Glass transition temperature configurational effects

The increase in the length of the side chain results normally in an internal plasticization effect caused by a lower polarity of the main chain and an increase in the configurational entropy. Both effects result in a lower activation energy of segmental motion and consequently a lower glass transition temperature. The modification of PPO with myristoyl chloride offers the best example. No side chain crystallization was detected by DSC for these polymers. 

Electron Beam Lithography. LB PMMA films with thicknesses of 6.3 nm (7 layers) are sufficient for patterning a Cr film suitable for photomask fabrication. For ultrathin PMMA films the resolution (see Fig. 1) is limited by the smallest spot diameter available on MEBES I (1/8 pm). However, it is not possible to obtain this resolution if a thicker resist (>100 nm) is used under the same exposure and development conditions, which demonstrates that ultrathin resists are able to minimize the proximity effect. Also, since the radius of gyration of 188,100 Mw PMMA is about 10 nm in the bulk, and the thickness of the 7 layer film (6.3 nm) is less than 10 nm, it is reasonable to assume there must be an alteration of chain configuration in the ultrathin films. This will be particularly true when the post-deposition baking temperature of the multilayer films is less than the glass transition temperature (115°C), as is the case for the present experiments. In such a case, interdiffusion of PMMA chains between the deposited layers may not result in chain configurations characteristic of the bulk. 

From these values, one may calculate and compare the effective glass transition temperature of the resin as a function of diluent concentration. Gordon et a1. have recently derived an expression relating the glass temperature of a polymer-plasticizer mixture to the glass temperatures of the components on the basis of the configurational entropy theory of glass formation (4). 

Until now, there has been no explicit discussion of the effect of temperature oi pressure on any of the viscoelastic functions, although it has been mentioned thai below the glass transition temperature the configurations of polymer chain backbones are largely immobilized and the tremendous changes in viscoelastic properties with time or frequency which characterize polymeric systems do not appear (curves V in the figures in Chapter 2). 

In the case of the glass transition, more complete experimental data are available, at least with respect to vinyl polymers. As will be discussed below, for certain types of structure a substantial effect of stereoregularity on the glass transition temperature, T, is found, and in addition a theoretical treatment is available which accounts for these effects. However, very little data is available with respect to the effect of stereoregularity on, for example, the configurational entropy S at T, on aC, the size of the heat capacity increment at T, 0 on other key thermodynamic parameters of the glassy state. ... 

---