Glass-Transition Temperature of Copolymers

Figure 3. Glass transition temperature of copolymers vs. weight fraction of monomer units (14)...

Thermomechanical studies of synthesized copolymers indicate that the glass transition temperature of copolymers is decreased with an increase linear dimethylsiloxane backbone length, n (Figure 8). Since n=12 carbotricyclodecasiloxane fragments in copolymers cause no effect on the dimethylsiloxane backbone and Tg of copolymer 6 (Table 6) remains equal -123°C. 

Figure 15 shows dependence of the glass transition temperature of copolymers on cyclic carbosilo-xane fragment content in dimethylsiloxane backbone. Similar to copolymers from poly(dimethyl-phenylsiloxane) sequence [53], the effect of non-dimethylsiloxane units on 7g of copolymers with cyclic carbosiloxane fragments in the backbone is primarily observed at 3% concentration of the latter. 

Figure 15. Dependence of glass transition temperature of copolymers on mol% concentration of cyclic carbosiloxane (A) fragments 1 -copolymers with m = 1 2 - with m = 2...

Calculated Solubility Parameters and Glass Transition Temperatures of Copolymers... 

The compatibility of SAN copolymers with an assortment of other polymers has been measured by a variety of techniques. Differential scanning calorimetry is used to determine the glass transition temperatures of copolymers. The values increase slightly with increasing acrylonitrile content and range from around 100 to 115 °C [98,99]. 

The influence of pressure and temperature on activity, monomer content, molar masses, and glass-transition temperatures of copolymers has been assessed [162]. 

In the early 1970s Barton [186] proposed an equation relating the glass transition temperature of copolymers to their molecular structure in terms of the mole fractions of the various dyad sequences of monomer units present in the copolymer chain, and temperature parameters (Ta) charactaistic of each type of sequence i j. The Tg of a copolymer chain then can be given by the following equation ... 

PVC melts have a dry appearance, little strength, and lack of adhesion to a metal surface. Process aids are designed to change all these properties. Almost all rigid formulations and many flexible ones use acrylic process aids. Acrylic process aids are copolymers of methylmethacrylate with ethyl acrylate, butyl acrylate, or butyl methacrylate.Selection of monomers is important because it affects the glass transition temperature of copolymer, which should be lower than that of PVC to cause additive to melt below PVC process temperature and thus help to process it. 

The glass transition temperature of copolymers depends on the mass functions Wa and wb of A and B monomeric units, the probabilities p of occurrence of AA, AB, and BB diads, and on their corresponding glass transition temperatures. Considering (rG)BA = (rc )AB, the following can be used empirically ... 

Comonomer having hexyl side chain was added to N-vinylpyrrolidone to improve its properties. It was fonnd that the inclusion of comonomer rednces glass transition temperature of copolymer because it acts as an internal plasticizer. Polyimides are internally plasticized with alkyl 3,5-diaminobenzoate compounds. Without internal plasticization a polymer has too high a glass transition temperature that makes processing veiy difficult. 

The glass transition temperatures of copolymers with high content of NVK deviate from Flory-Fox or Gordon-Tailor equations, but they fit the Johnston equation. 

The description of the historic Gordon-T ay lor and Wood equations for the glass transition of solutions and copolymers can be found in Gordon M, Taylor IS (1952) Ideal Copolymers and the Second-order Transitions of Synthetic Rubbers. I. Noncrystalline Copolymers. J Appl Chem 2 493-500 Wood LA (1958) Glass Transition Temperatures of Copolymers. 1 Polymer Sci 28 319-330 for the relationship to the volume changes, see Kovacs AJ (1964) Glass Transition in Amorphous Polymers. Phenomenological Study. Fortschr Hochpolym Forsch 3 394-508. 

Williams G, Watts DC (1970) Non-symmetrical dielectric relaxation behavior arising from a simple empirical decay function. Trans Faraday Soc 66 80-85 Williams ML, Landel RR, Ferry ID (1955) The temperature dependence of relaxation mechanisms in amorphous polymers and other glass-forming liquids. J Am Chem Soc 77 3701-3707 Wood LA (1958) Glass transition temperatures of copolymers. J Polym Sci 28 319-330 Wu SH (1985) Phase structure and adhesion in polymer blends a criterion for rubber toughening. Polymer 26 1855-1863... 

The Fox equation [4] for glass transition temperature of copolymers is as follows ... 

K. R. Sharma, Glass Transition Temperature of Copolymers and Blends A Survey of Mathematical Models, 214th ACS National Meeting, Las Vegas, NV, September 1997. 

Glass transition temperatures of copolymers as function of their lactide contents are shown in Fig. 3. 

Vulcanized vinylidene fluoride-chlorotrifluoroethylene copolymers also have good thermal stability, withstanding prolonged heating at 200°C without serious deterioration. Low temperature performance is limited the glass transition temperatures of copolymers with 50 and 70 mole % vinylidene fluoride are 0°C and — 15°C respectively. The principal application of the elastomers is for components of systems handling strong mineral acids. 

Figure 1. Glass transition temperatures of copolymers generally decrease as the styrene content increases. Copolymers with acetoxy derivative (trian es) and with 4-hydro)y styrene (circles).

The glass transition temperature of copolymers usually lies between the Tg values of the two homopolymers (say, and Tg2) and is normally correlated through... 

---