Poly(vinyl acetate)-Based Block Copolymer/Clay Nanocomposites Prepared by In Situ Atom Transfer Radical Polymerization

Atom transfer radical polymerization of styrene (St) and methyl methacrylate (MMA) was performed at 90oC in the absence and presence of nanoclay (Cloisite 30B). Trichloromethyl-terminated poly(vinyl acetate) telomerand CuCl/ PMDETA were used as a macroinitiator and catalyst system, respectively. The experimental results showed that the atom transfer radical polymerization of St and MMA in the absence or presence of nanoclay proceeds via a controlled/living mode. It was observed that nanoclay significantly enhances the homopolymerization rate of MMA, which was attributed to the activated conjugated C=C bond of MMA monomer via interaction between the carbonyl group of MMA monomer and the hydroxyl moiety (Al-O-H) of nanoclay as well as the effect of nanoclay on the dynamic equilibrium between the active (macro) radicals and dormant species.Homopolymerization rate of St (a non-coordinative monomer with nanoclay) decreased slightly in the presence of nanoclay. This could be explained by insertion of a portion of macroinitiator into the clay galleries, where no sufficient St monomer exists due to the low compatibility or interaction of St monomer with nanoclay to react with the macroinitiator. The results obtained from XRD, TEM and TGA analyses were fully in agreement with the kinetic data. Structure of the poly(vinyl acetate)-bpolystyrene nanocomposite was found to be a combination of stacking layers and exfoliated structures while poly(vinyl acetate)-b-poly(methyl methacryale) nanocomposite had an exfoliated structure. This difference in the structure of nanocomposites was attributed to the different capability of the monomers (styrene and methyl methacrylate) to react with the hydroxyl moiety (Al-O-H) of nanoclay

Structure/Glass Transition Temperature Relationship of PVAc-b-poly(MA-co-MMA) Terpolymers with Theoretical and Topological Methods

The glass transition temperature of several PVAc(1)-b-poly(MA-co-MMA) (2) terpolymers with different fractions of methyl acrylate (MA) and methyl methacrylate (MMA) repeating units in random copolymer (block 2) were calculated with Barton, Kwei and topological equations. The calculation was on the basis of the correlation between the fraction of repeating units in random copolymers and theoretical equations and linear correlation of topological index of VAc, MA and MMA atomic structures in topological equations. The experimental values of the glass transition temperature of block 2 show a positive deviation from linearity in both Barton and Kwei theoretically calculated values. Therefore, agreement between the theoretical and experimental values were reached with summation of the effects of sequence distributions in random copolymer (R, calculated with 1H NMR and statistical methods) to the linear theoretical data in Barton equation and the effect of interactions between the copolymer chains in Kwei equation (q = 14.9). The glass transition temperature of 308 K was calculated for PVAc block with topological equation and it was near to the experimental value (310 K). Furthermore, the calculated glass transition temperatures of the block 2 with linear method were considerably close to the experimentally obtained data and increased with mole fraction of MMA in random copolymer

Prediction of Optimum Time for Oxygen Clearance in Solution Polymerization of Vinyl Acetate in Isopropyl Alcohol

As we know oxygen is one of the main inhibitors of polymerization of vinyl acetate. Therefore, nitrogen is used in order to make sure of system's high purity. To maintain purity it is necessary to find out the rate of the oxygensolution in polymerization system under different conditions of polymerization. It is concluded that incoming nitrogen to the system would remove the oxygen from the system and on the other hand the increase in temperatureis a great help. The time length for this process is evaluated in polymerization system at the same time

Thermal Property and Microstructures of Poly(VAc-b-MA) and PVAc-b-Poly(MA-co-MMA) Block Copolymers and Terpolymers

The microstructure and thermal properties of the synthesized block copolymers and terpolymers via atom transfer radical polymerization (ATRP) were studied. The mole fraction of the blocks and chain length of the PVAc-b-PMA block copolymers were estimated with 1H NMR spectroscopy.Differential scanning calorimety measurement shows two different transitions at 36°C and 8°C assigned to PVAc and PMA blocks. Thermogravimetric analysis demonstrated the similar thermal degradation behavior of the block copolymers and a three-step degradation around 238, 295 and 345°C were attributed to dechlorination step and decomposition of the PVAc and PMA blocks. Study of thermal properties of PVAc-b-Poly(MA-co-MMA) copolymers indicated that glass transition temperature of second block increased from 49°C to 91°C with increase in MMA mole fraction from 0.358 to 0.733. The losses in the thermal degradation of block terpolymers were similar, and the higher thermal degredation temperature of MA unit has delayed the thermal degredation temperature of MMA in copolymer

Effect of carbon nanotubes content on the vulcanization kinetic in styrene–butadiene rubber compounds

Styrene–butadiene rubber compounds reinforced with commercial multiwall carbon nanotubes (MWCNT) in amounts between 0.5 and 10 parts per hundred of rubber (phr) were mixed in a two-roll mill. A compound with 40 phr of carbon black (CB) was prepared as reference. From rheometric curves at five different temperatures (between 140°C and 180°C), a similar maximum torque and vulcanization time values in the samples reinforced with 10 phr of MWCNT and 40 phr of CB were obtained. The Kamal–Sourour model was used to analyze the influence of the MWCNT content and the vulcanization temperature on the cure rate and induction time. Then, through an Arrhenius plot, it became evident the effect of the reinforcement content on the activation energy of the vulcanization process. Mechanical properties of normalized sheets vulcanized at 160°C indicate that content between 5 and 10 phr of MWCNT are enough to reach a similar performance to that sample with 40 phr of CB. SEM analysis exhibits a good dispersion of MWCNT. Swelling experiments point out a similar absorption degree of toluene in the compounds with 5 phr of MWCNT and 40 phr of CB. POLYM. ENG. SCI., 59:E327–E336, 2019.Fil: García, Daniela Belen. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Mansilla, Marcela A.. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Crisnejo, Matías. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Farabollini, Hernán. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Escobar, Mariano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentin