Synthesis and characterization of polymers and copolymers of vinylruthenocene

Homopolymers of vinylruthenocene and its copolymers with methyl acrylate, styrene, and n-vinylpyrrolidinone have been prepared by free-radical polymerization. No evidence for the electron transfer termination mechanism postulated for polymerization of vinylferrocene was observed. Yields of soluble polymers were 40–90% with M _w (4–25) × 10³ and M _w/M _n = 3.0–13.2. TGA analysis showed little weight loss up to 300°C but rapid decomposition above 300°C. Polyvinylruthenocene is a highly brittle material with T_g above 250°C. Torsional braid analysis of the copolymer samples showed T_g in the range 90–130°C which in some samples increased upon cooling and reheating. Several samples showed weak thermal transitions occurring prior to or following T_g. The rise in T_g upon cooling and reheating is indicative of possible decomposition, crosslinking, or realignment of the polymer chains.     

Evidence of two relaxation processes in the photon correlation spectra of poly(methyl methacrylate) above Tg

Photon correlation functions of a high-molecular-weight PMMA (M_w = 1.06 × 10⁷, M_n = 2.2 × 10⁶, T_g = 103°C) have been studied in the temperature range 98 ? 149°C. In contrast to previous results, two relaxation modes are observed in relaxation functions. The observed relaxation functions of PMMA are analyzed for the first time in terms of a continuous spectrum representing the distribution of retardation times. Using a modified computer program originally developed by Provencher, we have computed the spectrum of retardation times at various temperatures. The appearance of two distinct relaxation modes is clearly evident in the distribution of the retardation times and in the time correlation functions below 123°C.     

Thermodynamic study of triclosan adsorption from aqueous solutions on activated carbon

The change in the thermodynamic properties of triclosan adsorption on three activated carbons with the different surface chemistry was studied through immersion calorimetry and equilibrium data; the amount adsorbed of triclosan (Q) during calorimetry was determined and correlated with the energy associated with adsorbate–adsorbent interactions in the adsorption process. It was noted that triclosan adsorption capacity decreases with an increase in oxygenated surface groups. For an activated carbon oxidized with HNO₃ (OxAC), the amount adsorbed was 8.50?×?10^?3 mmol g^?1, for a activated carbon without modification (GAC) Q?=?10.3?×?10^?3 mmol g^?1 and for a activated carbon heated at 1073 K (RAC1073) Q?=?11.4?×?10^?3 mmol g^?1. The adsorbed amounts were determined by adjusting the isotherms to the Sips model. For the activated carbon RAC1073, the immersion enthalpy (ΔH_imm) was greater than those of the other two activated carbons due to the formation of interactions with the solvent (ΔH_immOxAC?=?? 27.3 J g^?1?<?ΔH_immGAC?=?? 40.0 J g^?1?<?ΔH_imm RAC1073?=???60.7 J g^?1). The changes in the interaction enthalpy and Gibbs energy are associated with adsorbate–adsorbent interactions and side interactions such as the adsorbate–adsorbate and adsorbate–solvent interactions.

     

Effect of Molecular Weight on Enthalpy Relaxation in Syndiotactic Poly(Methyl-Methacrylate)

The structural relaxation behaviour of narrow fractions (M_w/M_n < 1.1) of syndiotactic poly(methyl methacrylate) with molecular masses ranging from 2,000 to 200,000 Daltons have been studied by DSC with two classical procedures, namely: the rate of cooling and the isothermal approaches. The apparent activation energy (Δh*) of enthalpy relaxation was evaluated from the dependence of the glass transition temperature on the cooling rate while a comparison of the apparent relaxation rates was appraised from the enthalpy loss by annealing the different samples at the same level of undercooling (T_a = T_g − 10 °C). As expected, the increase of molecular weights gives rise to both a continuous increase of Δh* and a decrease of the apparent isothermal relaxation rate. More interestingly, both Δh* and the apparent isothermal relaxation rate showed abrupt changes around the syndiotactic PMMA entanglement mass (M_e ).     

