Crystalline polymers glass transition temperature

In the case of a crystalline polymer the maximum service temperature will be largely dependent on the crystalline melting point. When the polymer possesses a low degree of crystallinity the glass transition temperature will remain of paramount importance. This is the case with unplasticised PVC and the polycarbonate of bis-phenol A. 

FIGURE 7.21 The effect of vinyl acetate content on the crystallinity and glass transition temperature of PEVAc. [Graph reconstructed from Johnson and Nachtrab, Ange. Macrom. Chem., 7, 134 (1969) and Reding et al., J. Polym. Sci., 57, 483 (1962).]... 

Hydrogenation of the aminonitrile with a Raney catalyst leads to a family of branched diamines. Because of the branching, most of the aminonitriles and diamines are liquids at low temperature and have low freezing points. They have found markets as comonomers or curatives, since they lower polymer viscosity, crystallinity, and glass transition temperature. Catalytic hydrogenation of MGN with a Raney catalyst gives the branched-amine methylpentamethylenediamine, MPMD, and 3-methylpiperidine (3MP) shown in equation 3. The product is dependent on conditions and choice of catalyst. The MPMD was initially isolated from plant streams to develop the market. Many applications were found as a polymer additive in... 

Methods for determining the presence, kind, and amount of configurational base units can be classified as relative or absolute. Absolute methods do not require calibration with polymers of known tacticity. Relative methods, on the other hand, require comparison with standard substances. X-ray crystallography, nuclear magnetic resonance, infrared spectroscopy, and optical activity measurements are all absolute methods. Relative methods include crystallinity, solubility, glass transition temperature, and melting temperature measurements as well as chemical reactions (Table 3-2). 

Following the same procedure, these authors incorporated a-TOC, BHT and fert-bufylhydroquinone (TBHQ) into PLA films at concentrations ranging from 0 to 10%. DSC results showed that the polymer glass transition temperature and the crystallinity slightly decreased with the increase of the antioxidant content. Permeability towards water vapour showed a decrease in the wettability of the prepared materials with the increase of the antioxidants content. Similar results were obtained for gas permeation. Barrier improvements could not be measured at high concentrations due to phase separation. 

The degradation rate of bioresorbable polymers depends on their intrinsic properties such as reactivity, hydrophilicity, molecular weight, degree of crystallinity, and glass transition temperature. However, other external factors such as the degradation media, sterilisation and sample size also play a role in the degree of degradation. 

Thermal Behavior of Semirigid Chain Polymers Glass Transition Temperature versus Crystallinity 238... 

The three polymers have different properties. 1,2-Polybutadiene is a hard and rough crystalline compound 1,4-polybutadiene is not. The crystalline and glass transition temperatures for cis- and rrans-1,4-polybutadiene are markedly different Tg is — 108 C for cis and 18°C for trans T, is 1°C for cis and 141°C for trans. The glass transition temperature Tg is the temperature below which an amorphous polymer can be considered to be a hard glass and above which the material is soft or rubbery Tm is the crystalline melting point where the crystallinity completely disappears. 

Other factors that affect the stress relaxation behavior of polymer fibers include, but are not limited to molecular weight, molecular orientation, molecular polarity, crystalhnity, and moisture or other additives. In general, the stress relaxation of polymer fibers decreases with increases in molecular weight, molecular orientation, molecular polarity, crystallinity, and glass transition temperature. However, the introduction of moisture or other small molecules into polymer fibers can facilitate faster stress relaxation since these small molecules can improve the molecular mobility of polymer chains. 

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