.54 for the copolymers with 3,4 and 6 carbon atoms in the spacers. Considering the molecular structure as well as the WAXD results of the copolymers, the possible molecular arrangement in the smectic S_Ad phase was proposed, in which the smectic layers were composed of the antiparallel mesogens and the antiparallel arrangement was considered to be enhanced due to the H bond between  COOH and  NO₂. The stress-induced orientational phenomena of Pn in the LC states was also discussed. © 1996 John Wiley & Sons, Inc.     

Synthesis and phase behavior of new cholesteric liquid‐crystalline copolymers containing chiral mesogenic groups derived from menthol derivatives

The synthesis of a new chiral mesogenic monomer ( M₁ ), a nematic monomer ( M₂ ), and a series of side chain cholesteric copolymers ( P₂ – P₆ ) containing the mesogenic menthyl groups is described. The chemical structures of the compounds were confirmed by FTIR and ¹H NMR. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. M ₁ showed an enantiotropic cholesteric phase, and M₂ revealed a nematic phase. The homopolymers P₁ and P₇ , respectively, displayed a chiral smectic A (S_A) phase and a nematic phase, while the copolymers P₂ – P₆ exhibited the Grandjean texture of the cholesteric phase. T_g, T_i, and ΔT of P₁ – P₇ increased with increasing the concentration of M₂ in the polymers. All of the obtained polymers displayed very good thermal stability and the wide mesophase temperature range. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008