Effect of pressure and temperature on chromophore reorientation in a new syndioregic main‐chain hydrazone nonlinear optical polymer

Second harmonic generation (SHG) was used to measure the temperature dependence of the reorientation activation volume (ΔV*) of a syndioregic main‐chain hydrazone (SMCH) nonlinear optical polymer. The decay of the SHG signal from poled films of SMCH was recorded at hydrostatic pressures up to 2924 atm and at temperatures between 25 °C below the glass‐transition temperature (T_g) to 20 °C above it. ΔV* for pressures less than 500–1000 atm and T > T_g decreased as the temperature was increased. For pressures greater than 1000 atm, ΔV* was essentially constant for all temperatures. In addition, the size of ΔV* indicated that the chromophore in this main chain was internally flexible. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 895–900, 2001     

Effect of pressure and temperature on chromophore reorientation in a side-chain nonlinear optical polymer

Second harmonic generation (SHG) was used to measure the temperature dependence of the reorientation activation volume of the side-chain copolymer poly(disperse red 1 methacrylate-co-methyl methacrylate) (DR1-MMA). The decay of the SHG signal from poled films of DR1-MMA was recorded at hydrostatic pressures up to 3060 atm and at different temperatures between 25°C below the glass transition temperature (T_g) to 35°C above it. The activation volume, ΔV^*, decreased with increasing temperature. The data suggests that the coupling between chromophore reorientation and the long-range motion of the polymer is stronger for the DR1-MMA side-chain system than in previously measured guest–host systems. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2793–2803, 1998     

Temperature dependence of molecular motions in bulk polystyrene

Time-resolved optical spectroscopy is used to investigate the reorientation of three rigid probes and one labeled chain in bulk polystyrene. Orientational correlation times for these probes and labels are found to be in the range of 10^?8–10^?10 s at temperatures of 180–300°C. Consistent with previous studies, the attachment of a chromophore into the chain backbone slows its dynamics by about an order of magnitude. The temperature dependences of the correlation times are similar to the temperature dependence of the viscosity. When combined with probe reorientation times near and below T_g, these results indicate that probe reorientation tracks the temperature dependence of the viscosity quite well over twelve decades in time. In contrast, literature results for the translational diffusion of similarly sized probes indicates a substantially weaker temperature dependence near T_g. Thus it appears that a fundamental change in the mechanism of probe motion occurs near T_g. © 1994 John Wiley & Sons, Inc.     

Micromechanical fast quasi‐static detection of α and β relaxations with nanograms of polymer

Micromechanical string resonators are used as a highly sensitive tool for the detection of glass transition (T_g or α relaxation) and sub‐T_g (β relaxation) temperatures of polystyrene (PS) and poly (methyl methacrylate) (PMMA). The characterization technique allows for a fast detection of mechanical relaxations of polymers with only few nanograms of sample in a quasi‐static condition. The polymers are spray coated on one side of silicon nitride (SiN) microstrings. These are pre‐stressed suspended structures clamped on both ends to a silicon frame. The resonance frequency of the microstrings is then monitored as a function of increasing temperature. α and β relaxations in the polymer affect the net static tensile stress of the microstring and result in measureable local frequency slope maxima. T_g of PS and PMMA is detected at 91 ±2°C and 114 ±2°C, respectively. The results match well with the glass transition values of 93.6°C and 114.5°C obtained from differential scanning calorimetry of PS and PMMA, respectively. The β relaxation temperatures are detected at 30 ± 2°C and 33 ± 2°C for PS and PMMA which is in accordance with values reported in literature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1035–1039     

Effect of sub-Tg relaxations on chromophore reorientation in corona-poled polymers

