Sub‐glass‐transition temperature interface formation between an immiscible glass rubber pair

We used neutron reflectivity to measure the interfacial width in the immiscible system polystyrene/poly(n‐butyl methacrylate) (PS/PnBMA). Measurements were made on the same samples at temperatures ranging from below the glass‐transition temperature (T_g) of PS to slightly above. We observed significant broadening of the interface at temperatures below the T_g of PS, indicating chain mobility below the bulk T_g value. The interfacial width exhibited a plateau at a value of 20 Å in the temperature range of 365 K < T < 377 K. A control experiment involving hydrogenated and deuterated PS films (hPS/dPS) showed no such broadening over the same temperature region. The results are consistent with a reduction of the T_g of PS in the interfacial region of ～20 K. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2664–2670, 2001     

Effects of water on epoxy cure kinetics and glass transition temperature utilizing molecular dynamics simulations

Effects of water on epoxy cure kinetics are investigated. Experimental tests show that absorbed water in an uncured bisphenol‐F/diethyl‐toluene‐diamine epoxy system causes an increase in cure rate at low degrees of cure and a decrease in cure rate at high degrees of cure. Molecular simulations of the same epoxy system indicate that the initial increase in cure rate is due to an increase in molecular self‐diffusion of the epoxy molecules in the presence of water. Effects of water on the glass transition temperature (T_g) of the crosslinked thermoset are also studied. Both experiments and simulations show that water decreases T_g. Both types of results indicate that T_g effects are small below 1% water by weight, but that T_g depression occurs much quickly with increasing water content above 1%. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1150–1159     

Graft copolymers via ROMP and Diels–Alder click reaction strategy

Anthracene‐functionalized oxanorbornene monomer and oxanorbornenyl polystyrene (PS) with ω‐anthracene end‐functionalized macromonomer were first polymerized via ring‐opening metathesis polymerization using the first‐generation Grubbs' catalyst in dichloromethane at room temperature and then clicked with maleimide end‐functionalized polymers, poly(ethylene glycol) (PEG)‐MI, poly(methyl methacrylate) (PMMA)‐MI, and poly(tert‐butyl acrylate) (PtBA)‐MI in a Diels–Alder reaction in toluene at 120 °C to create corresponding graft copolymers, poly(oxanorbornene)‐g‐PEG, poly(oxanorbornene)‐g‐PMMA, and graft block copolymers, poly(oxanorbornene)‐g‐(PS‐b‐PEG), poly(oxanorbornene)‐g‐(PS‐b‐PMMA), and poly(oxanorbornene)‐g‐(PS‐b‐PtBA), respectively. Diels–Alder click reaction efficiency for graft copolymerization was monitored by UV–vis spectroscopy. The dn/dc values of graft copolymers and graft block copolymers were experimentally obtained using a triple detection gel permeation chromatography and subsequently introduced to the software so as to give molecular weights, intrinsic viscosity ([η]) and hydrodynamic radius (R_h) values. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Glass transition and its characteristic length for thin crosslinked polystyrene shells of rodlike capsules

Rodlike capsules consisting of a calcium carbonate core and a crosslinked polystyrene shell were synthesized, and the glass transition temperature (T_g) and characteristic length of the glass transition ξ(T_g) for the thin outer shells were investigated by temperature‐modulated differential scanning calorimetry. The shell thickness ranged from 20 to 129 nm. The ratio of the T_g for the outer shell to the bulk T_g increases with decreasing shell thickness d. The d‐dependence of T_g is interpreted in terms of a simple two‐layer model which assumes that an immobile layer exists near the core‐shell interface. Shells of hollow capsules unexpectedly exhibit a similar d‐dependence of T_g to that for the filled capsules. This is characteristic of the crosslinked polymeric shells, and is attributed to certain spatial heterogeneity of crosslink distribution, and/or to the unstable configuration in the ultrathin shell that does not undergo relaxation due to the crosslink. The latter idea is based on the assumption that unstable configurational state is responsible for the T_g shift from the bulk value observed for nanosized polymeric materials. The ratio of the characteristic length for the shell of the filled capsule to that of the bulk ξ_f(T_g)/ξ_b(T_g) decreases with decreasing d. The results are interpreted in terms of the configurational entropy, and it is also suggested that the configurational state of network polymer chains in the shell affects the characteristic length. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2116–2125, 2008     

