Gradient copolymers, compositional

Seymour and coworkers (27,28,29,30) actually used these composition gradients to prepare block copolymers by swelling particles containing occluded (i.e., living) macroradicals with a second monomer. Such block copolymers were prepared from occluded vinylacetate, methyl methacrylate, and acrylonitrile macroradicals, and the yield of block copolymers was studied as a function of the solubility and rate of diffusion of the swelling monomer in the particles. 

Figure 14. The phase diagram of the gradient copolymer melt with the distribution functions g(x) = l — tanh(ciit(x —fo)) shown in the insert of this figure for ci = 3,/o = 0.5 (solid line), and/o — 0.3 (dashed line), x gives the position of ith monomer from the end of the chain in the units of the linear chain length. % is the Flory-Huggins interaction parameter, N is a polymerization index, and/ is the composition (/ = J0 g(x) dx). The Euler characteristic of the isotropic phase (I) is zero, and that of the hexagonal phase (H) is zero. For the bcc phase (B), XEuier = 4 per unit cell for the double gyroid phase (G), XEuier = -16 per unit cell and for the lamellar phases (LAM), XEuier = 0.

Comb copolymers, 7 610t Combed yarn, 11 178 Combes synthesis, of quinolines, 21 189 Combicat, 7 387, 392 Combinational libraries, 7 382 characterization, 7 404-405 composition gradient libraries, 7 407 design, 7 399-400 fabrication, 7 414-419 temperature gradient libraries, 7 407—408 thickness gradient libraries, 7 406 Combination electrodes, 14 30 Combination vaccines, 25 504-505 Combinatorial biology, 16 414 Combinatorial biosynthesis, 15 301-302, 305... 

As mentioned above, copolymers with a compositional gradient can serve as precursors for generating gradient-graft copolymers, where the number of... 

Xu C, Barnes SE, Wu T, Eischer DA, DeLongchamp DM, Batteas JD, Beers KL (2006) Solution and surface composition gradients via microfluidic confinement fabrication of a statistical-copolymer-brush composition gradient. Adv Mater 18 1427-1430... 

In addition to the triblock thermoplastic elastomers, other useful copolymers of styrene with a diene are produced commerically by living anionic polymerization. These include di-and multiblock copolymers, random copolymers, and tapered block copolymers. A tapered (gradient) copolymer has a variation in composition along the polymer chain. For example, S-S/D-D is a tapered block polymer that tapers from a polystyrene block to a styrene-diene random copolymer to polydiene block. (Tapered polymers need not have pure blocks at their ends. One can have a continuously tapered composition from styrene to diene by... 

The synthesis of a gradient copolymer is sometimes desirable in a living polymerization to produce a copolymer with a variation in composition along the polymer chain. This is achieved either by carrying out the copolymerization without addition of monomer to maintain a constant feed composition or addition of monomer to deliberately change the feed composition from its original state. 

Fig. 2.50 An entangled diblock copolymer chain in a lamellar morphology with a sinusoidal composition profile (Lodge and Dalvi 1995). Entanglement constraints are indicated by x. Coupling between the thermodynamic forces produced by the composition gradients and replation dynamics leads to an anisotropic diffusion coefficient.

Polymers prepared via CRP show promise for applications like photoresists [112], liquid-crystalline displays [147-149, 154], and photo catalysts [151]. Incorporating blocks prepared using CRP techniques into copolymers with conductive or luminescent blocks [240,241,243,251] may impart better processability and make them useful for a broader range of applications. Block or gradient copolymers with highly controlled compositions may also be industrially useful as blend compatibilizers or as surfactants [194],perhaps improving upon already existing materials. Well-defined or functional compatibilizers and stabilizers could potentially result in lower production costs if less material is needed to impart the desired properties. 

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