Supramolecular Assembly between Polystyrene-block-Poly(4-vinylpyridine) and 4-Dodecylbenzenesulfonic Acid

In this study, the desired polymer was prepared by complexing the surf molecule, i.e., 4-dodecylbenzenesulfonic acid (DBSA), with polystyrene-block-poly(4-vinylpyridine) (PS-P4VP) and a comb-coil A-block-(B-graft-C) type of copolymer can be generated through a supramolecular assembly route. On the block copolymer scale, the PS blocks are phase-separated from the P4VP(DBSA) _x block (x denotes the molar ratio between DBSA and pyridine groups) according to the relatively constant low-temperature glass transition (T _g) corresponding to the PS phase. In contrast, the high-temperature T _g increased with the DBSA content; a fact associated with the chain packing situation in the P4VP(DBSA) _x block. Both low and high T _g's became more visible if samples were subjected to a two-stage annealing process. Corresponding X-ray diffraction study also indicates that annealing enhanced the layered structure in the P4VP(DBSA) _x phase. The corresponding one-dimension correlation function suggests that both polymer and surfactant layers increased with the increasing DBSA content. In addition, amounts of the associated DBSA related to the formation of macroscopic anisotropic domains, that is, birefrigency can only be detected for copolymers of high P4VP(DBSA) _x content (>70 wt%).     

Nucleophilic Displacement Polymerlzation of N,N'-BIS(p-Chlorobenzylidine)-4, 4'-Diaminodiphenyl Ether with Sodium Sulfide

A novel poly(Schiff-base sulfide) polymer was synthesized by nucle-ophilic displacement polymerization of N,N'-bis(p-chlorobenzylidine)-4, 4'-diaminodiphenyl ether with sodium sulfide in anhydrous condition. The resulting polymer was soluble in some aprotic solvents having inherent viscosity of 0.18 dL/g in dimethylacetamide at 30°C. The monomer and the polymer were characterized by elemental analysis, infrared, and ¹H NMR (nuclear magnetic resonance) spectroscopy. The thermal characteristics of the polymer were also studied by thermo-gravimetric analysis and differential scanning calorimetry. The temperature of 10% weight loss, glass transition temperature (T _g). and crystalline melting point (T _m) of the polymer were found to be 420, 91.89, and 38575°C respectively.     

Dielectric relaxations in poly [2,2-propane-bis-(4-phenyl thiocarbonate)]

The dielectric relaxation properties of poly[2,2-propane-bis-(4-phenyl thiocarbonate)] (PTC) have been studied. The existence of crystallinity, which can be eliminated by quenching, is detected. The degree of crystallinity of polymer samples was determined by differential scanning calorimetry in order to investigate the effect of this factor on the dielectric behaviour of this polymer. The thermal degradation of the samples was studied by thermogravimetry. The degradation of the polymer begins before the glass transition temperature T_g. The dielectric spectrum is complex showing several relaxation phenomena. With increasing temperature a γ relaxation can be observed at - 100°C (5 kHz). The activation energy obtained from an Arrhenius plot (lnfvs T^?1) is 6 kcal mol^?1. At 160°C the α relaxation which is associated with the glass transition temperature T_g is detected. The dielectric behaviour of this poly(thiocarbonate) is compared with the corresponding poly(carbonate).     

Effect of polymer latexes with varied glass transition temperature on cement hydration

Influence of styrene‐acrylate latexes with varied glass transition temperature (T_g) on cement hydration was studied and the mechanism was analyzed. Results show that polymer latexes with varied T_g retard cement hydration to different extents. Specifically, low T_g polymer shows stronger retardation effect than the high T_g polymer. Despite similar surface charges, colloidal particles with lower T_g exhibit higher affinity to surface of cement grains than the high T_g polymer, indicated by the higher adsorption amount and denser covering layer. The low T_g polymer experiences particle packing, deforming, and film forming processes along with the consumption of water during cement hydration, which eventually produces a covering layer of polymer surrounding cement grains. However, for the high T_g polymer, film forming process is absent. Consequently, the higher adsorption amount and the film‐formation process along with cement hydration are the two reasons for the stronger retardation effect of the low T_g polymer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45264.     