Surface mobility and diffusion at interfaces of polystyrene in the vicinity of the glass transition

Symmetric polydisperse (M_w = 23 × 10⁴, M_w/M_n = 2.84) and monodisperse (M_w = 21 × 10⁴, M_w/M_n < 1.05) polystyrene (PS), and asymmetric polydisperse PS/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) interfaces have been bonded in the vicinity of the glass transition temperature (T_g) of PS. In a lap-shear joint geometry, strength develops in all cases with time to the fourth power, which indicates that it is diffusion controlled. Strength developing at short times at the polydisperse PS/PS interface, at 90°C, is higher than that at the monodisperse interface, at 92°C (at T_g − 13°C in both cases), presumably due to the contribution of the low molecular weight species. The decrease of strength at the PS/PPO interface when the bonding temperature decreases from 113 to 70°C, i.e., from T_g + 10°C to T_g − 33°C of the bulk PS, indicates a high molecular mobility at the surface as compared to that in the bulk, and can be expressed by a classical diffusion equation, which is valid above T_g (of the surface layer). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 567–572, 1998     

Thermal Decomposition and Glass Transition Temperature of Poly(phenyl Methacrylate) and Poly(cyclohexyl Methacrylate)

The thermal decomposition and the glass transition temperature T_g of poly(phenyl methacrylate) (PPhMA) and poly(cyclohexyl methacrylate) (PcHU) were studied with a differential scanning calorimeter (DSC). The undecomposed and decomposed polymers were analyzed by gel permeation chromatography (GPC) for molecular weight distributions and by DSC for changes in the thermal properties, e.g., T_g. For all values of weight-loss α, the thermal stability of the polymers follows the order: Poly-(methyl methacrylate) (PMMA) = PcHMA > poly(ethyl methacrylate) (PEMA) > PPhMA > poly(n-butyl methacrylate) (PnBuMA) > poly(isobutyl methacrylate) (PiBuMA). In the depolymerization reactions that occur during the isothermal decomposition of PPhMA, there is no specific preference for longer or shorter chains although a minor fraction of the volatilized fraction with an [Mbar]_w 10^?5 of 2.5 and an [Mbar] _n |MX 10.^?5 of 1.5 does undergo chain recombination yielding high molecular weight products with an M_w × 10^?6 of 1.35 and an M_n × 10^?6 of 1.0 to 1.23. In the case of PcHMA, depolymerizations did show a preference for longer chains. No chain recombination, however, was found to take place. Activation energy of decomposition for substituted poly-methacrylates follows the order: PnBuMA = PiBuMA >; PEMA >; PcHMA >; PMMA >; PPhMA. T_{g e} values of PPhMA samples varied from 362 K for undecomposed polymers to 396 K for a polymer treated at 300° C. The literature value of 383 K does fall within this range. In the case of PcHMA, an average T_ge of 356 f 6.0 ± is not far removed from the reported value of 359 K.     

Synthesis of polyimides containing triphenylamine‐substituted triazole moieties for polymer memory applications

A series of thermally stable aromatic polyimides containing triphenylamine‐substituted triazole moieties ( AZTA‐PI )s were prepared and characterized. The glass transition temperatures (T_g) of the polyimides were found to be in the range of 262–314 °C. The polyimides obtained by chemical imidization had inherent viscosities of 0.25–0.44 dL g^?1 in N‐methyl‐2‐pyrrolidinone. The number average molecular weights (M_n) and weight average molecular weights (M_w) were 1.9–3.2 × 10⁴ and 3.2–5.6 × 10⁴, respectively, and the polydispersity indices (PDI = M_w/M_n) were in the range of 1.70–1.78. A resistive switching device was constructed from the 4,4′‐hexafluoroisopropylidenediphthalic dianhydride‐based soluble polyimide ( AZTA‐PIa ) in a sandwich structure of indium‐tin oxide/polymer/Al. The as‐fabricated device can be switched from the initial low‐conductivity (OFF) state to the high‐conductivity (ON) state at a switching threshold voltage of 2.5 V under either positive or negative electrical sweep, with an ON/OFF state current ratio in the order of 10⁵ at ?1 V. The device is able to remain in the ON state even after turning off the power or under a reverse bias. The nonvolatile and nonrewritable natures of the ON state indicate that the device is a write‐once read‐many times (WORM) memory. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Dynamic light scattering from bulk poly(n-hexylmethacrylate) near and above the glass transition

