Copolymer power-feed

The effect of non-uniform polymer composition is shown in Figure 11 for the case of a 50/50-methyl methacrylate/ethyl acrylate copolymer made by a linear power feed process in which the near tank initially contained only ethyl acrylate and the far tank only methyl methacrylate. Compared with its uniform counterpart, the non-uniform polymer had a T D approximately 25° lower and a respectable... 

The toughness parameter q is defined by Equation 13. The effect of nonuniform polymerization is shown for a 50/50 copolymer in which the power feed profile involved a decreasing ethyl acrylate concentration (0 1), with x = 1 (linear). (( ) power feed, q = 0.19)... 

Figures 2, 3 and 4 illustrate the differences between conventional mixed feed, staged and power-feed copolymers whose average composition is 50/50 ethyl acrylate/styrene. In the case of the staged polymerization, all the ethyl acrylate was fed first followed by the styrene. The power-feed copolymer was prepared with ethyl acrylate linearly increasing as a function of time, i.e., x = 1.0, = 0.

The differences in the three polymerization processes are immediately apparent in the spectra. For the conventional copolymer, Figure 2, there is a predominance of BAB triads (EA = A). The power-feed copolymer appears to have relatively higher concentrations of mixed (AAB = BAA) and homo (AAA) triads. In the case of the stage polymerization, Figure 3, the carbonyl resonance is essentially identical to that for poly(ethyl acrylate), that is, AAA triads. 

Figure 4. The 13C NMR spectrum of a 50/50—styrene/ethyl acrylate copolymer prepared using a linear power feed profile with ethyl acrylate increasing 0—> 1.0, and styrene decreasing 1.0 —> 0 with time...

Figure 5. Linear power feed profile for a 50/50—styrene/ethyl acrylate copolymer in which ethyl acrylate decreases 1.0 -> 0 and styrene increases 0 -> 1.0 with...

A series of computer programs was written to test models for predicting sequence distribution for the power-feed copolymers. The programs consist of ... 

C nuclear magnetic resonance spectroscopy can be employed to study changes in copolymer sequence distribution brought about by differences in monomer feed profiles. Sequence distributions characteristic of conventional, staged, and power-feed copolymers are easily distinguishable in a model system of the type described here. 

Figure 9. Correlation of calculated and measured triad fractions for a model 50/50—styrene/ethyl acrylate copolymer prepared with a linear power feed profile in which ethyl acrylate increases 0—> 1.0 and styrene decreases 1.0 — 0 with time (n = 0.16 r2 = 0.82 (A) EA-EA-EA EA-EA-STY = STY-EA-EA ...

Triad sequence assignments have been made for ethyl acrylate-centered triads. Apparent reactivity ratios have been calculated for the semi-batch copolymers using run number theory. A model has been developed to describe the power-feed systems and predict the triad distributions in the incremental and final copolymer using the experimentally determined r-j and r values. 

A further development of the concept of copolymer composition control has been the invention of power feeds by Bassett and Hoy [64,65]. This takes the starve-fed control of copolymer composition one stage further by providing an easy means of continuously varying the composition of the comonomer mixture being fed into the reaction vessel, and may be considered as a means of achieving controlled composition drift. The simplest power feed Systran employs two monomer feed tanks and is illustrated in Figure 7.4a, whitli shows that tank 2 feeds into tank 1 from which monomer is supplied to the reaction vessel. Consider the mass balance in tank 1 with respect to monomer A ... 

Although there have been a number of studies of the mechanical properties of latex films, a detailed discussion of this topic is beyond the scope of this review. Thoe are several excellent reviews on the mechanical properties of coatings in gennal [65]. One of the main focus points in these reviews is the influence of CTosslinking in the polymer on its mechanical properties. In flie area of latex films, Larntda [66] has shown, for copolymer latex, how sensitive the mechanical propoties are to the details of latex synthesis (e.g. batch, sani-c itinuous or power-feed). Here the key feature is that different synthesis strat es give rise... 

Guyot et a/. have described a so-called corrected-batch process for producing copolymers of constant composition by emulsion polymerization. Unlike the power-feed process, the polymerization is carried out in the presence of excess monomer. The principle is to monitor the composition of the unreacted monomer by gas-liquid chromatography, and then to use this information to correct for difference in the rates of copolymerization of the two monomers by controlling the relative rates of feed of the two monomers to the reactor. The objective is to keep the monomer-feed composition constant, and hence also the composition of the copolymer which is being produced instantaneously. 

