Polar anchoring strengths of nematic liquid crystal on high-density polymer brush surfaces

ABSTRACT

Herein, the polar anchoring energy coefficient (A_θ) of nematic liquid crystal (NLC) was examined for high-density polymer brushes via capacitance measurements. The A_θ is 10^?4 J m^?2 for the brushes of poly(methyl methacrylate), poly(ethyl methacrylate) and poly(styrene). The value decreases to 10^?5 J m^?2 for poly(n-butyl methacrylate) and poly(hexyl methacrylate) with lower glass transition temperatures. However, each polymer brush displays a constant A_θ value over a temperature range of ?15°C to 90°C, which is hardly affected by the graft density and brush thickness. At 25°C, A_θ is 10 times greater than the corresponding azimuthal anchoring energy coefficient (A_φ); therefore, NLCs on polymer brushes can be preferentially aligned along the in-plane component of the applied field.     

Thermoelastic and dielectric studies of poly(3,3-dimethyl oxetane) chains

Poly(3,3-dimethyl oxetane) was synthesized by ring opening polymerization of 3,3-dimethyl oxetane. Elongation experiments were performed on unswollen elastomeric networks prepared from this polymer over the temperature range 30–90°C. The changes in the tensile stress while the networks crystallized were examined at various elongations. From thermoelastic data which were free from the effects of network crystallization, the temperature coefficient of the chain dimensions was found to be 1.1 × 10^?3 K^?1 in the vicinity of 60°C. The dipole moment ratio and its temperature coefficient were also measured; the average values of these parameters at 30°C were 0.20₆ and 2.5 × 10^?3 K^?1, respectively. All of these experimental-configuration-dependent properties were critically interpreted in terms of the rotational isomeric-state model. In comparing theory and experiment, conclusions were obtained which confirm earlier results according to which gauche states about C—C skeletal bonds in poly(3,3-dimethyl oxetane) are strongly favored over the alternative trans states.     

Oxyalkylene polymers with alkylsulfonylmethyl side chains: Gas barrier properties

Gas barrier properties of alkylsulfonylmethyl-substituted poly(oxyalkylene)s are discussed. Oxygen permeability coefficients of three methylsulfonylmethyl-substituted poly(oxyalkylene)s, poly[oxy(methylsulfonylmethyl)ethylene] (MSE), poly[oxy(methylsulfonylmethyl)ethylene-co-oxyethylene] (MSEE), and poly[oxy-2,2-bis (methylsulfonylmethyl)trimethylene oxide] (MST) were measured. MSEE, which has the most flexible backbone of the three polymers, had an oxygen permeability coefficient at 30°C of 0.0036 × 10⁻¹³ cm³(STP)·cm/cm²·s·Pa higher than that of MSE, 0.0014 × 10⁻¹³ cm³(STP)·cm/cm²·s·Pa, because the former polymer's T_g was near room temperature. MST with two polar groups per repeat unit and the highest T_g showed the highest oxygen permeability, 0.013 × 10⁻¹³ cm³(STP) · cm/cm²·s·Pa, among the three polymers, probably because steric hindrance between the side chains made the chain packing inefficient. As the side chain length of poly[oxy(alkylsulfonylmethyl)ethylene] increased, T_g and density decreased and the oxygen permeability coefficients increased. The oxygen permeability coefficient of MSE at high humidity (84% relative humidity) was seven times higher than when it was dry because absorbed water lowered its T_g. At 100% relative humidity MSE equilibrated to a T_g of 15°C after 2 weeks. A 50/50 blend of MSE/MST had oxygen barrier properties better than the individual polymers (O₂ permeability coefficient is 0.0007 × 10⁻¹³ cm³(STP)·cm/cm² ·s·Pa), lower than most commercial high barrier polymers. At 100% relative humidity, it equilibrated to a T_g of 42°C, well above room temperature. These are polymer systems with high gas barrier properties under both dry and wet conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 75–83, 1998     

Unperturbed dimensions of isotactic poly(tert-butylethylene oxide)

The root-mean-square end-to-end distances of isotactic poly(tert-butylethylene oxide) fractions were determined in xylene at 80°C from intrinsic viscosity measurements and in o-dichlorobenzene at 80 and 100°C by light scattering. The characteristic dimension (〈L²〉₀/M)^1/2 was 1.04 × 10^?8 cm in xylene and 0.9 and 0.7 × 10^?8 cm in o-dichlorobenzene at 80 and 100°C, respectively. The value in xylene corresponds to a C_∞ of 15.9. This observation and the large negative temperature coefficient of (〈L²〉₀/M)^1/2 suggest that poly(tert-butylethylene oxide) exists in a helical block conformation under these experimental conditions. This conclusion is in agreement with earlier reported NMR measurements.     

