Macromolecular Segments Research Articles

Nonisothermal crystallization behavior and kinetics of poly(l-lactide-co-propylene carbonate)

Poly(l-lactide-co-propylene carbonate) was synthesized via the terpolymerization of l-lactide, CO2 and propylene oxide using zinc carboxylates as catalyst. The nonisothermal crystallization behavior and kinetics of the samples with and without catalyst residual were investigated using differential scanning calorimetry. Both the peak of melt crystallization temperature (T p) and the enthalpy of the cold crystallization process (∆H) decrease with increasing PC content. Avrami–Jeziorny model, Owaza model and Mo model were used to describe the crystallization process. Avrami–Jeziorny analysis presents the crystallization kinetics, while neither the Ozawa nor the Mo model could successfully describe them. Kissinger’s method was finally employed to calculate the activation energy for the transport of the macromolecular segments to the growing crystal surface. The results show that the existence of catalyst within polymer sample and increased PC content lead to an increase of energy barrier.

X-ray investigations of proton irradiation induced structure development in polyester fibers

The role of proton irradiation on the structural changes in partially crystalline poly (ethylene terephthalate) (PET) fibres has been investigated using a wide-angle X-ray scattering (WAXS). Experimental data about the influence of the exposure dose and the irradiation conditions in the processes of destruction and crosslinking in the irradiated objects have been obtained. The structural changes and the packing density of the macromolecular chain segments of the poly (ethylene terephthalate) filaments irradiated with different doses have been analyzed. A mechanism of the structural reorganization initiated by the irradiation has been supposed on the basis of the changes in the geometry of the intensity distribution of the X-ray diffraction patterns of the studied objects.

EFFECT OF PROTON IRRADIATION ON THE STRUCTURE DEVELOPMENT OF POLYETHYLENE TEREPHTHALATE FIBERS

The influence of proton irradiation on the structural changes in partially crystalline poly(ethylene terephthalate) (PET) filaments has been investigated using a wide-angle X-ray scattering (WAXS). Experimental data about the role of the exposure dose and the irradiation conditions in the processes of destruction and crosslinking in the irradiated objects have been obtained. The structural changes and the packing density of the macromolecular chain segments of the polyethylene terephthalate filaments irradiated with different doses have been analyzed. A mechanism of the structural reorganization initiated by the irradiation has been supposed on the basis of the changes in the geometry of the intensive distribution of the X-ray diffraction patterns of the objects.

Temperature and frequency analysis of the dynamical visco–elastic properties of high–density polyethylene

The behaviour of the dynamical visco–elastic functions in high–density polyethylene (HDPE), which carries the trade mark 'Bulen', in the region of gamma and beta relaxation transitions was studied. The method of forced torsion vibrations was used to obtain curves for the storage modulus (G′), loss modulus (G2) and loss tangent (tg δ) in the temperature interval (–180 to +20)°C and torsion frequency (0.1 to 100) rad/s. The maximum values of the storage modulus, the temperature at which these maximums appear and the full width at half maximum show an increase with the increase in the torsion frequency, but the most outstanding and prominent change is in the interval (0.1 to 10) rad/s. This fact is explained with reference to the processes of the deformational orientation of the macromolecular chain segments leading to changes in the intensity of the anelastic intermolecular interactions, the frequency response of the kinetic elements responsible for the realization of the gamma relaxation transitions, etc. The analogical frequency dependencies, derived from the loss tangent curves, show that the greatest changes take place in the same frequency interval (0.1 to 10) rad/s, although certain differences can be seen, and some of them are explained by the greater sensibility of tg δ changes in the physical kinetics of the gamma transition. The specific region in PE characterizing the local minimum of the mechanical losses is also discussed.

EFFECT OF PROTON IRRADIATION ON THE STRUCTURE DEVELOPMENT OF POLYETHYLENE TEREPHTHALATE FIBERS

The influence of proton irradiation on the structural changes in partially crystalline poly(ethylene terephthalate) (PET) filaments has been investigated using a wide-angle X-ray scattering (WAXS). Experimental data about the role of the exposure dose and the irradiation conditions in the processes of destruction and crosslinking in the irradiated objects have been obtained. The structural changes and the packing density of the macromolecular chain segments of the polyethylene terephthalate filaments irradiated with different doses have been analyzed. A mechanism of the structural reorganization initiated by the irradiation has been supposed on the basis of the changes in the geometry of the intensive distribution of the X-ray diffraction patterns of the objects.

