Pulse radiolysis studies of poly(methyl methacrylate) containing pyrene

A pulse radiolysis study of poly(methyl methacrylate) in the presence of pyrene has been carried out in the temperature range 100–295 K. The concentration of pyrene was changed from 10⁻³ to 10⁻¹ mol dm⁻³. The absorption/emission spectra and kinetics of solute excited states and solute radical ions were investigated. It was found that pyrene excited states were formed as a result of their radical ion recombination in a time scale up to seconds. The decay of solute radical ions was influenced by photobleaching and can be described by a time-dependent rate constant. The activation energy of Py ions decay was temperature dependent and was equal to 35.7 and 1.2 kJ/mol for temperatures >T_γ and <T_γ, respectively, where T_γ ∼ 175 K represented the transition temperature responsible for γ-relaxation. The reaction mechanism was proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1209–1215, 1998     

Molecular mobility of substituted poly(p-phenylenes) characterized by a range of polymer relaxation techniques

The free volume and related mobility properties of substituted poly(p-phenylene) polymers are examined. The techniques used range from positron annihilation, dielectric relaxation, and dynamic mechanical spectroscopy to thermally stimulated currents. Fractional free volume is determined for the samples with different substituted side groups and related to the glass transition temperature. Bulkier groups lead to a greater fractional free volume and lower glass transition temperatures. Comparison of molecular relaxation times using the different characterization techniques demonstrates that there is strong coupling between motion of the main chain and the side groups, on which the dipoles reside. Intermolecular coupling between the main chains at the primary relaxation is shown in this work to be related to the nature of the side chains and resultant free volume, as are the temperature locations of local, secondary relaxations. A qualitative model describing the effect of regiochemistry on the motions and packing of these materials is also proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1465–1481, 1998     

Synthesis of poly[N‐isopropylacrylamide‐g‐poly(ethylene glycol)] with a reactive group at the poly(ethylene glycol) end and its thermosensitive self‐assembling character

Poly[N‐isopropylacrylamide‐g‐poly(ethylene glycol)]s with a reactive group at the poly(ethylene glycol) (PEG) end were synthesized by the radical copolymerization of N‐isopropylacrylamide with a PEG macromonomer having an acetal group at one end and a methacryloyl group at the other chain end. The temperature dependence of the aqueous solutions of the obtained graft copolymers was estimated by light scattering measurements. The intensity of the light scattering from aqueous polymer solutions increased with increasing temperature. In particular, at temperatures above 40°C, the intensity abruptly increased, indicating a phase separation of the graft copolymer due to the lower critical solution temperature (LCST) of the poly(N‐isopropylacrylamide) segment. No turbidity was observed even above the LCST, and this suggested a nanoscale self‐assembling structure of the graft copolymer. The dynamic light scattering measurements confirmed that the size of the aggregate was in the range of several tens of nanometers. The acetal group at the end of the PEG graft chain was easily converted to the aldehyde group by an acid treatment, which was analyzed by ¹H NMR. Such a temperature‐induced nanosphere possessing reactive PEG tethered chains on the surface is promising for new nanobased biomedical materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1457–1469, 2006     

Heat capacity of poly(vinyl methyl ether)

The heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (?25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ₁ = 647 K, Θ₂ = Θ₃ = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by C_p(liquid) = 72.36 + 0.136 T in J K^?1 mol^?1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing C_p of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005     

Characterization of poly(silylenemethylene)s by positron annihilation lifetime spectroscopy. I.

Amorphous and crystalline poly(silylenemethylene)s with the repeating PhRSiCH₂ (R : Me or Ph) units were characterized by positron annihilation lifetime spectroscopy (PALS) to gain insights into the molecular motions of these polymers. The temperature dependence of the ortho-positronium lifetime (τ₃) and intensity (I₃) was examined from 50 to 470 K for each sample. The glass transition temperature of each polymer was easily distinguished by a change in the slope of τ₃ spectrum. Both polymers exhibited a steep drop of I₃ at 130–140 K being probably assignable to the transition arising from the motions of phenyl groups, which was almost undetectable by means of differential scanning calorimetry or dynamic mechanical analysis. Several other transitions of these polymers detected by PALS are also discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 755–761, 1998     

Novel polyisobutylene/poly(dimethylsiloxane) bicomponent networks. I. Synthesis and characterization