Preparation and physical properties of poly(4,4′‐diamino‐3′‐carbamoylbenzanilide terephthalamide) and poly(4,4′‐diamino‐3′‐carbamoylbenzanilide isophthalamide) films

To prepare thermally stable and high‐performance polymeric films, new solvent‐soluble aromatic polyamides with a carbamoyl pendant group, namely poly(4,4′‐diamino‐3′‐carbamoylbenzanilide terephthalamide) (p‐PDCBTA) and poly(4,4′‐diamino‐3′‐carbamoylbenzanilide isophthalamide) (m‐PDCBTA), were synthesized. The polymers were cyclized at around 200 to 350 °C to form quinazolone and benzoxazinone units along the polymer backbone. The decomposition onset temperatures of the cyclized m‐ and p‐PDCBTAs were 457 and 524 °C, respectively, lower than that of poly(p‐phenylene terephthalamide) (566 °C). For the p‐PDCBTA film drawn by 40% and heat‐treated, the tensile strength and Young's modulus were 421 MPa and 16.4 GPa, respectively. The film cyclized at 350 °C showed a storage modulus (E′) of 1 × 10¹¹ dyne/cm² (10 GPa) over the temperature range of room temperature to 400 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 775–780, 2000     

Random-coil configurations of aromatic polyesters: Birefringence of poly(triethylene glycol terephthalate) networks in elongation

Hydroxyl-terminatd poly(triethylene glycol terephthalate) was crosslinked with an aromatic triisocyanate. Birefringence–stress–strain experiments, performed on the networks at 70°C, showed an anomalous increase in the modulus and a downturn in the birefringence–strain isotherms at high elongations. These results suggest that crystallinity is not responsible for the non-Gaussian behavior of the chains at high extension. The same kind of experiments were performed over the range 20–70°C. Values of the optical configuration parameter Δa of the order of 13.3 × 10^?24 cm³ with negligible temperature coefficient were found for these networks. The quantities Δa and d In Δa/dT were calculated by means of the rotational isomeric state model. Better agreement between the theoretical and experimental values of these parameters was found for poly(triethylene glycol terephthalate) than for poly(diethylene glycol terephthalate). Since the polarities of the two chains are similar, intermolecular interactions involving terephthaloyl residues may be responsible for the discrepancies observed between theory and experiment for Δa in aromatic polyesters.     

Synthesis and characterization of high molecular weight poly(1,2-propylene carbonate-<Emphasis Type="Italic">co</Emphasis>-1,2-cyclohexylene carbonate) using zinc complex catalyst

Using supported multi-component zinc dicarboxylate catalyst,poly（1,2-propylene carbonate-co-1,2-cyclohexylene carbonate）（PPCHC） was successfully synthesized from carbon dioxide（CO₂） with propylene oxide（PO） and cyclohexene oxide（CHO）.The conversion of epoxides dramatically increased up to 89.7%（yield:384.2 g of polymer per g of Zn） with increasing reaction temperature from 60℃to 80℃.The optimized reaction temperature is 80℃.The chemical structure,the molecular weight,as well as thermal and mechanical properties of the resulting terpolymers were investigated extensively. When CHO feed content（mol%） is lower than 10%,the PPCHC terpolymers have number average molecular weight（M_n） ranging from 102×10³ to 202×10³ and molecular weight distribution（MWD） values ranging from 2.8 to 3.5.In contrast to poly（propylene carbonate）（PPC）,the introduction of small amount of CHO leads to increase in the glass transition temperature from 38.0℃to 42.6℃.Similarly,the mechanical strength of the synthesized terpolymer is greatly enhanced due to the incorporation of CHO.These improvements in mechanical and thermal properties are of importance for the practical application of PPC.     

