No abstract

Poly(urethane-isocyanurate)s were synthesized by reacting toluene diisocyanate and poly(propylene glycol) with various stochiometric ratios (1-3) in the presence of different concentrations of dibutyltin dilaurate (DBTDL) and ferric acetylacetonate (FeAA). The influence of the NCO/OH ratio and the catalyst type and concentration on the extent of urethane and isocyanurate formation were examined using Fourier transform IR spectroscopy. No trimer formation was observed in the presence of the FeAA catalyst. The percentage of the trimer group and the trimer/ urethane content were found to be increased with increasing the stochiometric ratio or DBTDL concentration. The thermal decomposition of the copolyurethanes in an inert atmosphere was studied by means of thermogravimetry (TG). The TG curves showed three decomposition steps with the principal degradation temperature at about 355-385°C. The effects of the NCO/OH ratio, catalyst type and concentration, and heating rate on the thermal stability of the copolyurethanes were determined. The Flynn-Wall, Kissinger, and Ozawa methods were used to calculate the activation energies of thermal decomposition. The swelling behavior of solid copolyurethanes in toluene showed that, as the DBTDL concentration and/or NCO/OH ratio increased, the swelling ratio and average molecular weight between crosslinks were decreased whereas the crosslink density was increased. The sol fraction of solid copolyurethanes was examined and found to be reduced when the percentage of DBTDL or the stochiometric ratio was raised.

No abstract

No abstract

Material encapsulation is a relatively new technique for coating a micro/nanosize particle or droplet with polymeric or inorganic shell. Encapsulation technology has many applications in various fields including drug delivery, cosmetic, agriculture, thermal energy storage, textile, and self-healing polymers. Poly(methyl methacrylate) (PMMA) is widely used as shell material in encapsulation due to its high chemical stability, biocompatibility, nontoxicity, and good mechanical properties. The main approach for micro/nanoencapsulation of materials using PMMA as shell comprises emulsion-based techniques such as emulsion polymerization and solvent evaporation from oilin-water emulsion. In the present review, we first focus on the encapsulation techniques of liquid materials with PMMA shell by analyzing the effective processing parameters influencing the preparation of PMMA micro/nanocapsules. We then describe the morphology of PMMA capsules in emulsion systems according to thermodynamic relations. The techniques to investigation of mechanical properties of capsule shell and the release mechanisms of core material from PMMA capsules were also investigated.