Glass softening temperature

Tg is the glass softening temperature, A5(7 j)the difference between the entropy of a glass and its crystal at Tg, To is the Vogel-Fulcher-Tatnman temperature and z(Tg) is the minimum size of the cooperatively rearranging region. 

Table 1 shows that most acryflcs have low glass-transition temperatures. Therefore, in copolymers they tend to soften and flexibHize the overall composition. Plasticizers also lower the transition temperature. However, unlike incorporated acryflc comonomers, they can be lost through volatilization or extraction. 

As appHed to hydrocarbon resins, dsc is mainly used for the determination of glass-transition temperatures (7p. Information can also be gained as to the physical state of a material, ie, amorphous vs crystalline. As a general rule of thumb, the T of a hydrocarbon resin is approximately 50°C below the softening point. Oxidative induction times, which are also deterrnined by dsc, are used to predict the relative oxidative stabiHty of a hydrocarbon resin. 

The dynamic mechanical properties of VDC—VC copolymers have been studied in detail. The incorporation of VC units in the polymer results in a drop in dynamic modulus because of the reduction in crystallinity. However, the glass-transition temperature is raised therefore, the softening effect observed at room temperature is accompanied by increased brittleness at lower temperatures. These copolymers are normally plasticized in order to avoid this. Small amounts of plasticizer (2—10 wt %) depress T significantly without loss of strength at room temperature. At higher levels of VC, the T of the copolymer is above room temperature and the modulus rises again. A minimum in modulus or maximum in softness is usually observed in copolymers in which T is above room temperature. A thermomechanical analysis of VDC—AN (acrylonitrile) and VDC—MMA (methyl methacrylate) copolymer systems shows a minimum in softening point at 79.4 and 68.1 mol % VDC, respectively (86). 

Before providing such an explanation it should first be noted that progressive addition of a plasticiser causes a reduction in the glass transition temperature of the polymer-plasticiser blend which eventually will be rubbery at room temperature. This suggests that plasticiser molecules insert themselves between polymer molecules, reducing but not eliminating polymer-polymer contacts and generating additional free volume. With traditional hydrocarbon softeners as used in diene rubbers this is probably almost all that happens. However, in the... 

A glass transition temperature of 215°C, a deflection temperature of 200°C and a Vicat softening point of 219°C. 

The TMC polycarbonate homopolymer has a glass transition temperature of 238°C, nearly 100°C above that of the bis-phenol A polycarbonate. Therefore, copolymers will have intermediate glass transitions depending on the relative proportions of TMC and bis-phenol A. Commercial grades (marketed by Bayer as Apec HT) have Vicat softening points from 158 to... 

High softening temperatures (glass-fibre-filled grades are better than polycarbonates and modified PPOs). 

Softening temperature The Littleton Softening Point is most commonly used. At this temperature the glass hs a viscosity of 10 N s/m. ... 

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