Polymerization azeotropic

Because of this parallel with liquid-vapor equilibrium, copolymers for which ri = l/r2 are said to be ideal. For those nonideal cases in which the copolymer and feedstock happen to have the same composition, the reaction is called an azeotropic polymerization. Just as in the case of azeotropic distillation, the composition of the reaction mixture does not change as copolymer is formed if the composition corresponds to the azeotrope. The proportion of the two monomers at this point is given by Eq. (7.19). 

It should be noted, too, that the r values for this system do not permit an azeotropic polymerization, as predicted by Eq. (2.39). With respect to the distribution of styrene monomer units in the copolymer, the monomer reactivity ratio product, rers = 0.8, is close to a value of 1.0, which would correspond to an ideal copolymerization (Odian, 2004b) which would correspond to a random distribution of styrene units along the chain. For an ideal copolymerization, the relative rates of incorporation of the two monomers are independent of the chain end unit as predicted by Eq. (2.42). 

SAN copolymers at the azeotropic polymerization ratio of 76/24 (by wt) are miscible with a-methyl styrene-AN copolymer at it s azeotropic ratio (69/31 (by wt) [747].aMS-AN (32 wt% AN) was shown to be miscible with SAN copolymers with AN contents of 28 to 40 wt% AN, with lest behavior observed [748]. As the a-methyl styrene-AN copolymer has a Tg 25 °C higher than SAN, it is commercially employed in blends with ABS to boost the heat distortion temperature up to 100 °C, required for some appliance applications. SAN copolymers are also miscible with styrene-maleic anyhdride (SMA) co- and terpolymers (e.g., with MMA), and the SMA co-and terpolymers with TgS in the range of 140 °C can also be employed to enhance the heat distortion temperature of ABS [749, 750]. SAN (styrene content = 75wt%) blends with styrene-N-phenyl maleimide copolymers (styrene content = 58 wt%) were found to be miscible and followed time-temperature superposition over the entire composition range [751 ]. N-phenyl maleimide groups can be prepared by reaction of aniline with maleic anhy-... 

Note / An azeotropic polymerization occurs at only one specific molar ratio of monomers in the feed. 

Note 2 Although, in its equality of copolymer and monomer-feed compositions, an azeotropic polymerization has the same feature as an ideal binary copolymerization in which i 2 = / 2J = 1, it is not an ideal copolymerization as it has rj2f2i 1-... 

Note 1 The instantaneous composition of copolymer generally changes during the course of a copolymerization due to the changing composition of the monomer mixture (but see azeotropic polymerization). 

The first quantitative model, which appeared in 1971, also accounted for possible charge-transfer complex formation (45). Deviation from the terminal model for bulk polymerization was shown to be due to antepenultimate effects (46). Mote recent work with numerical computation and C-nmr spectroscopy data on SAN sequence distributions indicates that the penultimate model is the most appropriate for bulk SAN copolymerization (47,48). A kinetic model for azeotropic SAN copolymerization in toluene has been developed that successfully predicts conversion, rate, and average molecular weight for conversions up to 50% (49). 

Methyl Vinyl Ketone. Methyl vinyl ketone [78-94-4] (3-buten-2-one) is a colorless Hquid with a pungent odor. It is stable only below 0°C, and readily polymerizes on standing at room temperature. It can be inhibited for storage and transportation by a mixture of acetic or formic acid and hydroquinone or catechol (266). This ketone is completely soluble in water, and forms a binary azeotrope with water (85 MVK 15 H2O vol %) at 75.8°C. 

NMP are examples of suitable solvents for PES and PPSF polymerizations. Chlorobenzene or toluene are used as cosolvents at low concentrations. These cosolvents form an azeotrope with water as they distill out of the reaction mixture, thereby keeping the polymerization medium dehydrated. Potassium carbonate is a suitable choice for base. The synthesis of PES and PPSE differ from the PSE case in that the reaction is carried out in a single-step process. In other words, the formation of the dipotassium salt of the bisphenol is not completed in a separate first step. Equations 2 and 3 represent polymerizations based on the dipotassium salts of bisphenol S and biphenol to make PES and PPSE, respectively. 

