Myongsoo Lee

Molecular Engineering of Liquid Crystal Polymers by Living Polymerization. XXIII. Synthesis and Characterization of AB Block Copolymers Based on ω-[(4-Cyano-4′ -Biphenyl)-oxy]alkyl Vinyl Ether, 1H, 1H, 2H, 2H-Perfluorodecyl Vinyl Ether, and 2-(4-Blphenyloxy)ethyl Vinyl Ether with 1H, 1H, 2H, 2H-Perfluorodecyl Vinyl Ether

Abstract This paper describes the synthesis and characterization of AB block copolymers based on ω-[(4-cyano-4′-biphenyl)oxy]alkyl vinyl ether (6-n), with alkyl being ethyl (6-2), propyl (6-3), nonyl (6-9), and undecanyl (6-11), with 1H, 1H, 2H, 2H-perfluorodecyl vinyl ether (CF8), poly[(-6-n)-b-CF8]X/Y (where X/Y refers to the weight ratio of the two segments), and of 2-(4-biphenyloxy)ethyl vinyl ether (BEVE) with 1H,-1H, 2H, 2H-perfluorodecyl vinyl ether, poly[BEVE-b-CF8]X/Y. They were prepared by living cationic polymerization and exhibit a narrow molecular weight distribution. All block copolymers display a micro-phase-separated morphology when the A segment is in the liquid crystalline phase. Block copolymers based on 6-2, 6-3, and BEVE with CF8 also exhibit a microphase-separated morphology in the melt phase of A and B blocks.

Phase morphology of injection-moulded polycarbonate/acrylonitrile-butadiene-styrene blends

Abstract The morphology of injection-moulded blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) has been examined across the entire composition range. Brittle fracture surfaces were etched to remove selectively the PC phase and viewed in the scanning electron microscope. Morphological features observed through the thickness of injection-moulded plaques were the basis for the identification of three composition ranges. In PC-rich blends, the ABS phase formed a bead-and-string structure oriented in the injection direction near the edge, while in the centre the ABS was dispersed as rubber domains and spherical particles of free styrene-acrylonitrile (SAN). A transition occurred between PC/ABS 70 30 and 60 40 wt% compositions from the bead-and-string structure with some interconnections to a coalesced, stratified morphology near the edge; while in the centre, the morphology changed from a dispersion of rubber particles and free SAN particles to thick coalesced ABS domains that created regions where ABS was co-continuous with PC. The ABS-rich blends had a conventional blend morphology with PC domains dispersed in ABS. Qualitatively, the solid-state morphology could be explained in terms of the melt morphology created by the melt flow pattern during mould filling, and subsequent relaxation during cooling prior to solidification.

Formation and break-up of a bead-and-string structure during injection moulding of a polycarbonate/acrylonitrile-butadiene-styrene blend

Abstract The morphology gradient through the thickness of an injection-moulded blend of 10% by weight acrylonitrile-butadiene-styrene (ABS) and 90% by weight polycarbonate (PC) has been characterized. Brittle fracture surfaces were etched and examined both parallel and perpendicular to the injection direction in the scanning electron microscope. In the centre of the plaque, the morphology was isotropic with the ABS phase dispersed in the PC matrix as large composite rubber particles about 1 μm in diameter and smaller particles of free styrene-acrylonitrile (SAN) about 0.3 μm in diameter. About half the distance from the centre to the edge, the morphology of the free SAN phase changed from predominantly spherical to predominantly string-like. The SAN strings connected the rubber particles to form an oriented ABS bead-and-string structure that was essentially continuous in the injection direction. It was thought that the free SAN was highly extended under elongational or shear flow while remaining attached to the rubber particles because of miscibility with grafted SAN. The bead-and-string structure was retained near the edge where the melt solidified most rapidly. In the centre of the plaque, the low shear rate during mould filling and longer cooling time after mould filling favoured relaxation of the bead-and-string structure. The morphology gradient through the thickness was created by the competition between the relaxation rate and the cooling rate after mould filling. In this case, relaxation was thought to occur by interfacial-tension-driven break-up and end-pinching mechanisms to produce the dispersion of rubber and free SAN particles. Evidence to support the break-up mechanism was obtained when annealing above the glass transition temperature of PC for a matter of seconds, the timescale of mould cooling, caused the bead-and-string structure to convert to a dispersion of composite rubber particles and SAN particles.

