Epoxides glass transition temperatures

As the name suggests, epoxidised NR is prepared by chemically introducing epoxide groups randomly onto the NR molecule. This chemical modification leads to increased oil resistance, greater impermeability to gases, but an increase in the glass transition temperature, Tg, and damping characteristics the excellent mechanical properties of NR are retained. 

The objectives of this work were to synthesize a series of arylether sulfone oligomers with an increased chain length between reactive sites by the proposed synthetic route. In addition, it was to be determined if the products obtained by this route would have initial glass transition temperatures near or below room temperature while having cured Tg s in the 300-350°F range of epoxides. 

Table IV summarizes the glass transition temperature of a number of special functional oil-based homopolymers. Many of the polymers shown indeed have T s below the critical value. It is now believed that the synthetically epoxidized oils were fully epoxidized, producing materials with unusually high degrees of crosslinking, which tended to raise their T s beyond the desirable range.

Epoxides can co-polymerize with CO2 to give aliphatic polycarbonates. The co-polymerization is one of the most promising methods to utilize GO2 as a Cl feedstock. The product polycarbonates have many potential applications because of their unique properties. For example, poly(propylene carbonate) (PPG) decomposes completely at 300 °G in any environment to leave a very small amount of ash. This feature makes it applicable to pore former for mesoporous carbon composites. Poly(cyclohexene carbonate) (PGG) has glass-transition temperature (Tg) of 115°G, higher than 35-40 °G of PPG, endowing the materials with properties very similar to polystyrene. ... 

Propylene oxide represents a very attractive epoxide monomer for copolymerization with C02, as polypropylene carbonate) is industrially valuable. The low glass transition temperature (Tg) of 313 K, the sharp and clean decomposition above 473 K, and biodegradability of this copolymer are the reasons for its attracting interest in several applications. On a similar basis, H NMR spectroscopy is useful for assessing the coupling products resulting from the reaction of PO and C02 (Figure 8.21). 

Adhesion studies of epoxy resins modified with high modulus and high glass transition temperature thermoplastics have shown adhesion can reach or even exceed that of the unmodified resin. The use of flexible polyamides or flexible epoxides resulted in shear strength increases in epoxy systems employed by Cunliffe et al. [144],polyethersulfones [18,145],polyetherimides [109,146,147], and polyetherketones [148-150]. 

Figures 14 and 15 show the relations between the amount of iron arene initiator, the reaction enthalpy (AHj and the glass transition temperature Tg of the polymerized Bisphenol-A diglycidylether (cf. Table 2, structure I, x = 0.15) and the oligomer product based on the former compound (cf. Table 2, structure I, x = 11.8). The maximum polymerization heat per mole of epoxide is observed ivith an initiator concentration of 1.5-2.5% (w/w). At this concentration, Tg of the crosslinked resin is about 115 °C for the polymerized low-molecular-weight expoxide and about 80 "C for the polymerized high-molecular-weight epoxide resin.

The glass transition temperatures themselves were, of course, lowered by the presence of the epoxidized oil (Table III). With the... 

When the respective component glass transition temperatures are close, the blend Tg is not a useful measure of blend homogeneity. In fact, excess mixing volumes and specific interactions can cause anomalous behavior. The Tg of such a blend can be lower (as seen in polychloroprene/epoxidized polyisoprene blends (McGrath and Roland, 1994)) or higher (as seen in polylepichlorohydrin/polyvinylmethylether blends (Alegria et al., 1995)), than Tg of either neat component. In blends of polymers having nearly equivalent... 

Table 3.2 also includes data for the advanced thermoplastic resins (PEEK) and for a thermosetting resin, an end-capped bismaleimide (BMI) called PMR-15. Moisture contents tend to be lower for these advanced materials [12,13]. One way to overcome the environmental sensitivity of epoxide resins is to employ these advanced resins, as demonstrated in Table 3.2. However, changing to other resin systems brings with it other concerns. For example, PEEK relies on crystallinity for its higher temperature performance. Its glass transition temperature is only 143°C and a change in modulus can be observed at that temperature. In addition, higher process temperatures are required both for high performance thermosets and thermoplastics. The consequent higher residual thermal stresses can off-set some of the advantages of a higher service temperature, in comparison with advanced epoxy resins.

In the same fashion, methacrylate groups have also been incorporated in soybean oils to generate similar polymer architectures. Acrylated epoxidized soybean oil and maleinated acrylated epoxidized soybean oil were reacted with methacrylated lauric acid as a method of reducing styrene input [41]. This increased both the visocosity and the glass transition temperature when compared with the styrene analogue as well as having the benefits of improving the environmental properties of the polymer even further. Acrylated, epoxidized soybean oil was copolymerized with methyl methacrylate in a polymerization initiated by benzoyl peroxide to produce a clear bioplastic [42]. 

Also similar to styrene and methyacrylates is the use of divinylbenzene as a comonomer. Acrylated, epoxidized soybean oil was polymerized with divinylbenzene or modified with phthalic anhydride before polymerization to give materials with increased glass transition temperatures [43]. Modification of the soybean oil with cinnamate esters and subsequent... 

Figure 11.28. Glass transition temperature, Tg, and crystallization temperature, T, of polylactide plasticized with variable amounts of epoxidized polypropylene glycol having molecular weight of 640 daltons. [Data from McCarthy S Song X, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 363.]...

In all these curing reactions, the degree of cross-linking, and also the glass transition temperature, increases with increasing conversion. The segments become less mobile, not all groups can react, and a complete network cannot be formed. Consequently, cured epoxide resins do not have the optimum properties expected of ideal networks. 

Hyperbranched polyethers can be synthesized via the A2+B3 approach, when diepoxides (3-24) are reacted with triols, such as TMP. Emrick et al. used 1,2,7,8-diepoxyoctane as the A2 monomer and TMP as the B3 monomer with tetra-n-butylam-monium chloride as the nucleophilic catalyst. Nucleophilic attack of the chloride ion on an epoxide at the less-hindered terminal carbon led to the formation of secondary alkoxide. Due to the equilibrium between primary and secondary alk-oxides via proton exchange, nucleophilic attack of primary alkoxides on the epoxide rings resulted in the formation of aliphatic hyperbranched polyether. As the feed ratio of the diepoxide and TMP was varied from 1.5 to 3, the resulting hb polyether contained two types of terminal units (T), one type of dendritic unit (D), and linear units (L) as shown in Scheme 4. The polydispersity index (PDI) of the polyether increased with the increase of molecular weight (from 1.5-1.8 at M = 1000 up to 5.0 at Mw = 7000). The products are viscous liquids with glass transition temperatures below room temperature. 

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