Length scale hierarchy in sol,gel, and coacervate phases of gelatin

Length scale hierarchy in gelatin sol, gel, and coacervate (induced by ethanol) phases, having same concentration of gelatin in aqueous medium (13% w/v), has been investigated through small angle neutron scattering and rheology measurements. The static structure factor profile, I(q) versus wave vector q, was found to be remarkably similar for all these samples. This data could be split into three distinct q‐regimes: the low‐q regime, I_ex(q) = I_ex(0)/(1+q²ζ²)² valid for q < 3R_g^?1; the intermediate q‐regime, I(q) = I(0)/(1+q²ξ²) for 3R_g^?1 < q < ξ^?1; and the asymptotic regime, I(q) = (c/q) exp(?R_c²q²/2) for q > ξ^?1. Consequently, three distinct length scales could be deduced from structure factor data: (a) inhomogeneity of size, ζ = 20 ± 1 nm for all the three phases; (b) average mesh size, ξ₀ = 2.6 ± 0.2 nm for sol and gel, and smaller mesh size, ξ_os = 1.2 ± 0.2 nm for coacervate; and (c) cross section of gelatin chains, R_c = 0.35 ± 0.04 nm. In addition, the structure factor data obtained from coacervating solution analyzed in the Guinier region, I(q) = exp(?q²R_g²/3), yielded value of typical radius of gyration of clusters, R_g ≈ 69 nm that indicated existence of triple‐helices of length, L ≈ 239 nm; (d) Frequency and temperature sweep measurements conducted on coacervate samples revealed two other length scales: (e) viscoelastic length, ξ_ve = 14 ± 2 nm and (f) correlation length at melting, ξ_T = 500 ± 70 nm. Thus, existence of six distinct length scales, (a–f), ranging from 1.2 to 500 nm has been established in the coacervate phase of gelatin–ethanol–water system. Results are discussed within the framework of Landau‐Ginzburg treatment of dynamically asymmetric systems (Prog Theor Phys 1977, 57, 826; Phys Rev A 1991, 44, R817; J Phys II (France) 1992, 2, 1631). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1653–1667, 2006     

Small‐angle x‐ray scattering study of thermoreversible poly(vinyl chloride) gels

Poly(vinyl chloride) (PVC)/bis(2‐ethylhexyl)phthalate (DOP) gels were prepared at room temperature from tetrahydrofuran solutions of PVC and DOP. PVC/DOP gels of different molecular weights at various PVC concentrations (c) were investigated with small‐angle X‐ray scattering (SAXS). The mean distance between two neighboring inhomogeneities (D) and two characteristic lengths, the intrainhomogeneity distance (d₁) and interinhomogeneity distance (d₂), were evaluated from Bragg's law and the distance distribution function, respectively. Both D and d₂ can be expressed by a power‐law relation (e.g., D and d₂ ∝ c^?0.5). After a period of rapid cooling to 25 °C from the sol state, the structural evolution was examined with time‐resolved SAXS measurements. An Avrami analysis with the SAXS invariant data revealed that the growth kinetics of PVC/DOP gels was one‐dimensional growth from predetermined nuclei, regardless of c. These results suggest that the PVC/DOP gels are constructed from a fibrillar structure that forms gel structures at high concentrations or low temperatures. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2340–2350, 2001     

Neutral polymer slow mode and its rheological correlate

Quasi‐elastic light scattering spectroscopy intensity–intensity autocorrelation functions [S(k,t)] and static light scattering intensities of 1 MDa hydroxypropylcellulose in aqueous solutions were measured. With increasing polymer concentration, over a narrow concentration range, S(k,t) gained a slow relaxation. The transition concentration for the appearance of the slow mode (c^t) was also the transition concentration for the solution‐like/melt‐like rheological transition (c⁺) at which the solution shear viscosity [η_p(c)] passed over from a stretched exponential to a power‐law concentration dependence. To a good approximation, we found c^t[η] ≈ c⁺[η] ≈ 4, [η] being the intrinsic viscosity. The appearance of the slow mode did not change the light scattering intensity (I): from a concentration lower than c^t to a concentration greater than c^t, I/c fell uniformly with increasing concentration. The slow mode thus did not arise from the formation of compact aggregates of polymer chains. If the polymer slow mode arose from long‐lived structures that were not concentration fluctuations, the structures involved much of the dissolved polymer. At 25 °C, the mean relaxation rate of the slow mode approximately matched the relaxation rate for the diffusion of 0.2‐μm‐diameter optical probes observed with the same scattering vector. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 323–333, 2005     