Activation volumes for chromophore reorientation were measured for a series of guest–host polymeric materials, indicating a significant coupling between chromophore motion and the glassy α and β relaxation dynamics of the polymer host. The specific systems studied were formed by individually dissolving N,N-dimethyl-p-nitroaniline (DpNA), 4-(dimethylamino)-4′-nitrotolane (DMANT), 4-(diethylamino)-4′-nitrotolane (DEANT), and 1-((4-(dimethylamino)phenyl)ethynyl)-4-((4-nitrophenyl)ethynyl)benzene (DMAPEANT) in poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(isobutyl methacrylate) (PiBMA). In each of these systems, the isothermal, sub-T_g decay of the second-order optical susceptibility χ⁽²⁾ was monitored as a function of pressure using second harmonic generation. In each system, the observed decay of χ⁽²⁾ was represented by a stretched exponential equation from which the decay time τ₀ and decay distribution width β_KWW were determined. For each dopant molecule, the decrease in activation volume with the increasing size of the polymer host's alkyl side group and the pressure dependence of β_KWW were indicative of partial coupling between chromophore rotation and the glassy β relaxation dynamics of the polymer host. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1013–1024, 1998     

The design,synthesis, and nonlinear optical properties of novel X‐type polyurethane containing dicyanovinylnitroresorcinoxy group with enhanced SHG thermal stability

Novel X‐type polyurethane 5 containing 4‐(2′,2′‐dicyanovinyl)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature (T_g) obtained from differential scanning calorimetry thermogram of around 120 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064‐nm fundamental wavelength is around 6.12 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 5 °C higher than T_g, and there was no SHG decay below 125 °C due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Segmental and secondary dynamics in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) blends

Broadband dielectric spectroscopy was used to study the segmental (α) and secondary (β) relaxations in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) (PVPh/PMMA) blends with PVPh concentrations of 20–80% and at temperatures from ?30 to approximately glass‐transition temperature (T_g) + 80 °C. Miscible blends were obtained by solution casting from methyl ethyl ketone solution, as confirmed by single differential scanning calorimetry T_g and single segmental relaxation process for each blend. The β relaxation of PMMA maintains similar characteristics in blends with PVPh, compared with neat PMMA. Its relaxation time and activation energy are nearly the same in all blends. Furthermore, the dielectric relaxation strength of PMMA β process in the blends is proportional to the concentration of PMMA, suggesting that blending and intermolecular hydrogen bonding do not modify the local intramolecular motion. The α process, however, represents the segmental motions of both components and becomes slower with increasing PVPh concentration because of the higher T_g. This leads to well‐defined α and β relaxations in the blends above the corresponding T_g, which cannot be reliably resolved in neat PMMA without ambiguous curve deconvolution. The PMMA β process still follows an Arrhenius temperature dependence above T_g, but with an activation energy larger than that observed below T_g because of increased relaxation amplitude. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3405–3415, 2004     

Enhanced Temporal Stability of an NLO Polyurethane via a Two‐Dimensional Chromophore

A new NLO‐active polyurethane (T_g = 145°C) based on a two‐dimensional NLO chromophore has been investigated. Two ends of this lambda‐shaped chromophore can be directly bound to the main chain of polyurethane. After poling, fast relaxation of the effective second harmonic (SH) coefficient was observed at temperatures higher than 122°C. Moreover, excellent temporal stability at 100°C was obtained despite the operating temperature being very close to the fast relaxation temperature. This is due to the fact that embedding the rigid lambda‐shaped chromophores into the polymer backbone effectively restricts molecular motion at temperatures close to T_g.     

Molecular design,synthesis, and properties of Y‐type nonlinear optical polyester containing tricyanovinylthiophene with enhanced thermal stability of second harmonic generation

1‐{3,4‐Di‐(2‐hydroxyethoxy)phenyl}‐2‐(2‐thiophenyl)ethene (5) was prepared and condensed with terephthaloyl chloride to yield polyester (6). Polymer 6 was reacted with tetracyanoethylene to give a new Y‐type polyester (7) containing 1‐(3,4‐dioxyethoxy)phenyl‐2‐{5‐(2,2,3‐tricyanovinyl)‐2‐thiophenyl)}ethenyl groups as NLO‐chromophores, which are components of the polymer backbones. Polyester 7 is soluble in common organic solvents such as N,N‐dimethylformamide and acetone. Polymer 7 showed a thermal stability up to 300 °C in thermogravimetric analysis with glass transition temperature (T_g) obtained from differential scanning calorimetry near 126 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at the 1560 nm fundamental wavelength was around 6.57 × 10^?9 esu. The dipole alignment exhibited high thermal stability up to the T_g, and there was no SHG decay below 125 °C due to the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1911–1919, 2009     