Molecular engineering of liquid crystal polymers by living polymerization: 9. Living cationic polymerization of 5-[(4-cyano-4′-biphenyl)oxy]pentyl vinyl ether and 7-[(4-cyano-4′-biphenyl)oxy]heptyl vinyl ether, and the mesomorphic behaviour of the resulting polymers

Abstract The synthesis and living cationic polymerization of 5-[(4-cyano-4′-biphenyl)oxy]pentyl vinyl ether ( 6-5 ) and 7-[(4-cyano-4′-biphenyl)oxy]heptyl vinyl ether ( 6–7 ) are present. The influence of molecular weight on the mesomorphic behaviour of poly( 6-5 ) and poly( 6–7 ) is discussed and compared to that of 5-[(4-cyano-4′-biphenyl)oxy]pentyl ethyl ether ( 8-5 ) and 7-[(4-cyano-4′-biphenyl)oxy]heptyl ethyl ether ( 8-7 ) which are models of the monomeric structural units of poly( 6-5 ) and poly( 6–7 ). Both ( 8-5 ) and ( 8-7 ) exhibit a monotropic nematic mesophase. Poly( 6-5 ) with degrees of polymerization equal to and lower than six exhibit an enantiotropic nematic mesophase. Poly( 6-5 )s with higher degrees of polymerization display both smectic A and nematic enantiotropic mesophases. Poly( 6–7 ) exhibits an enantiotropic smectic A mesophase over the entire range of molecular weights.

Molecular Engineering of Liquid Crystal Polymers by Living Polymerization. VIII. Influence of Molecular Weight on the Phase Behavior of Poly {ω-[(4-Cyano-4′-biphenyl)-oxy]alkyl Vinyl Ether}s with Ethyl, Propyl, and Butyl Alkyl Groups

Abstract The synthesis and living cationic polymerization of 2-[4-cyano-4′-biphenyl)oxy]ethyl vinyl ether (6–2), 3-[4-cyano-4′-biphenyl)oxy]-propyl vinyl ether (6-3), and 4-[4-cyano-4′-biphenyl)oxy]butyl vinyl ether (6-4) are described. The mesomorphic behaviors of poly(6–2), poly(6-3), and poly(6-4) with different degrees of polymerization and narrow molecular weight distributions were compared to those of 6–2, 6–3, and 6–4 and of 2-[(4-cyano-4′-biphenyl)oxy]ethyl ethyl ether (8–2), 3-[(4-cyano-4′-biphenyl)oxy]propyl ethyl ether (8–3), and 4-[4-cyano-4′-biphenyl)oxy]butyl ethyl ether (8–4) which are model compounds of the monomeric structural units of poly(6–2), poly(6–3), and poly(6–4). In the first heating scan, all three polymers exhibit an x (unidentified) mesophase which overlaps the glass transition temperature, and an enantiotropic nematic mesophase. In the second and subsequent heating and cooling scans, poly(6–3) and poly(6–4) display only the enantiotropic nematic mesophase. Both in the first a...

Molecular engineering of liquid crystal polymers by living polymerization: 5. Synthesis and mesomorphic behaviour of poly{2-[(4-cyano-4′-biphenyl)oxy]ethyl vinyl ether-co-8-[(4-cyano-4′-biphenyl)oxy]octyl vinyl ether}

Abstract The synthesis and characterization of poly{2-[(4-cyano-4′-biphenyl)oxy]ethyl vinyl ether} [poly(6-2)], poly{8-[(4-cyano-4′-biphenyl)oxy]octyl vinyl ether) [poly(6–8)] and of poly (6-2-co-6–8) X Y (where X Y is the molar ratio of the two monomeric structural units) with degrees of polymerization of about 10 and narrow molecular weight distribution are described. Both homopolymers and copolymers were prepared by the living cationic polymerization and copolymerization of 6-2 and 6–8. During the first heating scan poly(6-2) presents an inverse monotropic sc mesophase. During subsequent heating and cooling scans, this polymer is amorphous regardless of the thermal history of the sample. Poly(6–8) exhibits an enantiotropic sA mesophase. During both the first and subsequent heating and cooling scans, the phase diagram which plots the dependence of mesomorphic transition temperatures as a function of copolymer composition is continuous. In the case of poly (6-2-co-6–8) 3 7 , which exhibits a triple point in its phase behaviour, the highest temperature mesophase changes from nematic to sA. During the first heating scan, poly (6-2-co-6–8) X Y with X Y = 10 0 to 6 4 represents an inverse sC monotropic mesophase. Poly (6-2-co-6–8) X Y with X Y = 8 2 to 6 4 show in addition to the sC phase an enantiotropic nematic mesophase. Poly (6-2-co-6–8) 5 5 exhibits only an enantiotropic nematic mesophase, while poly (6-2-co-6–8) 4 6 displays both a nematic and a sA enantiotropic mesophase. Poly (6-2-co-6–8) X Y with X Y = 3 7 to 0 10 present an enantiotropic sA mesophase. The second and subsequent heating scans and first and subsequent cooling scans provide an identical phase behaviour with that obtained from the first heating scan, except that the sc mesophase is absent.