Conformation of comb‐like liquid crystal polymers in isotropic solution probed by small‐angle neutron scattering

The conformational characteristics of a comb‐like side‐chain liquid crystal polysiloxane (SCLCP), dissolved in deuterated chloroform, were evaluated by small‐angle neutron scattering (SANS) measurements over a wide q range. SANS studies were carried out on specimens with constant backbone length (DP = 198) and variable spacer length (n = 3, 5, and 11), and with constant spacer length (n = 5) and variable DP (45, 72, 127, and 198). The form factor P(q) at high q was analyzed using the wormlike chain model with finite cross‐sectional thickness (R_c) and taking into account the molecular weight polydispersity. The analysis generated values of persistence length in the range l_p = 28–32 Å, considerably larger than that of the unsubstituted polysiloxane chain (l_p = 5.8 Å), with contour lengths per monomer comparable to the fully‐extended polysiloxane backbone (l_m = 2.9 Å). This indicates a relatively rigid SCLCP chain due to the influence of the densely attached mesogenic groups. The SCLCP with n = 11 is more flexible (l_p = 28 Å) than those with n = 3 and n = 5 (l_p = 32 Å). The cross‐sectional thickness increases with spacer length, R_c ～ n^0.21±0.02 (3 ≤ n ≤ 11), and the contour length per monomer decreases with increasing spacer length, l_m ～ n^?0.35±0.01. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2412–2424, 2006     

A SAXS and swelling study of cured natural rubber/styrene–butadiene rubber blends

A small‐angle X‐ray scattering (SAXS) and swelling study of natural rubber and styrene–butadiene rubber blends (NR/SBR) is presented. To this aim, specimens of NR and SBR and blends with 75/25, 50/50, and 25/75 NR/SBR ratios (in phr) were prepared at a cure temperature of 433 K and the optimum cure time (t₁₀₀). This time was obtained from rheometer torque curves. The system of cure used in the samples was sulfur/n‐t‐butyl‐2‐benzothiazole sulfenamide. From swelling tests of the cured samples, information about the molecular weight of the network chain between chemical crosslinks was obtained. For all cured compounds, in the Lorentz plots built from SAXS scattering curves, a maximum of the scattering vector q around 0.14 Å^?1 was observed. However, the q position shows a linear‐like shift toward lower values when the SBR content in the SBR/NR blend increases. In pure NR or SBR the q values show a different tendency. The results obtained are discussed in terms of the existence of different levels of vulcanization for each single phase forming the blend and the existence of a third level of vulcanization located in the interfacial NR/SBR layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2320–2327, 2009     

Dynamic light scattering and rheology studies of aqueous solutions of amphiphilic sodium maleate containing copolymers

Light scattering techniques, video particle‐tracking microrheology, and bulk rheology were employed to examine the structure and dynamics of a series of alternating sodium maleate copolymers with moderately hydrophobic comonomers (diisobutylene, styrene, and isobutylene) in aqueous solutions. The scaling dependence of the specific viscosity (η_sp) on the polyelectrolyte concentration (c) was studied with and without added salt; similar trends were found in both conventional rheology and particle‐tracking microrheology measurements, showing good performance of the technique with flexible polyelectrolytes. Furthermore, with dynamic light scattering performed in high added salt conditions, we examined the behavior of the amplitude of the fast mode, which is in agreement with scaling predictions. In contrast, the slow modes are not understood and display three separate behaviors for the wavevector q dependence of the decay rate (Γ), depending on the comonomer; superdiffusive (Γ ～ q^2.7, isobutylene) possibly because of sticky aggregates, wavevector independent (Γ ～ q⁰, styrene) most likely because of coupled polyion‐ion diffusion and diffusive (Γ ～ q^2.0, diisobutylene) presumably because these aggregates are not sticky. The hydrophobicity of the comonomer appears to switch the aggregation process between “open,” “closed,” and “non” association for isobutylene, diisobutylene, and styrene respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 774–785, 2007     

Scaling analysis of cotton cellulose/LiCl·DMAc solution using light scattering and rheological measurements