Synthesis and nonlinear optical properties of novel Y‐type polyester containing tricyanovinylthiazolylazoresorcinoxy group with enhanced thermal stability of dipole alignment

Novel Y‐type polyester 4 containing 5‐methyl‐4‐{5‐(1,2,2‐tricyanovinyl)‐2‐thiazolylazo}resorcinoxy groups as nonlinear optical (NLO) chromophores, which are parts of the polymer backbone, was prepared, and its NLO properties were investigated. Polyester 4 is soluble in common organic solvents such as N,N‐dimethylformamide and dimethylsulfoxide. Polymer 4 shows a thermal stability up to 250 °C from thermogravimetric analysis with glass‐transition temperature obtained from differential scanning calorimetry of approximately 94 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1560‐nm fundamental wavelength is 8.12 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 6 °C higher than glass‐transition temperature (T_g), and no significant SHG decay is observed below 100 °C due to the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A new technique for measuring retrograde vitrification in polymer–gas systems and for making ultramicrocellular foams from the retrograde phase

A stepwise temperature‐ and pressure‐scanning thermal analysis method was developed to measure glass‐transition temperature T_g in the two‐phase polymer–gas systems as a function of gas pressure p, and was used to confirm recent theoretical predictions that certain polymer–gas systems exhibit retrograde vitrification, that is, they undergo rubber‐to‐glass transition on heating. A complete T_g‐p profile delineating the glass–rubber phase envelope was established for the PMMA‐CO₂ system. The retrograde vitrification behavior observed, where at certain gas pressures the polymer exists in the rubbery state at low and high temperatures and in the glassy state at intermediate temperatures, was similar to that reported previously based on the creep‐compliance measurements. The existence of the rubbery state at low temperatures was used to generate foams by saturating the polymer with CO₂ at 34 atm and at temperatures in the range −0.2 to 24 °C followed by foaming at temperatures in the range 24 to 90 °C. Foams with very fine cell structure never reported before could be prepared by this technique. For example, PMMA foams with average cell size of 0.35 μm and cell density of 4.4 × 10¹³ cells/g were prepared by processing the low temperature rubbery phase. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 716–725, 2000     

Polymer thin film properties as a function of temperature and pressure

We report on evanescent wave optical measurements of the glass transition temperature, T_g, of spin-cast PMMA films as a function of film thickness and molecular weight. It was found that for films of high molecular weight PMMA (M_n > 100,000 g mol⁻¹) a strong T_g depression occurs for films that are thinner than 100 nm in case they are deposited on hydrophobic substrates. This strong T_g depression of up to 25°C decreases if similarly thick films of PMMA of low molecular weights are investigated and vanishes completely for PMMA with M_n < 12,000 g mol⁻¹. For films made of these materials T_g is found to be identical to that of the bulk even for films as thin as 5 nm. The results might be interpreted in terms of free volume considerations. To check this assumption we also designed and built a pressure cell that can be used together with the evanscent wave optical techniques for similar measurement, but with the additional option to do the measurements at different pressures up to ca. 100 MPa to further vary the free volume of these polymer films in constrained geometry. Some first results obtained with this setup are also described.     

Synthesis and properties of novel Y‐type nonlinear optical polyimides with high thermal stability of second harmonic generation

2,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐1‐(2,2‐dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 4,4′‐oxydianiline, 4,4′‐diaminobenzanilide and 4,4′‐(hexafluoroisopropylidene)dianiline to yield novel Y‐type polyimides 5‐7 containing 2,4‐dioxybenzylidenemalononitrile groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone. The resulting polyimides 5‐7 are soluble in polar solvents such as dimethylsulfoxide and N,N‐dimethylformamide. Polymers 5‐7 showed a thermal stability up to 330 °C in thermogravimetric analysis thermograms with T_g values obtained from differential scanning calorimetry thermograms in the range 179–194 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength were around 5.56 × 10^?9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 20 °C higher than the glass‐transition temperature there was no SHG decay below 215 °C because of the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3078–3087, 2008     