Tri-Phasic Size- and Janus Balance-Tunable Colloidal Nanoparticles (JNPs).

These studies show synthesis of triphasic size- and Janus balance (JB)-tunable nanoparticles (JNPs) utilizing a two-step emulsion polymerization of pentafluorostyrene (PFS) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) and n-butyl acrylate (nBA) in the presence of poly(methyl methacrylate (MMA)/nBA) nanoparticle seeds. Each JNP consists of three phase-separated copolymers: p(MMA/nBA) core, temperature, and pH-responsive (p(DMAEMA/nBA)) phase capable of reversible size and shape changes, and shape-adoptable (p(PFS/nBA)) phase. Due to built-in second-order lower critical solution temperature (II-LCST) transition of p(DMAEMA/nBA) copolymer, macromolecular segments collapse when temperature increases from 30 to 45 °C, resulting in size and shape changes. The p(DMAEMA/nBA) and p(MMA/nBA) phases within each JNP assume concave, flat, or convex shapes, forcing p(PFS/nBA) phase to adopt convex, planar, or concave interfacial curvatures, respectively. As a result, the JB can be tuned from 3.78 to 0.72. The presence of pH-responsive DMAEMA component also facilitates the size and JB changes due to protonation of the tertiary amine groups of p(DMAEMA/nBA) backbone. Synthesized in this manner, JNPs are capable of stabilizing oil droplets in water at high pH to form Pickering emulsions, which at lower pH values release oil phase. This process is reversible and can be repeated many times.

Intriguing crystallization behavior and rheological properties of radical-based crosslinked biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

A series of branched/crosslinked poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with changing gel fractions were obtained by adding small amounts of crosslinking agents dicumyl peroxide (DCP) and triallyl isocyanurate (TAIC). The thermal and rheological properties of the samples were investigated. The chain branches formed by adding a certain amount of DCP bring in not only excess free volume which enhanced the cold crystallization ability but also defective crystals which decreased the melting temperature. Additionally, the rheological properties of branched samples were improved compared with those of neat P(3HB-co-4HB). The most intriguing result was the crystallization behavior of crosslinked P(3HB-co-4HB). The crosslinks, acting as favorable nucleation sites, can enhance the crystallization nucleation rate markedly. However, too many crosslinks could impede the transportation of macromolecular chain segments during the crystallization, resulting in a decreased crystallization rate, and the final crystallinity of crosslinked P(3HB-co-4HB) was independent of the degree of crosslinking. Furthermore, due to the formation of a gel network, crosslinked biodegradable P(3HB-co-4HB) exhibited remarkable improvement in rheological properties than branched samples, extending its processing methods, like foaming and film blowing. Accordingly, the practical applications of this biosourced and biocompatible polymer can be widely achieved.

Heterogeneous fluorine-containing surface macro-, micro- and nanostructures in polymer films and their applications

The methods of heterogeneous macro-, micro- and nanostructure formation on the surfaces of polymer films via their modification with gaseous fluorine have been considered. The successive fluorination and sulfonation of polyolefin films allows the synthesis of heterounit bi- and polyfunctional molecular fragments, thereby providing controlled chemical structuring at the nanolevel within a macromolecular segment. The combined use of the above methods of polymer-surface modification and intermediate film deformation under uniaxial tension results in the formation of surface microzones with fluorinated and sulfonated structures. Fluorinated and sulfonated macro- and microzones are formed via mechanical fracture of the fluorinated layer before sulfonation or via shielding of the polymer surface before sulfonation according to a given pattern through photolithographic methods. The practical applications of polymer films with heterogeneous surface structures are discussed.

Energy and acid-base characteristics of the surfaces of polymeric modifiers for filled cellulose nitrate composites

The energy and acid-base characteristics of the surface of butadiene-nitrile (SKN-18, SKN-26, SKN-40) and urethane (SKU-8A, SKU-8TB) rubbers, and also of polyvinyl nitrate and polyvinyl butyral were determined. Butadiene-nitrile rubbers are characterized by the highest, and vinyl polymers, by the lowest free surface energy. The free surface energy of urethane rubbers has intermediate values. The results obtained show that the surface energy of the polymers is determined both by the chemical nature of functional groups located directly in the surface layer and by the macromolecular packing density. The surface acidity increases in the order polyvinyl butyral < polyvinyl nitrate < SKU < SKN. The nature of the surface of the polymers under consideration is determined by prevalence of certain acid-base sites of adhesion interaction as a result of conformational turns of macromolecular chain segments.

