Glass-transition temperature diluent

Plasticizers are substances (usually low molecular weight diluents) that are incorporated into polymeric materials to improve their workability and increase flexibility. Polymeric plasticizers are low glass transition temperature (Tg) poly-... 

As a consequence, the overall penetrant uptake cannot be used to get direct informations on the degree of plasticization, due to the multiplicity of the polymer-diluent interactions. The same amount of sorbed water may differently depress the glass transition temperature of systems having different thermal expansion coefficients, hydrogen bond capacity or characterized by a nodular structure that can be easily crazed in presence of sorbed water. The sorption modes, the models used to describe them and the mechanisms of plasticization are presented in the following discussion. 

The glass transition temperature of a dilute system, according to the free volume changes, is determined by the diluent volume fraction Vd, and changes of the thermal expansion coefficient, a, at Tg by using ... 

Bueche (16,172) proposed that the viscosity is proportional to the fourth power of the polymer concentration and a complex function of the free volume of the mixture. Kraus and Gruver (170) find that the 3.4 power fits experimental data better than does the fourth power. They used equation (58) with (r2) replaced by the mean-square radius of gyration (s2). The term r2)/(rf) indicates that poor solvents should lower the viscosity more than a good solvent. As the temperature increases, the factor increases as a function of the ratio (T - 7 (tJJ)/(7 - 7 ). The glass transition temperatures of the polymer and diluent are andT o, respectively. 

Table V. Glass Transition temperatures of cured HEMA samples. Formulation HEMA/EGDMA/BME/Diluent 85/0.34/0.17/X...

These authors were the first FGSE workers to make extensive use of the concept of free volume 42,44) and its effect on transport in polymer systems. That theory asserts that amorphous materials (liquids, polymers) above their glass transition temperature T contain unoccupied volume randomly distributed and in parcels of sufficient size to permit jumps of small molecules — and of polymer jumping segments — to take place. Since liquids have a fractional free volume fdil typically greater than that, f, of polymers, the diffusion rate both of diluent molecules and (uncrosslinked and unentangled) polymer molecules should increase with increasing diluent volume fraction vdi,. The Fujita-Doolittle expression 43) describes this effect quantitatively for the diluent diffusion ... 

Chow TS (1980) Macromolecular interpretation of the glass-transition temperature of polymer-diluent systems. Macromolecules 13 362-364... 

Plasticizers and flexibilizers are incorporated into an adhesive formulation to provide it with flexibility and/or elongation. Plasticizers may also reduce the melt viscosity of hot melt adhesives or lower the elastic modulus of a solidified adhesive. Similar to diluents, plasticizers are nonvolatile solvents for the base resin, and by being incorporated into the formulation, they separate the polymer chains and enable their deformation to be more easily accomplished. Plasticizers generally affect the viscoelastic properties of the base resin whereas diluents simply reduce the viscosity of the system. Whereas diluents result in brittle, hard adhesive systems, plasticizers result in increased flexibility and lower modulus. The temperature at which polymers exhibit rubbery properties (i.e., the glass transition temperature) can also be modified by incorporating plasticizers. 

The PS-2100/PMMA thermal data of Figure 3 also show two glass-transition temperatures for the 25% blend, indicating incompatibility. The dynamic mechanical results for blends of PS-600 in PMMA are consistent with the thermal and optical results, as Figure 4 shows. The PMMA secondary loss shoulder is diminished somewhat as the concentration of PS-600 is increased, in a manner similar to that observed in other polymer-diluent systems in which the diluent is monomeric (15) until phase separation occurs. Thereafter, the phase-separated PS-600 shows up as a characteristically narrow peak at about — 10°C. 

Ten Brinke, G., Karasz, F.E., and Ellis, T.S. (1983). Depression of glass transition temperatures of polymer networks by diluents. Macromolecules, 16, 244-299. 

Diluents affect the free volume of the polymer. As the free volume increases, the glass transition temperature tends to decrease. The depression of Tg with the addition of diluents, including gases such as CO2, can be estimated following Royer [37] by the expression... 

Fig. 1. Glass transition temperature T vs diluent concentration c for mixtures of polycarbonate with dimethyl phthalate (A) and of po tyrene with didecyl phthalate (O)...

A fraction of poly (methyl acrylate) presents maximum damping at 0.50 Hz at 25°C. Make a rough estimation of the diluent that must be added to shift the maximum damping to 100 Hz at the same temperature. The glass transition temperatures of the diluent and the polymer are —70°C and 10°C, respectively, and their expansion coefficients are 8.5xlO K and 4,2 X respectively. 

Camacho-Zuniga, C. and Ruiz-Trevino, F.A. (2003) A new group contribution scheme to estimate the glass transition temperature for polymers and diluents. Ind. Eng. Chem. Res., 42, 1530-1534. 

The effect of adding a low-molecular-weight substance to a polymer is to lower its glass transition temperature. The effect is well known, and is exploited in practice to obtain flexible products of poly(vinyl chloride) by adding relatively nonvolatile diluents such as dibutyl phthalate or tricresyl phosphate as plasticizers to the polymer. 

Empirically Tg of a polymer-diluent mixture could be expressed in terras of the glass transition temperature of the pure polymer 9V and that of the pure diluent Tgd by... 

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