Semidilute solution of cotton lint (CC1) in 8 wt % LiCl/N,N‐dimethylacetamide was investigated using static light scattering (SLS) and rheological measurements. The reduced osmotic modulus estimated by SLS measurements for CC1 solutions are proportional to c^1.16 in the semidilute region. From the exponent of 1.16, de Gennes' scaling theory derives the relationship between radius of gyration, R_g, and molecular weight, M_w, of CC1 as R_g ∝ M^0.62 This corresponds to the Mark‐Houwink‐Sakurada exponent of 0.86. This exponent is very close to that estimated from scaling analysis of zero shear rate viscosity, that is 0.85. Apparent radius of gyration, R_g,app, estimated by SLS measurements for CC1 solutions are proportional to c^?0.5 in the semidilute region. R_g,app indicates the mesh size of polymer entanglement in the semidilute region. On the assumption of the Gaussian behavior of CC1 molecule in the semidilute region, the exponent of ?0.5 gives the relationship between the molar mass between entanglements, M_e, and c as following relationship: M_e ∝ c^?1. This agrees with the concentration dependence on plateau modulus estimated from the dynamic viscoelastic measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2155–2160, 2006     

Dynamic light scattering of semidilute hydrophobically modified alkali‐soluble emulsion solutions with different lengths of poly(ethylene oxide) spacer chain

Semidilute solutions of hydrophobically modified alkali‐soluble emulsion (HASE) were examined by dynamic light scattering and rheological techniques. For the model polymer without associative macromonomer, two q² dependent diffusional modes were detected in the decay time distributions. With increasing hydrophobicity of the associative macromonomer, the narrow fast peak was substituted by a shallow broad peak and only one q² dependent slow mode could be accurately detected, which indicated that the heterogeneity of these associated clusters increases with increasing carbon number. The bulk steady‐shear viscosity exhibits similar results to the diffusion coefficients of the aggregate observed from light scattering measurements. The length of poly(ethylene oxide) (PEO) spacer chain alters the solution properties as well as the associative cluster structure. With increasing length of PEO spacer chain, intramolecular association was substituted by intermolecular association. For EO segment larger than 32 units, intramolecular association dominates, where the formation of HASE aggregates is controlled by the balance of electrostatic repulsion and hydrophobic attraction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3288–3298, 2005     

Electrical and optical properties of ceramic–polymer nanocomposite coatings

Transparent, conductive composite coatings were fabricated from suspensions of poly(vinyl acetate‐acrylic) (PVAc‐co‐acrylic) copolymer latices (50–600 nm) and nanosized antimony‐doped tin oxide (ATO) particles (～15 nm). The suspensions were deposited as coatings onto poly(ethylene terephthalate) substrates and dried at 50 °C. Microstructure studies using field emission scanning electron microscopy and tapping‐mode atomic force microscopy (TMAFM) indicated that the latex particles coalesced during drying and forced the ATO particles to segregate into the boundaries between the latex particles. Low phase contrast was observed with TMAFM; this result was consistent with the presence of PVAc‐co‐acrylic in the ATO‐rich phase of the composite. The conductivity of the composite coatings followed a percolation power‐law equation, with the percolation threshold between 0.05 and 0.075 volume fractions of ATO and the critical conductivity exponent ranging from 1.34 to 2.32. The highest direct‐current conductivity of the composite coatings was around 10^?2 S/cm. The optical transmittance and scattering behavior of the coatings were also investigated. Compared with the PVAc‐co‐acrylic coating, the composite coatings had lower transparency because of the Rayleigh scattering. The transparency of the composite coatings was improved by a reduction in the coating thickness. The best transparency for the coatings with a direct‐current conductivity of approximately 10^?2 S/cm was around 85% at a wavelength of 600 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1744–1761, 2003     

Interactions among spherical poly(acrylic acid) brushes: Observation by rheology and small angle X‐ray scattering

Interactions among annealed spherical polyelectrolyte brushes (SPB) in concentrated aqueous dispersion under the effect of concentration, pH, and salt concentration are investigated by means of rheology, and small angle X‐ray scattering (SAXS). SPB consist of a solid polystyrene (PS) core and linear poly(acrylic acid) (PAA) chains densely grafted onto the core by one end. Rheological investigation demonstrates that the viscosity, the storage modulus G′ and the loss modulus G″ of SPB dispersion increase significantly upon increasing the SPB concentration and pH value which reflects the enhanced interactions among SPB. At high pH, a further increase in pH from 8 to 13 has almost no impact on the rheological properties and SAXS curves, while a “Uniform Shell Model” can fit the SAXS data very well probably due to the uniform filling of polyelectrolyte chains among SPB. When increasing the salt concentration from 10^?5 to 10^?3 M, the so‐called “polyelectrolyte peak” appears at middle to high q range in SAXS curves which means the overlapped polyelectrolyte chains are associated under the bridging effect of counterions, which disappears at higher salt concentration due to the screening effect of further added salts. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 405–413     