Foaming behavior of polypropylene/polystyrene blends enhanced by improved interfacial compatibility

A series of polypropylene (PP)/polystyrene (PS) blends were prepared by solvent blending with PS‐grafted PP copolymers (PP‐g‐PS) having different PS graft chain length as compatibilizers. The interfacial compatibility was significantly improved with increasing PS graft chain length until the interface was saturated at PS graft chain length being 3.29 × 10³ g/mol. The blends were foamed by using pressure‐quenching process and supercritical CO₂ as the blowing agent. The cell preferentially formed at compatibilized interface because of low energy barrier for nucleation. Combining with the increased interfacial area, the compatibilized interface lead to the foams with increased cell density compared to the uncompatibilized one. The increase in interfacial compatibility also decreased the escape of gas, held more gas for cell growth, and facilitated the increase in expansion ratio of PP/PS blend foams. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1641–1651, 2008     

Preparation and characterization of cyclic polystyrene with short poly(2‐tert‐butylbutadiene) sequences

A polystyrene‐block‐oligo(2‐tert‐butylbutadiene)‐block‐polystyrene triblock copolymer was prepared and cyclized by end‐to‐end ring closure. Ring‐shaped polystyrene‐block‐oligo(2‐tert‐butylbutadiene) was isolated from the coupling product via gel permeation chromatography (GPC) fractionation. The ring polymer was ozonized for decomposition of the oligo(2‐tert‐butylbutadiene) sequences selectively referring to the linear molecule. From GPC analysis of the decomposed products by ozonolysis, it was quantitatively confirmed that the fractionated product was 86% ring molecules. Single chain dimensions of the ring and linear molecules in a good solvent, benzene, and in a θ solvent, cyclohexane, were measured with small‐angle neutron scattering. The ratios of the radii of gyration, R_g(ring)/R_g(linear), were 0.780 in benzene and 0.789 in cyclohexane. These were compared with theoretically predicted values. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1582–1589, 2002     

Strength of polymer phase boundaries with large interfacial width: Effects of interfacial profile and phase separation morphology

In this study, we investigate the effect of random copolymer additives on the interfacial profile, the lateral phase separation morphology, and the interfacial fracture toughness (G_c) between two immiscible polymers. The interface between polystyrene (PS)/poly(methyl methacrylate) (PMMA) was reinforced with a random copolymer mixture when two or more PS_f ‐r‐PMMA_1‐f random copolymers with different volume fraction, f, were blended. For short annealing time (<3 h), the random copolymer mixture exhibits a disordered and large domain structure (>1 lm) from which crazes can be extensively initiated and developed, leading to a large interfacial fracture energy. With increasing annealing time, the random copolymer mixture self‐organizes as multiple layers, with the composition that changes gradually from PS‐rich layers to PMMA‐rich layers across the interface, leading to a large interfacial width. However, within each layer, the random copolymer mixture microphase separates laterally into smaller domains (<200 nm). We found that the microphase‐separated domains with nanometer‐sized structure significantly affect the stability of craze fibrils that can be initiated and widened at the interface, leading to a decrease in the fracture energy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1834–1846, 2010     

A novel temperature‐step method to determine the glass transition temperature of ultrathin polymer films by liquid dewetting

A novel temperature‐step experimental method that extends the Bodiguel‐Fretigny liquid dewetting method of investigating polymer thin films is described and results presented from an investigation of thickness effects on the glass transition temperature (T_g) of ultrathin polystyrene (PS) films. Unlike most other methods of thin film investigation, this procedure promises a rapid screening tool to determine the overall profile of T_g versus film thickness for ultrathin polymer films using a limited number of samples. Similar to our prior observations and other literature data, with this new method obvious T_g depression was observed for PS thin films dewetting on both glycerol and an ionic liquid. The results for PS dewetting on the two different liquids are similar indicating only modest effects of the substrate on the T_g‐film thickness relationship. In both instances, the T_g depression is somewhat less than for similar PSs supported on silicon substrates reported in the literature. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1343–1349     

Effect of PS‐b‐PCL block copolymer on reaction‐induced phase separation in epoxy/PEI blend