Photon correlation spectra of polarized scattered light from poly(n-hexylmethacrylate) PHMA (M_w = 1.6·10⁵, T_g = ?5°C) have been studied in the temperature range of ?2–25°C. The experimental time correlation functions over the time range 10^?6?10² s were represented by the Kohlrausch-Williams-Watts (KWW) function exp{?(t/τ)^β} with a virtually temperature-independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass-rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass-rubber or α-relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10^?6 s near T_g. © 1992 John Wiley & Sons, Inc.     

Thermal analyses of poly(N-isopropylacrylamide) in aqueous solutions and in nanocomposite gels

The coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPA) prepared by free-radical redox polymerization in aqueous solutions and its nanocomposite (NC) gels were investigated by differential scanning calorimetery. The lower critical solution temperatures (LCST) of aqueous solutions of PNIPA of different molecular weights were not significantly affected by molecular weight (M _w: 0.19?×?10⁶?4.29?×?10⁶?g?×?mol^?1) or polymer concentration (1?10?wt%), although the enthalpy of transition increased with molecular weight, at M _w (<1.2?×?10⁶ g?×?mol^?1). The glass-transition temperature of PNIPA in the dried state also remained constant (138?°C), regardless of molecular weight. On the other hand, the enthalpy of the coil-to-globule transition of PNIPA in NC gels consisting of a PNIPA/clay network decreased with increasing clay concentration (C _clay), while the onset temperature (≡LCST) was almost constant, regardless of C _clay. The PNIPA chains in NC gels could be classified into the following three types: P-1, which exhibits a normal LCST transition, similar to that of linear PNIPA; P-2, exhibiting restricted transition at higher temperatures as a result of interactions with the clay; and P-3, which does not undergo that transition because of stronger restrictions. It was found that the proportion of P-3 increases with increasing C _clay. However, some P-1 and P-2 was still observed, even in NC gels with high C _clay. That the transition to the hydrophobic globular state was restricted by interactions with the clay was confirmed by measurements on PNIPA after removal of the clay from NC gels.     

Effects of composition on the solution properties of styrene–acrylonitrile copolymers

Short-range interactions between chain units of random copolymers in solution may be influenced by the composition or precisely by the distribution of sequence lengths of the same monomer units. Steric factors were derived for random copolymers of styrene and acrylonitrile with different compositions from the relation between the limiting viscosity number and the molecular weight. Mark-Houwink relations were obtained in methyl ethyl ketone (MEK) or in N,N′-dimethylformamide (DMF) at 30°C. for random copolymers containing 0.383 (Co-1) and 0.626 (Co-2) mole fraction of acrylonitrile, the expressions are: [η] = 3.6 X 10^?4 M _w^0.62, for Co-1 in MEK; [η] = 5.3 X 10^?4 M _w^0.61, for Co-2 in MEK; [η] = 1.2 × 10^?4M _w^0.77 for Co-2 in DMF. With the Stockmayer-Fixman expression, these correlations become, respectively: [η]/M^1/2 = 1.24 × 10^?3 + 8.0 × 10^?7 M^1/2; and [η]/M^1/2 = 1.70 × 10^?3 + 6.3 × 10^?7 M^1/2; and [η]/M^1/2 = 1.68 × 10^?3 + 31.3 × 10^?7 M^1/2. From the unperturbed mean-square end-to-end distances, 〈L²〉₀, determined from the first terms of the latter expressions, together with 〈L²〉_0f calculated by assuming the completely free rotation, gives the steric factor σ = (〈L²〉₀/〈L²〉_0f)^1/2 as 2.25 ± 0.05 for Co-1, and 2.31 ± 0.10 for Co-2. These values of σ are close to those for polystyrene (σ = 2.22 ± 0.05) and for polyacrylonitrile (σ = 2.20 ± 0.05). Therefore, it is concluded that the dimensions of random copolymers of styrene and acrylonitrile in solution are not significantly influenced by the composition. In other words, the unperturbed dimensions are not affected by a change in the alternation tendency between styrene units with phenyl side groups having a large molar volume and acrylonitrile units with nitrile groups responsible for the electrostatic interactions. On the other hand, the long-range interactions reflect the effect of sequence length. The Huggins constant and the second virial coefficient obtained from the light-scattering measurements have optimum values at about 0.5 mole fraction of acrylonitrile, where the greatest tendency for alternation seems to exist.     

