Dissolution of latex films after γ‐ray treatment

Latex films were prepared by annealing pyrene (Py)‐labeled poly(methyl methacrylate) particles at glass‐transition temperature (100°C). These films were then irradiated by γ‐rays from ⁶⁰Co in a gamma cell at room temperature at the same dose rate (rad/h) for 30 min. Before dissolution films were annealed at elevated temperatures for a 30‐min time interval to complete the film formation process. Steady‐state fluorescence (SSF) technique were used to monitor the dissolution of these irradiated latex films. The dissolution of films in chloroform–heptane (80–20%) mixture was monitored in real time by the Py fluorescence intensity change. Relaxation constants k₀ and desorption coefficients D_d of polymer chains were measured. It was observed that both D_d and k₀ values first increased and then decreased by increasing the annealing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 129–137, 2002     

Percolation cluster on partially dissolving polymer film

Steady state fluorescence (SSF) technique was used for studying dissolution of UV-induced polymer films. These films are formed from poly(methyl methacrylate) (PMMA) chains labeled with pyrene (P) which was introduced as a fluorescence probe to monitor the dissolution processes. PMMA films in various ethylene glycol dimethacrylate (EGDM) content, cured by UV radiation, were dissolved in chlorofrom-heptane (20-80%) mixtures. Dissolution of the films were monitored in real-time by the P fluorescence intensity change in the solvent reservoir. It is observed that P intensity decreased dramatically above a critical EGDM content, which was atributed to the formation of a percolation cluster. The measured percolation threshold, (p_c=0.25) was found to be in accord with the bond percolation model. Desorption coefficients, D_d were measured for films prepared with various EGDM content and it was observed that D_d values are much lower above p_c than below p_c.     

Dilute-solution structure of charged arborescent graft polymer

The solutions of charged G1 arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers in methanol-d4 and D₂O were investigated over a dilute concentration range ?=0.005-0.05 (?: mass fraction) using small-angle neutron scattering (SANS). Upon addition of acid (HCl) arborescent graft polymers became charged and a peak appeared in SANS data. The interparticle distance (d_exp) calculated from a peak position corresponded to the expected value (d_uni) for a uniform particle distribution. This indicates the formation of liquid-like ordering due to long-range Coulombic repulsions. The smaller dielectric constant of methanol-d4 resulted in long-range electrostatic repulsions persisting to lower polymer concentration than in D₂O. The slow mode scattering was observed by dynamic light scattering measurements for the same polymer solutions, indicating the presence of structural inhomogeneity in the solutions. Both the peak and slow mode disappeared by addition of NaCl or excess HCl into the solutions due to the screening of electrostatic interactions. The G1 polymer grafted with longer P2VP chains (M_w∼30,000 versus 5000 g mol) formed a gel on addition of HCl. This result reveals that molecular expansion is more significant for arborescent polymers with longer (M_w∼30,000) linear polyelectrolyte branches, resulting in gelation for ?>0.01. Upon addition of NaCl or excess HCl a gel transformed back to a liquid resulted from the screening of electrostatic interactions.     

In situ fluorescence experiments for real-time monitoring of annealed high-T latex film dissolution

A new technique, based on steady-state fluorescence measurements, is introduced for studying dissolution of polymer films. These films are formed from naphthalene and pyrene labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by polyisobutylene. Diffusion of solvent (chloroform) into the annealed latex film was followed by desorption of polymer chains. Annealing was performed above T_g at various temperatures for 30-min time intervals. Desorption of pyrene labeled PMMA chains was monitored in real time by the pyrene fluorescence intensity change. Desorption coefficients were found to be between 1 and 4 × 10⁻¹⁰ cm²/s and two different dissolution mechanisms were detected. © 1996 John Wiley & Sons, Inc.     

