Amorphous state glass transition temperature

Gwyther, 1. and Manners, 1. (2009) Diblock copolymers with amorphous, high glass transition temperature, organometallic block synthesis, characterisation and self-assembly of polystyiene-i -poly(ferrocenylisopropyl-methylsilane) in the bulk state. Polymer 50, 5384—5389... 

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. 

As-polymerized PVDC does not have a well-defined glass-transition temperature because of its high crystallinity. However, a sample can be melted at 210°C and quenched rapidly to an amorphous state at <—20°C. The amorphous polymer has a glass-transition temperature of — 17°C as shown by dilatometry (70). Glass-transition temperature values of —19 to — 11°C, depending on both method of measurement and sample preparation, have been determined. 

Further developments in this area have included the neparation of several additional N,N -diaryl indolo[3,2-h]carbazoles with substituents such as m-tolyl, ffi-anisoyl, or triarylamine-containing species. Like 221, these compounds, possessing excellent hole-transport properties, also occurred in stable amorphous states and displayed high glass-transition temperatures. LED devices involving these systems were also constructed and showed promising characteristics [OOSMO11-112)42]]. 

Molecular Motion in amorphous atactic polystyrene (PS) is more complicated and a number of relaxation processes, a through 5 have been detected by various techniques as reviewed recently by Sillescu74). Of course, motions above and below the glass transition temperature Tg have to be treated separately, as well as chain and side group mobility, respectively. Motion well above Tg as well as phenyl motion in the glassy state, involving rapid 180° jumps around their axes to the backbone has been discussed in detail in Ref.17). Here we will concentrate on chain mobility in the vicinity of the glass transition. 

The crystallinity in PET soft drink bottles is about 25%. Because a more crystalline state is normal for PET, the amorphous content is increased intentionally by copolymerization and rapid cooling for the molten PET from the melt to a temperature below the glass transition temperature. Companies which perform high-speed blow molding of PET prefer PET resins made with small amounts of glycol and diacid comonomers. 

This difference in spatial characteristics has a profound effect upon the polymer s physical and chemical properties. In thermoplastic polymers, application of heat causes a change from a solid or glassy (amorphous) state to a flowable liquid. In thermosetting polymers, the change of state occurs from a rigid solid to a soft, rubbery composition. The glass transition temperature, Tg, ... 

The presence of a solvent, especially water, and/or other additives or impurities, often in nonstoichiometric proportions, may modify the physical properties of a solid, often through impurity defects, through changes in crystal habit (shape) or by lowering the glass transition temperature of an amorphous solid. The effects of water on the solid-state stability of proteins and peptides and the removal of water by lyophilization to produce materials of certain crystallinity are of great practical importance although still imperfectly understood. 

Amorphous polymers convert reversibly between the rubbery and glassy states as their temperature rises or falls. Below their glass transition temperature, amorphous polymers exist in a glassy state. Above their glass transition temperature they are rubbery. We can demonstrate this easily with a racquet ball, which is made of an amorphous polymer. At room temperature, as we all know, the ball bounces at this temperature it is in the rubbery state. If we immerse the ball in liquid nitrogen it becomes brittle and will shatter when we drop it, i.e., it has become a glass, If we were to allow the frozen ball to warm up to room temperature, it would become rubbery once more. We can freeze and thaw the same ball repeatedly with no loss of its properties at room temperature. 

At room temperature, atactic polystyrene is well below its glass transition temperature of approximately 100 °C. In this state, it is an amorphous glassy material that is brittle, stiff, and transparent. Due to its relatively low glass transition temperature, low heat capacity, and lack of crystallites we can readily raise its temperature until it softens. In its molten state, it is quite thermally stable so we can mold it into useful items by most of the standard conversion processes. It is particularly well suited to thermoforming due to its high melt viscosity. As it has no significant polarity, it is a good electrical insulator. 

The nature of the hard domains differs for the various block copolymers. The amorphous polystyrene blocks in the ABA block copolymers are hard because the glass transition temperature (100°C) is considerably above ambient temperature, i.e., the polystyrene blocks are in the glassy state. However, there is some controversy about the nature of the hard domains in the various multiblock copolymers. The polyurethane blocks in the polyester-polyurethane and polyether-polyurethane copolymers have a glass transition temperature above ambient temperature but also derive their hard behavior from hydrogen-bonding and low levels of crystallinity. The aromatic polyester (usually terephthalate) blocks in the polyether-polyester multiblock copolymer appear to derive their hardness entirely from crystallinity. 

Probably most of these investigators were studying poly(dichlorophosphazene) in the partially crosslinked state. Most of this was summarized by Allcock (.9). More recently, highly purified, uncrosslinked II has been examined in the solid state (21). The unstressed polymer is amorphous at room temperature, but crystallization can be induced by cooling or stretching techniques. The glass transition temperature, measured by Torsional Braid Analysis, is -66°C (22). 

The effect of physical aging on the crystallization state and water vapor sorption behavior of amorphous non-solvated trehalose was studied [91]. It was found that annealing the amorphous substance at temperatures below the glass transition temperature caused nucleation in the sample that served to decrease the onset temperature of crystallization upon subsequent heating. Physical aging caused a decrease in the rate and extent of water vapor adsorption at low relative humidities, but water sorption could serve to remove the effects of physical aging due to a volume expansion that took place in conjunction with the adsorption process. 

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