BACKGROUND: The nature of phase transitions and apparently irreversible phase homogenization upon heating in blends of biodegradable poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were proven using differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy and 1H NMR spectroscopy. The complex phase behaviour in this blend system is puzzling and is a matter of debate; this study attempts to clarify the true nature of the phase behaviour.RESULTS: A PMMA/PLLA blend is immiscible at ambient temperature but can become miscible upon heating to higher temperatures with an upper critical solution temperature (UCST) at 230 °C. The blends, upon rapid quenching from the UCST, can be frozen into a quasi‐miscible state. In this state, the interaction strength was determined to be χ12 = − 0.15 to − 0.19, indicating relatively weak interactions between the PLLA ester and PMMA acrylic carbonyl groups.CONCLUSION: The absence of chemical exchange reactions above the UCST and phase reversibility back to the original phase separation morphology, assisted by solvent re‐dissolution, in the heat‐homogenized PLLA/PMMA blend was shown. Verification of UCST behaviour, phase diagrams and solvent‐assisted phase reversibility were experimentally demonstrated in PMMA/PLLA blends. Copyright © 2008 Society of Chemical Industry

The thin-film morphologies of double-ring-banded and ringless spherulites in melt-crystallized poly(ethylene adipate) (PEA) were examined using atomic-force microscopy (AFM) and polarizing optical microscopy techniques with phase image and depth profiles. For the PEA ring-banded spherulites (T c ) 30 °C), edge-on lamellae, with top views shaped like a figure 8, are arranged in an orderly fashion on the ridges of ring bands, and the valley region of the ring bands is filled mainly with flat-on oval-shaped platelets. Between the edgeon and flat-on band regions, some ribbonlike long lamellae are present that propagate across these two regions. However, these three lamellar types are discrete, discontinuous, and independent, and they are not necessarily inter-related by physical turning. By contrast, in the ringless Maltese-cross spherulite (PEA crystallized at T c ) 35 °C), similarly figure-8-shaped edge-on lamellae and flat-on platelets are also present, but they are scattered randomly, and no long lamellae are present. Near or within the edge-on lamellae, cavities are present as a result of densification and/or reorientation. In contrast with some single-banded spherulites where the valleys usually have a featureless amorphous texture, the valleys in the double-ring-banded PEA spherulites are filled with plateletlike lamellae, whereas the ridges contain mainly figure-8-shaped lamellae.

Spherulite morphology and growth kinetics of poly(octamethylene terephthalate) (POT), cast on single-side glass or confined between two slides in thin-film forms, were characterized using polarized versus nonpolarized optical microscopy, scanning electron microscopy (SEM), and wide-angle X-ray (WAXD) analysis. POT can simultaneously display solely one type of spherulite or dual types of spherulites (double-ring-banded and ringless ones), depending on T c or T max imposed. Fractions of these two types depend on T c when quenched from a fixed T max = 160 degrees C. At lower T c's, POT exhibits higher crystallization rates leading to higher fractions of ringless spherulites; at higher T c's, POT exhibits lower crystallization rates leading to ring-banded spherulites. At intermediate to high T c's where the growth kinetics of POT could be monitored, the ring-band type dominates and the fraction of ringless spherulites is insignificantly small. Both ringless and ring-banded spherulites can be seen in regime III ( T c = 70-110 degrees C), with fractions of ringless type of spherulites decreasing with temperature. Thus, growth kinetics for POT was mainly focused on the regime of ring-banded spherulites. In regime III, the ring-band pattern is more orderly concentric with smaller inter-ring spacing (1-2 mum) for lower T c's but intermediately larger spacing (3-5 mum) for higher T c's. The orderly lamellar orientation in the ring-bands in contrast with the inter-ring valley region is discussed. In regime II (115 degrees C and above), the ring-band pattern is first distorted to highly zigzag irregularity at higher T c's and then eventually disappears at extremely high T c, with the lamellar crystals eventually turning dendritic with no rings. Apparently, the types of spherulites in polymers are more influenced by the growth rates as determined by T c and slightly less by T max, but not by the substrate surface nucleation.

Nanoscale colloidal silica showed high reactivity toward curing epoxy resins to form epoxy-silica nanocomposites under mild conditions. Adding a certain amount (5000 ppm) of magnesium chloride lowered the activation energy of the reaction from 71 to 46 kJ/mol. Less and more magnesium chloride both exhibited counter action on lowering the activation energy of the curing reaction. Tin chloride dihydrate and zinc acetylacetonate hydrate were also added into the curing compositions, however, showing no significant effect on promoting the curing reaction. Through this curing reaction, epoxy-silica nanocomposites containing high silica contents up to 70 wt % were obtained. Therefore, this reaction provided a novel and convenient route in preparation of epoxy-silica nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1237-1245, 2005

Differential scanning calorimetry (DSC), Fourier transformed infrared spectroscopy (FT-IR) and polarized optical microscopy (POM) characterizations were performed to reveal interaction between amorphous poly(p-vinyl phenol) (PVPh) and crystalline stereocomplex of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA). The negative value of the interaction parameter 12 clearly confirms a thermodynamic miscibility in the ternary blend. At low contents, PVPh is well dispersed in the ternary blends, but PVPh may aggregate to nanodomains by self-associated hydrogen-bonding upon annealing. In addition, PVPh serves as an effective agent in reducing the spherulite sizes of the PLLA/PDLA crystals, which may be favorable in controlling the macroscopic properties. The Avrami and Tobin kinetic analysis methods were carried out to analyze the nonisothermal crystallization data, and the results showed that the ternary blends with an optimal range of 2-10 wt % PVPh were faster in the crystallization rate and smaller in the spherulite size than those with no PVPh or with PVPh contents greater than 10 wt %. Ternary blend containing higher PVPh contents may form large phase-separated domains and growth of the stereocomplex is hindered under the nonisothermal crystallization condition.