Physical aging in the glassy state of a thermosetting system vs. extent of cure

The physical aging behavior of a high-T_g amine/epoxy thermosetting system has been investigated vs. change of chemical structure induced by cure and vs. aging temperature (T_a) using the Torsional Braid Analysis (TBA) technique. The chemical structure was changed systematically from monomer to highly crosslinked polymer by curing in the equilibrilium state (T > T_g). The aging temperatures ranged from just below the glass transition temperature to deep in the glassy state (T_a > T_g). In the absence of chemical reaction, the physical aging rate at a given temperature, T_a, passes through a minimum with increasing chemical conversion (i.e., change of chemical structure). Analysis of this behavior is simplified by using T_g as an index of measurement of extent of cure. There is a superposition principle for normalizing the physical aging behavior of the thermosetting glasses, which involves a shift of T_g–T_a and a shift of C(T_a) (a function of aging temperature), regardless of chemical structure. Analysis reveals that: (1) this behavior is the consequence of the T_g and T_β transitions, (2) the segmental mobility (1/τ) is a function of the deviation from equilibrium (as measured by T_g–T_g and the aging time), (3) the segmental mobility, which is involved in the physical aging process in the glassy state, is insensitive to the extreme changes of chemical structure (from monomer, to sol/gel polymer, and to highly crosslinked polymer), and (4) physical aging deep in the glassy state affects both segmental mobility and cohesive energy density. © 1993 John Wiley & Sons, Inc.     

Influence of silica reinforcement upon the glass transition behavior of acrylic polymers

The glass transition temperatures (T_g) of poly(acrylic acid), poly(methyl acrylate), and poly(ethyl acrylate) filled with submicron particulate silicas and silicates have been measured by dynamic mechanical spectroscopy and differential scanning calorimetry. The peak temperatures of the damping factor (tan δ) and the dynamic shear loss modulus (G″) were shifted by an amount which depended upon the quantity and type of filler added to each polymer. The temperatures corresponding to the step discontinuity of specific heat also shifted, but to a lesser extent than those measured mechanically. The degree of T_g shift per unit of volumetric filler addition increased with polymer pendant group polarity for both measurement methods. Utilizing a T_g-crosslinking analogue, a model was developed that related positive T_g shifts to polymeric segmental adsorption onto filler surfaces. This model also incorporated negative contributions to the T_g shift from energy storage mechanisms arising from particle–particle interactions, as well as corrections due to effective surface area available for polymer adsorption.     

Plasticating single-screw extrusion of amorphous polymers: Development of a mathematical model and comparison with experiment

A mathematical model was developed for plasticating single-screw extrusion of amorphous polymers. We considered a standard metering screw design. By introducing a ‘critical flow temperature’ (T_cf), below which an amorphous polymer may be regarded as a ‘rubber-like’ solid, we modified the Lee-Han melting model, which had been developed earlier for the extrusion of crystalline polymers, to model the flow of an amorphous polymer in the screw channel. T_cf is de facto a temperature equivalent to the melting point of a crystalline polymer. The introduction of T_cf was necessary for defining the interface between the solid bed and the melt pool, and between the solid bed and thin melt films surrounding the solid bed. We found from numerical simulations that (1) when the T_cf was assumed to be close to its glass transition temperature (T_g), the viscosity of the polymer became so high that no numerical solutions of the system of equations could be obtained, and (2) when the value of T_cf was assumed to be much higher than T_g, the extrusion pressure did not develop inside the screw channel. Thus, an optimum modeling value of T_cf appears to exist, enabling us to predict pressure profiles along the extruder axis. We found that for both polystyrene and polycarbonate, T_cf lies about 55°C above their respective T_gs. In carrying out the numerical simulation we employed (1) the WLF equation to describe the temperature dependence of the shear modulus of the bulk solid bed at temperatures between T_g and T_cf, (2) the WLF equation to describe the temperature dependence of the viscosity of molten polymer at temperatures between T_cf and T_g + 100°C, (3) the Arrhenius relationship to describe the temperature dependence of the viscosity of molten polymer at temperatures above T_g + 100°C, and (4) the truncated power-law model to describe the shear-rate dependence of the viscosity of molten polymer. We have shown that the T_g of an amorphous polymer cannot be regarded as being equal to the T_m of a crystalline polymer, because the viscosities of an amorphous polymer at or near its T_g are too large to flow like a crystalline polymer above its T_m. Also conducted was an experimental study for polystyrene and polycarbonate, using both a standard metering screw and a barrier screw design having a length-to-diameter ratio of 24. For the study, nine pressure transducers were mounted on the barrel along the extruder axis, and the pressure signal patterns and axial pressure profiles were measured at various screw speeds, throughputs, and head pressures. In addition to significantly higher rates, we found that the barrier screw design gives rise to much more stable pressure signals, thus minimizing surging, than the metering screw design. The experimentally measured axial pressure profiles were compared with prediction.     

