Polymerization index, polymer glass

Glass transition temperature is one of the most important parameters used to determine the application scope of a polymeric material. Properties of PVDF such as modulus, thermal expansion coefficient, dielectric constant and loss, heat capacity, refractive index, and hardness change drastically helow and above the glass transition temperature. A compatible polymer blend has properties intermediate between those of its constituents. The change of glass transition temperature has been a widely used method to study the compatibility of polymer blends. Normally, the glass transition temperatme of a compatible polymer blend can be predicted by the Gordon-Taylor relation ... 

Different polymeric materials show different UV transmittance, as shown in Figure 2.27. PDMS which is optically transparent down to 230 nm has a lower UV cutoff than glass [159,242]. Since the UV transparency of olefin polymers is down to 300 nm, these materials may be better substrates than PMMA or PC when UV radiation is used for detection [243]. PDMS has a relatively low refractive index ( = 1.430), and this reduces the reflectance and hence the amount of reflected excitation light and hence lowers the background [159]. 

The results obtained under microwave irradiation were compared with those from conventional experiments. Under the action of microwaves the amount of initiator needed to achieve constant conversion was reduced by 50% at the same polymerization rate if the same initiator concentration was used (0.15 and 0.20% wjw) the rate of polymerization increased by factors of 131 and 163%, respectively. The molecular weights of the polymers were 1.1 to 2.0 times higher than those obtained by use of conventional conditions. The glass transition temperatures (Tg), polydispersity index, and regularity of the polymers obtained by use of the two processes (microwave and conventional) were similar, indicating an analogous mechanism of polymerization. 

The product of this polymerization is applied in specialty areas, such as the manufacture of recording tapes and toners for photocopiers. When styrene (St) and butylmethacrylate (BMA) are mixed in the molar ratio 1 1, the polymer formed is transparent and has a glass transition temperature of about 30°C. Figure 8.3 shows the two monomers. The conversion in this case is measured gravimetrically. The product was dissolved in THF, and a small amount of hydroquinone was added to inhibit further reaetion. The molecular weight distribution was determined by gel permeation ehromato-graphy (GPC) with two mixed columns of polymer laboratories. The detection method used was by reactive index. 

---