Effects of humidity,imidization history,and thickness on water sorption behavior of poly(p-phenylene biphenyltetracarboximide) films

Poly(p-phenylene biphenyltetracarboximide) films with various thicknesses were prepared from the poly(amic acid) precursor by thermal imidization at 230–400°C for 1–10 h under a nitrogen atmosphere. The water sorption in the films was measured at 25°C over 22–100% relative humidity using a Cahn microbalance as a function of film thickness and thermal imidization history. The water diffusion in all the films followed nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. The diffusion coefficient and water uptake varied in 0.85 × 10^?10 ? 7.50 × 10^?10 cm²/s and 0.12–2.4 wt %, respectively, depending upon humidity, film thickness, and imidization history. Both diffusion coefficient and water uptake increased with increasing humidity, but decreased as imidization temperature and time increased. With increasing film thickness, the diffusion coefficient increased whereas the water uptake decreased. The water sorption behavior was interpreted with the consideration of morphological variations, such as polymer chain order, in-plane orientation, and intermolecular packing order due to the film thickness and imidization history. © 1995 John Wiley & Sons, Inc.     

The synthesis of poly(phenylacetylene)s with bulky chiral silyl groups and the thermal stability of their helical conformation

The polymerization of (−)‐p‐[(tert‐butylmethylphenyl)silyl]phenylacetylene (t‐BuMePhSi*PA) and (+)‐p‐[{methyl(α‐naphthyl)phenyl}silyl]phenylacetylene (MeNpPhSi*PA) with the [(nbd)RhCl]₂ Et₃N catalyst yielded polymers with very high molecular weights over 2 × 10⁶ in high yields. The optical rotations of the formed poly(t‐BuMePhSi*PA) and poly(MeNpPhSi*PA) were as high as −356 and −150° (c = 0.11 g/dL in CHCl₃), respectively. The circular dichroism (CD) spectrum of poly(t‐BuMePhSi*PA) in CHCl₃ exhibited very large molar ellipticities ([θ]) in the UV region: [θ]_max = 9.2 × 10⁴ ° · cm² · dmol⁻¹ at 330 nm and −8.0 × 10⁴ ° · cm² · dmol⁻¹ at 370 nm. The [θ]_max values of poly(MeNpPhSi*PA) were also fairly large: [θ]_max = 7.1 × 10⁴ ° · cm² · dmol⁻¹ at 330 nm and −5.3 × 10⁴ ° · cm² · dmol⁻¹ at 370 nm. The optical rotations of poly(t‐BuMePhSi*PA) and poly(MeNpPhSi*PA), measured in tetrahydrofuran, chloroform, and toluene solutions, were hardly dependent on temperature in the range 22–65 °C. The CD effects of these polymers hardly changed in the temperature range 28–80 °C, either. These results indicate that the helical structures of these polymers are thermally appreciably stable. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 71–77, 2001     

Preparation and Pyroelectric Properties of Poly(pentafluorostyrene)-r-Poly(4-vinylaniline) Copolymer Films

Abstract: In this study poly(pentafluorostyrene)-ran-poly(4-vinylaniline) (PPFS-r-PVA) was synthesized by solution polymerization with AIBN utilized as an initiator. The dilute THF solution of the resultant copolymer was spin-coated onto clean Ag/Si(100) substrates, and then the copolymer film was electrically poled at 85 °C for 30 min using a plane poling method with a poling voltage of 7.0 kV. The pyroelectric coefficient was determined by a digital integral method and carried out with a charge integral instrument. It was observed that the average pyroelectric coefficient of the resultant PPFS-r-PVA was 20.4 µC/cm²K in the range of 20–45 °C, and the average dielectric loss is about 0.2298 between 3.2 × 10⁴–1.0 × 10⁶ Hz.     

