On the continuity of the diffusion behaviour at amorphous polymer–polymer interfaces on both sides of the bulk glass transition temperature

The diffusion behaviour at amorphous polystyrene (PS)–PS interfaces has been investigated over an interval of temperatures (T) from below to above the bulk glass transition temperature (T _g ^bulk) using the Arrhenius and Vogel-Fulcher approaches. No discontinuity in the variation of the logarithm of the diffusion coefficient versus 1/T has been observed when going through the PS T _g ^bulk over a broad interval of T, from T _g ^bulk???50 °C to T _g ^bulk?+?50 °C. The molecular mechanism of interdiffusion has been discussed.     

Inclusion of the regioisomeric nitrobenzene derivatives and ferrocene guests by β-cyclodextrin polymer and their transport through the polymer matrix

Host-guest equilibria have been investigated involving inclusion sites of the microparticulate amorphous β-cyclodextrin polymer, β-CDP-25, and a range of redox guests comprising regioisomeric nitrobenzene derivatives and ferrocene. The equilibria were studied by the batch method. Inclusion-governed, Langmuir-type sorption equilibria occurred in the β-CDP-25/guest systems studied in 1:1 (v/v) aqueous methanolic solutions. A 1:1 (host inclusion site)/guest stoichiometry was found and sorption equilibrium constants were determined. The values of the constants changed by a factor of 20 between the most weakly and strongly included guests. Regioselective discrimination of β-CDP-25 was most pronounced with respect to nitrophenols. Transport phenomena of guest molecules in the β-CDP-25 matrix have also been studied. The apparent diffusion coefficients of guest molecules were determined in the β-CDP-25 matrix by chronamperometry at the (β-CDP-25)-PTFE-carbon composite electrodes. These diffusion coefficients were almost four orders of magnitude lower than the corresponding coefficients of guest molecules in solution in the absence of β-CD. The diffusion mechanism was postulated for the guest molecules in the β-CDP-25 matrix, which invoked hopping of the molecules between inclusion sites.     

What is the unperturbed state in polymer solutions?

We report theoretical results about amphiphilic random copolymers in a quasi‐ideal conformation with an overall size very close to that of the analogue homopolymers. We found that a few states may coexist with about the same free energy and a similar radius of gyration, but with different intramolecular conformations. We also argue that, in most cases, amphiphilic copolymers may never achieve the unperturbed Θ state, defined thermodynamically by a vanishing second virial coefficient. Thus, we suggest that such copolymers usually show neither an unperturbed conformation nor an unperturbed state from the thermodynamic viewpoint. We also briefly discuss star homopolymers, which show a depression of the Θ temperature with respect to linear chains and a significant, though finite, Θ swelling, as well as linear chains in the Θ state and in the melt. The main general conclusion is that interactions between chain segments do not cancel each other and are non‐negligible. Accordingly, we suggest that the word "unperturbed" be used only with reference to solution thermodynamics and not for the chain size or conformation.     

An important biodegradable polymer – polylactone-family polymer

Systemic investigation on the synthesis and properties of aliphatic polylactones were carried out. And various materials were obtained with different degradation rates and mechanical properties. Two in vivo experiments were presented in this study to envision the biomedical applications of this kind of aliphatic polylactones.     

Reviewing extrapolation procedures of the electronic properties on the π-conjugated polymer limit

In this article, the extrapolation procedures of π-π* electronic transition energy on π-conjugated oligomers are reexamined. Different models, including the simplest coupled oscillator, the free electron, the Hückel approach, the molecular exciton model, and some specific fitting-functions, are compared using the transition energies derived from theoretical calculations on three thiophene-based oligomer series. Specifically, oligomers of up to 30 repeating units have been considered to include the saturation effects as a function of chain length. The coupled oscillator model of W. Kuhn and the fitting-function of Hirayama are the models that present the better suit on the transition energy interpolation as a function of chain length. Using only the first four oligomers of the series (n = 2 up to 8) yields an estimation of the transition energy on the polymer limit with an average error of ～1.5%. The vertical and adiabatic ionization potential present a better fit with the Hückel model approach. Finally, implications of the environmental polarity on the electronic properties, molecular geometry, charge distribution, and aromaticity are shortly discussed.     

