Copolymer distribution

Random copolymer—Distribution of the monomer units does not follow any definite sequence. These are produced in bulk, aqueous, suspension, or emulsion using free radical initiators of the peroxide type or redox systems. 

By using two or more polymerization catalysts simultaneously, polymer chemists can produce copolymers tvith a bimodal composition distribution. This is made possible by the fact that no two catalysts incorporate monomers at exactly the same rate. The net result is that short chain branches may be preferentially incorporated into either the higher or lower molecular weight fractions. Polymer manufacturers can obtain a similar result by operating two polymerization reactors in series. Each reactor produces a resin with a different copolymer distribution, which are combined to form a bimodal product. Copolymers with a bimodal composition distribution provide enhanced toughness when extruded into films. 

Discuss the dependence of the micro structure of 2,4-hexadiene monomeric units (cis-1,4 or trans-1,4) in 2,4-hexadiene/l,3-butadiene copolymers on the composition of these copolymers (distribution of comonomers along copolymer chains). 

Figure 2.10 Homopolymer/copolymer distribution for impact copolymers made in a series of two tubular reactors or two CSTRs. The wide residence time distribution of the CSTRs is reflected in the non-uniform homopolymer/copolymer distribution in the particles. The distribution of homopolymer (light gray) and copolymer (dark gray) phases is only to illustrate the effect of reactor residence time distribution. In reality, one phase is dispersed into the other.

This broad homopolymer/copolymer distribution is, sometimes, even visible with the naked eye when examining impact copolymer pellets. Pellets where the homopolymer phase is dominant appear opaque due to their higher crystallinity, while those where the amorphous copolymer is the major component are translucent. 

Even though tubular reactors are not used industrially for the production of impact copolymers, some reactor technologies (such as gas phase horizontal reactors) were developed to narrow the reactor residence time distribution and, consequently, produce impact copolymer with narrower homopolymer/copolymer distributions. 

Low-mass and (b) high-mass region of the copolymer distribution. All-trans retinoic acid was used as the matrix. The number shown... 

Figure 6.10 Scanning electron microscopy and confocal Raman images of a ternary blend— polystyrene (PS), pentafluorostyrene)-b-polystyrene (P5FS-b-PS), and polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS-b-PPEGMA). Solvent casting under 70% relative humidity induces regular pores in which the copolymer distribution depends on the polarity of the component. Red color indicates the presence of PS and P5FS-b-PS, and blue color is indicative of PS-b-PPEGMA. Depth analysis of the pore composition evidenced a heterogeneous distribution of the block copolymer within the pore.

Fig. 20 Copolymer distribution for a dPS-b-P2VP 391-68 diblock copolymer added at constant concentration to the top PS layer (overlaid onto a P2VP layer) following by an 8-h annealing at 178°C. For this sample, the final equilibrium copolymer concentration in the PS phase was 2.1%. The interface copolymer excess, z(, corresponding to the shaded area, was equal to 100...

This equation permits the direct and explicit calculation of the various copolymer distribution functions v f,y) from the distribution function W oo( i3 )-... 

The high fractionation effectivity allows correct estimation of the initial copolymer distribution (15) according the molecule weight if only five firactions are formed (Fig. 23). Copolymers distributed according to the Stockmayer distribution function (15) are characterized by a relatively small polydispersity with respect to the chemical composition. In contrast, copolymers showing a distribution given in... 

Fig. 27 Influence of the number of theoretical plates, on the fractionation efficiency with respect to the segment number of CPF, if the (uiginal copolymer distribution is given by (15). The stars represent the values of the sol fraction and the crosses the values from the gel fractions...

Jeon HK, Macosko CW. Visualization of block copolymer distribution on a sheared drop. Polymer 2003 44(18) 5381-5386. 

An initial polymer system is characterized by (a) an initial weight distribution of polymer chains (b) an initial size distribution of polymer aystals, and (c) copolymer distributions. Implementations for each inpnt will be discussed one by one in the succeeding sections. 

The use of a delayed addition of part of the monomer is very common in industrial practice. In this instance it allows a relatively constant monomer concentration to be maintained. The addition of initiator over the same two and a half hour period gives a slight increase in the rate of radical production, which will increase the rate of polymerisation whilst reducing the molecular weight. The reactivity ratios of 2.0 and 0.26, for methyl methacrylate and ethyl acrylate respectively, means that the initial copolymer will be rich in methyl methacrylate. The delayed addition of monomer mixture means that the range of copolymer distribution will be narrower than would be the case if all the monomer were added initially. The initial reflux temperature is about 85 C and will rise slightly to about 90°C towards the end of the polymerisation. 

Segmented block copolymers distribution of block sizes 260-262... 

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