Where is the glass transition temperature of poly(tetrafluoroethylene)? A new approach by dynamic rheometry and mechanical tests

Polytetrafluoroethylene (PTFE) has been used for many years in different application fields due to its outstanding chemical and physical properties. But, the value of its glass transition temperature is still today a matter of controversy and very different values are proposed in the literature. This paper proposes to answer to this scientific question using dynamic mechanical measurements. First, the viscoelastic properties of PTFE are described on a large temperature range and the influence of the shearing frequency is carefully investigated. Then, the effects produced by the polymer annealing on its thermomechanical behavior are detailed. This study comforts the idea that PTFE amorphous phase should be considered as comprised of two distinct regions. The first one named “mobile amorphous fraction” (MAF) is able to relax at low temperature (T=−103°C). The other one is specific of the macromolecular segments present at the boundaries between crystalline and amorphous domains. Due to the close vicinity of the crystallites, these macromolecular segments present a more restricted mobility. The corresponding phase is designated as the “rigid amorphous fraction” (RAF) and its mechanical relaxation produces itself at higher temperature (T=116°C). Actually, this latter value is strongly dependent on the material crystallinity degree. In particular, it is shifted to higher temperature after occurrence of a recrystallization that is accompanied by a further reduction of the RAF’s dynamic. Instead, the characteristics of the MAF relaxation are poorly affected. Tensile tests also support that the “real” Tg of the polymer is located at low temperature. All these results have been compared to those of the literature to propose a real scientific discussion and to understand the origin of somewhat contradictory interpretations.

Flow birefringence and optical anisotropy of poly(N-vinylpyrrolidone) molecules

Concentration dependences of flow birefringence and viscosity of poly(N-vinylpyrrolidone) solutions in water and benzyl alcohol are investigated. The intrinsic anisotropy for a poly(N-vinylpyrrolidone) macromolecular segment, (α1 − α2) = −(82 ± 8) × 10−25 cm3, is determined from the results of birefringence measurements in benzyl alcohol. For aqueous solutions, a strong concentration dependence of the specific anisotropy of solution is obtained, a result that may be explained by the heterogeneity of coils. A model allowing for this heterogeneity is suggested. It makes it possible to fit the concentration dependence to a hyperbolic function, to separate contributions of heterogeneity anisotropy and form anisotropy to the birefringence of a solution, and to estimate the segment asymmetry parameter as p = 3.0 ± 0.5.

Retrostructural Model To Predict Biomass Formulations for Barrier Performance

Barrier performance and retrostructural modeling of the macromolecular components demonstrate new design principles for film formulations based on renewable wood hydrolysates. Hardwood hydrolysates, which contain a fair share of lignin coexisting with poly- and oligosaccharides, offer excellent oxygen-barrier performance. A Hansen solubility parameter (HSP) model has been developed to convert the complex hydrolysate structural compositions into relevant matrix oxygen-permeability data allowing a systematic prediction of how the biomass should be formulated to generate an efficient barrier. HSP modeling suggests that the molecular packing ability plays a key role in the barrier performance. The actual size and distribution of free volume holes in the matrices were quantified in the subnanometer scale with Positron annihilation lifetime spectroscopy (PALS) verifying the affinity-driven assembly of macromolecular segments in a densely packed morphology and regulating the diffusion of small permeants through the matrix. The model is general and can be adapted to determine the macromolecular affinities of any hydrolysate biomass based on chemical composition.

Computer-aided simulation of the influence of collective effects on polymer-melt dynamics in a straight cylindrical tube: Observation of the onset stage of the corset effect

The results of the computer-aided simulation of the dynamics of a polymer melt consisting of Fraenkel chains in straight cylindrical tubes and in bulk are discussed. Two different models are studied. In the first model, the dynamics of the polymer melt is simulated via the molecular dynamics simulation. The interaction of unbound polymer segments is described by the Lennard-Jones potential, which excludes any chain crossing of macromolecules and generates collective acoustic waves. In the second model, which serves as a reference, the system is studied via the Brownian dynamics method, in which intermolecular interactions are allowed for phenomenologically via friction and stochastic Langevin forces. In this case, cooperative effects are absent and the effect of spatial confinements makes itself evident only in a narrow near-wall layer. For the two models under consideration, there is a significant difference in the decay of dynamic correlation functions C αβ(t) = 〈b α(t)b β(t)b α(0)b β(0)〉〈b α 2 b β 2 〉−1, where averaging is performed over all macromolecular segments and b α (t) is the component of the end-to-end-segment vector (α ≠ β = x,y, and the cylindrical axis of the tube is directed along the z axis). For the first model allowing for collective effects, the dynamics of decay of C αβ (t)functions is much slower than that for the melt in bulk, and for the second model, in which the presence of the tube leads only to spatial confinements for the polymer segments in the direct vicinity of walls. This difference indicates the fundamental significance of the collective effects in the dynamics of polymer melts confined in porous media. This phenomenon is the first computer-simulated evidence of the onset stage of the so-called corset effect, which was first observed experimentally with the use of NMR relaxometry.