Thermal and ion transport properties of hydrophilic and hydrophobic polymerized styrenic imidazolium ionic liquids

Polymerized ionic liquids (PILs) are a platform for fundamental studies of structure‐property relationships in single ion conductors, with potential applications in energy storage and conversion. The synthesis, thermal properties, and ionic conductivities of homologous, narrow dispersity styrenic PILs are described. Hydrophilic poly(4‐vinylbenzyl alkylimidazolium chloride) (PVBn(alkyl)ImCl) homopolymers with constant average degrees of polymerization were synthesized by post‐synthetic functionalization of a poly(4‐vinylbenzyl chloride) (M_n = 15.9 kg/mol, M_w/M_n = 1.34) master batch with N‐alkylimidazoles (alkyl = ? CH₃ (Me), ? C₄H₉ (Bu), and ? C₆H₁₃ (Hex)). The chloride counterions of PVBnHexImCl were exhaustively metathesized with BF, PF, and bis(trifluoromethanesulfonyl)imide (TFSI^?) to yield a series of hydrophobic PILs. Thermogravimetric analyses indicate that PVBn(alkyl)ImCl homopolymers are unstable above 220 °C, whereas the hydrophobic PILs remain stable up to 290 °C. The glass transition temperatures (T_g) decrease with both increasing alkyl side‐chain length and increasing counterion size, exemplified by T_g = 9 °C for PVBnHexImTFSI. Hydrophilic PILs exhibit high ionic conductivities (as high as ～0.10 S cm^?1) that depend on the relative humidity, water uptake, and the PIL side chain length. The hydrophobic PILs exhibit lower conductivities (up to ～5 × 10^?4 S cm^?1) that depend predominantly on the polymer T_g, however, counterion size and symmetry also contribute. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1287–1296, 2011     

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     

Use of Styrene as Sole Carbon Source by the Fungus Exophiala oligosperma: Optimization and Modeling of Biodegradation, Pathway Elucidation, and Cell Membrane Composition

Biodegradation of styrene by Exophiala sp. was tested at different initial concentrations (19.3?C170.6?mg?l^?1), pH (2.8?C8.7), and temperatures (19.8?C45.1?°C), for 120?h according to a 2³ full-factorial central composite design. The specific growth rate (SGR, per hour) and specific styrene utilization rate (SUR, milligrams of styrene per milligram of biomass per hour) values were used as the response variables for optimization purposes. The interactions between concentration and temperature (P?=?0.022), and pH and temperature (P?=?0.010) for SGR, and interactions between concentration and temperature (P?=?0.012) for SUR were found to be statistically significant. The optimal values for achieving high SGR (0.15?h^?1) and SUR (0.3622?mg styrene mg^?1 biomass h^?1) were calculated from the regression model equation. Those values are C _o ?=?89.1?mg?l^?1, pH?=?5.4, and T?=?31.5?°C for SGR and C _o ?=?69.2?mg?l^?1, pH?=?5.5, and T?=?32.4?°C for SUR. It was also observed that the Exophiala strain degrades styrene via phenylacetic acid, involving initial oxidation of the vinyl side chain. Besides, in the presence of styrene, changes in the fatty acids profile were also observed. It is hypothesized that an increasing amount of linoleic acid (18:2) may be involved in the protection of the fungus against toxic substrate.     

