Composition dependence copolymers

An important industrial example of W/O emulsions arises in water-in-crude-oil emulsions that form during production. These emulsions must be broken to aid transportation and refining [43]. These suspensions have been extensively studied by Sjoblom and co-workers [10, 13, 14] and Wasan and co-workers [44]. Stabilization arises from combinations of surface-active components, asphaltenes, polymers, and particles the composition depends on the source of the crude oil. Certain copolymers can mimic the emulsion stabilizing fractions of crude oil and have been studied in terms of their pressure-area behavior [45]. 

In this section we have seen that the copolymer composition depends to a large extent on the four propagation constants, although it is sufficient to consider these in terms of the two ratios ri and r2. In the next section we shall examine these ratios in somewhat greater detail. 

Fig. 3. Dependence of the composition of copolymers of AN with DMVPS (Mj) on the composition of the initial mixture, (o) copolymerization in solution in DMSO (x) copolymerization in water...

Harwood112 proposed that the solvent need not directly affect monomer reactivity, rather it may influence the way the polymer chain is solvated. Evidence for the proposal was the finding for certain copolymerizations, while the terminal model reactivity ratios appear solvent dependent, copolymers of the same overall composition had the same monomer sequence distribution. This was explained in... 

If the chains are long, the composition of the copolymer and the arrangement oi units along the chain are determined almost entirely by the relative rates of the various chain propagation reactions. On the other hand, the rate of polymerization depends not only on the rates of these propagation steps but also on the rates of the termination reactions. Copolymer composition has received far more attention than has the rate of copolymerization. The present section will be confined to consideration of the composition of copolymers formed by a free radical mechanism. 

In summary, the copolymer composition depends on the monomer ratio in the monomer mixture and on r1 and rz reactivity ratios. 

Another differential reaction is copolymerization. An equi-molar mixture of styrene and methyl methacrylate gives copolymers of different composition depending on the initiator. The radical chains started by benzoyl peroxide are 51 % polystyrene, the cationic chains from stannic chloride or boron trifluoride etherate are 100% polystyrene, and the anionic chains from sodium or potassium are more than 99 % polymethyl methacrylate.444 The radicals attack either monomer indiscriminately, the carbanions prefer methyl methacrylate and the carbonium ions prefer styrene. As can be seen from the data of Table XIV, the reactivity of a radical varies considerably with its structure, and it is worth considering whether this variability would be enough to make a radical derived from sodium or potassium give 99 % polymethyl methacrylate.446 If so, the alkali metal intitiated polymerization would not need to be a carbanionic chain reaction. However, the polymer initiated by triphenylmethyl sodium is also about 99% polymethyl methacrylate, whereas tert-butyl peroxide and >-chlorobenzoyl peroxide give 49 to 51 % styrene in the initial polymer.445... 

The rate of copolymerization, unlike the copolymer composition, depends on the initiation and termination steps as well as on the propagation steps. In the usual case both monomers combine efficiently with the initiator radicals and the initiation rate is independent of the feed composition. Two different models, based on whether termination is diffusion-controlled, have been used to derive expressions for the rate of copolymerization. The chemical-controlled termination model assumed that termination proceeds with chemical control, that is, termination is not diffusion-controlled [Walling, 1949]. But this model is of only historical interest since it is well established that termination in radical polymerization is generally diffusion-controlled [Atherton and North, 1962 Barb, 1953 Braun and Czerwinski, 1987 North, 1963 O Driscoll et al., 1967 Prochazka and Kratochvil, 1983] (Sec. 3-10b). 

It is important to note that the tendency of a monomer towards polymerization and therefore also towards copolymerization is strongly dependent on the nature of the growing chain end. In radical copolymerization the composition of the copolymer obtained from its given monomer feed is independent of the initiating system for a particular monomer pair, but for anionic or cationic initiation this is normally not the case. One sometimes observes quite different compositions of copolymer depending on the nature of the initiator and especially on the type of counterion. A dependence of the behavior of the copolymerization on the used catalyst is often observed with Ziegler-Natta or metallocene catalysts. 

In homogeneous copolymerization, the instantaneous composition of copolymer is decided only by monomer reactivity ratio. On the contrary, in emulsion copolymerization, the copolymer composition depends not only on the monomer reactivity ratio but also on the distribution of monomers between oil (polymer-monomer particles) and aqueous phases (18). 

The composition dependence of Tm is investigated for RIS models of atactic PP and random ethylene - propylene copolymers using a modified Flory s equation. 

Fig. 12. The relative viscosity of polyacrylamide-co-acrylates versus different copolymer compositions depending on the presence of the low-molecular-weight electrolyte sodium sulfate. All Samples have the same degree and distribution of polymerization...