Effect of chain architecture on the phase transition of star and cyclic poly(N‐isopropylacrylamide) in water

The heat‐induced phase transition of aqueous solutions of Poly(N‐isopropylacrylamide) (PNIPAM) in water is examined for a four‐arm PNIPAM star (s‐PNIPAM), a cyclic PNIPAM (c‐PNIPAM), and their linear counterparts (l‐PNIPAM) in the case of polymers (1.0 g L^?1) of 12,700 g mol^?1 < M_n < 14,700 g mol^?1. Investigations by turbidity, high‐sensitivity differential scanning calorimetry (HS‐DSC), and light scattering (LS) indicate that the polymer architecture has a strong effect on the cloud point (T_c: decrease for s‐PNIPAM; increase for c‐PNIPAM), the phase transition enthalpy change (ΔH decrease for s‐PNIPAM and c‐PNIPAM), and the hydrodynamic radius of the aggregates formed above T_c (R_H: c‐PNIPAM < s‐PNIPAM < l‐PNIPAM). The properties of s‐PNIPAM are compared with those of previously reported PNIPAM star polymers (3 to 52 arms). The overall observations are described in terms of the arm molecular weight and the local chain density in the vicinity of the core of the star, by analogy with the model developed for PNIPAM brushes on nanoparticles or planar surfaces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2059–2068.     

Persistence of nematic liquid crystalline phase in a polyfluorene‐based organic semiconductor: A high pressure study

The role of high pressure on a low molecular weight nematic liquid crystalline organic semiconductor, ethyl‐hexyl substituted polyfluorene (PF2/6) is investigated using photoluminescence (PL), Raman scattering, and X‐ray scattering studies at pressures from 1 to 8 GPa. The PL and the Raman data under pressure are consistent with each other with no abrupt changes in the pressure coefficients of PL or Raman peaks. The PL energies redshift and broaden, consistent with both enhanced intra‐ and interchain interactions. The Raman peak positions yield pressure coefficients similar to other phenyl based π‐conjugated polymers. The broadening of a doublet peak in the 1135 cm^?1 region indicates a more planar backbone conformation with increasing pressure. X‐ray scattering indicates that the torsion angle between adjacent repeats reduces with increasing pressure and reverts back with decompression. The intermolecular structure is weakly ordered (frozen nematic) and essentially maintained with increasing pressure, in contrast to a high molecular weight PF2/6. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1014–1023     

Synthesis and characterization of cyclic P3HT as a donor polymer for organic solar cells

In this study, cyclic poly(3‐hexylthiophene‐2,5‐diyl) (c‐P3HT) with a controlled M_n was synthesized by the intramolecular cyclization of α‐bromo‐ω‐ethynyl‐functionalized P3HT via the Sonogashira coupling reaction. The effect of the cyclic structure, which does not have terminal groups of polymers, on the photoelectric conversion characteristics was investigated in comparison to linear P3HT (l‐P3HT). c‐P3HT was successfully synthesized with M_n ≈ 17,000, dispersity ≈ 1.2, and regioregularity ≈ 99%. The hole mobility was determined to be 5.1 × 10^?4 cm² V^?1 s^?1 by time‐of‐flight (TOF) experiment. This was comparable to that of l‐P3HT of 5.6 × 10^?4 cm² V^?1 s^?1. Organic solar cell systems were fabricated with each polymer by blending them with [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM). The l‐P3HT:PC₇₁BM system showed a dispersive TOF photocurrent profile for electron transport, whereas a nondispersive profile was observed for c‐P3HT:PC₇₁BM. In addition, an amount of collected electrons in c‐P3HT:PC₇₁BM was greater than that in l‐P3HT:PC₇₁BM for TOF experiments. The photoelectric conversion characteristics were improved by using c‐P3HT rather than l‐P3HT (power conversion efficiency [PCE] = 4.05% vs 3.23%), reflecting the nondispersive transport and the improvement of electron collection. PCEs will be much improved by applying this cyclic concept to highly‐efficient OSC polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 266–271     

