Polydimethylsiloxane glass transition temperature

Silicones. Polydimethylsiloxanes, polydiphenylsiloxanes, and polymethylphenylsHoxanes are generally called siUcones (see Silicon COMPOUNDS, silicones). With a repeating unit of alternating siUcon-oxygen, the siloxane chemical backbone stmcture, siUcone possesses excellent thermal stabiUty and flexibility that are superior to most other materials. Polydimethjisiloxane provides a very low glass-transition temperature T material but is suitable for use... 

Although each of these cyclic siloxane monomers can be polymerized separately to synthesize the respective homopolymers, in practice they are primarily used to modify and further improve some specific properties of polydimethylsiloxanes. The properties that can be changed or modified by the variations in the siloxane backbone include the low temperature flexibility (glass transition temperature, crystallization and melting behavior), thermal, oxidation, and radiation stability, solubility characteristics and chemical reactivity. Table 9 summarizes the effect of various substituents on the physical properties of resulting siloxane homopolymers. The... 

The most commonly used siloxane modifiers are those having phenyl, trifluoro-propyl and cyanopropyl substituents. Introduction of phenyl units into the polydimethylsiloxane backbone either in the form of methylphenylsiloxane or diphenyl-siloxane increases the thermal and oxidative stability, glass transition temperature and the organic solubility characteristics of the resulting copolymers. At low levels (5-10 percent by weight) of incorporation, bulky phenyl groups also break up the regularity of polydimethylsiloxane chains and inhibit the crystallization (Tc... 

Preparation and thermal crosslinking reactions of oc, -vinylbenzyl terminated polysulfone-b-polydimethylsiloxane, ABA type block copolymers have been discussed 282,313) However, relatively little characterization was reported. Molecular weights of polysulfone and PDMS segments in the copolymers were varied between 800-8,000 and 500-11,000 g/mole, respectively. After thermal curing, the networks obtained showed two phase morphologies as indicated by the detection of two glass transition temperatures (—123 °C and +200 °C) corresponding to PDMS and polysulfone phases, respectively. No mechanical characterization data were provided. 

FIGURE 10-65 The approximate glass transition temperatures of polyethylene, polydimethylsiloxane and poly(2.6-dimethylphenylene oxide). 

Using results such as these, c.ie can predict the Tg of any polymer for which the group contributions are known. The glass transition temperature for polydimethylsiloxane, for example, is Tg = (1/2) 20 + (1/2) 280 = 150 K = -123 0. The approach was originally applied to linear polymers but has been extended to cross-linked polymers as well (24) ... 

However, for other polymers, the glass transition temperature is much lower thus Tt a 188 K for polydimethylsiloxane (see Chapter 1, Section 4.5) and... 

Keywords Fumed Silica / Polydimethylsiloxane / PDMS / Differential Scanning Calorimetry (DSC) / Glass Transition Temperature... 

F. Y. Stepanov, G. V., Efffect of Iron Particles on Dielectric Properties of Polydimethylsiloxane near Crystallization and Glass Transition Temperatures. Polym. Set, Ser. B 2006,48,1898-1902. 

Work in Taiwan has centred on examination of polydimethylsiloxane (PDMS), which has unusual properties such as high dynamic flexibility, low entropy of dilution, high oxidative stability, and low glass transition temperature. The initial work was directed towards incorporating the functionalized polymer PDMS into vinyl block polymers, producing copolymers that are of considerable interest in fields such as adhesion, coating and printing. 

Silicon-based polymers have interesting properties for the development of new materials. They are characterized by high hydrophobicity and low glass transition temperatures, thus yielding soft materials. Polydimethylsiloxanes, for example, are known for their oxygen permeability, which leads to their application in biomedical sciences. Therefore, a number of studies have concentrated on the amphiphilic self-assembly of block copolymers based on silicon-containing blocks. 

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