The synthesis of novel polyisobutylene (PIB)/poly(dimethylsiloxane) (PDMS) bicomponent networks is described. The synthesis strategy (see Figure 1) was to prepare well-defined and -characterized allyl-tritelechelic polyisobutylenes [ϕ(PIB—C—C=C)₃] and SiH-ditelechelic poly(dimethylsiloxanes) (HSi–PDMS–SiH) and then crosslink these moieties by hydrosilation. The ϕ(PIB—C—C=C)₃ was prepared by living isobutylene polymerization followed by end-quenching with allyltrimethylsilane, whereas the HSi–PDMS–SiH was obtained by equilibrium polymerization of octamethylcyclotetrasiloxane and tetramethyldisiloxane. The detailed structures of the starting polymers were characterized by GPC and ¹H-NMR spectroscopy. A series of PIB/PDMS bicomponent networks of varying compositions and average molecular weights between crosslinks (M _c) of ∼ 20,000 g/mol were assembled. Optimum crosslinking conditions were defined in terms of H₂PtCl₆ catalyst concentration, nature of solvent, time, temperature, and stoichiometry of ∼ CH₂CH=CH₂/∼SiH groups, allowing for the convenient synthesis of well-defined model bicomponent networks. Swelling studies and elemental analysis confirm the correctness of the synthetic strategy. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1891–1899, 1998     

Structure and molecular motion of poly(ethylene oxide) chains adsorbed on a silica-tethered poly(methyl methacrylate) by the spin label method

The spin-label method was used to study the structure and molecular motion of poly(ethylene oxide) (PEO) chains adsorbed on a silica-tethered poly(methyl methacrylate) (PMMA). Spin-labelled PEO with a narrow molecular weight distribution, having number averaged molecular weight (M _N)=6.0×10³, was adsorbed on the surface of the silica-tethered PMMA with various grafting ratios in carbon tetrachloride solution at 35?°C. ESR spectra were measured at various temperatures after the samples were completely dried. The ESR spectra are composed of two spectra arising from spin-labels attached to “train” and “tail” segments, which are strongly and weakly interacted with the silica surface, respectively. The fractional amount of the “tail” segments increases extremely with the grafting ratio of PMMA. Molecular mobility of the PEO chains estimated from the temperature dependence of the ESR spectra also decreases significantly with the grafting ratio of PMMA. Structure and molecular motion of the PMMA chains tethered on the silica were also studied using the spin-labelled PMMA. Consequently, parts of the PEO segments penetrate into the PMMA chains and is adsorbed on the silica surface (“train” segments), whereas parts of the PMMA segments protrude from the surface. The other PEO segments are entangled with the tethered PMMA chains (“tail” segments).     

Regio‐selective peroxybromination of poly(vinyl methyl ketone) as versatile tool for generation active ATRP initiation sites on solid surfaces

Peroxybromination or so‐called radical bromination is an environmentally friendly process which involves the use of in situ generated bromine by action of hydrogen peroxide on sodium or ammonium bromide in acid medium. The reaction takes place at room temperature without eliminating hydrobromic acid and no needs the use of elemental bromine. The reaction with poly(vinyl methyl ketone) in biphasic system was demonstrated to result in quantitative bromination exclusively at the methyne carbon of the polymer. The brominated polymer was successfully used as multifunctional macroinitiator for atom transfer radical polymerization (ATRP) of styrene and MMA to give bottlebrush polymers, as evidenced by ¹H NMR and GPC. This strategy was demonstrated to provide a means of easy bromination of solid polystyrene microspheres (210–420 μm) constituting with vinyl methyl ketone copolymer segments. Bromoalkyl groups generated (1.3 mmol g^?1) in aqueous mixture were used for surface initiated ATRP of glycidyl methacrylate and styrene monomers to give dense graft chains tethered to the surfaces with hydrolysis‐proof linkages. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3892–3900     

Pressure and volume dependence of thermal conductivity and isothermal bulk modulus up to 1 GPa for poly(isobutylene)