Light scattering from a nematic monodomain in an electric field Twist elastic constant and viscosity coefficient of nematic polymer–solvent mixtures

Abstract The light scattering technique was used to investigate the viscoelastic parameters characterizing director twist distortions in miscible nematic mixtures of 5CB (pentacyanobiphenyl) with two side chain liquid crystal polymers and a main chain liquid crystal polymer. By applying an AC electric field to homeotropically-aligned nematic monodomains of the mixtures, the field-dependent scattering intensities and director orientation fluctuation relaxation rates yield, respectively, the twist elastic constant K 22 and viscosity coefficient γ1. The results directly demonstrate that the addition of liquid crystal polymers causes substantial decreases of the relaxation rates for dynamic light scattering from the twist mode and these changes are due to small decreases in K 22 coupled with large increases in γ1. The decrements in K 22 are comparable for both side chain and main chain liquid crystal polymers. The relative increase in the twist viscosity for the side chain liquid crystal polymers is much smal...

Molecular engineering of liquid crystal polymers by living polymerization. XIX: Synthesis and characterization of poly[2-(4-biphenyloxy)ethyl vinyl ether]

Abstract The synthesis and living cationic polymerization of 2-(4-biphenyloxy)ethyl vinyl ether (BEVE) are described. Polymers and oligomers with degrees of polymerization from 3.8 to 22.1 and narrow molecular weight distribution were synthesized and characterized by differential scanning calorometry (DSC) and thermal optical polarized microscopy. When determined from their first DSC heating scans, poly(BEVE)s exhibit only a crystalline phase over the entire range of molecular weights. When determined from the second and first cooling scans, poly(BEVE) with a degree of polymerization of 3.8 exhibits an enantiotropic smectic mesophase and a crystallization process on the heating scan, while the oligomers with degrees of polymerization from 4.7 to 8.1 exhibit only an enantiotropic smectic mesophase. The polymers with higher degrees of polymerization do not exhibit any mesophase. An explanation for this behavior is provided.

Structural rearrangements during mesomorphic phase transitions in poly{10-[(cyano-4′-biphenyl)oxy]decanyl vinyl ether}

Abstract The structures displayed by poly{10-[(4-cyano-4′-biphenyl)oxy]decanyl vinyl ether} were studied by small- and wide-angle X-ray scattering. It is shown that this polymer possesses two different smectic phases: an ordered smectic E phase at low temperatures, and a smectic A phase at higher temperatures. The smectic A phase is characterized by a double-layer packing with partial overlap of the cyanobiphenyl groups, while the ordered smectic E phase displays a layer packing characterized by the presence of two incommensurate periodicities. The structural rearrangements accompanying the phase transformation from the ordered to the disordered smectic phase are discussed in detail.

Molecular engineering of liquid crystal polymers by living polymerization. XXII. Synthesis and characterization of binary copolymers of 11-[4-cyano-4′-biphenyl)oxy]undecanyl vinyl ether with (2S, 3S)-(+)-2-chloro-3-methylpentyl 4′-(8-vinyloxyoctyloxy)biphenyl-4-carboxylate, and of (2S, 3S)-(+)-2-chloro-3-methylpentyl 4′-(8-vinyloxyoctyloxy)biphenyl-4-carboxylate with 3-[4-cyano-4′-biphenyl)oxy]propyl vinyl ether

Abstract The synthesis and characterization of poly{11-[(4-cyano-4′-biphenyl)oxy]undecanyl vinyl ether-co-(2S, 3S)-(+)-2-chloro-3-methylpentyl 4′-(8-vinyloxyoctyloxy)biphenyl-4-carboxylate}X/Y {poly[(6–11)-co-(15–8)]X/Y} (where X/Y represents the molar ratio of the two structural units) and poly {(2S, 3S)-(+)-2-chloro-3-methylpentyl 4′-(8-vinyloxyoctyloxy)biphenyl-4-carboxylate-co-3-[(4-cyano-4′-biphenyl)oxy]propyl vinyl ether}X/Y poly[(15–8)-co-(6–3)]X/Y} with degree of polymerization of about 20 and molecular weight distribution of about 1·1 are described. The mesomorphic behaviour of all copolymers determined from both first, second and subsequent DSC scans was discussed as a function of composition. As determined from the second DSC scans, poly(6–11) exhibits enantiotropic smectic A (SA) and SX (unidentified smectic), poly(6–3) enantiotropic nematic, while poly(15–8) exhibits enantiotropic SA, chiral smectic C (SC*) and SX (unidentified smectic) mesophases. Poly[(6–11)-co-(15–8)]X/Y exhibit a SA phase...