Macromolecular Reaction Engineering最新文献

The demand for sustainable polymer particles production is growing, driven by the need for efficient, biocompatible, and biodegradable materials. In this context, the present study explores the production of poly(butylene succinate) (PBS) particles in a single step using a green heterogeneous suspension process, using vegetable oil as the suspending medium. Particularly, the effects of oil type (soybean, corn, sunflower), dispersed phase holdup (10–30 wt.%), stabilizers (Span 20, Span 80, Tween 80, Brij 52, Brij 93, Igepal-co-520,  Polyglycerol polyricinoleate (PGPR)), reaction time (1–5 h), and temperature (100–160 °C) on the suspension polymerization are investigated. Results indicate that particle size and shape are influenced by the vegetable oil and stabilizer. Additionally, it is shown that the particle size distribution is affected by the use of a sonicator, allowing the manufacture of even smaller microsized particles. Based on the results, a 30 wt.% holdup in corn oil with a blend of surfactants can be recommended, producing spherical particles with an average diameter of 100 µm. Moreover, higher reaction temperatures (160 °C) and longer reaction times (5 h) positively impacted the molar mass of the obtained particles. Finally, cytotoxicity tests using Bone Marrow-Derived Macrophages cells confirmed the safe use of PBS microparticles at concentrations up to 1000 µg mL⁻¹

One of the questions still remaining regarding emulsion polymerization is the issue of mass transfer versus reaction limitation since, by its nature, emulsion polymerization requires monomer transport across an aqueous phase. This question is brought into focus lately by the growing use of miniemulsion polymerization in which the monomer transport step is much less important. This paper will explore the possible rate of monomer transport via collision and ratio this to the maximum rate of polymerization using the Damkohler analysis formality. Results indicate that systems relying on monomer transport by collision will be almost universally monomer-transport-limited, thus exhibiting lower-than-expected rates of polymerizations.

Transport of monomer from droplets to growing latex particles in emulsion polymerization in general is assumed to proceed via diffusion through the aqueous phase. Especially in miniemulsion polymerizations the direct transfer of very hydrophobic species from droplet to droplet is assumed to also proceed via collisions. Amongst the hydrophobic species where this is shown to play a role are monomers, initiators, inhibitors and (catalytic) chain transfer agents. It is well known that the reactor geometry and the stirring speed can have a profound effect on emulsion polymerizations. The 1972 paper of Nomura on the effect of stirring on emulsion polymerization is cited more than 100 times and until today keeps scientists intrigued. Diffusion limitations of monomer going from the droplet into the aqueous phase can occur for very hydrophobic monomers. The alternative route of transport via collisions is often not considered. In this perspective, paper will discuss the evidence for collision based transfer in miniemulsion polymerization and also consider whether collision based monomer transport can play a role in regular emulsion polymerizations.

This study investigates polyaniline (PANI) for its sensing characteristics for detecting acetaldehyde. Pristine PANI is further modified in two ways to improve its sensing capabilities: 1) addition of a side chain (i.e., two methyl groups) to form poly (2,5-dimethylaniline), 2) addition of small amounts of metal oxide dopant (In₂O₃ in this case) to PANI. All the materials are evaluated for their sensing characteristics with respect to both sensitivity and selectivity. The sensitivity of PANI toward acetaldehyde is found to improve with both types of modification (i.e., poly (2,5-dimethylaniline) and PANI doped with different wt.% of In₂O₃). However, upon evaluating selectivity toward acetaldehyde using binary and ternary gas mixtures, pristine PANI exhibited higher selectivity compared to its modified counterparts.

The effect of solvents on kinetic parameters of anionic polymerization is complex and a comprehensive theoretical study has been rare. In this work, four solvent polarity descriptors (i.e., polarizability, dipole moment, nucleophilic index, electrophilic index) are correlated with solvent parameters (E_a, A, ΔH‡, and ΔS‡) by multiple linear regression using the Catalan linear free-energy relationship (LFER) equation for the anionic polymerization of styrene. The results show that E_a, ΔH‡, and ΔS‡ have a low correlation with dipole moment, whereas A is strongly correlated with dipole moment. Given the fact that the larger A the larger effective collision frequency Z, it is hypothesized that in polar solvents, the polymer chains are more extended, enabling more effective collisions between monomers and active anionic species during polymerization. In contrast, in nonpolar solvents, the polymer chains collapse, making it more difficult for the monomer to be inserted into the ion pairs. Subsequently, n-pentane and tetrahydrofuran are chosen as representatives to confirm this conjecture by molecular simulations. Lastly, E_a, A and k_p are predicted for 173 solvents using well-established descriptive relationships.

A rationale for droplet nucleation during inverse emulsion polymerization (IEP) (reported by previous investigators) is proposed. Based on the idea that smaller monomer droplets are nucleated into polymer particles, while larger droplets serve as reservoirs for monomer (as in a micellar nucleation mechanism) the question of possible monomer-transport limitation during polymerization is explored.

Polydiacetylene (PDA) is a kind of photopolymerizable polymer, which exhibits a unique color transition in response to external stimuli such as heat, pH, and solvent. PDAs are attractive as eye-detection stimulus sensors with excellent time performance; however, the sensitivity of PDAs should be improved. Considering the biological membrane-like structure of diacetylene (DA) vesicles, their modification by incorporating membrane lipids (e.g., diacylphosphocholine, PC) can be used to control the membrane fluidity, and consequently molecular ordering of DAs in the vesicle. Inspired by biological membrane systems, lipid vesicles are employed as platforms to generate PDA, and essential factors that influence the sensitivity of PDA are investigated. By lowering the polymerization temperature, the generation of PDA becomes slower, while the sensitivity improves. By adding PCs at the molar ratio of lipid:DA = 1:1, the sensitivity of PDA can be varied: the PCs with lower phase transition temperatures (T_m) made PDA insensitive, while the PCs with higher T_m improved the sensitivity as compared to pure poly(PCDA). It is concluded that the photopolymerization of DAs with a lower membrane fluidity induces highly sensitive PDA, while the photopolymerization of DAs with a higher membrane fluidity induces insensitive PDA with robustness toward stimuli.