PS‐b‐PCL block copolymer is used to study its influence on the phase evolution of epoxy resin/polyetherimides (PEI) blends cured with methyl tetrahydrophthalic anhydride. The effect of PS‐b‐PCL on the reaction‐induced phase separation of the thermosetting/thermoplastic blends is studied via optical microscopy, scanning electron microscope, and time‐resolved light scattering. The results show that secondary phase separation and typical phase inverted morphologies are obtained in the epoxy/PEI blends with addition of PS‐b‐PCL. It can be attributed to the preferential location of the PS‐b‐PCL in the epoxy‐rich phase, which enhances the viscoelastic effect of epoxy/PEI system and leads to a dynamic asymmetry system between PEI and epoxy. The PS‐b‐PCL block copolymer plays a critical role on the balance of the diffusion and geometrical growth of epoxy molecules. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1395–1402     

Molecular weight dependence of polystyrene segmental dynamics in dilute blends with poly(vinyl methyl ether)

The segmental dynamics of backbone‐deuterated polystyrenes (d₃PS) with varying molecular weights (1.7–67 kg/mol) have been measured in blends with poly(vinyl methyl ether) (PVME). ²H NMR T₁ values at 15 and 77 MHz are reported for the pure d₃PS and for the dilute d₃PS component in PVME matrices. The temperature shift that is needed to superpose the NMR T₁ data for the pure d₃PS and the d₃PS as a dilute component in the blend ranges from 45 to 70 K. In the framework of Lodge/McLeish model, the self‐concentration value for d₃PS in these dilute blends with PVME is found to be independent of molecular weight. We thus establish for this system that the substantial influence of molecular weight on the blend segmental dynamics can be explained by homopolymer T_g differences. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2252–2262, 2007     

Glass transition temperature of colloidal polystyrene dispersed in various liquids

Recently, there has been significant interest in measuring the glass transition temperature (T_g) of thin polymer films floated atop liquid substrates. However, such films still have intrinsically asymmetric interfaces, that is, a free surface and a liquid–polymer interface. In an effort to analyze the influence of different liquids on the T_g of confined polymers in which there is no interfacial asymmetry, a colloidal suspension of polystyrene (PS) nanoparticles (NPs) was employed. The T_gs of PS NPs suspended in either glycerol or an ionic liquid were characterized using differential scanning calorimetry. Nanoparticles suspended in an ionic liquid showed an invariance of T_g with confinement, that is, decreasing diameter. In contrast, nanoparticles suspended in glycerol showed a slight decrease in T_g with confinement. The dependence of NP T_g on the nature of the surrounding liquid exhibited a positive correlation with the interfacial energy of the liquid–PS interface and no correlation with interfacial softness, as measured by viscosity. A comparison of the results with thin films supported by liquid or solid substrates revealed a nontrivial interplay between interfacial softness and interfacial interactions on the T_g of confined PS. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1776–1783     

Interphase development in a three‐component polymer system with asymmetric mobility

We report a study on the interphase evolution in a system composed by three polymeric components with markedly different mobility distributed between two layers. One of the layers is a low‐T_g blend containing a low molecular weight polystyrene (PS) as a plasticizer (low‐M PS) and PS chains with much higher molecular weight (high‐M PS). The counterpart is a high‐T_g layer composed by polyphenylene oxide. The system was annealed at several temperatures between T_g of the polymer layers and the subsequent interphase development probed by optical sectioning with confocal Raman microspectroscopy. The profiles obtained revealed the existence of two diffusion fronts that advance in opposite directions, both showing a similar response with time and temperature. These fronts act as well‐defined boundaries that structure the interphase into three well‐defined regions with almost constant PS volume fraction. We discuss this particular phenomenology proposing a simple diffusion model that describes the main interphase features. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 627–633, 2010     

Analysis of polystyrene surface properties on thin film bonding under carbon dioxide pressure using nanoparticle embedding technique

A gold nanoparticle embedding technique is used to determine how vacuum and pressured carbon dioxide (CO₂) affect polystyrene (PS) thin film properties. The pressured CO₂ greatly increased the gold nanoparticle embedding depth, possibly due to a low cohesive energy density near the film surface. For the monodisperse PS used in this study (M_n = 214,000), two spin‐coated thin films with intimate contact can be bonded below the bulk glass transition temperature (T_g) under CO₂ pressure when the embedded depth is larger than half of the gyration radius of PS molecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1535–1542, 2009     