Synthesis and electro‐optic properties of novel X‐type polyurethane containing nitrophenylazonitroresorcinoxy group with highly enhanced thermal stability of dipole alignment

Novel X‐type polyurethane 4 containing 4‐(4‐nitrophenylazo)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which are parts of the polymer main chains, was prepared and characterized. Polyurethane 4 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stabilities up to 270 °C from thermogravimetric analysis with glass transition temperature obtained from differential scanning calorimetry of about 134 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064 nm fundamental wavelength is 5.37 × 10^?9 esu. Polymer 4 exhibits a thermal stability up to T_g, and no significant SHG decay is observed below 135 °C, which is acceptable for NLO device applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 760–766     

Thermal Characterization of Polymethyl(α-n-Pentyl)Acrylate

This work presents new results concerning characterization of polymethyl(α-n-pentyl)acrylate polymer by means of thermal analysis. In differential scanning calorimetry investigations, the measured values of T _g, T _f and ΔC _p, i.e. the glass transition temperature, the fictive temperature and the heat capacity step at T _g, show that the polymer can be considered as fragile. Thermogravimetric analysis revealed two mass losses, the first, at low temperature, being associated with the evaporation of water molecules, and the second, at high temperature, corresponding degradation of the polymer. This degradation is a two-step phenomenon. Finally, study of the β and the α transitions by elementary and complex TSDC led to the following values: T _β=?40°C, T _α=36°C, T _c=47°C, τ_c=2.5 s and ΔH=85 to 165 kJ mol^?1.     

Synthesis and nonlinear optical properties of novel Y‐type polyurethane containing tricyanovinylthiazole with enhanced thermal stability of second harmonic generation

A novel Y‐type poly[iminocarbonyloxyethyl‐5‐methyl‐4‐{2‐thiazolylazo‐4‐(1,2,2‐tricyanovinyl)}resorcinoxyethyloxycarbonylimino‐(3,3′‐dimethoxy‐4,4′‐biphenylene)] 4 containing 5‐methyl‐4‐{5‐(1,2,2‐tricyanovinyl)‐2‐thiazolylazo}resorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 4 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It showed a thermal stability up to 250 °C in thermogravimetric analysis thermogram and the glass‐transition temperature (T_g) obtained from differential scanning calorimetry thermogram was around 118 °C. The second harmonic generation coefficient (d₃₃) of poled polymer films at 1560 nm fundamental wavelength was around 8.43 × 10^?9 esu. The dipole alignment exhibited a thermal stability even at 12 °C higher than T_g, and there was no SHG decay below 130 °C due to the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1166–1172, 2010     

Synthesis of nonlinear optical maleimide copolymer by polymer reaction and their electro-optic properties

Thermally stable poly(α-methyl styrene-co-maleimide) (MSMI) and poly(α-methyl styrene-co-4-carboxyphenyl maleimide) (MSCM) substrate polymers were obtained readily by free radical polymerization of comonomers. Introduction of a DR1 chromophore to the maleimide units of MSMI substrate polymer by the Mitsunobu reaction was dependent on the reaction solvent. The degree of substitution of DR1 into the MSMI polymer was bound to be 91.1 mol % and 0.4 mol % by UV spectrometers in the THF and DMF solvent, respectively. DR1 chromophore was, however, substituted in the MSCM polymer at 33.0 mol % by Mitsunobu reaction in the THF solvent. Both substrate and NLO polymer exhibited high thermal stability due to the incorporation of maleimide units in the polymer chain. The glass transition temperature (T_g) and initial decomposition temperature (T_i) of the NLO polymer were in the range of T_g = 185°C and T_i = 310–345°C. The electro-optic coefficient (r₃₃) of NLO polymer was determined with an experimental setup capable of the real-time measurement while varying both the poling field and temperature. The NLO polymer MSMI-THF had a higher r₃₃ value than MSCM-DR due to an increased degree of substitution of DR1 chromophore. MSMI-THF had a maximum r₃₃ value of 16 pm/V at 135 MV/m poling field with a 632.8 nm light source. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3715–3722, 1999     

