Fluoride glasses: transition temperature

The homopolymers poly(methyl methacrylate) and poly-(ethyl methacrylate) are compatible with poly(vinylidene fluoride) when blended in the melt. True molecular com-patibility is indicated by their transparency and a single, intermediate glass transition temperature for the blends. The Tg results indicate plasticization of the glassy methacrylate polymers by amorphous poly(vinylidene fluoride). The Tg of PVdF is consistent with the variation of Tg with composition in both the PMMA-PVdF and PEMA-PVdF blends when Tg is plotted vs. volume fraction of each component. PEMA/PVdF blends are stable, amorphous systems up to at least 1 PVdF/I PEMA on a weight basis. PMMA/ blends are subject to crystallization of the PVdF component with more than 0.5 PVdF/1 PMMA by weight. This is an unexpected result. 

At least two different glass transition temperatures have been reported for PVdF homopolymer. Owing to the large proportion of crystalline structure in this polymer and the rapid crystallization which occurs while heating quenched amorphous samples, it is difficult experimentally to obtain an unambiguous, well-defined second-order transition. Mandel-kem, Martin, and Quinn (16) reported a value below — 40°C based upon an extrapolation of the Tg data for vinylidene fluoride-chlorotri-fluoroethylene copolymers in accordance with the Fox equation (6),... 

Mixtures of poly(vinylidene fluoride) with poly (methyl methacrylate) and with poly (ethyl methacrylate) form compatible blends. As evidence of compatibility, single glass transition temperatures are observed for the mixtures, and transparency is observed over a broad range of composition. These criteria, in combination, are acceptable evidence for true molecular intermixing (1, 19). These systems are particularly interesting in view of Bohns (1) review, in which he concludes that a compatible mixture of one crystalline polymer with any other polymer is unlikely except in the remotely possible case of mixed crystal formation. In the present case, the crystalline PVdF is effectively dissolved into the amorphous methacrylate polymer melt, and the dissolved, now amorphous, PVdF behaves as a plasticizer for the glassy methacrylate polymers. 

Planar and channel waveguides can be obtained by ion-exchange technique with fluoride glasses. The experiment is carried out with Er +-doped ZBLA fluoride glass samples, treated by HCl gas at a temperature below the glass transition temperature Tg (Tg = 307 °C for ZBLA). The chemical reaction at the glass surface is ... 

The following data were obtained [L. Mandelkern, G. M. Martin and F. A. Quinn, J. Res. Natl. Bur. Stand., 58, 137 (1957)] for the values of glass transition temperature Tg of poly[(vinylidene fluoride)-co-chlorotrifluoroethylene as a function of the weight fraction W of vinylidene fluoride. 

Figure 1 Thermal analysis of a fluoride glass showing characteristic temperatures Tg is the glass transition temperature Tx corresponds to the begiiming of the crystallization T is where the crystalline phase starts to melt T is the liquidus temperature corresponding to the end of the melting process...

The glass transition temperature of poly(vinyl fluoride) was determined to be 43°C. The transition is independent of the molecular weight of the polymer. Polymers, for this study, were prepared in the presence of a variety of initiators such as 2,2 -azobisisobutyronitrile, tributylborane monoperoxide, or diisopropyl diperoxycarbonate [17]. 

Fig. 12.9 Glass-transition temperatures Tg of copolymers of polychlorotrifluoroethylene with polylvinylidene fluoride) plotted against the weight fraction of the latter. The curve is the theoretical curve equation (12.8) with a = 1.75. (Reproduced by permission from John Wiley Sons Limited.)...

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Figure 35-5. Glass transition temperatures of single phase mixtures of poly(methyl methacrylate) with poly(vinylidene fluoride). (After J. S. Noland, N. N. Hsu, R. Saxon, and J. M. Schmitt.)...

PVB and cationic PVB was blended with poly(vinyUdene fluoride) (PVDF). These blends were used to fabricate hydrophihc ultrafiltration membranes (32). A visual inspection method and a glass transition temperature method were applied to study the miscibility of the blends. PVDF is immiscible with PVB, but with cationic PVB it is partially miscible. 

Copolymers from tetrafluoroethylene and 40% perfluorovinyl methyl ether are also elastomers (glass-transition temperature — 12°C). The copolymerization is carried out in aqueous emulsion with ammonium perfluoro-octanoate as emulsifier. Vulcanization is possible with hexamethylene diamine via the small amount of perfluoro(4-carboxy methyl butyl vinyl ether) also polymerized into the copolymer. This ether is produced from perfluoroglutaryl fluoride and hexafluoropropylene oxide. 

One of the unusual properties of (PNF2) is its low-tanperature elasticity, which reflects a relatively high degree of torsional mobility of the chain. Of the three polymeric phosphazene halides, the fluoride has the lowest glass transition temperature, which is in accord with it having least interchain interaction and highest torsional freedom at low tanperatures (Table 12.37). 

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