Studies of the mechanism and kinetics of plasma-initiated polymerization of methyl methacrylate

Electric Field Effect of the Plasma-Initiated Polymerization of Methyl Methacrylate: A Negatively Charged Long-Lived Radical

Plasma-initiated polymerization (PIP) is generally attributed to a radical process due to its inhibiting property. However, its unique polymerization behaviors like long-lived radical and solvent effect do not comply well with the traditional radical mechanism. Herein, the PIP of methyl methacrylate (MMA) was conducted in a high-voltage DC electric field to investigate the charged nature of its radicals. Consequently, the polymerization presented a preferential distribution of polymers at the anode but not the cathode, revealing the negatively charged nature of the growing radicals. An acceleration phenomenon, accompanied by the growth in molecular weights and the reduction in molecular weight distributions (Ð), was observed at the voltages above 16 kV, suggesting the dissociation of ion pairs of growing radicals. The PIP yielded PMMA with analogous chemical and steric structures to those of PMMA from traditional radical initiation, whether in the presence or absence of the external electric field. This work offers new insights into the PIP of vinyl monomers, wherein a one-electron transfer reaction is inferred to be involved in the monomer activation.

Controlled Radical Polymerization Initiated by Solvated Electrons

Solvated electron (esol - ) is highly reducing species and apt to initiate monomers via one-electron transfer reaction. Herein, utilizing the esol - solution of Na/hexamethylphosphoramide, radical and anionic initiations are observed respectively, which heavily depend on Na concentrations. Interestingly, this initiation system, in states of lower Na concentrations, higher molar conductivities and less paired esol - , give rise to a controlled radical polymerization (CRP) to yield polymers with predictable molecular weights and narrow molecular weight distributions (the lowest Ð = 1.25). This CRP presents unique behaviors, like solvent effect, electric field effect, and unusual copolymerization phenomenon. A semi-conjugated radical carrying a negative charge is proposed to be responsible for the CRP. This system gives a distinct way to regulate CRP from current CRPs, and offers new insights into the monomer initiation by esol - .

Development of Synthesis and Application of High Molecular Weight Poly(Methyl Methacrylate)

Poly(methyl methacrylate) (PMMA) is widely used in aviation, architecture, medical treatment, optical instruments and other fields because of its good transparency, chemical stability and electrical insulation. However, the application of PMMA largely depends on its physical properties. Mechanical properties such as tensile strength, fracture surface energy, shear modulus and Young’s modulus are increased with the increase in molecular weight. Consequently, it is of great significance to synthesize high molecular weight PMMA. In this article, we review the application of conventional free radical polymerization, atom transfer radical polymerization (ATRP) and coordination polymerization for preparing high molecular weight PMMA. The mechanisms of these polymerizations are discussed. In addition, applications of PMMA are also summarized.

Plasma activated 1-hexene oligomerization in a gas-liquid microreactor

The oligomerization of 1-hexene under argon plasma was investigated in a gas-liquid, continuous flow microreactor. The evolution of the yields of the reaction products as a function of the residence...

Facile Synthesis of Ultrahigh Molecular Weight Poly(Methyl Methacrylate) by Organic Halides in the Presence of Palladium Nanoparticles

A facile and versatile approach for the synthesis of ultrahigh molecular weight poly(methyl methacrylate) (PMMA) at mild conditions was developed. Certain organic halides combined with a catalytical amount of palladium nanoparticles (Pd NPs) were found to be very effective in initiating polymerizations of methyl methacrylate (MMA), methyl acrylate, vinyl acetate and other vinyl monomers. An ultrahigh molecular weight PMMA with a number-average molecular weight of 4.65 × 10⁶ Da and a weight-average molecular weight of 8.08 × 10⁶ Da was synthesized at 70 °C using 2-bromoisobutyric acid ethyl ester (EBiB) as an initiator in the presence of catalytical amount (10.1 ppm) of Pd NPs. A kinetic investigation found that the orders of polymerization with respect to EBiB, Pd NP and MMA were 0.23, 0.50, and 0.58, respectively. Proton nuclear magnetic resonance (¹H NMR) combined with matrix-assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF) and gel permeation chromatography (GPC) were used to prove that the macromolecular chain had an end-group of EBiB residue. The electron spin resonance (ESR), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) results reveal that the reaction of EBiB with Pd NPs caused a bromo atom (Br) transfer from EBiB to Pd NPs and resulted in the generation of EBiB residue radical to initiate the polymerization of MMA and the formation of Pd^IIBr₂ on the surface of Pd nanoparticles.

Development of a molecular recognition ion gating membrane and estimation of its pore size control

We have fabricated a molecular recognition ion gating membrane. This synthetic membrane spontaneously opens and closes its pores in response to specific solvated ions. In addition to this switching function, we found that this membrane could control its pore size in response to a known concentration of a specific ion. The membrane was prepared by plasma graft copolymerization, which filled the pores of porous polyethylene film with a copolymer of NIPAM (N-isopropylacrylamide) and BCAm (benzo[18]crown-6-acrylamide). NIPAM is well-known to have an LCST (lower critical solution temperature), at which its volume changes dramatically in water. The crown receptor of the BCAm traps a specific ion, and causes a shift in the LCST. Therefore, selectively responding to either K(+) or Ba(2+), the grafted copolymer swelled and shrank in the pores at a constant temperature between two LCSTs. The solution flux in the absence of Ba(2+) decreased by about 2 orders of magnitude over a solution flux containing Ba(2+). The pore size was estimated by the filtration of aqueous dextran solutions with various solute sizes. This revealed that the membrane changed its pore size between 5 and 27 nm in response to the Ba(2+) concentration changes. No such change was observed for Ca(2+) solutions. Furthermore, this pore size change occurred uniformly in all pores, as a clear cut-off value for a solute size that could pass through pores was always present. This membrane may be useful not only as a molecular recognition ion gate, but also as a device for spontaneously controlling the permeation flux and solute size.

Effect of albumin immobilization by plasma polymerization on platelet reactivity

Albumin was immobilized on polyethylene (PE) film by the plasma polymerization method. Immobilized albumin on formaldehyde polyermized PE film was hard to desorb even when the film was dipped in blood plasma. Amounts of platelet adhesion on the film and serotonin release decreased clearly. Aggregated platelets were observed on PE film but not observed on the albumin immobilized surface. These results seemed to be due to not only immobilized albumin, but also the surface charge determined by plasma protein adsorption. That is, the slightly negatively charged surface indicated good anti-thrombogenicity.