Nuclear relaxation in atactic polystyrenes: T1 and T1ρ measurements

Measurements have been made on a series of linear atactic polystyrenes whose molecular weights range from 900 to 1.8 × 10⁶, where M _w/M _n ? 1.2. Spin lattice relaxation times have been measured in the laboratory frame (T₁) and in the rotating frame (T_1ρ) in the temperature range 90–500°K. Two major relaxation minima were observed in both sets of measurements. The high temperature process corresponds to the glass transition (α process), the position of the minimum depending on the chain length. The low temperature process appears to originate from the n-butyl endgroups in the polymer, its position being independent of chain length while its intensity is inversely proportional to molecular weight. No other minima were observed, in contrast to some other observations made by broadline and pulsed NMR techniques. Relaxation was exponential in all cases except in the region of the high temperature T_1ρ minimum and above. This nonexponential behavior is possibly connected with the transition at T > T_g observed by a number of other techniques and which is thought to correspond to a transition between two types of liquid state. A correlation frequency diagram has been drawn for all the processes observed in polystyrene by other techniques, (α, β, αβ, γ, and δ) which shows that the T₁ and T_1ρ minimum positions correlate well with the α process and that there is a possible contribution to the relaxation due to the γ process on the low temperature side of the α process. At these measurement frequencies the α and β processes are merged into an αβ process. There is no evidence for a contribution from the mechanical δ process. The effect of the endgroups is observed to very high molecular weights (4.98 × 10⁵), and it seems that a three-dimensional diffusion model would be more adequate than the one-dimensional model used to interpret similar behavior of paraffins and polyethylenes. Measurements of T₁ in the low-temperature region would constitute a method for a rough measurement of the molecular weight of these polymers.     

Ion-aggregation and thermal expansion in styrene-based ionomers

The linear thermal-expansion coefficients (α) of styrene–sodium methacrylate copolymers were studied as a function of the concentration of sodium methacrylate comonomer. Over the concentration range studied (0.61–9.0 mole % sodium methacrylate), the expansion coefficients of the glass α_g and of the liquid α_l were independent of ion concentration. Average values for these quantities were α_g = (6.9 ± 0.9) × 10^?5 deg^?1 and α_l = (16.0 ± 2.0) × 10^?5 deg^?1. When samples of concentrations above 6 mole % were heated from room temperature, a low value for the liquid-expansion coefficient α_l was observed in the first runs. This quantity had an average value of (12.0 ± 1.9) × 10^?5 deg^?1. Heating of the 6.5 mole % sample from room temperature followed by cycling from the glass transition temperature T_g to successively higher temperatures resulted in a gradual increase in liquid-expansion coefficient. The results are consistent with the hypothesis of the existence of various types of ionic aggregates in these polymers, with the state of aggregation changing at approximately (5–6) % of ions. Experimental T_g values, which increase with ion concentration over the entire range, are consistent with the results of previous studies.     

Rotational diffusion of 9,10-diphenylanthracene in di-n-butyl phthalate solutions of polystyrenes by the fluorescence polarization method: Dependence on polymer concentration and molecular weight

A versatile double-beam polarization fluorimeter has been constructed for measuring the polarization of fluorescence from polymer solutions, melts, and glasses. Polarizations can be determined over a range of temperatures from ?20 to +80°C in a controlled atmosphere with a precision of ±0.001 to ±0.005 for the studies reported herein. Data collected at different temperatures for 1.5 × 10^?5M solutions of 9,10-diphenylanthracene (PA) in di-n-butyl phthalate (BP) fit a relation of the Perrin type, 1/P = (1/P₀) + (ST/_η1), where P is the polarization, T is the absolute temperature, and _η1 is the solvent viscosity. The constants P₀ and S were 0.400 ± 0.005 and (7.4 ± 0.3) × 10^?3 P/°K, respectively. Polarizations were also determined at 25.0 ± 0.1°C for BP solutions containing 1.5 × 10^?5M PA and polystyrenes at various weight fractions w₂ and molecular weights M. Rotational friction coefficients ζ_r deduced from these data showed no dependence on M from 5.1 × 10⁴ to 8.6 × 10⁵ g/mole, and a gradual increase as w₂ was varied from 0 to 0.1. It is concluded from these results that PA is an especially attractive emitter for rotational diffusion studies in nonaqueous systems, and that the abrupt changes in ζ_r with w₂ and M observed for some other emitter–polymer systems and attributed to onset of coil overlap are not universal characteristics of such systems.     

Synthesis,crystal structure and non-linear optical properties of a new cyanide-containing compound

Reaction of K₃[Fe(CN)₆], NiCl₂ and diethylenetriamine (dien) resulted in the formation of a cyanide-containing heterometallic compound [Ni(dien)₂]₂[Fe(CN)₆]·4H₂O 1. The structure consists of two octahedral [Ni(dien)₂]²⁺ cations, one octahedral [Fe(CN)₆]^4? anion and four crystallization water molecules, which are held together by hydrogen-bonding interactions. Its TG curve exhibits two stages of mass loss. Compound 1 in DMF solutions has a very strong third-order non-linear optical (NLO) behavior with an absorption coefficient and refractive index α₂?=?1.10?×?10^?11?m?w^?1, n ₂?=??3.05?×?10^?19?m²?w^?1, respectively, and third-order NLO susceptibility χ⁽³⁾ 4.34?×?10^?13?esu.     

Dispersion of polymeric-coated–silica aerogel particles in unsaturated polyester composites: Effects on thermal-mechanical properties

The thermal-mechanical properties of unsaturated polyester (UP) composite were enhanced by the dispersion of silica aerogel (SA) with preserved pores. Low-cost SA was prepared from rice husk via the sol-gel process and ambient pressure drying. A new method was proposed to encapsulate the hydrophobic aerogel surface pores with hydrophilic polyvinyl alcohol (PVA) film using the fluidized-bed coating process. The dispersion of PVA-coated aerogel with preserved pores in the polyester matrix resulted in an increase of specific compressive strength (44.1?MPa?·?cm³?g^?1), thermal insulation (0.23?W?m^?1?K^?1), and thermal stability (T_onset?=?310°C), but decreased the glass transition temperature (T_g?=?260°C).     

Third virial coefficient of polystyrene in benzene

Second virial coefficients A₂ and third virial coefficients A₃ for benzene solutions of ten polystyrene fractions ranging in weight-average molecular weight M_w from 10⁴ to 2 × 10⁷ at 25°C were determined by light scattering. The third coefficient is represented approximately by A₃ = 8.0 × 10^?6 M mol g^?3 cm⁶ for M_w above 10⁵. In this molecular weight region, the factor g defined by A₃/AM_w/ This trend of g is consistent with predictions of early two-parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for M_w ? 2 × 10⁵) and the mean-field two-parameter theory of Stockmayer and Casassa.     

SURFACE RHEOLOGY OF POLYMERIC SOLIDS

Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of scanningviscoelasticity microscopic (SVM) and lateral force microscopic (LFM) measurements. SVM and LFM measurements werecarried out for films of conventional monodisperse polystyrene (PS) with sec-butyl and proton-terminated end groups atroom temperature. In the case of the number-average molecular weight, M_n, less than ca. 4.0×10~4, the surface was in a glass-rubber transition state even though the bulk glass transition temperature, T_g was far above room temperature, meaning thatthe surface molecular motion was fairly active compared with that in the bulk. LFM measurements of the, monodisperse PSfilms at various scanning rates and temperatures revealed that the time-temperature superposition was applicable to thesurface mechanical relaxation behavior and also that the surface glass transition temperature, T_g~σ, was depressed incomparison with the bulk one even though the magnitude of M_n was fairly high at 1.40×10~5. The surface molecular motionof monodisperse PS with various chain end groups was investigated on the basis of temperature-dependent scanningviscoelasticity microscopy (TDSVM). The T_g~σs for the PS films with M_n of 4.9×10~6 to 1.45×10~6 measured by TDSVMwere smaller than those for the bulk one, with corresponding M_ns, and the T_g~σs for M_ns smaller than ca. 4.0×10~4 were lowerthan room temperature (293 K). The active thermal molecular motion at the polymeric solid surface can be interpreted interms of an excess free volume near the surface region induced by the surface localization of chain end groups. In the case ofM_n=ca. 5.0×10~4, the T_g~σs for the α, ω-diamino-terminated PS (α,ω-PS(NH_2)_2) and α, ω-dicarboxy-terminated PS (α, ω-PS(COOH)_2) films were higher than that of the PS film. The change of T_g~σ for the PS film with various chain end groups canbe explained in terms of the depth distribution of chain end groups at the surface region depending on the relativehydrophobicity.