Semidilute solutions of poly(methacrylic acid) in the absence of salt: Dynamic light-scattering study

Water solutions of poly(methacrylic acid) of molecular weight M_w = 3.0 × 10⁴ and M_w = 4.0 × 10⁵, neutralized with NaOH, were investigated by photon correlation spectroscopy. At a low degree of neutralization α, the short-time decay only is observed. When α > 0, a second, much slower, process becomes noticeable. It gains quickly in influence when α increases. The reciprocal values of characteristic relaxation times for both dynamic processes were found to decrease linearly with the square of the scattering vector, showing that both processes are diffusive. The following interpretation of these processes founded on the concentration and angle dependences of the corresponding diffusion coefficients and scattering amplitudes is given: (1) for the low-molecular-weight sample (M_w = 3.0 × 10⁴), D_∫ (fast process) and be attributed to the Nernst-Hartley diffusion coefficient of polyions, and D_s (slow process) to a diffusion of interchain domains (clusters) with a radius of gyration R_G ≈ 50 nm; (2) for the high-molecular-weight sample (M_w = 4.0 × 10⁵), where an overlap of polymer chains occurs, D_f can be attributed to a cooperative diffusion coefficient reflecting the concentration fluctuations due to the polyions and counterions, and D_s to slow concentration fluctuations having a large correlation length (≈ 100 nm). The existence of two diffusive modes in salt-free solutions of polyelectrolytes cannot be explained within the framework of the scaling approach as proposed by de Gennes and Odijk.     

Fluorescence technique to study thickness effect on dissolution of latex films

In situ steady‐state fluorescence (SSF) measurements were used for studying dissolution of Latex films in real time. Latex films with various thicknesses are formed from pyrene (P) labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by polyisobutylene (PIB). Annealing of latex films were performed above T_g at 220°C temperature for 60 min. UV‐Visible (UVV) spectrometer was used to measure the transparency of latex films. It was observed that thicker films formed more opaque films than thinner films. Heptane (20%), chloroform (80%) mixture was used as a dissolution agent. Diffusion of pyrene labeled PMMA chains was monitored in real time by the change of pyrene fluorescence intensity, I_P in the polymer‐solvent mixture. Diffusion coefficients, D, and relaxation constants, k₀, of PMMA chains were measured and found to be strongly dependent on the latex films thicknesses. It is observed that thicker and opaque films dissolved much faster than the thinner and transparent films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1087–1095, 2000     

Craze microstructure and molecular entanglements in polystyrene-poly(phenylene oxide) blends

Polystyrene and poly(phenylene oxide) are miscible over the entire range of compositions. Thin films of five blends of high molecular weight polystyrene (PS) with high molecular weight poly(phenylene oxide) (PPO), and four blends of low molecular weight PS (whose molecular weight lies below its entanglement molecular weight M_e) with the same PPO have been prepared. Following bonding of these films to copper grids, crazes were grown by uniaxial straining in air. Suitable crazes were then observed by transmission electron microscopy. From microdensitometry of the image plates it is possible to measure the extension ratio λ_craze within crazes in the nine blends. These measured values are compared with predicted values of λ_max, computed from λ_max = I_ed, where I_e is the chain contour length between entanglements and d is the root mean square end-to-end distance for a chain of molecular weight M_e. For the high molecular weight PS blends λ_max depends on the entanglement properties of both PS and PPO chains. For the low molecular weight PS blends, the PS chains cannot form part of the entanglement network and the correct value of λ_max is obtained from appropriate scaling of the pure PPO value. Comparison of λ_craze and λ_max for both types of blends shows excellent agreement, demonstrating the importance of the entanglement network in determining craze parameters and hence the toughness of a given polymer.     

Modelling the post treatment process of model implants prepared by in situ polymerized poly(ε-caprolactone) using a BF3-glycerol catalyst system

The post treatment process of a poly(ε-caprolactone) (PCL) model implant prepared using a boron trifluoride (BF₃) catalyst and glycerol initiator by in situ polymerisation process for craniofacial and maxillofacial treatment is modelled using a ‘moving-boundary’ diffusion model. A numerical method was used to solve a system of diffusion equations of the model. The variable diffusion coefficient (D) was correlated with crystallinity (x_c) of the polymer which is a function of its molecular weight (M_w) and its degradation rate constant (k_d), D=f(x_c(M_w,k_d)). The post treatment time and the molecular weight retained after post treatment can be obtained using this model. The modelling results show that the process is potentially suitable for manufacturing thin model implants of complex shape.     