A new kinetic model for predicting polyamide 6-6 hydrolysis and its mechanical embrittlement

PA 6-6 hydrolysis at 60, 70, 80 and 90 °C in distilled water has been studied by Fourier transform infrared spectroscopy, viscometry in molten state, differential scanning calorimetry and uniaxial tensile testing. The molar mass decreases sharply from the early periods of exposure to reach an equilibrium value of about MnE ≈ 10−11 kg mol−1 almost temperature independent. Hydrolytic chain scissions destroy the entanglement network in the amorphous phase and liberate small macromolecular segments which rearrange locally and initiate a chemicrystallisation. As expected, the embrittlement occurs at a very low conversion of the hydrolysis, in particular when the number average molar mass becomes lower than a critical value of about MnF ≈ 17 kg mol−1, i.e. very close to its initial value. A new kinetic model has been derived from the classical mechanistic scheme of reversible hydrolysis. This model describes satisfyingly all the kinetic characteristics of the reversible hydrolysis of PA 6-6 not controlled by water diffusion: decrease in molar mass, increase in crystallinity ratio and decrease in ultimate elongation, but also of other types of polyamides previously studied, such as PA 11. Moreover, when it is used as an inverse method, this model gives access to the rate constants of hydrolysis and condensation reactions. It is thus an interesting tool for elucidating structure/rate constant relationships in common families of hydrolysable polymers.

Diffusion relaxation of photoinduced gratings in polyvinyl acetate latex films

The features of the postexposure relaxation of holographic gratings recorded in inhomogeneous polyvinyl acetate latex films with photosensitive agents (photochromic molecules of fulgide dyes and phenanthrenequinone) have been considered. The diffusion coefficients and rms displacements of izomerized probe in polymer latex particles and aqueous environment are determined within the model of two diffusion states. The effective diffusion coefficient of the molecular probe, which is responsible for the relaxation of gratings, increases with an increase in their period in wet films, whereas in dry films, this parameter is independent of the grating period. In the films subjected to high-temperature treatment the effective diffusion coefficient decreases with an increase in the grating period. The successive stages of grating relaxation in latex films with phenanthrenequinone are related to the diffusion of free molecules, radicals, and polymer chains, as well as to the local displacement of macromolecular segments at distances of 5–25 nm.

Poly(carbonate-urethane): an isocyanate-free procedure from α,ω-di(cyclic carbonate) telechelic poly(trimethylene carbonate)s

A simple isocyanate-free method to synthesize poly(trimethylene carbonate hydroxy-urethane)s is described. The strategy first involves the synthesis of α,ω-di(cyclic carbonate) telechelic polycarbonate precursors upon ring-opening polymerization of trimethylene carbonate using a cyclic carbonate alcohol as chain transfer agent, followed by the ring-opening polyaddition of the terminal cyclic carbonate with a diamine. Such poly(carbonate-hydroxyurethane)s exhibit macromolecular carbonate segments of tunable length/molar mass.

Sensing macromolecular rearrangements in polymer networks by stimuli-responsive crosslinkers

A new family of azobenzene crosslinked brominated vinyl ester (DABA–BrVE) polymer networks was developed that exhibits reversible photochromic and fluorescence properties in which azobenzene serves as a crosslinker as well as a molecular sensor of structural and conformational changes of the surrounding macromolecular segments. The covalently “build-in” azobenzene crosslinker functions as a light emitting group capable of sensing stresses or damages, thereby altering photochromic and fluorescence properties. These reversible processes induced by structural network rearrangements may offer numerous application possibilities ranging from molecular stress sensors or nano-crack detectors in composites and other materials.