On the scaling law of the evolution of lap-shear strength with healing temperature at amorphous polymer−polymer interfaces and surface glass transition

The evolution of lap-shear strength (σ) with healing temperature T _h at symmetric and asymmetric amorphous polymer−polymer interfaces formed of the samples with vitrified bulk has been investigated. It has been found that the square root of the lap-shear strength behaves with respect to healing temperature as σ ^1/2 ~ T _h both at symmetric and asymmetric interfaces. Basing on this scaling law between σ and T _h, the values of the surface glass transition temperature ( T_g^surface ) \left( {T_{\rm{g}}^{\rm{surface}}} \right) have been estimated for a number of amorphous polymers by the extrapolation of the experimental curves σ ^1/2 ~ T _h for symmetric polymer−polymer interfaces and, in some cases, for asymmetric, both compatible and incompatible, polymer−polymer interfaces, to zero strength. A significant reduction in surface glass transition temperature T_g^surface T_{\rm{g}}^{\rm{surface}} with respect to the glass transition temperature of the polymer bulk ( T_g^bulk ) \left( {T_{\rm{g}}^{\rm{bulk}}} \right) , reported earlier, has been confirmed by the use of the new proposed approach. The quasi-equilibrium surface glass transition temperature T_g^surface T_{\rm{g}}^{\rm{surface}} of amorphous polystyrene (PS) has been predicted in the framework of an Arrhenius approach using the plot “logarithm of healing time − reciprocal surface glass transition temperature T_g^surface￠￠ T_{\rm{g}}^{\rm{surface}}\prime \prime and the activation energy of the surface alpha-relaxation of PS has been calculated.     

What is the flow activation volume of entangled polymer melts?

We evaluate the flow activation volume in polymer melts of isotactic polypropylene and atactic polystyrene with step-shear experiments at different melt temperatures. The melt is initially sheared with constant shear rate until the attainment of a melt state with nearly constant viscosity. Perturbations to this experiment, involving shear steps in short-time intervals with decreasing rates, are induced next. Measurements of the shear stress value at each shear rate step allow the evaluation of an experimental (apparent) flow activation volume. The true flow activation volume is evaluated by extrapolating the experimental data to infinite shear stress values. The value obtained is larger than the physical volume of the chain and agrees with the volume of a tube confining chains with a molecular weight between M _n and M _w. Besides supporting the validity of tube model, experiments based on this protocol may be used on model polymer samples, in composites with nanoparticles and in polymer blends to access the validity of mechanisms considered by flow models.     

Studies on the synthesis and properties of malachite green imprinted polymer

A new molecularly imprinted polymer was synthesized with malachite green (MG) as molecular template, methacrylic acid (MAA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and azobisisobutyronitrile (AIBN) as initiator. Recognition properties of the MG imprinted polymer were studied by equilibrium adsorption and HPLC. The results showed that the imprinted polymer had good affinity and marked selectivity for MG, and can separate MG with its analogue commendably. The new polymer can be used for the enrichment of MG in complex sample, and can work as separation media to separate and detect MG by HPLC.     

Novel polymer system for molecular imprinting polymer against amino acid derivatives

Molecular imprinting polymers (MIPs) against N-Cbz-L-Tyr were prepared utilizing different polymer systems and evaluated in HPLC mode. It was found that MEP utilizing cocktail functional monomers, acrylamide 2-vinylpyridine showed better molecular recognition and better separation ability for the template molecule than those utilizing other functional monomers. MIP utilizing trimethylolpropane trimethacrylate as cross-linker showed higher load capacity and separation factor than those utilizing ethylene glycol dimethacrylate as cross-linker. Increasing the concentration of competing solvent, acetic acid weakened the ionic interaction and hydrogen bonding between the analyte and the functional monomers, 2-vinylpyridine and acrylamide, when the template enantiomer was separated by HPLC. Therefore increasing of the concentration of acetic acid leads to decreasing of capacity factor, separation factor and resolution.     