Synthesis and self‐assembly of polystyrene‐grafted multiwalled carbon nanotubes with a hairy‐rod nanostructure

Polystyrene‐grafted multiwalled carbon nanotubes (PS‐g‐MWNTs) with a hairy‐rod nanostructure were synthesized by the in situ free‐radical polymerization of styrene in the presence of multiwalled carbon nanotubes (MWNTs) terminated with vinyl groups. To quantitatively study the molecular weight and composition of polystyrene (PS) chains in PS‐g‐MWNTs, PS‐g‐MWNTs were fully defunctionalized by hydrolysis. The results showed that 1 of every 100 carbon atoms in MWNTs was functionalized at the tips and outer walls of the carbon nanotubes and grafted by PS with a weight‐average molecular weight of 9800 g/mol; therefore, a uniform thin layer (ca. 8–10 nm) of a PS shell was formed on the outer wall of MWNTs. PS‐g‐MWNTs were soluble in dimethylformamide and tetrahydrofuran. The thermal stability and glass‐transition temperature of PS in PS‐g‐MWNTs were obviously increased. Nanopins were formed on the glass substrates by the self‐assembly of PS‐g‐MWNTs, and the dewetting effect between the glass substrate and PS chains covered MWNTs during the evaporation of the solution. Both the length and diameter of the nanopins increased with the solution concentration. When PS‐g‐MWNTs were compression‐molded, MWNTs were dispersed uniformly in the PS matrix and formed good networks, such as circlelike and starlike structures, because of the entanglements of hairy PS chains on MWNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3869–3881, 2006     

Effect of sample preparation on the glass‐transition of thin polystyrene films

We have investigated the effect of sample preparation on the glass‐transition temperature (T_g) of thin films of polystyrene (PS). By preparing and measuring the glass‐transition temperature T_g of multilayered polymer films, we are able to assess the contribution of the spincoating process to the reduced T_g values often reported for thin PS films. We find that it is possible to determine a T_g even on the first heating cycle, and that by the third heating cycle (a total annealing time of 15 min at T = 393 K) the T_g value has reached a steady state. By comparing multilayered versus single layered films we find that the whole T_g depends only on the total film thickness, and not on the thickness of the individual layers. These results strongly suggest that the spincasting process does not contribute significantly to T_g reductions in thin polymer films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4503–4507, 2004     

Epoxy resin/poly(ϵ‐caprolactone) blends cured with 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane. I. Miscibility and crystallization kinetics

Crystalline thermosetting blends composed of 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane (BAPP)‐cured epoxy resin (ER) and poly(?‐caprolactone) (PCL) were prepared via the in situ curing reaction of epoxy monomers in the presence of PCL, which started from initially homogeneous mixtures of diglycidyl ether of bisphenol A (DGEBA), BAPP, and PCL. The miscibility of the blends after and before the curing reaction was established with differential scanning calorimetry and dynamic mechanical analysis. Single and composition‐dependent glass‐transition temperatures (T_g's) were observed in the entire blend composition after and before the crosslinking reaction. The experimental T_g's were in good agreement with the prediction by the Fox and Gordon–Taylor equations. The curing reaction caused a considerable increase in the overall crystallization rate and dramatically influenced the mechanism of nucleation and the growth of the PCL crystals. The equilibrium melting point depression was observed for the blends. An analysis of the kinetic data according to the Hoffman–Lauritzen crystallization kinetic theory showed that with an increasing amorphous content, the surface energy of the extremity surfaces increased dramatically for DGEBA/PCL blends but decreased for ER/PCL blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1085–1098, 2003     

Influence of carboxyl‐terminated (butadiene‐co‐acrylonitrile) loading on the mechanical and thermal properties of cured epoxy blends

A mixture of epoxy with liquid nitrile rubber, carboxyl‐terminated (butadiene‐co‐acrylonitrile) (CTBN) was cured under various temperatures. The cured resin was a two‐phase system, where spherical rubber domains were dispersed in the matrix of epoxy. The morphology development during cure was investigated by scanning electron microscope (SEM). There was slight reduction in the glass transition temperature of the epoxy matrix (T_g) on the addition of CTBN. It was observed that, for a particular CTBN content, T_g was found to be unaffected by the cure temperature. Bimodal distribution of particles was noted by SEM analysis. The increase in the size of rubber domains with CTBN content is due probably to the coalescence of the rubber particles. The mechanical properties of the cured resin were thoroughly investigated. Although there was a slight reduction in tensile strength and young's modulus, appreciable improvements in impact strength, fracture energy, and fracture toughness were observed. Addition of nitrile rubber above 20 parts per hundred parts of resin (phr) made the epoxy network more flexible. The volume fraction of dispersed rubbery phase and interfacial area were increased with the addition of more CTBN. A two‐phase morphology was further established by dynamic mechanical analysis (DMA). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2531–2544, 2004     