Challenges in forming successful mixed matrix membranes with rigid polymeric materials

Mixed matrix materials comprised of molecular sieve domains embedded in processable polymer matrices have the potential to provide membranes with higher permselectivity and equivalent productivity compared to existing membrane materials. It has been shown that successful mixed matrix materials can be formed using relatively low glass transition (T_g) polymers that have a favorable interaction with the sieves. This article extends this earlier work to include the use of more practical rigid matrix polymers with high T_gs that can ultimately be used in forming high‐performance mixed matrix layers for composite membranes. Initial attempts to form mixed matrix materials based on high T_g polymers with a type 4A zeolite resulted in poor adhesion between the polymer and sieve. Correcting this problem was pursued in this study by forming the composite material close to the T_g of the polymer by addition of a plasticizer to match the matrix T_g with the solvent volatility. Forming the films at elevated temperatures presented substantial challenges, and this work discusses overcoming these challenges in detail. With some modifications in the film casting procedure, successful materials were achieved. Promising oxygen/nitrogen transport results are presented for these zeolite 4A–Matrimid®/plasticizer membranes, and this data compares favorably with predictions of the well‐known Maxwell model for composite systems. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 881–890, 2002     

Film formation from polymer dispersions

The coalescence of a poly(vinylidene chloride/methyl acrylate/acrylic acid) latex was found to occur only above the T_g. The various theories of film formation from polymer dispersions attribute latex coalescence to three types of forces: the pressure due to the polymer–air interface, the pressure due to a polymer–water interface, and the pressure due to capillary action. Analysis of the forces indicates that none are sufficient to cause coalescence below T_g while any, or all, may cause coalescence above T_g.     

Effects of fibers on the glass transition temperature of polyphenylene sulfide composites

The glass transition temperature (T_g) of polyphenylene sulfide (PPS), and of several commercial and model PPS prepregs with aramid, carbon, and glass fibers was studied by means of differential scanning calorimetry. The T_g of unreinforced PPS was found to range between 83–90°C, depending on source and molecular weight. The T_g of the commercial prepregs was depressed by about 3–5°C from that of the corresponding unfilled PPS, an effect that was ascribed to the plasticization of the PPS by one or more components of the fiber finish (size) that was assumed to have diffused into the PPS polymer. In the case of model prepregs prepared with finish-free reinforcing fibers, an expected increase in T_g was observed. In model prepregs prepared with finished (sized) aramid fibers, the T_g was depressed as in the case of the commercial prepregs. With sized AS-4 carbon fibers, the T_g was increased, but significantly less so than with unsized AS-4 fibers. With sized glass fibers, the same slight increase in T_g was observed as with unsized glass fibers. The increase or decrease of T_g in all cases was a function of the fiber content in the model PPS prepregs.     

The effect of disperse dyes on the glass transition temperature of polymers

The lowering of the glass transition temperature (T_g) of a polymer produced by the incorporating various concentrations of azo disperse dyes has been investigated, and the effects of the structure and concentrations of the dyes were examined. The T_g values were lowered with increasing dye concentrations in the polymer, and the lowering of T_g produced by the dyes was influenced not only by the molecular structure of the dyes but also the dye-polymer interactions.     