Fracture of polymer interfaces: what are the relevant length scales?

While it is tempting to relate directly the molecular structure of an interface (between glassy or between semi‐cristalline polymers) with its fracture toughness, these two parameters are simply the two end‐points of a complex network which needs to be understood in order to control the mechanical strength of the interface. The important mechanisms occur at three different length scales: the molecular scale (stress‐transfer across the interface), the microscopic scale (plastic deformation at the crack tip) and the macroscopic scale (loading geometry and elastic constants of the polymers). The couplings existing between these length scales in glassy polymer interfaces are reviewed in this paper in light of the latest experimental studies.     

Thermodynamic aspects of the heterogeneous structure of “golf-ball-like” polymer particles

Recently, we found that “golf-ball-like” polystyrene (PS)/poly(butyl acrytlate) composite particles could be produced by seeded emulsion polymerization of butyl acrylate with PS seed particles. In this article, the theoretical and experimental thermodynamic instabilities of the golf-ball-like structure are discussed and are compared with core-shell and hemispherical morphologies. Received: 2 February 1999 Accepted in revised form: 3 June 1999     

Production of polymer microparticles by “dissolution” of submicron-sized water-insoluble ionized carboxylated polymer particles in the presence of various nonionic emulsifiers

Styrene-butyl acrylate-methacrylic acid terpolymer (50.4/40.9/8.7, molar ratio) particles, 276 nm in diameter, were produced by emulsifier-free emulsion terpolymerization. The emulsifier-free carboxylated terpolymer particles did not dissolve in water even under alkaline condition. However, they dissolved in the presence of nonionic emulsifier under alkaline condition, resulting in polymer microparticles having diameter less than 40 nm. Such a dissolution behavior was examined using five kinds of different polyoxyethylene nonylphenylether nonionic emulsifiers having hydrophilic-lipophilic balance values between 12.2 and 17.5 at various initial pH values, temperatures and times, and its mechanism was discussed.Part CXLIV of the series Studies on Suspension and Emulsion.     

Topology change by screening the electrostatic interactions in a polymer–surfactant system

We show that a neutral polymer (PEG) induces a topology transition of the bilayers of an ionic surfactant system (SDS–hexanol–brine), provided that the electrostatic interactions between membranes are screened. Hexanol is used as a cosurfactant in order to get a lamellar or a sponge phase, depending on the cosurfactant/surfactant mass ratio. Using brine as solvent, the addition of polymer triggers a transformation between flat or saddle-like bilayers into vesicles. This modification is not observed in pure water because of the electrostatic repulsion between membranes. The effect can be understood in terms of the modification of the membrane Gaussian modulus due to polymer adsorption and of the entropy gain of the adsorbed polymer when the membrane bends to form a vesicle.     

Research on association between multi-sticker amphiphilic polymer and water-soluble β-cyclodextrin polymer

The host cyclodextrin polymer-P(AM/A-β-CD/NaA) is prepared by redox free-radical copolymerization. Additionally, the multi-sticker amphiphilic polymer-P(AM/BHAM/NaA) as a guest polymer is synthesized using micellar polymerization. The copolymer structures are characterized by ¹H NMR. Subsequently, all the polymers and inclusion complexes are evaluated in terms of apparent viscosity, optical absorption spectra and rheological property. The results indicate that the inclusion association between the cyclodextrin group (CD) and multi-sticker hydrophobic monomer (BHAM) is in accordance with ternary interaction (CD/BHAM?=?2:1). Because of the inclusion association between the host and guest polymers, the solution of inclusion complex has much higher viscoelasticity even under the low amphiphilic polymer concentration. When the molar ratio of CD to BHAM is 1:1, the critical aggregation concentration (CAC) of the inclusion complex solution still remains. Furthermore, above the CAC, two types of associations, inclusion association and inter-molecular hydrophobic association, can occur in the complex solution and these interactions were also verified by fluorescence spectroscopy and atomic force microscopy (AFM). In this paper, the inclusion rule of cyclodextrin polymer with the multi-sticker amphiphilic polymer is discussed, and the rule of the enhanced solution viscosity is further explored.     