Viscoelasticity Analysis of Spherical Nano-CaCO3-Filled Isotactic Polypropylene During a Uniaxial Tensile Test

The tensile behavior of spherical nano-CaCO3 filled isotactic polypropylene over a wide range of strain rates were investigated to analyze the influence of nanofiller concentration and filler-matrix interaction on the motion of macromolecular chains and segments of iPP in the nonlinear region. The Eyring model can be well applied to describe the dependence of yield stress on strain rates. Both the activation energy and activation volume of the nanocomposites were higher than those of pure iPP, indicating the simultaneous restriction and activation effects of nanoparticles on the segmental mobility. Substantial reduction of yield stress was observed in the nanocomposites with increasing filler loading, especially at high strain rates. However, the yield stress of the nanocomposites containing 6 wt% stearic acid (SA)-treated CaCO3 was not further deteriorated relative to the nanocomposites containing 2 wt% SA-treated CaCO3. It can be interpreted in light of a three-parameter constitutive model by the influence of compliance function being significantly weakened in the nanocomposites containing 6 wt% SA-treated CaCO3, due to the stronger spatial restriction of better-dispersed nanoparticles on the segmental motion compared with the nanocomposites containing 2 wt% SA-treated CaCO3.

Effect of Spherical Nanoparticles on the Motion of Macromolecular Chains and Segments of Isotactic Polypropylene. I. Dynamic Mechanical and Thermal Properties

The role of spherical nano-CaCO3 particles treated with 2 wt% and 6 wt% stearic acid (SA), respectively, on the motion of macromolecular chains and segments of isotactic polypropylene (iPP) was studied through the dynamic mechanical analysis and nonisothermal crystallization. Higher nucleation activity of the particles and more nucleating sites were achieved in the 6 wt% SA treated particle nanocomposites with respect to the 2 wt% SA counterpart. The increased nucleation efficiency caused high inhomogeneity and thus large mobility of the amorphous phase of iPP, which favored a low glass transition temperature (Tg ) in the nanocomposites. However, the spherical nanoparicles also spatially restrained the motion of macromolecular chains and segments, and the better the nanoparticles dispersed, the stronger the restriction was. Thus the glass transition temperature (Tg ) of the nanocomposites decreased with increasing filler loading but recovered at a certain particle concentration. At this filler content, the maximal α-transition temperature (Tα ) and the main melting peak temperature (Tm1 ) as well as the lowest degree of crystallinity (XPP ) also occurred. This critical filler loading appeared at lower value (20 wt%) in 6 wt% SA treated nano-CaCO3 composites with respect to 2 wt% SA counterpart (25%) due to the better dispersion of particles in the former. It was concluded that the mobility of the macromolecular chains and segments of iPP was dominated by the competition of the spatial confinement and nucleation effect of nano-CaCO3 particles in the matrix.

The effect of chain packing on the thermal and dynamic mechanical behaviour of liquid‐crystalline epoxy thermosets

AbstractLiquid‐crystalline thermosets (LCTs) have received considerable attention since they exhibit many interesting properties. However, some aspects concerning LCTs are still unexplored. In particular, the structure–property relationships, as far as the organization of liquid‐crystalline (LC) domains in cured thermosets is concerned, have not been fully elucidated yet. We investigated the effect of the presence of a nematic mesophase on the thermal and dynamic mechanical behaviour of p‐(2,3‐epoxypropoxy)phenyl‐p‐(2,3‐epoxypropoxy)benzoate cured with 2,4‐diaminotoluene. Fourier transform infrared spectral analysis showed that epoxy group conversion was complete in both LC and isotropic (ISO) systems; moreover, a greater amount of intermolecular hydrogen bonding in the LC material was found. Thermogravimetric analysis evidenced similar thermal stability for the two systems, but a kinetic analysis of the data showed that the degradation process is more complex for the LC sample, and is characterized by higher activation energy. Dynamic mechanical thermal analysis (DMTA) showed lower glass transition temperature values for the LC system. Solid‐state NMR analysis evidenced lower paramagnetic oxygen absorption for this system. DMTA results show that the ISO material possesses a larger number of physical crosslinks, which act as extra constraints on the molecular motions. In the case of the LCT, the formation of a locally more dense structure is postulated, where the presence of more extended macromolecular segments leads to a smaller number of physical crosslinks, as also confirmed by solid‐state NMR analysis. A more compact molecular packing also leads to an increase of the activation energies of the thermal degradation process of the LC system. Copyright © 2010 Society of Chemical Industry