Polyester-forming systems

Table I. Values of b for polyester-forming systems derived(21 ) from Figure 5 and plots of X b versus (cac + Cbc)-1 according to equations(7). vA(-/v-fractional length of acid chloride residue in the chain of v bonds, (i) cext = cao + cbo- (ii) cext = cac + cbc For explanation of reactants see Figure 5.

Behaviour similar to that shown by the polyester-forming systems is shown by the several polyurethane-forming systems which have been studied(3,4,6,15,23-28), and Figure 6 and Table II give the results(29) for polyurethane-forming systems from which network materials have been formed at complete reaction. 

In general, compared with the polyester-forming systems, curved... 

Curves 1 and 2, and 3 to 6 in Figure 1 refer, respectively, to HDI/POP triol and HDI/POP tetrol polymerisations with different values of V. Marked reductions in modulus occur even for bulk reaction systems, which give the points at the lowest values of Pj- q for the different systems. More inelastic chains are formed in trifunctional as compared with tetrafunctional networks for a given value of pp q (cf. curves 1 and 2 with 3 to 6. In addition, for a given functionality, as V decreases the proportion of inelastic loops increases. Similar results have been obtained for polyester-forming systems using POP triols and diacid chlorides(13). 

The slopes of the lines in fig 2 relate to proportions of inelastic loops formed for given extents of pre-gel intramolecular reaction. Thus, for a given value of p more inelastic loops are formed in the triol networks (systems 1 and 2) compared with the tetrol networks (systems 3 and 4). In addition, for a given functionality, as v increases the proportion of inelastic loops decreases (compare systems 1 and 2 and systems 3 and 4). Similar results have been obtained from polyester-forming systems using... 

The initial, linear portions of the experimental plots in Figure 2 were used to determine the values of b for each PDMS-forming system, and the results are listed in Table 3. The values of b for the polyurethane- and polyester-forming systems are also shown in Table 3. It can be seen that, in spite of the very large ranges of covered (148... 

Figure 4. versus Hcm for the six PDMS-forming systems listed in Table 2 the corresponding data for the polyurethane- and polyester-forming systems analysed previously are also plotted, for comparison (+). 

Those polymers which are the condensation product of two different monomers are named by applying the preceding rules to the repeat unit. For example, the polyester formed by the condensation of ethylene glycol and terephthalic acid is called poly(oxyethylene oxyterphthaloyl) according to the lUPAC system, as well as poly (ethylene terephthalate) or polyethylene terephthalate. 

The processed pulp is converted into a paper product via a paper production machine, the most common of which is the Fourdrinier paper machine (see Figure 21.6). In the Fourdrinier system,3 the pulp slurry is deposited on a moving belt (made from polyester forming fabrics) that carries it through the first stages of the process. Water is removed by gravity, vacuum chambers, and vacuum rolls. This waste water is recycled to the slurry deposition step of the process due to its high fiber content. The continuous sheet is then pressed between a series of rollers to remove more water and compress the fibers. 

Equations of an analogous type can be used for other polyurethane-forming systems, although the numerical values of the constants may be different, because Eq. (2.29) must be treated primarily as empirical. It is reasonable to expect that an adequate approximation for other systems would be n equal to 2 (which is typical for polyaddition reactions) and m also equals to 2. Such values of the constants m and n are valid, for example, for RIM-2200 (produced by Union Carbide ), which consists basically of polyester and 4.4-diphenylmethane diisocyanate.4... 

Morphology. Phase inversion in polymer mixtures occurs when the volume fraction of the dispersed phase becomes equal to or exceeds 0.5 (14). The driving force is to minimize the interfacial energy of the system. This is not the case here because the volume fraction of the rubber-rich phase at phase inversion is about 0.85. After inversion, the fraction of the continuous rubber-rich phase is only 0.28, and it increases to 0.63 at 12.5% rubber content. Initially, the components are fully soluble and compatible, but as the reactions proceed, the molecular weight of the products increases and phase separation results. The ability to separate and invert is dependent on the viscosity of the medium. The unsaturated polyester forms a gel at conversions as low as 2 to 5%, and both the ability to separate and to invert is impeded. Thus the morphology depends on the two competing effects of phase inversion and... 

Poly(e-caprolactone) is another practically important polyester formed by ionic polymerization of the cyclic ester. Cationic polymerization requires relatively high temperatures this enhances proton transfer and decreases the molecular weight, whereas anionic polymerization provides living systems. 

From the investigations reported, it may be concluded that the concentration dependences of the physical and mechanical properties of unsaturated polyesters formed in the presence of surfactants are of extremal character. This extremal character corresponds essentially to the same dependences of surface tension, turbidity, and viscosity of system with surfactant present. 

Similar to all commercial plastics, the traditional and more commonly used thermosetting resins are considered as petrochemicals, having been manufactured from petroleum. Some of the primary distillation products of crude oil, which can be classified either as olefins or aromatics, serve as precursors for the synthesis of thermosets. For example, epoxy resins are manufactured by the reaction of epichlorohydrin, a chloro-oxirane, and a derivative of propylene, with bisphenol A, which is a derivative of cumene. Another example would be the unsaturated polyesters (UPs), which are derivatives ultimately originating from ethylene (ethylene glycol) and benzene (maleic acid) [6]. Epoxies and polyesters constitute more than 95% of the thermoset composite market of the two, polyester-based systems predominate in volume by about 10-fold [6, 7]. Other thermoset resins used in reinforced form are phenolics, vinyl esters, and polyimides. Details of the properties and applications of these thermoset systems will be further discussed in the following section. 

Unsaturated polyesters 44 containing multiple electron-deficient maleate and/or fumarate double bonds along the polymer chain are readily prepared by the reaction of maleic anhydride or fumaric acid with a diol. In many cases, other diacids or dianhydrides are also included as comonomers to improve the final mechanical properties. The polyester is combined with styrene monomer and photopolymerization is carried out using a radical photoinitiator. Due to the reactivity ratios of the two vinyl components, there is a tendency toward alternation. However, the length of crosslinks between the polymer chains can be controlled by the amount of excess styrene present. This allows appreciable control over the structure of the network polymer formed, and this has a considerable impact on its mechanical and chemical properties. Photocurable unsaturated polyester-styrene systems have found numerous uses, but the major applications are in wood... 

The concept of functionaUty and its relationship to polymer formation was first advanced by Carothers (15). Flory (16) gready expanded the theoretical consideration and mathematical treatment of polycondensation systems. Thus if a dibasic acid and a diol react to form a polyester, assumiag there is no possibihty of other side reactions to compHcate the issue, only linear polymer molecules are formed. When the reactants are present ia stoichiometric amouats, the average degree of polymerization, follows the equatioa ... 

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