Amorphous polymers plasticisers

Plasticisers are known for their effectiveness in producing flexible polymers such as flexible PVC, acrylate copolymers and so on. Plasticisers are normally liquids, and are used in glassy polymers to reduce their glass transition temperature (Tg) with compatibility to avoid phase separation. Phase separation would cause migration to the surface. The rubbery effect results from the high levels of plasticiser bringing the Tg of the polymer to below room temperature. In semi-crystalline polymers, plasticisers would not only reduce the Tg of the amorphous domain but also decrease the melting point of the crystalline phase. 

Two distinct models have been used for interpreting the influence of features such as chemical stmcture, molecular mass, cross-linking and plasticisers on the glass transition in amorphous polymers. The first approach considers changes in moleeular flexibility, which modify the ease with which conformational changes can take place. The alternative approach relates all these effects to the amount of free volume, which is assumed to attain a critical value at the glass transition. 

DMA measurements are intensively used to investigate the amorphous phase transitions of polymers. The results of DMA studies were published by authors like Schmieder and Wolf [2], Nielsen and Buchdahl [3] and Heijboer [4]. Neat polymers, but also polymer blends and polymer systems blended with fillers, plasticisers or impact improvers were investigated by DMA. An example of such an application is given for toughened polypropylene in 4.1.2. 

We expected that am improvement of the Tg-value estimation was still possible by careful selection of the reference Tg-values used. These Tg-values should preferably be self determined values measured under standard conditions (see 1.1.3) or selected literature values. They should have been determined on amorphous or low crystalline polymers with a sufficient high molecular weight i.e. Mn value 50.000. Besides, these polymers should not contain fillers, plasticisers, residual monomer and/or solvents. 

Therefore, the ideal solution in this field would he the use of solid plasticisers , namely of solid additives which would promote amorphicity at ambient temperature without affecting the mechanical and the interfacial properties of the electrolyte. A result that approaches this ideal condition has been obtained by dispersing selected ceramic powders, such as Ti02, AI2O3 and Si02, at the nanoscale particle size, in the PEO-LiX matrix [35-41]. The conductivity behaviour of a selected example of these nanocomposite polymer electrolytes is shown in Figure 7.5. 

Compatibility can often be predicted from theoretical considerations, such as tables of solubility products, provided that the polymer is mainly amorphous. The solubility parameter of the polymer and that of the plasticiser must be similar. 

Intermediate form between A and B. Amorphous or crystalline complex with other molecules (eg lipids in native starch, plasticiser or other polymer in TPS or TPS blends). Insoluble in water. Single helical structure. Can be either Vh (hydrated) or Va (anhydrous) depending on moisture content. 

Many approaches have been used to improve the conductivity of polymer electrolytes. Studies have focused on the development of copolymers " and cross-linked polymers""" to create completely amorphous electrolytes with enhanced conductivity at room temperature. One method involves the addition of various plasticisers, such as ethylene carbonate (EC), propylene carbonate (PC) and tetraethylene glycol (TEG), which have been added to... 

Usually, both crystalline and amorphous phases are present in polymer electrolytes. Since only amorphous phases present high conductivity, plasticiser solvents are usually added to enhance the amorphous phase and thus the ionic conductivity. Here, propylene carbonate (PC), EC,y-butyrolactone (y-BL) and their binary mixtures are usually used as plasticiser solvents. Hie stereo structures of the polymer matrix molecules are given in Fig. 12.3, including linear, comb, crossing, star, hyper-branched and comb crosslinking. 

---