Molecular weight effect on polymer dissolution: a steady state fluorescence study

In situ steady state fluorescence (SSF) technique was used to study the dissolution of disc-shaped polymer glasses in various molecular weights, M_W. The glass discs were formed by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the dissolution process in chloroform. Desorption of poly(methyl methacrylate) (PMMA) chains from discs were monitored simultaneously by observing the change of P fluorescence intensity, I. Diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It is observed that desorption coefficient, D decreased by increasing molecular weight, M_W by obeying D≈M⁻¹ law.     

Grafted polytriphenylamines synthesized by atom transfer radical polymerization in tandem with oxidative polycondensation

Arylamine polymers are among the most studied conducting polymers due to a whole range of interesting properties and applications. In this paper, we describe the synthesis of soluble and processable electroactive poly(triphenylamine-g-oligostyrene) by two polymerization methods in tandem. In the first step, oligostyrene macromonomers with well-defined molecular weight, polydispersity and chain-end functionality were obtained by radical-controlled polymerization (i.e., atom transfer radical polymerization, ATRP) of styrene. The styrene oligomerization was carried out using a new triphenylamine-based initiator, [4-(diphenylamino)benzyl 2-bromo-2-methylpropanoate], cuprous bromide as co-initiator and bipyridine as ligand, at 100 °C, in bulk. Using two feed molar ratios of components: [styrene]₀:[initiator]₀:[CuBr]₀:[bipyridine]₀, two macromonomers with M _n = 9,900; M _w/M _n = 1.25 and M _n = 3,460; M _w/M _n = 1.22, respectively, were synthesized. The presence of triphenylamine moiety at one end of the macromonomer allowed the chemical and electrochemical polymerization of macromonomers to polytriphenylamine brushes having short oligostyrene grafts in every structural unit. The oligostyrene substituents confer processability and good solubility in common organic solvent characteristics for polystyrene while preserving the optoelectronic properties of arylamine-conjugated main chain. The chemical oxidative polymerization of macromonomer was carried out using iron (III) chloride dissolved in nitrobenzene. The redox behavior of the initiator, macromonomer and graft polymer was investigated by cyclic voltammetry. In all cases, it was observed that the reversible oxido-reduction of arylamine sites was accompanied by irreversible oxidative electropolymerization by free-para positions of triphenylamine substituents and deposition of thin films on working electrode. The structures of the initiator, macromonomers and graft copolymers were determined by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy. The absorption and fluorescence spectroscopy have revealed absorption and emission maxima characteristics for triphenylamine group. DSC studies have confirmed glass transitions characteristics for styrene oligomers.     

Fluorescence response from anthracene labeled polystyrene to study its thermal transitions

In this work, thermal transitions of polystyrene, PS, were studied as a function of molecular weight (M_w) and thermal history using the fluorescence response of anthracene chemically bonded to the polymer chain ends. For each PS sample the fluorescence spectra of the anthracene were collected as a function of temperature in cycles of heating and cooling. Two photophysical parameters were selected in order to study thermal transitions of the PS samples: (i) the first moment of the fluorescence band, 〈ν〉; and (ii) the integrated fluorescence intensity, I. In every case, a sharp change in the photophysical parameter was observed at a certain temperature that was assigned to the α relaxation temperature and which was clearly different depending on the PS molecular weight and the thermal history. In fact, the relaxation temperature increased with M_w during a heating scan, decreased with M_w during a cooling scan and was clearly lower in the cooling scans. These results were interpreted in terms of a reorientation of the anthryl groups to the surface of the polymer.     

Real time monitoring of latex film dissolution by UVV technique

UV–visible (UVV) technique is used for monitoring of polymer film dissolution. These films are formed from pyrene (P)‐labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by poly isobutylene (PIB, Annealing of films was performed above T_g at various temperatures for 30‐min time intervals. Diffusion of solvent molecules (chloroform) into the annealed latex film was followed by desorption of PMMA chains. Desorption of P‐labeled PMMA chains was monitored in real time by the absorbance change of P in the polymer–solvent mixture. A diffusion model with a moving boundary was used to quantify real time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10⁻¹¹ cm² s⁻¹ in the 100 and 275°C temperature range. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1075–1082, 2000     

Catalytic Cu(II)–polymer complexes as recyclable catalysts for the synthesis of poly(2,6-dimethyl-1,4-phenylene oxide)s in water

Water-soluble polymers comprising itaconic amide acid with acrylic acid or acrylamide, which contain carboxylic acid and amide groups capable of coordinating to the copper catalyst, were synthesized by radical polymerization using an azobisisobutyronitrile initiator. These polymers were used as polymer ligands to prepare copper complexes, which were subsequently analyzed by UV–Vis spectroscopy. The complexes were then used as catalysts for the oxidative polymerization of 2,6-dimethylphenol (DMP) to synthesize poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) under oxygen and in the presence of a surfactant in alkaline water. The polymerization conditions were optimized by varying the amounts of polymer ligands and copper precursors, the concentrations of surfactant and hydrogen chloride, and the temperature, resulting in PPO with a maximum yield of 93%, a number-average molecular weight (M _n) of 3700, and a molecular weight distribution (M _w/M _n) of 2.12. This yield is higher than that previously achieved using arginine ligand in water (72%). Furthermore, the optimum conditions were applied in the copolymerization of DMP and 2-allyl-6-methylphenol to obtain a thermally crosslinkable copolymer in 95% yield (M _n = 3000, M _w/M _n = 2.5). In addition, the catalyst complex of the copper–polymer ligand was recovered and reused after the polymerization of DMP. The catalyst maintained its activity even after being recycled five times, without the addition of copper precursor or polymer ligand, thereby demonstrating an environmentally friendly process wherein environmental emissions and production costs can be substantially reduced.     

Studies on bulk diffusion and local diffusion of polystyrene in melt

Results of bulk viscosity (η) and local viscosity (ξ) of various molecular weights of polystyrene (PS) have been reported. In this paper the relationship between η and bulk diffusion coefficient (D_B), and that between ξ and local diffusion coeffizient (D_L) are presented. Data obtained lead to several conclusions. From the results of unperturbed dimensions and a universal constant (Φ), it was found that F. Bueche's equation D_B · η = const. is valid for polystyrenes with molecular weights over 600. Temperature and component concentration dependence of bulk diffusion coefficient for the two-component blend system may be interpreted in terms of the free volume theory. At an iso-free volume state, molecular weight dependences of bulk diffusion coefficients for both PS of narrow distribution of molecular weight and blend PS can be composed to a single curve, which is composed of two straight lines in a double logarithmic presentation with intersection at M_w = 1.78 × 10⁴ g/mol. The slopes of these two lines were ? 1.0 and ? 3.3, respectively. The product D_L · ξ was determined to be 1.10 × 10^?7 (c.g.s) for n-paraffines from the data of self-diffusion coefficient and ξ. This made it possible to determine D_L from ξ. For higher molecular weights of PS, log D_B is a linear function of log M_w while log D_L stays almost constant.     

The effect of solid content on latex coalescence and film formation: Steady-state energy transfer study with fluorescence labeled polymers

The steady-state fluorescence technique was used to examine the healing and interdiffusion of polymer molecules as a function of solid content during annealing of latex films above the glass transition (T_g). Films were prepared from a mixture of naphthalene (N)- and pyrene (P)-labeled poly(methy methacrylate) (PMMA) latex particles. Above T_g, interdiffusion of polymer chains was observed by detecting the steady-state energy transfer from excited naphthalene to pyrene molecules. Various latex films with different latex content were used to measure the critical occupation percent for the reliable steady-state fluorescence measurements. Diffusion activation energies in these latex films were measured and found to be around 30 kcal/mol, which was attributed to the backbone motion of PMMA chains. © 1996 John Wiley & Sons, Inc.     

