Temperature, glass transition preparative

A reexamination of polycarbonate chemistry was carried out about 50 years after the first aromatic polycarbonates of resorcinol and hydroquinone were discovered. In independent investigations at Bayer AG and General Electric, it was discovered that the polycarbonates of BPA could be prepared (eq. 2). Unlike the ahphatic polycarbonates prepared earlier, which were either hquids or low melting sohds, the aromatic polycarbonates were amorphous sohds having elevated glass-transition temperatures. 

Since successful commercialization of Kapton by Du Pont Company in the 1960s (10), numerous compositions of polyimide and various new methods of syntheses have been described in the Hterature (1—5). A successful result for each method depends on the nature of the chemical components involved in the system, including monomers, intermediates, solvents, and the polyimide products, as well as on physical conditions during the synthesis. Properties such as monomer reactivity and solubiHty, and the glass-transition temperature,T, crystallinity, T, and melt viscosity of the polyimide products ultimately determine the effectiveness of each process. Accordingly, proper selection of synthetic method is often critical for preparation of polyimides of a given chemical composition. 

Polymers of Styrene Derivatives. Many styrene derivatives have been synthesized and the corresponding polymers and copolymers prepared (61). Glass-transition temperatures for a series of substituted styrene polymers are shown in Table 3. The highest T is that of... 

As-polymerized PVDC does not have a well-defined glass-transition temperature because of its high crystallinity. However, a sample can be melted at 210°C and quenched rapidly to an amorphous state at <—20°C. The amorphous polymer has a glass-transition temperature of — 17°C as shown by dilatometry (70). Glass-transition temperature values of —19 to — 11°C, depending on both method of measurement and sample preparation, have been determined. 

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

Glass-Transition Temperature. The T of PVP is sensitive to residual moisture (75) and unreacted monomer. It is even sensitive to how the polymer was prepared, suggesting that MWD, branching, and cross-linking may play a part (76). Polymers presumably with the same molecular weight prepared by bulk polymerization exhibit lower T s compared to samples prepared by aqueous solution polymerization, lending credence to an example, in this case, of branching caused by chain-transfer to monomer. 

Prepa.ra.tion, The preparation of amorphous high (99%) 1,2-polybutadiene was first reported iu 1981 (27). The use of a heterocycHc chelating diamine such as dipiperidine ethane iu the polymerization gave an amorphous elastomeric polymer of 99.9% 1,2 units and a glass-transition temperature of +5°C. In a previous description (53,54) of the use of a chelating diamine such as A/A/N(N -tetramethylethylene diamine, an 80% 1,2-polybutadiene with a glass-transition temperature of —30°C was produced. 

Polymers have been prepared from nuclear substituted di-(4-hydroxyphenyl)-alkanes, of which the halogenated materials have been of particular interest. The symmetrical tetrachlorobis-phenol A yields a polymer with a glass transition temperature of 180°C and melting range of 250-260°C but soluble in a variety of solvents. 

The presence of ether linkages in the polymer molecule imparts chain flexibility, lowers glass transition temperature, and enhances solubility while maintaining the desired high temperature characteristics [192]. Recently, polyether imines were prepared by the reaction of different diamines with 4,4 -[l,4-phenylene bis(oxy)] bisbenzaldehyde [184]. The polymers synthesized by the solution method were yellow to white in color and had inherent viscosities up to 0.59 dl/g in concentrated H2SO4. Some of these polyimines can be considered as... 

C—S—C) in the main chain. The new polyethers prepared either by new heteroarylene activated or by aromatic activated systems have good melt processability. The thermal stability and glass transition temperature of bisphenol-A based new polymers are shown in Table 10. 

Park et al. [20] reported on the synthesis of poly-(chloroprene-co-isobutyl methacrylate) and its compati-bilizing effect in immiscible polychloroprene-poly(iso-butyl methacrylate) blends. A copolymer of chloroprene rubber (CR) and isobutyl methacrylate (iBMA) poly[CP-Co-(BMA)] and a graft copolymer of iBMA and poly-chloroprene [poly(CR-g-iBMA)] were prepared for comparison. Blends of CR and PiBMA are prepared by the solution casting technique using THF as the solvent. The morphology and glass-transition temperature behavior indicated that the blend is an immiscible one. It was found that both the copolymers can improve the miscibility, but the efficiency is higher in poly(CR-Co-iBMA) than in poly(CR-g-iBMA),... 

---