Evaluating the Role of Nanomontmorillonite in Bulk in Situ Radical Polymerization Kinetics of Butyl Methacrylate through a Simulation Model

Anomalous Loss of Stiffness with Increasing Reinforcement in a Photo-Activated Nanocomposite

Hydrogels are commonly doped with stiff nanoscale fillers to endow them with the strength and stiffness needed for engineering applications. Although structure-property relations for many polymer matrix nanocomposites are well established, modeling the new generation of hydrogel nanocomposites requires the study of processing-structure-property relationships because subtle differences in chemical kinetics during their synthesis can cause nearly identical hydrogels to have dramatically different mechanical properties. The authors therefore assembled a framework to relate synthesis conditions (including hydrogel and nanofiller mechanical properties and light absorbance) to gelation kinetics and mechanical properties. They validated the model against experiments on a graphene oxide (GO) doped oligo (ethylene glycol) diacrylate (OEGDA), a system in which, in apparent violation of laws from continuum mechanics, doping can reduce rather than increase the stiffness of the resulting hydrogel nanocomposites. Both model and experiment showed a key role light absorbance-dominated gelation kinetics in determining nanocomposite mechanical properties in conjunction with nanofiller reinforcement, with the nanofiller's attenuation of chemical kinetics sometimes outweighing stiffening effects to explain the observed, anomalous loss of stiffness. By bridging the chemical kinetics and mechanics of nanocomposite hydrogels, the authors' modeling framework shows promise for broad applicability to design of hydrogel nanocomposites.

Effect of Na- and Organo-Modified Montmorillonite/Essential Oil Nanohybrids on the Kinetics of the In Situ Radical Polymerization of Styrene

The great concern about the use of hazardous additives in food packaging materials has shown the way to new bio-based materials, such as nanoclays incorporating bioactive essential oils (EO). One of the still unresolved issues is the proper incorporation of these materials into a polymeric matrix. The in situ polymerization seems to be a promising technique, not requiring high temperatures or toxic solvents. Therefore, in this study, the bulk radical polymerization of styrene was investigated in the presence of sodium montmorillonite (NaMMT) and organo-modified montmorillonite (orgMMT) including thyme (TO), oregano (OO), and basil (BO) essential oil. It was found that the hydroxyl groups present in the main ingredients of TO and OO may participate in side retardation reactions leading to lower polymerization rates (measured gravimetrically by the variation of monomer conversion with time) accompanied by higher polymer average molecular weight (measured via GPC). The use of BO did not seem to affect significantly the polymerization kinetics and polymer MWD. These results were verified from independent experiments using model compounds, thymol, carvacrol and estragol instead of the clays. Partially intercalated structures were revealed from XRD scans. The glass transition temperature (from DSC) and the thermal stability (from TGA) of the nanocomposites formed were slightly increased from 95 to 98 °C and from 435 to 445 °C, respectively. Finally, better dispersion was observed when orgMMT was added instead of NaMMT.

Effect of the side ethylene glycol and hydroxyl groups on the polymerization kinetics of oligo(ethylene glycol methacrylates). An experimental and modeling investigation

Polymerization of oligo(ethylene glycol) methyl ether methacrylate (POEGMMA₃₀₀) and oligo(ethylene glycol) hydroxyethyl methacrylate (POEGHEMA).

Effect of Graphene oxide or Functionalized Graphene Oxide on the Copolymerization Kinetics of Styrene/n-butyl Methacrylate

Nanocomposite materials based on copolymers of styrene and n-butyl methacrylate with either graphene oxide (GO) or functionalized graphene oxide (F-GO) were synthesized using the in-situ bulk radical copolymerization technique. Reaction kinetics was studied both experimentally and theoretically using a detailed kinetic model also taking into account the effect of diffusion-controlled phenomena on the reaction kinetic rate constants. It was found that the presence of GO results in lower polymerization rates accompanied by the synthesis of copolymers having higher average molecular weights. In contrast, the presence of F-GO did not seem to significantly alter the conversion vs time curves, whereas it results in slightly lower average molecular weights. The first observation was attributed to side reactions of the initiator primary radicals with the hydroxyl groups on the surface of GO, resulting in lower initiator efficiency, whereas the second to grafted structures formed from copolymer macromolecules on the F-GO surface. The copolymerization model predictions including MWD data were found to be in satisfactory agreement with the experimental data. At least four adjustable parameters were employed and their best-fit values were provided.

Effect of Graphene Oxide on the Reaction Kinetics of Methyl Methacrylate In Situ Radical Polymerization via the Bulk or Solution Technique

The synthesis of nanocomposite materials based on poly(methyl methacrylate) and graphene oxide (GO) is presented using the in situ polymerization technique, starting from methyl methacrylate, graphite oxide, and an initiator, and carried out either with (solution) or without (bulk) in the presence of a suitable solvent. Reaction kinetics was followed gravimetrically and the appropriate characterization of the products took place using several experimental techniques. X-ray diffraction (XRD) data showed that graphite oxide had been transformed to graphene oxide during polymerization, whereas FTIR spectra revealed no significant interactions between the polymer matrix and GO. It appears that during polymerization, the initiator efficiency was reduced by the presence of GO, resulting in a reduction of the reaction rate and a slight increase in the average molecular weight of the polymer formed, measured by gel permeation chromatography (GPC), along with an increase in the glass transition temperature obtained from differential scanning calorimetry (DSC). The presence of the solvent results in the suppression of the gel-effect in the reaction rate curves, the synthesis of polymers with lower average molecular weights and polydispersities of the Molecular Weight Distribution, and lower glass transition temperatures. Finally, from thermogravimetric analysis (TG), it was verified that the presence of GO slightly enhances the thermal stability of the nano-hybrids formed.