Separation above glass transition

The equilibriiun process of the surface segregation is possible only at the constant temperatru e of the melt. At conditions of the formation of filled alloys by transition from hquid to solid states, the segregation proceeds until the nec-essaiy molecular mobility is preserved in the system, i.e., up to ciystalhzation or vitrification temperature of one of the melt components. It means that sixrface segregation proceeds in non-equilibrimn conditions in the definite temperatru e interval. If the phase separation temperature is above glass transition or crystallization temperature, the surface segregation may proceed from each evolved phase separately. 

Elastomeric Modified Adhesives. The major characteristic of the resins discussed above is that after cure, or after polymerization, they are extremely brittie. Thus, the utility of unmodified common resins as stmctural adhesives would be very limited. Eor highly cross-linked resin systems to be usehil stmctural adhesives, they have to be modified to ensure fracture resistance. Modification can be effected by the addition of an elastomer which is soluble within the cross-linked resin. Modification of a cross-linked resin in this fashion generally decreases the glass-transition temperature but increases the resin dexibiUty, and thus increases the fracture resistance of the cured adhesive. Recendy, stmctural adhesives have been modified by elastomers which are soluble within the uncured stmctural adhesive, but then phase separate during the cure to form a two-phase system. The matrix properties are mosdy retained the glass-transition temperature is only moderately affected by the presence of the elastomer, yet the fracture resistance is substantially improved. 

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. 

Wood Hill (1991b) induced phase-separation in the clear glasses by heating them at temperatures above their transition temperatures. They found evidence for amorphous phase-separation (APS) prior to the formation of crystallites. Below the first exotherm, APS appeared to take place by spinodal decomposition so that the glass had an intercoimected structure (Cahn, 1961). At higher temperatures the microstructure consisted of distinct droplets in a matrix phase. 

In the case of the higher temperature crystallization, as will be shown in Sect. 4, the theory of Doi et al. is applicable without doubt since the primary phase separation involves the transition from the isotropic to nematic phase, but in the case of the glass crystallization near Tg described above its applicability is unclear since the observed data may correspond to the secondary phase separation. However, if the secondary phase separation occurs, the primary phase separation must have proceeded prior to that. In a rapidly quenched glass even if the primary phase separation had already taken place, it would be still incomplete, so that it will re-start by heating. 

The dynamic mechanical behavior indicates that the glass transition of the rubbery block is basically independent of the butadiene content. Moreover, the melting temperature of the semicrystalline HB block does not show any dependence on composition or architecture of the block copolymer. The above findings combined with the observation of the linear additivity of density and heat of fusion of the block copolymers as a function of composition support the fact that there is a good phase separation of the HI and HB amorphous phases in the solid state of these block copolymers. Future investigations will focus attention on characterizing the melt state of these systems to note if homogeneity exists above Tm. 

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