Concentrations Of PMMA Research Articles

Coupled relaxations in a blend of PMMA and a polycarbonate

Proton lineshape and proton spin-lattice relaxation, T 1 ρ , measurements were made on blends of bisphenol chloral polycarbonate and perdeutero poly(methyl methacrylate) (PMMA). The solution-cast blends are optically clear and display a single thermal glass transition temperature, T g, as reported. The proton lineshape and proton relaxation data are used to follow the dynamics of the polycarbonate in the blend. The glass transition process is monitored by lineshape collapse as a function of temperature and the sub-glass transition process associated with π flips of the phenylene group is monitored by the proton T 1 ρ values as a function of temperature. The glass transition as viewed from the polycarbonate remains similar in character to the behaviour observed in pure polycarbonate. Below T g, the lineshape consists of a broadened Pake doublet and above T g a narrow Lorentzian grows in on top of the Pake pattern. The bimodal behaviour and the growth of the narrow line with temperature can be described by the Vogel-Tamman-Fulcher equation with T 0 values which decrease with PMMA concentration. The proton T 1 ρ data show antiplasticization in the form of suppression of the π flip process as PMMA is added. In addition, a new minimum associated with the motion of the polycarbonate is observed at the temperature and time scale of the ester group rotation of the PMMA. This apparent coupling of the sub- T g relaxation processes is related to the behaviour of polycarbonate upon addition of low-molecular-weight ester diluents. The level of antiplasticization and the amount of coupling is underestimated by a lattice model and an assumption of random mixing. On the very local scale of the π flip motion and at the higher concentrations of PMMA, there are apparently fewer PMMA-polycarbonate contacts than a random mixing assumption indicates.

Fast ion transport in new lithium electrolytes gelled with PMMA. 1. Influence of polymer concentration

Conductivities and viscosities of gel electrolytes made of poly (methylmethacrylate) (PMMA)-LiClO 4-propylene carbonate have been measured. In this paper, the influence of the concentration of polymer in the gelled electrolytes is investigated. These gels are both anhydrous and lithium ionic conductors. It is found that ionic conductivity decreases with increasing amount of polymer and lies in the range 5×10 −3to5×10 −5 S/cm at room temperature. On the other hand, the viscosity varies greatly from 8×10 −3to6×10 6 Pa.s leading to a solid adhesive material. The thermal dependence of both conductivity and viscosity can be accurately described by a VTF expression. The experimental results show that some change occurs in the conduction path of the gel around 30–35 w/o of polymer. For low concentrations of PMMA, the gelatinized electrolytes can be considered as a liquid electrolyte encaged in a polymer matrix. On the other hand, for high concentrations, some interactions may be created between the polymer chains and the conducting electrolyte leading to both a decrease of conductivity and an increase of the activation energy of conduction.

A study of the microhardness of ethylene glycol dimethacrylate (EGDM)/Poly (methyl methacrylate) (PMMA) network polymer

The application of the network formed from ethylene glycol dimethacrylate and poly (methyl methacrylate) (PMMA) in dentistry and orthopaedics has generated interest among material scientists in the study of its mechanical behaviour. This paper reports the preparation of the network polymer with varying concentrations of PMMA in the network and its effect on the Vickers microhardness (H v ) of the specimens at different loads ranging from 80 to 160 g. The increasing and decreasing trend in values of H v have been observed with varying concentrations of PMMA in the network. The observed behaviour has been attributed to the effect of localized plastic deformation and cross-linking density. The role of phase separation has also been envisaged.