Effect of morphology on shear viscosity for binary blends of polycarbonate and polystyrene

The structure and rheological properties of binary blends of polycarbonate (PC) and polystyrene (PS) were investigated using various PS samples with different molecular weights, namely PS1k (M_w = 1,000), PS53k (M_w = 53,000), and PS240k (M_w = 240,000). The blends with PS53k and PS240k show phase-separated structures, whereas the blend with PS1k is miscible. The shear viscosity decreases greatly on addition of PS53k and PS240k, especially at high shear rates, which would be a great advantage at processing operations. Because the nonlinear response occurs in the small strain region for multilayered films of PC and PS240k, the origin of the significant viscosity drop for the phase-separated system is interfacial slippage at the phase boundary.     

Comparison of dissolution and mutual diffusion coefficients during dissolution of poly(methyl methacrylate) films

Steady state fluorescence measurements have been used for studying the dissolution of polymer films. These films are formed by free radical polymerization of methyl methacrylate (MMA) in which pyrene ( P_y ) was introduced as a fluorescence probe. Dissolution of poly(methyl methacrylate) (PMMA) films in chloroform–heptane mixtures were monitored in real-time by the P_y fluorescence intensity change. Dissolution coefficients D_d of P_y molecules were measured during dissolution of PMMA films, and found to be about 10⁻⁶ cm² s⁻¹. After dissolution, fluorescence quenching measurements were performed and the Stern–Volmer equation was employed to measure the mutual diffusion coefficients of heptane (D_h) and P_y (D_Py) molecules; these were found to be about 10⁻⁵ cm² s⁻¹. © 1999 Society of Chemical Industry     

Solubility and diffusion in latex films formed from high glass transition temperature particles

In situ steady-state fluorescence measurements were used to study the dissolution of polymer films. These films were formed from pyrene labeled poly(methyl methacrylate) (PMMA) latex particles that were sterically stabilized by polyisobutylene. Annealing was performed above the glass transition temperature at 180°C at 1-h time intervals for film formation. Desorption of pyrene labeled PMMA chains was monitored in real time by the change of pyrene fluorescence intensity. Dissolution experiments were performed in various solvents with different solubility parameters, δ, at room temperature. Diffusion coefficients, D, in various solvents were measured and found to be around 10⁻¹⁰ cm²/s. A strong relation between D and δ was observed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1493–1502, 1998     

Photon transmission method for studying film formation from polstyrene latexes with different molecular weights

A photon‐transmission method was used to probe the evolution of transparency during film formation from polystyrene (PS) particles with different molecular weights. The latex films were formed at room temperature from the PS particles having two different average molecular weights and annealed at elevated temperatures in various time intervals above the glass transition (T_g). Onset temperatures (T_H) at given times (τ_H) for the optical clarity of films formed from low (LM) and high molecular (HM) weight PS particles were used to calculate the healing activation energies for the minor chains and found to be 22.0 ± 0.5 and 27.0 ± 0.6 kcal/mol, respectively. The increase in the transmitted photon intensity, I_tr, above the T_H was attributed to increase in the number of interfaces that disappeared. The Prager–Tirrell (PT) model was employed to interpret the increase in crossing density at the junction surface. The backbone activation energies (ΔE) were measured and found to be 127.8 ± 2.5 kcal/mol for a diffusing polymer chain across the junction surface for LM and HM latex films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 866–874, 2000     

Influence of polymer microstructure on the performance of post‐treated latex‐based pressure sensitive adhesives

Latex‐based butyl acrylate (BA)/acrylic acid (AA)/2‐hydroxyethyl methacrylate (HEMA) pressure sensitive adhesive (PSA) films with various microstructures were heated to improve their performance. The treated PSA films showed significantly better performance than original latex‐based PSA films with similar polymer microstructures. The effect of the heat treatment depended on the polymer microstructure of the untreated PSA films (or corresponding latices). Decreasing the amount of very small sol polymers (i.e., M_x < 2M_e) in gel‐free untreated PSA films, or both very small (i.e., M_x < 2M_e) and very large sol polymers (i.e., M_x > 20M_e) in gel‐containing untreated PSA films led to treated PSA films with significantly better performance. (Note: M_e is the molecular weight between two adjacent entanglement points in a polymer material.) In addition, simultaneously increasing the sol polymer molecular weight (M_w) as well as the size of the chain segments between two adjacent cross‐linking points (M_c) of the gel polymer in the original PSAs resulted in treated PSA films with better performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012