Low glass transition temperature polymer electrolyte prepared from ionic liquid grafted polyethylene oxide

In this contribution, we report a new type of poly (ionic liquids) prepared by imidazolium ionic liquids directly grafting onto polyethylene oxide backbone. Different molecular weights of poly (ionic liquids) are obtained with a low glass transition temperature up to ?14 °C. The materials as polymer electrolyte achieve a high conductivity around 10^?5 S cm^?1 at 30 °C and close to 10^?3 S cm^?1 at 90 °C. High viscosity up to 4000 Pa s at room temperature would minimize the electrolytes leaking in electrochemical devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2104–2110     

Preparation and characterization of cyclic poly(oxypropylene)

Poly(propylene glycol) [α-hydro-ω-hydroxypoly(oxypropylene)] of number-average molar mass M̄_n ≈ 2000 g · mol⁻¹ (PPG2000) was cyclised with high conversion (ca. 75%) by reaction with dichloromethane in the presence of powdered KOH. The cyclic product was separated from chain extended polymer by preparative GPC, giving an overall yield of polymer (M̄_n ≈ 2000 g · mol⁻¹, narrow molar mass distribution) in excess of 50%. Characterisation by analytical GPC and ¹³C NMR spectroscopy confirmed cyclisation. DEPT and ¹H-coupled NMR spectra were used to show that the links in cyclic poly(oxypropylene) were 77% single acetal, 12% double acetal and 11% triple acetal (or higher). This complexity probably results from competitive reaction with water introduced with KOH.     

Poly(carbon suboxide): A photosensitive paramagnetic ladder polymer

Carbon suboxide was found to give, on photo- and thermal-polymerization, a photosensitive paramagnetic polymer. Studies of the kinetics of the ESR signal growth accompanying the polymerization process complement documented results obtained from monitoring the rate of polymer production and monomer disappearance. The spin concentration of the polymer increases with higher reaction temperature, reaching 2 × 10¹⁹ spin/g at a polymerization temperature of 105°C. The paramagnetism of poly(carbon suboxide) follows the Curie—Weiss law. Relaxation behavior at room temperature and g values for the spin systems have been obtained. The 105°C polymer shows a Weiss constant equal to 17°K and an extremely narrow ESR line width, ca. 10 mG, at 5°K. The ¹³C coupling constant from the selectively labeled polymer indicates π-electron delocalization over the ladder polymer. The polymer paramagnetism can be further reversibly enhanced by visible light irradiation. The steady-state concentration of the photo-ESR signal is proportional to the square root of incident light intensity, with a quantum yield at room temperature for charge accumulation equal to 5% at an incident light level of 10¹⁵ photons/sec-cm². Fluorescence and excitation spectra of the soluble fraction of poly(carbon suboxide) are presented together with the quantum yield. The polymer has also been found to be an effective photopolymerization initiator at wavelengths longer than 340 nm.     

Hydrogenation of poly(myrcene) and poly(farnesene) using diimide reduction at ambient pressure

Ambient pressure chemical hydrogenation using p-toluene sulfonyl hydrazide (TSH) via thermal diimide formation (N₂H₂) permitted reduction of double bonds of poly(myrcene) (poly[Myr]) and poly(farnesene) (poly[Far]). Both pendent and backbone double bonds in poly(Myr) (M_n = 56 kg/mol) and poly(Far) (M_n = 62 kg/mol) synthesized by conventional free radical polymerization were hydrogenated to almost completion. Furthermore, TSH semi-batch addition efficiently hydrogenated double bonds, while avoiding undesired autohydrogenation of diimides that occurred in batch mode. Thermal stability improved for hydrogenated poly(Myr) and poly(Far), where temperature at 10% weight loss (T_10%) increased from 188 to 404°C for poly(Myr) and from 310 to 379°C for poly(Far). T_gs of poly(Myr) and poly(Far) also increased by about 10–25°C, indicating increased stiffness after hydrogenation. Finally, viscosities of poly(Myr) and poly(Far) were also increased after hydrogenation, and a greater increase was observed for poly(Myr) (by two orders of magnitude from 10² to 10⁴ Pa s) due to its M_n being much higher than its entanglement molecular weight. Poly(Far) viscosity only increased by 1.5 times after hydrogenation (~10⁴ Pa s), comparable to the poly(Myr) after hydrogenation, suggesting unsaturated poly(Far) was more entangled than unsaturated poly(Myr) because of its longer side chains.     