Optical properties of LLDPE resins also depend on the degree of branching uniformity, Resins with a uniform branching distribution make highly transparent film with haze as low as 3-4%. In contrast, film manufactured from compositionally nonunifonn copolymers is much more opaque, with haze of over 10-15% this is due to the presence of large crystalline lamellae consisting of nearly nonbranched PE chants. 

The mechanical and thermal properties of a range of poly(ethylene)/ poly(ethylene-propylene) (PE/PEP) copolymers have been examined by Mohajer et al. (1982). They studied the effect of variation of composition and copolymer architecture on the polymer properties by synthesizing a range of PE-PEP-PE and PEP-PE-PEP triblocks and PE-PF.P diblocks with high molecular weights (M > 200 kg mol (.The crystallinity, density and melting enthalpy for all copolymers were found to be linearly dependent on the PE content, indicating microphase separation of PE and rubbery PEP in the solid state. The... 

In order to go further in the understanding of the temperature and composition dependence of toughness, it is useful to examine the morphology in front of the crack. Such a study has been carried out [52] in the case of MGIM58 copolymer. The applied technique concerns the stable fracture regime optical and electron microscopies are combined to lead to a precise analysis. 

The properties of copolymers primarily depend upon their chemical composition but also on the microstructure of the polymer chains. However, the chemical composition of copolymers can often depend on their molecular weight fractions [1,8-10],... 

A similar evaluation was made for the other series of CA-g-PHAs to establish a general relationship between their molecular architecture and thermal transition behavior [24]. Of particular interest is the finding that the composition dependence of the Tg of the cellulosic graft copolymers was represented well in terms of a formulation based on a comb-like polymer model [29], when CAs of acetyl DS 2 were employed as a trunk polymer. 

Blending of polymers is an attractive method of producing new materials with better properties. Blends of aliphatic polyesters, especially of poly(e-CL), have been investigated extensively and have been the subject of a recent review paper [170]. Poly(e-CL) has been reported to be miscible with several polymers such as PVC, chlorinated polyethylene, SAN, bisphenol A polycarbonate, random copolymers of Vdc and VC, Vdc and AN, and Vdc/VAc, etc. A single composition-dependent Tg was obtained in the blends of each of these polymers with poly(e-CL). This is of interest as a polymeric plasticizer in these polymers. Blends of PVC and poly(e-CL) with less than 50 wt % of poly(e-CL) were homogeneous and exhibited a single Tg. These blends were soft and pliable because the inherent crystallinity of poly(e-CL) was destroyed and PVC was plasticized... 

In the copolymerisation of butadiene and isoprene with Ti-based catalysts, both monomeric units of the copolymers obtained are essentially of a ciy-1,4 structure the microstructure of monomeric units in the copolymers does not differ substantially from that in the homopolymers [196-198], Nd-based catalysts provide butadiene/isoprene copolymers with more than 95% cis-1,4 monomeric units [89,199,200], On the other hand, Co-based catalysts give copolymers in which the structure of the monomeric units depends markedly on copolymer composition [19,201,202], Similarly, the structure of the monomeric units depends on copolymer composition in copolymers of butadiene and 2,3-dimethylbutadiene obtained by copolymerisation with Co-based catalysts [201,203],... 

From the copolymer composition dependence of the molar ratio of the d- and L-enantiomeric units of 15e in the copolymer, the rate of reaction of the growing chain end of 21 with the D-enantiomer of 15e was estimated to be about four times faster than that with the L-enantiomer. Such asymmetric selection is mainly ascribable to the steric and electronic interactions between the asymmetric environment created by the bulky terminal unit of 21 and the rigid bicyclic monomer having three asymmetric centers and a polar bulky bromine substituent (Scheme 6, [23]). 

As can be seen, the interaction energy is supposed to be of the same form as in Eq. (7), however, the scale factors and are now average composition-dependent parameters. Moreover, for blends based on random copolymers the quantities e a, r A et cetera of the right-hand side of Eq. (8) also have to be replaced by average parameters , and so on. The latter mean values are now number averages over the copolymer composition in terms of mole fractions. 

Figure 10. Composition dependence of Tg and HDT for the blends of polymer K with aMS/AN copolymer...

The composition dependence of the flexural strength of the aMS/AN-copolymer blend with polyarylether K appears in Figure 13. As the composition of the copolymer increases, the strength first increases, reaches a maximum, and then decreases. It actually exhibits a minimum at about 80% < MS/AN. This behavior can only substantiate earlier suggestions regarding the possible immiscibility of these systems. All of the other mechanical properties indicate that mixtures with polyarylether K may not be miscible but are mechanically compatible. Finally, it is interesting to note that at least one of the pendant chemical groups present on K exists on either of the a-methyl styrene interpolymers. It... 

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