Thermomechanical investigation of a thick film of aniline-formaldehyde copolymer and poly(methyl methacrylate)

A thick film of aniline-formaldehyde copolymer and PMMA is synthesized via dispersion of aniline-formaldehyde copolymer powder as filler particles in PMMA with two different concentrations. Variation of the complex elastic modulus and mechanical loss factor (tanδ) with temperature is studied. It is observed that the complex elastic modulus decreases with temperature owing to thermal expansion of films. On the other hand, tanδ increases up to a characteristic temperature beyond which it shows a decreasing trend toward melting. Transition temperature T _g of sample S₁ (pure PMMA) is found to be 80°C. In sample S₂ (1 wt % aniline formaldehyde copolymer), the peak of tanδ at a lower temperature (66°C) corresponds to glass transition temperature T _g of the PMMA matrix, while the peak of tanδ at a higher temperature (107.8°C) corresponds to T _g of a polymer chain restricted by filler particles of aniline-formaldehyde copolymer. A further increase (10 wt % aniline-formaldehyde copolymer) in the concentration of filler particles of aniline-formaldehyde copolymer results in a more compact structure and a shift of T _g to a higher temperature, 122.2°C. This shift in the glass transition temperature of thick films of aniline-formaldehyde copolymer and PMMA is dependent upon the concentration of filler particles in the sample.     

Rubbing‐induced molecular alignment and its relaxation in polystyrene thin films

Rubbing‐induced molecular alignment and its relaxation in polystyrene (PS) thin films are studied with optical birefringence. A novel relaxation of the alignment is observed that is distinctly different from the known relaxation processes of PS. First, it is not the Kohlrausch–Williams–Watts type but instead is characterized by two single exponentials plus a temperature‐dependent constant. At temperatures several degrees or more below the glass‐transition temperature (T_g), the relaxation time falls between that of the α and β relaxations. Second, the decay time constants are the same within 40% for PS with weight‐average molecular weights (M_w's) of 13,700–550,000 Da at temperatures well below the sample T_g's, indicating that the molecular relaxations involved are mostly local within the entanglement distance. Nonetheless, the temperature at which the rubbing‐induced molecular alignment disappears (T₀) exhibits a strong M_w dependence and closely approximates the T_g of the sample. Furthermore, T₀ depends notably on the thickness of the polymer in much the same way as previously found for the T_g of supported PS films. This suggests that the α process becomes dominant near T_g. Preliminary spectroscopic studies in the mid‐infrared range show a significant degree of bending of the phenyl ring toward the sample surface, with the C? C bond connecting the phenyl ring and the main chain tends to lie along the rubbing direction, which indicates that the relaxation is connected with the reorientation of this C? C bond. We exclude the observed relaxation, as predominantly a near‐surface one, because detailed studies on the effects of rubbing conditions on the degree of molecular alignment indicate that the alignment is not local to the polymer–air surface. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2906–2914, 2001     

Influence of interaction between poly(methyl methacrylate) and clay on the properties of nanocomposites prepared by a heterocoagulation method

To have a better insight into the effect of interaction between polymer matrix and clay on the properties of nanocomposite, poly(methyl methacrylate)/clay nanocomposites were prepared by a heterocoagulation method. Using a reactive cationic emulsifier, methacryloyloxyethyltrimethyl ammonium chloride (METAC), a strong polymer–clay interaction was obtained with the advantage of keeping a consistent polymer matrix property. X‐ray diffraction and transmission electronic microscopy indicated an exfoliated structure in nanocomposites. The glass transition temperature (T_g) of the nanocomposites was measured by DSC and DMA. The DMA results showed that with a strong interaction, PMMA–METAC nanocomposite showed a 20 °C enhancement in glass transition temperature (T_g), whereas a slight increase in T_g was observed for PMMA–cetyl trimethylammonium bromide (CTAB)/clay nanocomposite with a weak interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 733–738, 2010