Desorption behavior of a surfactant in a linear low‐density polyethylene blend at elevated temperatures

The desorption behavior of a surfactant in a linear low‐density polyethylene (LLDPE) blend at elevated temperatures of 50, 70, and 80 °C was studied with Fourier transform infrared spectroscopy. The composition of the LLDPE blend was 70:30 LLDPE/low‐density polyethylene. Three different specimens (II, III, and IV) were prepared with various compositions of a small molecular penetrant, sorbitan palmitate (SPAN‐40), and a migration controller, poly(ethylene acrylic acid) (EAA), in the LLDPE blend. The calculated diffusion coefficient (D) of SPAN‐40 in specimens II, III, and IV, between 50 and 80 °C, varied from 1.74 × 10^?11 to 6.79 × 10^?11 cm²/s, from 1.10 × 10^?11 to 5.75 × 10^?11 cm²/s, and from 0.58 × 10^?11 to 4.75 × 10^?11 cm²/s, respectively. In addition, the calculated activation energies (E_D) of specimens II, III, and IV, from the plotting of ln D versus 1/T between 50 and 80 °C, were 42.9, 52.7, and 65.6 kJ/mol, respectively. These values were different from those obtained between 25 and 50 °C and were believed to have been influenced by the interference of Tinuvin (a UV stabilizer) at elevated temperatures higher than 50 °C. Although the desorption rate of SPAN‐40 increased with the temperature and decreased with the EAA content, the observed spectral behavior did not depend on the temperature and time. For all specimens stored over 50 °C, the peak at 1739 cm^?1 decreased in a few days and subsequently increased with a peak shift toward 1730 cm^?1. This arose from the carbonyl stretching vibration of Tinuvin, possibly because of oxidation or degradation at elevated temperatures. In addition, the incorporation of EAA into the LLDPE blend suppressed the desorption rate of SPAN‐40 and retarded the appearance of the 1730 cm^?1 peak. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1114–1126, 2004     

Synthesis,structure, and properties of poly[1‐(trimethylgermyl)‐1‐propyne]

Polymerization of 1‐(trimethylgermyl)‐1‐propyne (TMGP) with TaCl₅ and NbCl₅ produced a colorless polymer in high yields, whose molecular weight reached about 3 × 10⁵–14 × 10⁵. The molecular weight distribution of the poly(TMGP) with NbCl₅ in cyclohexane was somewhat narrow (M_w /M_n = ∼1.54). The TaCl₅‐based poly(TMGP) dissolved in toluene, chloroform, cyclohexane, carbon disulfide, carbon tetrachloride, tetrahydrofuran, hexane, and so forth; the NbCl₅‐based polymer was less soluble and did not dissolve in hexane, despite its lower molecular weight. The cis contents of the NbCl₅‐ and TaCl₅‐based poly(TMGP)s determined by ¹³C NMR were 67 ± 5 and 28 ± 3%, respectively. The onset temperature of the weight loss of poly(TMGP) in air was 350 °C, indicating fair thermal stability. The oxygen permeability coefficient (P) of poly(TMGP) at 25 °C was 7800 barrer after the methanol conditioning, and the permeability was fairly stable to aging. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2964–2969, 2000     

Influence of tertiary diamines on the synthesis of high‐molecular‐weight poly(1,3‐cyclohexadiene)