Studies on the glass transition of blends of nylon-6 and polyacrylic acid

The glass transition temperatures (T_g) of blends of polyacrylic acid (PAA)–Nylon 6 in various proportions used as membrane material in pervaporation separation of acetic acid–water and ethanol–water mixtures were determined using differential scanning calorimetry (DSC). All the samples examined showed a single T_g which lay between the T_g of Nylon 6 and PAA, indicating that complete miscibility was achieved in these polymer blends. Further evidence of complete miscibility was obtained by scanning electron microscopy (SEM) of cross sections of the blended films which showed a uniform structure. An interesting phenomenon was observed during the DSC measurements which showed a shift in T_g of the blended samples with scanning time. Infrared and thermogravimetric measurements were conducted to further investigate this phenomenon and the results were explained as the change in T_g being caused by the elimination of water molecules and the formation of anhydrides in the polyacrylic acid portion of the polymer blends.     

Multiwavelength interferometry and competing optical methods for the thermal probing of thin polymeric films

Multiple‐wavelength interferometry (MWI), a new optical method for the thermal probing of thin polymer films, is introduced and explored. MWI is compared with two standard optical methods, single‐wavelength interferometry and spectroscopic ellipsometry, with regard to the detection of the glass transition temperature (T_g) of thin supported polymer films. Poly(methyl methacrylate) films are deposited by spin coating on Si and SiO₂ substrates. MWI is also applied to the study of the effect of film thickness (25–600 nm) and polymer molecular weight (1.5 × 10⁴ to 10⁶) on T_g, the effect of film thickness on the coefficients of thermal expansion both below and above T_g, and the effect of deep UV exposure time on the thermal properties (glass transition and degradation temperatures) of the films. This further exploration of the MWI method provides substantial insights about intricate issues pertinent to the thermal behavior of thin polymer films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4764–4774, 2006     

Preparation and properties of ester or cyano group substituted ring-opening polymers and their hydrogenated derivatives

Ester or cyano substituted tetracyclo [4.4.0.1^2,5.1^7,10]dodec-3-enes (1) were synthesized and their metathesis ring-opening polymerization was examined. The tungsten-based ternary catalyst system polymerized them very well. The polymers showed high glass transition temperatures (T_g) and no evidence of crystallization (e.g., the T_g of the polymer derived from 8-methyl-8-methoxycarbonyl substituted monomer (1a) was 207°C, and colorless transparent films could be casted from the solution of the polymer). The stability of these high T_g polymers were too unstable, so practical thermal molding methods could not be applied to them. The hydrogenation of these polymers with a palladium catalyst decreased T_g and greatly increased thermal stability. The physical and thermal properties of the hydrogenated polymers were thoroughly investigated. Monomer 1 was successfully copolymerized with other cyclic olefins. The resultant copolymers were hydrogenated, giving thermally stable polymers. In all cases examined in this study, a decrease of T_g by hydrogenation was about 35°C, regardless of the monomer structure. These results indicate that the main-chain mobility is the major contribution to the decrease of T_g. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 367–375, 1997     

Thermal and current noise in carbon black-filled polystyrene and polyethylene in the vicinity of Tg and Tm

Thermal and current noise in carbon black-filled polystyrene and polyethylene was studied in the vicinity of T_g and T_m. A highly conductive grade of carbon black was used (Ketjenblack EC): 4% for PS and 6.5% for PE. Pronounced maxima in noise voltage were found at T_g for PS and T_m for PE. Prolonged storage at T lower than T_g enhanced the intensity of the noise peak at T_g for PS. A hysteresis occurred on cooling after a heating cycle, with the current and thermal noise being lower on the cooling cycle (no maximum in the case of PS). The peak temperature was lower for PE on the cooling cycle. Good agreement was found between experimental and calculated thermal noise values. The thermal noise spectra were white within the temperature range of 20° to 140°C. The appearance of the current noise peaks could be associated with a conduction model where a decrease in the number of contact points in the carbon black network occurs in the transition regions. This is in accordance with the concept proposed earlier that the carbon black network existing in a polymer undergoes a rearrangement when the polymer melts (softens) or solidifies.     

Phase relationships of rigid rod polymer/flexible coil polymer/solvent ternary systems

Phase diagrams of two types of rigid rod polymer/flexible coil polymer/methanesulfonic acid (MSA) ternary systems were determined by polarized optical microscopy at ambient conditions. The rigid rod polymer is a wholly aromatic high temperature resistant (no measurable T_g) poly (p-phenylenebenzobisthiazole) (PPBT). One of the flexible coil polymers is a wholly aromatic high temperature resistant poly (2,5′(6′) benzimidazole) (ABPBI), the other is a thermoplastic poly[2,2′ -(1–4-phenylene)-6,6′ -bis (3-phenyl-quinoxaline)] (PPQ) with T_g of 359°C. The solvent is methane-sulfonic acid (MSA). The experimentally determined critical concentration points, C_cr, are in excellent agreement with Flory's recent theory. Total phase segregation between the polymer pair in ternary solution was predicted and observed at C > C_cr. Different decomposition mechanisms of phase separation were observed as a function of concentration.     

