Polycarbonates, antiplasticization

For many years, it has been known that a small quantity of plasticizer acts as an anti plasticizer for polyvinyl chloride (PVC). During a recent search for effective plasticizers for polycarbonate, W. J. Jackson and J. R. Caldwell found several groups of compounds which acted as antiplasticizers. They increased the tensile modulus and strength and reduced the elongation of polycarbonate films. In contrast to plasticizers, these antiplasticizers affected glass transition temperature quite differently. Their mechanism is explained by the fact that they either increase crystallinity or reduce the mobility of the polymer chain through the bulkiness of their molecules. 

The book closes with two chapters on the plasticization and antiplasticization of polycarbonate by A. Conix and L. Jeurissen and G. W. Jackson and J. R. Caldwell, respectively. It would have been possible to include more examples of the interaction between polymers and plasticizers, for instance on the effect in lacquers, in latices, or adhesives. Some are mentioned in the first chapter. 

Since each of these polycarbonates had exceptionally high glass transition temperatures—256° and 290°C., respectively—it was possible to add appreciable amounts of antiplasticizers without depressing the glass transition temperatures to room temperature or lower. In addition, since the bisphenol II polycarbonate already had a relatively high tensile modulus (4.7 X 105 p.s.i.), it was of interest to determine how much this modulus could be increased. 

To determine if the tensile properties of the commercially available polycarbonate from 4, 4 -isopropylidenediphenol were similarly affected, several of the antiplasticizers were also added to this polymer. The bisphenol itself is commonly known as bisphenol A. 

It is surprising that the tensile moduli of the polycarbonate films were increased so much by the antiplasticizers, and it is even more surprising that antiplasticizer concentrations of 30% (and even 40% in two cases) could be tolerated before the... 

Whereas Sears and Darby (7) found many types of compounds which would plasticize bisphenol A polycarbonate when the plasticizer concentration was 25 to 30%, the norbornane-tvpe polycarbonates could be plasticized only with larger amounts of plasticizer. When present in concentrations of 20 to 30%, conventional plasticizers acted as diluents—that is, the tensile modulus and tensile strength were depressed, as occurs with plasticizers, but the elongation was not appreciably increased. The antiplasticizers also acted similarly and became diluents after their peak antiplasticizing action was reached. 

The antiplasticization phenomenon is presumably common to all the polymers exhibiting a relatively strong (5 transition, well separated from the a transition. It has been observed for both linear (PVC, polycarbonate, poly-sulphones) and network polymers (amine-crosslinked epoxies). For the case of thermosets, the phenomenon may be a consequence of both internal (change of the network structure) and external (incorporation of miscible additives) modifications of the structure or the composition but it always seems to be a consequence of the plasticization, as shown in Fig. 11.7. 

The effect of diluents on the viscoelastic behavior of amorphous polymers is more complex at temperatures below T, i.e., in the range of secondary relaxation processes. Mechanical, dielectric and NMR measurements have been performed to study the molecular mobility of polymer-diluent systems in this temperature range (see e.g. From extensive studies on polymers such as polycarbonate, polysulfone and polyvinylchloride, it is well known that diluents may suppress secondary relaxation processes. Because of the resulting increase in stiffness, these diluents are called antiplasticizers . Jackson and Caldwell have discussed characteristic properties... 

Figure 6. Inverse of the proton spin lattice relaxation time (T,p)" as a function of temperature for polycarbonate as-extruded () and on addition of antiplasticizer ( ). (Adapted from ref. 36.)...

Polycarbonate appears to an almost unique extent to be subject to an anti-plasticizing effect on the addition of low molecular weight compounds. It is reported that the derivatives of l,l-bis(4-hydroxyphenyl)-2,2-propane operate in this context by tightly filling the free volume between the polymer molecules. Charge-transfer complexes , for example tetracyanoethylene-A-stilbene s, antiplasticizing action has been explained in terms of aandyff relaxations. ... 

Figure 5.33. Storage modulus and tan 5 curves for antiplasticized polysulfone (a) and polycarbonate (b) both polymers in the pure state have well-defined p relaxations at about -100 °C (173 K) at high diluent levels these relaxations are greatly reduced and virtually eliminated. [From Robeson and Faucher (1969) reprinted with permission of John Wiley and Sons, Inc.]...

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