The thermal conductivity λ and heat capacity per unit volume ρc_p of poly(isobutylene)s, one 2.8 in weight average molecular weight and one 85 kg mol⁻¹ in viscosity average molecular weight (PIB-2800 and PIB-85000), have been measured in the temperature range 170–450 K at pressures up to 2 GPa using the transient hot-wire method. At 297 K and atmospheric pressure, λ = 0.115 W m⁻¹ K⁻¹ for PIB-2800 and λ = 0.120 W m⁻¹ K⁻¹ for PIB-85000. The bulk modulus B_T has been measured in the temperature range 170–297 K up to 1 GPa. At atmospheric pressure, the room temperature bulk moduli B_T are 2.0 GPa for PIB-2800 and 2.5 GPa for PIB-85000 with dB_T/dp = 10 for both. These data were used to calculate the volume dependence of λ, At room temperature and atmospheric pressure (liquid phase) we find g = 3.4 for PIB-2800 and g = 3.9 for PIB-85000, but g depends strongly on temperature for both molecular weights. The difference in g between the glassy state and liquid phase is small and just outside the inaccuracy of g of about 8%. The best predictions for g are given by the theoretical model of Horrocks and McLaughlin. We have found that PIB exhibits two relaxations, where one is associated with the glass transition. The value for dT_g/dp at atmospheric pressure (for the main glass transition) is about 0.21 K MPa⁻¹ for both molecular weights. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1781–1792, 1998     

Compatibilization of blends of polybutadiene and poly(methyl methacrylate) with poly(butadiene-block-methyl methacrylate)

Compatibilization of blends of polybutadiene and poly(methyl methacrylate) with butadiene-methyl methacrylate diblock copolymers has been investigated by transmission electron microscopy. When the diblock copolymers are added to the blends, the size of PB particles decreases and their size distribution gets narrower. In PB/PMMA7.6K blends with P(B-b-MMA)25.2K as a compatibilizer, most of micelles exist in the PMMA phase. However, using P(B-b-MMA)38K as a compatibilizer, the micellar aggregation exists in PB particles besides that existing in the PMMA phase. The core of a micelle in the PMMA phase is about 10 nm. In this article the influences of temperature and homo-PMMA molecular weight on compatibilization were also examined. At a high temperature PB particles in blends tend to agglomerate into bigger particles. When the molecular weight of PMMA is close to that of the corresponding block of the copolymer, the best compatibilization result would be achieved. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 85–93, 1998     

Dynamic mechanical properties of extruded rods of poly(dimethylsilylene‐co‐methyl‐n‐propylsilylene)

Tractable polysilanes were prepared by the copolymerization of a methyl‐n‐propylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolves in common solvents nor melts before decomposition. Although poly(dimethylsilylene‐co‐methyl‐n‐propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 ∼ 9/1), the copolymers form the columnar mesophase at elevated temperatures. Highly oriented rods were prepared via the extrusion of the copolymers with a circular tube die in a temperature range in which the transition to the columnar mesophase began to occur (70°C when DM/MP = 7/3 and 8/2 and 120°C when DM/MP = 9/1). The extruded rods were characterized in detail by dynamic viscoelasticity and wide‐angle X‐ray diffraction (WAXD) to clarify the structure–mechanical‐property relationship. The orientation functions of the extruded rods were determined by the azimuthal intensity distribution of the WAXD reflection. The orientation function and dynamic storage modulus increased with an increasing extrusion ratio. The dynamic storage modulus at −150°C was 8 ∼ 10 GPa at the highest extrusion ratio and correlated well with the crystal orientation function. The dynamic storage modulus at room temperature was lowered by the structural relaxations at −100 ∼ +30°C, which corresponded to the molecular motion of the rigid molecular chains of the copolymer and the local molecular motion of the MP unit. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 698–706, 2000     

Preparation and cryogenic mechanical properties of epoxy resins modified by poly(ethersulfone)

A thermoplastic, poly(ethersulfone) (PES) was used to modify a bisphenol‐F based epoxy resin cured with an aromatic diamine. The initial mixtures before curing, prepared by melt mixing, were homogeneous. Scanning electron microscopy (SEM) micrographs of solvent‐etched fracture surfaces of the cured blends indicated that phase separation occurred after curing. The cryogenic mechanical behaviors of the epoxy resins were studied in terms of tensile properties and Charpy impact strength at cryogenic temperature (77 K) and compared to their corresponding behaviors at room temperature (RT). The addition of PES generally improved the tensile strength, elongation at break, and impact strength at both RT and 77 K except the RT tensile strength at 25 phr PES content. It was interesting to observe that and the maximum values of the tensile strength, elongation at break, and impact strength occurred at 20 phr PES content where a co‐continuous phase formed. Young's modulus decreased slightly with the increase of the PES content. Moreover, the tensile strength and Young's modulus at 77 K were higher than those at RT at the same composition, whereas the elongation at break and impact strength showed the opposite results. Finally, the differential scanning calorimetry analysis showed that the glass transition temperature (T_g) was enhanced by the addition of PES. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 612–624, 2008     

