Polymer characterization, glass transition

The measured G(x) value of representative epoxy polymers is approximately 10, but this value depends strongly on the structure of the polymer, its glass transition temperature and other characteristics. Since the crosslinking reaction that characterizes the COP resist functionality is a chain reaction, in theory, a single, electron-initiated event could result in the insolublization of an entire film of the resist material. Fortunately, because of the existence of chain terminating reactions, this does not occur and high resolution imaging of the resist material can be accomplished. 

In polymers, the glass transition phenomenon has been related to the dielectric a-relaxation processes through the Vogel-Fulcher-Tammann (VET) equation [9], and it can be characterized by means of their molecular dynamics analysis. 

Experimental data from our laboratories will be shown for an extensive series of amorphous polymers with glass transitions between Tg = 200 and 500 K. We discuss the temperature dependence of the hole-size distribution characterized by its mean and width and compare these dependencies with the hole fraction calculated from the equation of state of the Simha-Somcynsky lattice-hole theory from pressure-volume-temperature PVT) experiments [Simha and Somcynsky, 1969 Simha and Wilson, 1973 Robertson, 1992 Utracki and Simha, 2001]. The same is done for the pressure dependence of the hole free-volume. The free-volume recovery in densified, and gas-exposed polymers are discussed briefly. It is shown that the holes detected by the o-Ps probe can be considered as multivacancies of the S-S lattice. This gives us a chance to estimate reasonable values for the o-Ps hole density. Reasons for its... 

As mentioned before, a polymer s glass transition can be characterized by the glass transition temperature (Tg) and the heat capacity jump at the glass... 

The glass transition temperature is an important characterizing parameter for amorphous polymers. The glass transition temperature is defined as the temperature at which a liquid or rubbery material becomes a glass, and hence, Tg can only correctly be measured on cooling [19-21]. 

In addition to thermodynamic appUcations, 62 values have also been related to the glass transition temperature of a polymer, and the difference 62-61 to the viscosity of polymer solutions. The best values of 6 have been analyzed into group contributions, the sum of which can be used to estimate 62 for polymers which have not been characterized experimentally. 

Solution Polymers. Acryflc solution polymers are usually characterized by their composition, solids content, viscosity, molecular weight, glass-transition temperature, and solvent. The compositions of acryflc polymers are most readily determined by physicochemical methods such as spectroscopy, pyrolytic gas—liquid chromatography, and refractive index measurements (97,158). The solids content of acryflc polymers is determined by dilution followed by solvent evaporation to constant weight. Viscosities are most conveniently determined with a Brookfield viscometer, molecular weight by intrinsic viscosity (158), and glass-transition temperature by calorimetry. 

Most Kaminsky catalysts contain only one type of active center. They produce ethylene—a-olefin copolymers with uniform compositional distributions and quite narrow MWDs which, at their limit, can be characterized by M.Jratios of about 2.0 and MFR of about 15. These features of the catalysts determine their first appHcations in the specialty resin area, to be used in the synthesis of either uniformly branched VLDPE resins or completely amorphous PE plastomers. Kaminsky catalysts have been gradually replacing Ziegler catalysts in the manufacture of certain commodity LLDPE products. They also faciUtate the copolymerization of ethylene with cycHc dienes such as cyclopentene and norhornene (33,34). These copolymers are compositionaHy uniform and can be used as LLDPE resins with special properties. Ethylene—norhornene copolymers are resistant to chemicals and heat, have high glass transitions, and very high transparency which makes them suitable for polymer optical fibers (34). 

Plots of loss modulus or tan 5 vs temperature for polymers give peaks at energy absorbing transitions, such as the glass transition and low temperature secondary transitions (Fig. 20). Such plots are useful for characterizing polymers and products made from them. 

The modified NBR samples were characterized by differential scanning calorimetry [11,78-80,98]. The glass-transition temperature (T ) decreased with the level of hydrogenation. In the case of HFNBR, Tg increased with an increase in the addition of aldehyde groups to the polymer chain. Thermogravimetric analysis of the modified polymers have also been carried out [15]. 

Other monomers, such as hexaflurohisphenol A and tetramethyl hisphenol F, are also used. These polymers are characterized hy high glass transition temperatures ranging between 192 to >350°C. 

As a consequence, the overall penetrant uptake cannot be used to get direct informations on the degree of plasticization, due to the multiplicity of the polymer-diluent interactions. The same amount of sorbed water may differently depress the glass transition temperature of systems having different thermal expansion coefficients, hydrogen bond capacity or characterized by a nodular structure that can be easily crazed in presence of sorbed water. The sorption modes, the models used to describe them and the mechanisms of plasticization are presented in the following discussion. 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

The greatest use for DSC has turned out to be for characterization of organic polymers. It has been found that most polymers are amorphous and have a characteristic Tg, i.e.- a "glass" transition temperature which leads to a... 

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