Figure 3, i.e., 50/50-styrene/ethyl acrylate copolymer made by uniform (random), staged, or power feed processes (24). Using the carbonyl carbon of the acrylate ester as a probe of the sequence distributions in a series of random styrene/ethyl acrylate copolymer, assignments were made for the three major resonance regions in terms of triad sequences. Figure 6 illustrates the differences observed. In the... 

The power feed addition strategy is also conducted under monomer starved conditions but aiming at producing a copolymer with varying composition, see Basset and Hoy (1981). In this case a heterogeneous copolymer composition distribution, that is, a copolymer product with a predefined composition distribution, is sought. This is obviously achieved by varying the ratio of the monomer flow rates into the reactor continuously with time. 

Figure 4.12 Two possible set-ups for power-feed control of copolymer composition.

This equation relates the (instantaneous) copolymer composition with the monomer feed of M and M2. Values for and are usually determined by graphical methods (9,10). Today, with the prevalence of powerful desktop computers, numerical minimisa tion methods are often used (11—14). 

Styrene-SQ., Copolymers. I would now like to discuss two systems which illustrate the power of C-13 nmr in structural studies. The first is the styrene-SO system. As already indicated, this is of the type in which the chain composition varies with monomer feed ratio and also with temperature at a constant feed ratio (and probably with pressure as well.) The deviation of the system from simple, first-order Markov statistics, —i.e. the Lewis-Mayo copolymerization equation—, was first noted by Barb in 1952 ( ) who proposed that the mechanism involved conplex formation between the monomers. This proposal was reiterated about a decade later by Matsuda and his coworkers. Such charge transfer com-... 

The copolymer feed ratio has a considerable effect on the power conversion efficiency. It increases with increasing MEH-PPV content. A max-imvun power conversion efficiency of 1.30% for a copolymer of (OCIO)-2-spiro-PFV and MEH-PPV 50 50 has been achieved. However, with a pristine MEH-PPV, a power conversion efficiency of 2.10% is found. 

Those hot-melts that find application in the household and DIY applications are usually based on ethylene-vinyl acetate copolymers (EVA) and contain tackifying resins (e.g. hydrocarbon resins). Today s pistols are equipped almost without exception with a mechanical feed, differ in their heating power, and are partly designed for cordless work. 

Another area in which both proton and carbon-13 nmr have proved very powerful is the determination of the structure of copolymers. This has a long history (ref. 6, Chap. X 15,16)9 beginning with the observations of butadiene-styrene copolymers in 1959, Again, the information content of the spectra has increased remarkably since these early reports. Although compositional sequence lengths and probabilities can be calculated from the copolymer equation using the traditional data of polymer composition vs. monomer feed composition, nmr allows direct measurement of the sequences and gives in addition much structural detail not available from overall composition alone. 

The significance of the counterion identity associated with Surlyn with regard to exfoliation efficiency and mechanical properties was explored by Shah and Paul [5]. The counterions were lithium (Surlyn 9945), sodium (8945 evaluated above), and zinc (Surlyn 7940). Each copolymer was neutralized to 40%. The procedures for preparation of the polymer nanocomposites and characterization were identical to that described above, except that the feed rate for the extruder was decreased to 800 g/h because the high build in viscosity associated with utilization of the zinc counterion 9945. This prevented the power capabilities of the extruder from being exceeded. Cloisite 20A was utilized as the organomontmor-illonite for the preparation of the polymer composite. The loading levels of organomontmorillonite in the polymers were 2.5, 5.0, and 10.0 wt. %. 

Current research activities are focused on the identification of membrane materials and structures with high proton conductivity and low methanol permeability. Ultimately, one would tike membranes that work well in a DMFC at 10-20 M methanol, but the focus of most research is on much lower methanol feed concentrations (0.5 and 1.0 M). Since DMFCs are designed primarily for the portable power/electronics market, operating temperatures in the 25-80°C range are usually considered. Extensive data is available in the literature on new membrane materials with reduced methanol permeability, including sulfonated or phosphonated copolymers, phosphoric-acid-doped polybenzimidazole, and various blends and composites (see Table 29.6 for a listing of DMFC properties). 

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