Morphology of polyethylene–carbon black composites

Carbon black is a common polymer additive that is used for reinforcement and for its ability to enhance physical properties, such as conductivity. This article pertains to an X‐ray scattering (SAXS) study of a conductive grade of carbon black and carbon black–polymer composites. The scattering pattern for such blacks displays a surface‐fractal‐like power‐law decay over many decades in scattering vector q. It is often assumed that small‐angle scattering from carbon black aggregates can be described in terms of surface‐fractal models, related to particles with fractally rough surfaces. Such self‐similar surface roughness is usually easy to identify by microscopy; however, electron microscopy from these blacks fails to support this assumption. It is proposed here that this apparent surface‐fractal scattering actually represents a more complicated morphology, including overlapping structural features and a power‐law scaling of polydispersity. One use of conductive black–polyethylene composites is in circuit protection devices where resistive heating leads to a reversible association of carbon black aggregates that controls switching between a conductive and a nonconductive state. Scattering can be used as an in situ tool to observe the morphological signature of this reversible structural change. Scattering patterns support a model for this switching based on local enhancement of concentration and the formation of linear agglomerates associated with the matrix polymer's semicrystalline morphology. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1105–1119, 1999     

Charge density effects in salt‐free polyelectrolyte solution rheology

Solution rheology of 2‐vinyl pyridine and N‐methyl‐2‐vinyl pyridinium chloride random copolymers in ethylene glycol was studied over wide ranges of concentration and effective charge. The fraction of quaternized monomers α and the fraction of monomers bearing an effective charge f of these copolymers were measured using counterion titration and dielectric spectroscopy, respectively. Ethylene glycol is a good solvent for neutral poly(2‐vinyl pyridine), with very few ionic impurities. The viscosity η and relaxation time τ of dilute and semidilute unentangled solutions exhibit the scaling with concentration and effective charge expected by the Dobrynin model. Reduced viscosity data are independent of concentration in dilute solution, giving an intrinsic viscosity that depends on effective charge, and the experimental data obey the Fuoss law in the semidilute unentangled regime. Scaling concentration with the overlap concentration (c/c*) reduces these data to common curves, and c* ～ f ^?12/7 as predicted by the Dobrynin model, where f is the fraction of monomers bearing an effective charge. While the overlap concentration depends strongly on effective charge until counterion condensation occurs, the entanglement concentration c_e is surprisingly insensitive to effective charge, indicating that entanglement effects are not understood using the Dobrynin model. The terminal modulus G = η/τ depends only on the number density of chains G = ckT/N for c* < c < c_e, and G ～ c^3/2 for c > c_e independent of the effective charge. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2001–2013, 2006     

Rheology of (±)‐camphor‐10‐sulfonic acid doped polyaniline‐m‐cresol conducting gel nanocomposites

The rheological behavior of polyaniline‐(±champhor‐10‐sulfonic acid)_0.5‐m‐cresol [PANI‐CSA_0.5‐m‐cresol] gel nanocomposites (GNCs) with Na‐montmorillonite clay (intercalated tactoids) is studied. The shear viscosity exhibits Newtonian behavior for low shear rate (<2 × 10^?4 s^?1) and power law variation for higher shear rate. The zero shear viscosity (η₀) and the characteristic time (λ) increase but the power law index (n) decrease with increase in clay concentration. In the GNCs storage modulus (G′) and loss modulus (G″) are invariant with frequency in contrast to the pure gel. The G′ and G′ exhibit the gel behavior of the GNCs up to 105 °C in contrast to the melting for the pure gel at 75.7 °C. The percent increase of G′ of GNCs increases dramatically (619% in GNC‐5) with increasing clay concentration. The conductivity values are 10.5, 5.65, 5.51, and 4.75 S/cm for pure gel, GNC‐1, GNC‐3, and GNC‐5, respectively, promising their possible use in soft sensing devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 28–40, 2008     

Investigation on LCST behavior of a new amorphous/crystalline polymer blend: Poly(n‐methyl methacrylimide)/poly(vinylidene fluoride)