Surface plasmon resonance as a tool for the estimation of adsorbed polymeric layer characteristics: Theoretical considerations and experiment

The potential application of Surface Plasmon Resonance (SPR) spectroscopy in evaluating the thickness and volume fraction of adsorbed macromolecular layers is discussed in this work. The sensitivity of SPR spectroscopy to different layer concentration and to the layer extension normal to the surface (thickness) is theoretically illustrated. A new approach for the interpretation of SPR data is presented, which is applicable whenever the functional form of the density profile is known. The use of the proposed procedure for the fitting of experimental results from PS‐PEO brush self‐assembly on alumina surface has allowed the determination of the layer parameters, which have been found to be in accordance with theoretical mean‐field and scaling predictions, being also in good agreement with previous results from neutron reflectivity experiments. Furthermore, it has been confirmed that the dependence of the brush layer thickness d on the molecular weight M_w obeys the scaling law d ～ M_w^0.63. Since surface plasmon measurements can be acquired quite fast, it is suggested that under the present analysis scheme, the technique may be implemented to probe the average conformational properties of adsorbed macromolecular layers during their formation or under external stimuli. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2060–2070, 2007     

Relation between the adhesion strength and interfacial width for symmetric polystyrene bilayers

Polystyrene (PS) bilayers were prepared and were adhered at a temperature between the surface and bulk glass-transition temperatures for a given time. Then, the interfacial adhesion strength (G_L) was examined with a conventional lap-shear measurement. G_L first increased with increasing adhesion time and then reached a constant value. This result implied that the segments moved across the interface, to a certain depth, even at a temperature below the bulk glass-transition temperature. To confirm this, the interfacial evolution for the PS/deuterated PS bilayers was examined with dynamic secondary-ion mass spectrometry. The G_L value was linearly proportional to the thickness of the interfacial adhesion layer. Finally, we propose a strategy for regulating the adhesion strength based on the chain-end chemistry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3598–3604, 2006     

Synthesis of hydroxyl‐terminated poly(ether ether ketone) with pendent tert‐butyl groups and its use as a toughener for epoxy resins

Hydroxyl‐terminated poly(ether ether ketone) with pendent tert‐butyl groups (PEEKTOH) was synthesized by the nucleophilic substitution reaction of 4,4′‐difluorobenzophenone with tert‐butyl hydroquinone with potassium carbonate as a catalyst and N‐methyl‐2‐pyrrolidone as a solvent. Diglycidyl ether of bisphenol A epoxy resin was toughened with PEEKTOHs having different molecular weights. The melt‐mixed binary blends were homogeneous and showed a single composition‐dependent glass‐transition temperature (T_g). Kelley–Bueche and Gordon–Taylor equations gave good correlation with the experimental T_g. Scanning electron microscopy studies of the cured blends revealed a two‐phase morphology. A sea‐island morphology in which the thermoplastic was dispersed in a continuous matrix of epoxy resin was observed. Phase separation occurred by a nucleation and growth mechanism. The dynamic mechanical spectrum of the blends gave two peaks corresponding to epoxy‐rich and thermoplastic‐rich phases. The T_g of the epoxy‐rich phase was lower than that of the unmodified epoxy resin, indicating the presence of dissolved PEEKTOH in the epoxy matrix. There was an increase in the tensile strength with the addition of PEEKTOH. The fracture toughness increased by 135% with the addition of high‐molecular‐weight PEEKTOH. The improvement in the fracture toughness was dependent on the molecular weight and concentration of the oligomers present in the blend. Fracture mechanisms such as crack path deflection, ductile tearing of the thermoplastic, and local plastic deformation of the matrix occurred in the blends. The thermal stability of the blends was not affected by blending with PEEKTOH. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 541–556, 2006