The living synthesis of poly(1,3‐cyclohexadiene) was performed with an initiator adduct that was synthesized from a 1:2 (mol/mol) mixture of N,N,N′,N′‐tetramethylethylenediamine (TMEDA) and n‐butyllithium. This initiator, which was preformed at 65 °C, facilitated the synthesis of high‐molecular‐weight poly(1,3‐cyclohexadiene) (number‐average molecular weight = 50,000 g/mol) with a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight = 1.12). A plot of the kinetic chain length versus the time indicated that termination was minimized and chain transfer to the monomer was eliminated when a preformed initiator adduct was used. Chain transfer was determined to occur when the initiator was generated in situ. The polymerization was highly sensitive to both the temperature and the choice of tertiary diamine. The use of the bulky tertiary diamines sparteine and dipiperidinoethane resulted in poor polymerization control and reduced polymerization rates (7.0 × 10⁻⁵ s⁻¹) in comparison with TMEDA‐mediated polymerizations (1.5 × 10⁻⁴ s⁻¹). A series of poly(1,3‐cyclohexadiene‐block‐isoprene) diblock copolymers were synthesized to determine the molar crossover efficiency of the polymerization. Polymerizations performed at 25 °C exhibited improved molar crossover efficiencies (93%) versus polymerizations performed at 40 °C (80%). The improved crossover efficiency was attributed to the reduction of termination events at reduced polymerization temperatures. The microstructure of these polymers was determined with ¹H NMR spectroscopy, and the relationship between the molecular weight and glass‐transition temperature at an infinite molecular weight was determined for polymers containing 70% 1,2‐addition (150 °C) and 80% 1,4‐addition (138 °C). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1216–1227, 2005     

Oxygen diffusion in poly(dimethyl siloxane) using fluorescence quenching. I. Measurement technique and analysis

The transport properties of oxygen in poly(dimethyl siloxane) have been measured using the method of quenching of fluorescence. This paper discusses the uniqueness of this method and its use in measuring the diffusion coefficient of oxygen in unfilled PDMS. The results show (1) a large value for the diffusion coefficient of oxygen in pure PDMS at 25°C, D = 3.55 × 10^?5 cm²/s, (2) a low value of the acitivation energy, E_D = 4.77 kcal/mole, which was not temperature dependent in the ranges evaluated, and (3) a large value of the preexponential term, D₀ = 0.115 cm²/s. The diffusion coefficient was found to be independent of both the oxygen concentration and fluorophor concentration in the pressure and temperature ranges used in these experiments. The import of these experiments lies in their application to a unique biomedical oxygen sensor which is fast, sensitive, and does not consume oxygen.     

Stress-optical behavior of cycloaliphatic polyesters

Stress-strain-birefringence measurements were carried out on elastomeric networks of poly(oxymethylene-1,4-cis-cyclohexylenemethyleneoxysebacoyl) at several temperatures between 5 and 80°C. The dependence of both the birefringence Δn and the true stress f/A on temperature was found to be linear for T > 30°C; for T < 30°C an anomalous increase in the birefringence and a sharp decrease in the stress was observed. This behavior suggests that crystallinity is developed in the strained networks at low temperatures, and the crystallites are oriented in the direction of the elongation. Values of the optical configuration parameter Δa ranged from 9.15 to 8.28 in units of 10²⁴ cm³ in the temperature range studied. The value at 40°C of 10²⁴Δa, obtained from experiments performed on swollen networks, amounted to 7.47 cm³. These results suggest that intermolecular interactions enhance the birefringence of the strained networks. The quantities Δa and d In Δa/dT were calculated by using the valence optical scheme. Although the calculations reproduce the temperature coefficient fairly well, the theoretical values of Δa are smaller than the experimental ones. The agreement between theory and experiment is better assuming that the CH₂CH₂? COOCH₂ segment is freely rotating.     

Henry's law and diffusion constants of vinyl chloride in poly(vinyl chloride) at high temperature

The Henry's law and diffusion constants of vinyl chloride in poly(vinyl chloride) were determined at temperatures of 24, 90, 120, 150, and 170°C for weight fractions of vinyl chloride between 0.2 × 10^?3 and 0.8 × 10^?3. Above 90°C, Henry's law applies; values of the constant increase with temperature from 1.8 × 10² to 5.5 × 10² atm per unit weight fraction of dissolved vinyl chloride. The heat of desorption is about 15 kJ/mole. At 24°C, the nominal Henry's law constant was smaller than would have been obtained by extrapolating the values found at higher temperature. The diffusion constants increase with temperature from about 2 × 10^?13 to 3 × 10^?7 cm²/sec. The activation energy for diffusion is about 110 kJ/mole between 90 and 170°C. Although all values were determined in the absence of air, it is likely that they apply to polymer in air. They may, therefore, be used to calculate the vinyl chloride content in the gas above poly(vinyl chloride) under specific processing conditions.