Light-scattering study of the coil-to-globule transition of linear poly(N-isopropylacrylamide) ionomers in water

The coil-to-globule transition of two poly(N-isopropylacrylamide) (PNIPAM) ionomers with different ionic contents (0.8 and 4.5 mol %), but similar weight average molar masses, in deionized water was investigated by a combination of static and dynamic light scattering. In spite of the large difference in their ionic contents, both the ionomers have a nearly same lower critical solution temperature (LCST, ∼ 32.5°C). At temperatures higher than the LCST, the ionomer chains undergo a simultaneous intrachain coil-to-globule transition and interchain aggregation to form nanoparticles thermodynamically stable in water. The average size of the nanoparticles decreases respectively as the ionic content increases and the ionomer concentration decreases. The interchain aggregation can be completely suppressed in an extremely dilute ionomer solution (< ∼ 5 × 10⁻⁶ g/mL), so that the intrachain coil-to-globule transition leads to the collapse of the ionomer chains into individual single-chain nanoparticles. Our results clearly indicate that there is a hysteresis in the colling process (the globule-to-coil transition). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1501–1506, 1998     

Oxygen diffusion in poly(methyl methacrylate) at low temperatures

Oxygen diffusion in atactic poly(methyl methacrylate) has been studied by anthracene luminescence quenching in geminate pairs anthracene-oxygen at 77–130 K. Analysis of the experimental data shows that the luminescence quenching is well accounted for by a polychromatic model assuming a log-normal diffusion coefficients distribution due to inhomogeneity of polymer structure. Energy activation is equal to 30 ± 1 KJ/mol. All diffusion coefficients data in the range 77–300 K demonstrate a good linear Arrhenius law. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 127–131, 1998     

Dielectric relaxations and electrical conductivities of poly(alkyl methacrylates) under high pressure

Dielectric properties of four methacrylate polymers (methyl, ethyl, n-butyl and n-octyl) were studied in the frequency range 0.0001 cps–300 kcps at temperatures above and below the glass transition temperature and at various pressures up to 2500 atm. At temperatures well above T_g a single relaxation peak (α′ peak) was observed in the case of the higher n-alkyl methacrylates. However, this peak was split into two peaks, α and β, with decrease in temperature or increase in pressure. The molecular motions corresponding to the α and the β relaxation processes are the micro-Brownian motions of amorphous main chains and of flexible side chains, respectively. From the temperature and the pressure dependence of the average dielectric relaxation time of these polymers the single relaxation process (the α′ process) was attributed to the micro-Brownian motion of the main chain coupled with that of the side chain. The effects of temperature and pressure on the d.c. conductivity of these polymers were also studied.     

Novel star‐block polymers: Three polyisobutylene‐b‐poly(methyl methacrylate) arms radiating from an aromatic core

A series of novel three‐arm star blocks consisting of three polyisobutylene‐b‐poly(methyl methacrylate) (PIB‐b‐PMMA) diblocks radiating from a tricumyl core were synthesized, characterized, and tested. The synthetic strategy involved three steps: the synthesis of Cl^t ‐tritelechelic PIB by living cationic isobutylene (IB) polymerization, the conversion of the Cl^t termini to isobutyryl bromide groups, and the initiation of living radical methyl methacrylate (MMA) polymerization by the latter groups. The PIB and PMMA segment lengths (M_n 's) could be controlled by controlling the conditions of the living cationic and radical polymerizations of IB and MMA, respectively. Core destruction analysis directly proved the postulated three‐arm microarchitecture. The structures of the products were analyzed by ¹H NMR and Fourier transform infrared spectroscopies, and their thermal properties were analyzed by differential scanning calorimetry and thermogravimetric analysis. The presence of a low‐ and a high‐temperature glass transition (T_g,PIB ∼ −63°C, T_g,PMMA ∼ 120°C) indicated a phase‐separated micromorphology. Stress/strain analysis showed a tensile strength of up to ∼ 22.9 MPa and an elongation of ∼ 200%. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 706–714, 2000     

Analysis of crystallization kinetics of poly(ether ether ketone)