Sorption of propane in poly(ethyl methacrylate) near Tg

The sorption of propane in poly(ethyl methacrylate) was investigated above and below the polymer T_g and the dual-mode sorption model parameters were evaluated. The Langmuir capacity decreased as the temperature was raised to T_g and the apparent Henry's law constant exhibited a discontinuity at T_g. The enthalpy of microvoid filling ΔH_H is more exothermic than the enthalpy of dissolution at T < T_g by about 8 kJ/mol.     

Synthesis and characterization of temperature‐sensitive block copolymers from poly(N‐isopropylacrylamide) and 4‐methyl‐ε‐caprolactone or 4‐phenyl‐ε‐caprolactone

This study synthesizes thermally sensitive block copolymers poly(N‐isopropylacrylamide)‐b‐poly(4‐methyl‐ε‐caprolactone) (PNIPA‐b‐PMCL) and poly(N‐isopropylacrylamide)‐b‐poly(4‐phenyl‐ε‐caprolactone) (PNIPA‐b‐PBCL) by ring‐opening polymerization of 4‐methyl‐ε‐caprolactone (MCL) or 4‐phenyl‐ε‐caprolactone (BCL) initiated from hydroxy‐terminated poly(N‐isopropylacrylamide) (PNIPA) as the macroinitiator in the presence of SnOct₂ as the catalyst. This research prepares a PNIPA bearing a single terminal hydroxyl group by telomerization using 2‐hydroxyethanethiol (ME) as a chain‐transfer agent. These copolymers are characterized by differential scanning calorimetry (DSC), ¹H‐NMR, FTIR, and gel permeation chromatography (GPC). The thermal properties (T_g) of diblock copolymers depend on polymer compositions. Incorporating larger amount of MCL or BCL into the macromolecular backbone decreases T_g. Their solutions show transparent below a lower critical solution temperature (LCST) and opaque above the LCST. LCST values for the PNIPA‐b‐PMCL aqueous solution were observed to shift to lower temperature than that for PNIPA homopolymers. This work investigates their micellar characteristics in the aqueous phase by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 0.29–2.74 mg L^?1, depending on polymer compositions, which dramatically affect micelle shape. Drug entrapment efficiency and drug loading content of micelles depend on block polymer compositions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Water effect on the morphology of EVOH copolymers

The effect of water on the morphology of four ethylene vinyl alcohol copolymers (EVOH) with different ethylene contents was studied by differential scanning calorimetry (DSC). EVOH film samples equilibrated in controlled atmospheres at different relative humidities (RH) and 23°C were analyzed. Under dry conditions, the glass transition temperature (T_g) was unaffected by copolymer ethylene content. As RH increases, T_g decreases. It seems that the presence of water within the polymer matrix results in plasticization of the polymer. T_g varies from around 50°C (dry) to below room temperature. EVOH copolymers are glassy polymers when dry and rubbery polymers at high RHs. Fox and Gordon–Taylor's equations well describe T_g depletion at low water uptake, although severe water gain results in a considerable T_g decrease, which is not predicted by these theories. Melting temperature, T_m, and enthalpy, ΔH_m, were also analyzed. When dry, T_m decreases as ethylene content increases. No significant water effect was found on either T_m or ΔH_m. Hence, crystallinity seems to be unaffected by water presence. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1201–1206, 1999     

Limiting surface tension by gas chromatography

The change in retention mechanism at the glass transition temperature (T_g) of a polymer stationary phase from surface adsorption below T_g to bulk sorption above T_g allows for a separate determination of the magnitude of the solute interaction with both the bulk and the surface of the polymer. As a result, the limiting surface tension of the polymer-probe solution can be obtained from the corresponding partition coefficients. Examples of such determinations are given for several polymer-solute systems.