The liquid–liquid phase‐separation (LLPS) behavior of poly(n‐methyl methacrylimide)/poly(vinylidene fluoride) (PMMI/PVDF) blend was studied by using small‐angle laser light scattering (SALLS) and phase contrast microscopy (PCM). The cloud point (T_c) of PMMI/PVDF blend was obtained using SALLS at the heating rate of 1 °C min^?1 and it was found that PMMI/PVDF exhibited a low critical solution temperature (LCST) behavior similar to that of PMMA/PVDF. Moreover, T_c of PMMI/PVDF is higher than its melting temperature (T_m) and a large temperature gap between T_c and T_m exists. At the early phase‐separation stage, the apparent diffusion coefficient (D_app) and the product (2Mk) of the molecules mobility coefficient (M) and the energy gradient coefficient (k) arising from contributions of composition gradient to the energy for PMMI/PVDF (50/50 wt) blend were calculated on the basis of linearized Cahn‐Hilliard‐Cook theory. The kinetic results showed that LLPS of PMMI/PVDF blends followed the spinodal decomposition (SD) mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1923–1931, 2008     

Multiple melting behavior of poly(butylene succinate). I. Thermal analysis of melt‐crystallized samples

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were cooled from the melt (150 °C) at various cooling rates (CRs) ranging from 0.2 to 50 K min^?1. The peak crystallization temperature (T_c) of the DSC curve in the cooling process decreased almost linearly with the logarithm of the CR. DSC melting curves for the melt‐crystallized samples were obtained at 10 K min^?1. Double endothermic peaks, a high‐temperature peak H and a low‐temperature peak L, and an exothermic peak located between them appeared. Peak L decreased with increasing CR, whereas peak H increased. An endothermic shoulder peak appeared at the lower temperature of peak H. The CR dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of log(CR). T_m(L), T_re, and ΔH decreased almost linearly with log(CR), whereas T_m(H) was almost constant. Peak H decreased with the molecular weight, whereas peak L increased. It was suggested that the rate of the recrystallization decreased with the molecular weight. T_m(L), T_m(H), T_re, and T_c for the lowest molecular weight sample were lower than those for the others. In contrast, ΔH for the highest molecular weight sample was lower than that for the others. If the molecular weight dependence of the melting temperature for PBSu is similar to that for polyethylene, the results for the molecular weight dependence of PBSu can be explained. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2411–2420, 2002     

Kinetics and electron spin resonance study of the radical polymerization of n‐butyl acrylate mediated by a nitroxide precursor: C‐phenyl‐N‐tert‐butylnitrone

The C‐phenyl‐N‐tert‐butylnitrone/azobisisobutyronitrile pair is able to impart control to the radical polymerization of n‐butyl acrylate as long as a two‐step process is implemented, that is, the prereaction of the nitrone and the initiator in toluene at 85 °C for 4 h followed by the addition and polymerization of n‐butyl acrylate at 110 °C. The structure of the in situ formed nitroxide has been established from kinetic and electron spin resonance data. The key parameters (the dissociation rate constant, combination rate constant, and equilibrium constant) that govern the process have been evaluated. The equilibrium constant between the dormant and active species is close to 1.6 × 10^?12 mol L^?1 at 110 °C. The dissociation rate constant and the activation energy for the C? ON bond homolysis are 1.9 × 10^?3 s^?1 and 122 ± 15 kJ mol^?1, respectively. The rate constant of recombination between the propagating radical and the nitroxide is as high as 1.2 × 10⁹ L mol^?1 s^?1. Finally, well‐defined poly(n‐butyl acrylate)‐b‐polystyrene block copolymers have been successfully prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6299–6311, 2006     

Ionic aggregation in random copolymers containing phosphonium ionic liquid monomers

Copolymers of n‐butyl acrylate and phosphonium ionic liquid monomers possessing various alkyl substituents and counterions were synthesized through a combination of conventional free radical copolymerization and anion exchange. Differential scanning calorimetry and dynamic mechanical analysis provided the thermal and mechanical properties of these phosphonium cation‐containing random copolymers. Factors including alkyl chain length of phosphonium substituents, counterion type, as well as ionic concentration significantly influenced the association of phosphonium cations. Phosphonium ionomers with trialkyl substituents on phosphonium cations did not display the characteristic small‐angle X‐ray scattering peak, suggesting the absence of ionic clusters. However, low q peaks in wide‐angle X‐ray diffraction was indicative of significant concentration fluctuations wherein the ionic monomeric units associated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012