An optical microscope equipped with a video photograph system was used to follow the growth of spherulites. Under nitrogen atmosphere, the growth rates at 290 and 300°C suggest that when the melt of PEEK has been equilibrated for 15 min at 400°C, the subsequent crystallization behavior was nearly independent of the prior thermal history. Linear growth rates of crystallization of PEEK have been measuredin the temperature range of 260–325°C for melt-pressed films and solvent cast films. Detailed kinetic analysis indicated that PEEK exhibited an unmistakable regime II → III transition at 296 ± 1°C. The II → III transition was clearly present irrespective of the rather drastic changes in U*. It is interesting that the branching and crosslinking retarded the growth rate of PEEK, but a transition from regime II to regime III still existed. For melt-pressed films after equilibration at 400°C for 15 min, values of σ and q suggest that U* should be taken nearer to 1500 cal/mol in the case of T_∞ = T_g − 30 K and 2000 cal/mol in the case of T_∞ = T_g − 51.6 K. The K_g(III)/K_g(II) ratio (1.32) was not as close to the predicted value of 2 as was Hoffman's ratio. For PEEK, the Thomas-Staveley constant (β) should be closer to 0.25 or 0.3 instead of 0.1. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1335–1348, 1998     

Heat capacity of poly(trimethylene terephthalate)

The heat capacity of poly(trimethylene terephthalate) (PTT) has been measured using adiabatic calorimetry, standard differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC). The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 to 570 K. The semicrystalline PTT has a glass transition temperature of 331 K. Between 340 and 480 K, PTT can show exothermic ordering depending on the prior degree of crystallization. The melting endotherm of semicrystalline samples occurs between 480 and 505 K, with a typical onset temperature of 489 K (216°C). The heat of fusion of the semicrystalline samples is about 15 kJ mol⁻¹. For 100% crystalline PTT the heat of fusion is estimated to be 30 ± 2 kJ mol⁻¹. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum and the Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations (θ₁ = 550.5 K and θ₂ = θ₃ = 51 K, N_skeletal = 19). The calculated and experimental heat capacities agree to better than ±3% between 5 and 300 K. The experimental heat capacities of liquid PTT can be expressed by: $ C^L_p(exp) $ = 211.6 + 0.434 T J K⁻¹ mol⁻¹ and compare to ±0.5% with estimates from the ATHAS data bank using contributions of other polymers with the same constituent groups. The glass transition temperature of the completely amorphous polymer is estimated to be 310–315 K with a ΔC_p of about 94 J K⁻¹ mol⁻¹. Knowing C_p of the solid, liquid, and the transition parameters, the thermodynamic functions enthalpy, entropy, and Gibbs function were obtained. With these data one can compute for semicrystalline samples crystallinity changes with temperature, mobile amorphous fractions, and resolve the question of rigid-amorphous fractions.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2499–2511, 1998     

Molecular relaxation in the blends of polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide) at low temperature

Molecular relaxation behavior in terms of the α, β, and γ transitions of miscible PS/PPO blends has been studied by means of DMTA and preliminary work has been carried out using DSC. From DSC and DMTA (by tan δ), the observed α relaxation (T_α or T_g) of PS, PPO, and the blends, which are intermediate between the constituents, are in good agreement with earlier reports by others. In addition, the β transition (T_β) of PS at 0.03 Hz and 1 Hz is observed at −30 and 20°C, respectively, while the γ relaxation (T_γ) is not observed at either frequency. The T_β of PPO is 30°C at 0.03 Hz and is not observed at 1 Hz, while the T_γ is −85°C at 0.03 Hz and −70°C at 1 Hz. On the other hand, blend composition-independent β or γ relaxation observed in the blends may be a consequence of the absence of intra- or intermolecular interaction between the constituents at low temperature. Thus it is suggested that at low temperature, the β relaxation of PS be influenced solely by the local motion of the phenylene ring, and that the β or γ relaxation of PPO be predominated by the local cooperative motions of several monomer units or the rotational motion of the methyl group in PPO. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1981–1986, 1998     

Molecular dynamics simulation of poly(3‐hexylthiophene) helical structure In Vacuo and in amorphous polymer surrounding

The stability of poly(3‐hexylthiophene) (P3HT) helical structure has been investigated in vacuo and in amorphous polymer surrounding via molecular dynamics‐based simulations at temperatures below and above the P3HT melting point. The results show that the helical chain remains stable at room temperature both in vacuo and in amorphous surrounding, and promptly loses its structure at elevated temperatures. However, the amorphous surrounding inhibits the destruction of the helix at higher temperatures. In addition, it is shown that the electrostatic interactions do not significantly affect the stability of the helical structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2448–2456