Vinyl acetate is a colorless, flammable Hquid having an initially pleasant odor which quickly becomes sharp and irritating. Table 1 Hsts the physical properties of the monomer. Information on properties, safety, and handling of vinyl acetate has been pubUshed (5—9). The vapor pressure, heat of vaporization, vapor heat capacity, Hquid heat capacity, Hquid density, vapor viscosity, Hquid viscosity, surface tension, vapor thermal conductivity, and Hquid thermal conductivity profile over temperature ranges have also been pubHshed (10). Table 2 (11) Hsts the solubiHty information for vinyl acetate. Unlike monomers such as styrene, vinyl acetate has a significant level of solubiHty in water which contributes to unique polymerization behavior. Vinyl acetate forms azeotropic mixtures (Table 3) (12). 

Suspension (co)polymerization is carried out in aqueous solutions of monomers dispersed in the form of 0.1-5 mm diameter droplets by stirring in nonmixed water-organic liquids in the presence of initiators. The organic liquids that are not dissolving monomers and (co)polymers are represented by solvents that either form azeotropic water mixtures (toluene, heptane, cy-... 

Scheme 3b). It is instructive at this point to reiterate that the furan nucleus can be used in synthesis as a progenitor for a 1,4-dicarbonyl. Whereas the action of aqueous acid on a furan is known to provide direct access to a 1,4-dicarbonyl compound, exposure of a furan to an alcohol and an acid catalyst should result in the formation of a 1,4-diketal. Indeed, when a solution of intermediate 15 in benzene is treated with excess ethylene glycol, a catalytic amount of / ara-toluenesulfonic acid, and a trace of hydroquinone at reflux, bisethylene ketal 14 is formed in a yield of 71 %. The azeotropic removal of water provides a driving force for the ketalization reaction, and the presence of a trace of hydroquinone suppresses the formation of polymeric material. Through a Finkelstein reaction,14 the action of sodium iodide on primary bromide 14 results in the formation of primary iodide 23, a substance which is then treated, in crude form, with triphenylphosphine to give crystalline phosphonium iodide 24 in a yield of 93 % from 14.

The existence of an azeotropic composition has some practical significance. By conducting a polymerization with the monomer feed ratio equal to the azeotropic composition, a high conversion batch copolymer can be prepared that has no compositional heterogeneity caused by drift in copolymer composition with conversion. Thus, the complex incremental addition protocols that arc otherwise required to achieve this end, are unnecessary. Composition equations and conditions for azeotropic compositions in ternary and quaternary eopolymerizations have also been defined.211,21... 

Using copolymerization theory and well known phase equilibrium laws a mathematical model is reported for predicting conversions in an emulsion polymerization reactor. The model is demonstrated to accurately predict conversions from the head space vapor compositions during copolymerization reactions for two commercial products. However, it appears that for products with compositions lower than the azeotropic compositions the model becomes semi-empirical. 

The esterification with methacrylic acid is performed at substantially lower temperatures than the above-mentioned procedures. An aerobic polymerization inhibitor is needed and an azeotropic removal of water with suitable solvents is also necessary. 

In a very similar way, hydroxy functionalized ATRP initiators such as 2,2,2-tribromoethanol can be used for the simultaneous polymerization of eCL and MMA (Scheme 25) [83]. Purposely, the ROP of eCL is promoted by Al(OfPr)3 added in catalytic amount so that the rapid alcohol-alkoxide exchange reaction (see Sect. 2.4) activates all the hydroxyl functions. In order to avoid initiation by the isopropoxy groups of Al(0/Pr)3. The in-situ formed zPrOH is removed by distillation of the zPrOH/toluene azeotrope. On the other hand, the ATRP of MMA is catalyzed by NiBr2(PPh3)3. The two aforementioned one-step methods provide block copolymers with controlled composition and molecular weights, but with a slightly broad MWD (PDI=1.5-2). 

In such cases the polymerization can be taken to relatively high conversion without change in composition of the copolymer formed (see Example 3-37). In the copolymerization diagram the azeotrope corresponds to the intersection point of the copolymerization curve with the diagonal. For example, from Fig. 3.4 it may be seen that in the radical copolymerization of styrene and methyl methacrylate the azeotropic composition corresponds to 53 mol% of styrene. 

---