How does solvent molecular size affect the microscopic structure in polymer solutions?

Monte Carlo simulation has been used to investigate the effects of linear solvent molecular size on polymer chain conformation in solutions. Increasing the solvent molecular size leads to shrinkage of the polymer chains and increase of the critical overlap concentrations. The root-mean-square radius of gyration of polymer chains (R(g)) is less sensitive to the variation of polymer concentration in solutions of larger solvent molecules. In addition, the dependency of R(g) on polymer concentration under normal solvent conditions and solvent molecular size is in good agreement with scaling laws. When the solvent molecular size approaches the ideal end-to-end distance of the polymer chain, an extra aggregation of polymer chains occurs, and the solvent becomes the so-called medium-sized solvent. When the size of solvent molecules is smaller than the medium size, the polymer chains are swollen or partially swollen. However, when the size of solvent molecules is larger than the medium size, the polymer coils shrink and segregate, enwrapped by the large solvent molecules.     

Collagen-like peptides and peptide–polymer conjugates in the design of assembled materials

Collagen is the most abundant protein in mammals, and there has been long-standing interest in understanding and controlling collagen assembly in the design of new materials. Collagen-like peptides (CLPs), also known as collagen-mimetic peptides (CMPs) or collagen-related peptides (CRPs), have thus been widely used to elucidate collagen triple helix structure as well as to produce higher-order structures that mimic natural collagen fibers. This mini-review provides an overview of recent progress on these topics, in three broad topical areas. The first focuses on reported developments in deciphering the chemical basis for collagen triple helix stabilization, which we review not with the intent of describing the basic structure and biological function of collagen, but to summarize different pathways for designing collagen-like peptides with high thermostability. Various approaches for producing higher-order structures via CLP self-assembly, via various types of intermolecular interaction, are then discussed. Finally, recent developments in a new area, the production of polymer–CLP bioconjugates, are summarized. Biological applications of collagen contained hydrogels are also included in this section. The topics may serve as a guide for the design of collagen-like peptides and their bioconjugates for targeted application in the biomedical arena.     

Materials for polymer electronics applications – semiconducting polymer thin films and nanoparticles

The paper presents two different approaches to nanostructured semiconducting polymer materials: (i) the generation of aqueous semiconducting polymer dispersions (semiconducting polymer nanospheres SPNs) and their processing into dense films and layers, and (ii) the synthesis of novel semiconducting polyfluorene-block-polyaniline (PF-b-PANI) block copolymers composed of conjugated blocks of different redox potentials which form nanosized morphologies in the solid state.     

What is the role of the interfacial interaction in the slow relaxation of nanometer-thick polymer melts on a solid surface?

At the nanoscale and interfaces, the relaxation behavior of polymer melts, which affects the polymer's long-term performance in many important applications, is very different from that in the bulk. The role of polymer-substrate interfacial interaction, which does not have a bulk counterpart, has not been fully understood to date. In this study, the relaxation of nanometer-thick perfluoropolyether melts on a silicon wafer has been investigated by water contact angle measurement. The polymer-substrate interactions have been systematically changed by tailoring the polymer structure to clarify the effect of the interfacial interaction. The experimental results show that (1) when there is attractive interaction at the interface, some polymers are anchored to the substrate and others are free, (2) the attractive interfacial interaction drives the free polymers to relax at the interface, and (3) the relaxation is much slower than in the bulk, which has been attributed to the low mobility of the anchored polymer chains and the motional cooperativity between anchored and free polymer chains in the nanometer-thick films.