Architecture, polymer

Explain the following terms in your own words (a) homopolymer, (b) tacticity, (c) polydispersity, (d) oligomer. 

Explain the difference between a homopolymer, a random copolymer, and a block copolymer. 

A random copolymer is composed of 20% polyethylene and 80% polyvinyl chloride. Make an estimate for the molecular weight if the average molecule is composed of 1000 monomers. 

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The main benefit of the Dow process was control of the polymer architecture. The polymer from the self-condensation process possessed a linear stmcture, but there were other difficulties. The monomer was cosdy and removal of the cuprous bromide by-product was difficult (17) ultimately, scale-up difficulties terrninated the Dow PPS development. However, there was a growing recognition that PPS was an attractive polymer with an excellent combination of properties. 

In the mid-1950s, the Nobel Prize-winning work of K. Ziegler and G. Natta introduced anionic initiators which allowed the stereospecific polymerization of isoprene to yield high cis-1,4 stmcture (3,4). At almost the same time, another route to stereospecific polymer architecture by organometaHic compounds was aimounced (5). 

More recent examples include end-functionalized multiarmed poly(vinyl ether) (44), MVE/styrene block copolymers (45), and star-shaped polymers (46—48). With this remarkable control over polymer architecture, the growth of future commercial appHcations seems entirely likely. 

As discussed in Section 7.3, conventional free radical polymerization is a widely used technique that is relatively easy to employ. However, it does have its limitations. It is often difficult to obtain predetermined polymer architectures with precise and narrow molecular weight distributions. Transition metal-mediated living radical polymerization is a recently developed method that has been developed to overcome these limitations [53, 54]. It permits the synthesis of polymers with varied architectures (for example, blocks, stars, and combs) and with predetermined end groups (e.g., rotaxanes, biomolecules, and dyes). 

The use of mono-, di- and multifunctional initiators provides scope for designing polymer architectures. The use of 14, 18 and 19 in the production of block or star polymers has been demonstrated.41 4445 Homopolymers of 20 or copolymers of 20 with S or MMA have been successfully used in photoinitiated... 

Monomers of die type Aa B. are used in step-growth polymerization to produce a variety of polymer architectures, including stars, dendrimers, and hyperbranched polymers.26 28 The unique architecture imparts properties distinctly different from linear polymers of similar compositions. These materials are finding applications in areas such as resin modification, micelles and encapsulation, liquid crystals, pharmaceuticals, catalysis, electroluminescent devices, and analytical chemistry. 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

In a seminal and seemingly forgotten paper, Burchard et al. " discussed the analysis of various polymer architectures based on integrated light scattering (LS) and quasielastic light scattering (QELS). They considered mono- and polydisperse linear and star-branched polymers with/number of arms ( rays ), and random polycondensates of Af or ABC type (identical or different... 

In summary, our new SEC system provides very useful information about branching. Together with selective link destruction, it is a very powerful tool in the analysis of polymer architectures. Further analysis of various model architectures is in progress in our laboratories. 

In the natural system the sites of spore wall formation, i.e. the sporan-gial loculus, act as mini-reactor vessels in which the above interactions can occur. If a polymerisation occurs within one such structure, the resulting (polymer) architectures will probably closely resemble the self-assembled ones formed in our artificial sporangia. 

Other properties such as solubility, viscosity (above Tg and T ), modulus of elasticity, and strength are highly dependent on the polymer architecture, or pattern of the interconnections between units. In other words, these properties vary to a marked degree with changes in the molecular weight and in the degree of cross-linking. 

Polyisoprenes, hydrophilicity, 223 Polymer architecture, role, 258-259 Polymer backbone... 

Poly[5-(alkylamino)borazines] 7-10 exhibited suitable viscoelastic and thermal stabilities to be extruded in the molten state through the monohole spinneret of a lab-scale melt-spinning apparatus. Thus, an extruded filament (diameter, 200 gm) was drawn with a windup unit, that is, a graphite spool. This provided green fibers with a wide range of diameters (16 =s (f> =s 50 gm Table 2), depending on polymer architecture. 

The heat of fusion AHf (obtained from the area under the DSC melting curve) and percentage crystallinity calculated from AHf is found to be linearly dependent on butadiene content, and independent of the polymer architecture. This is shown in Figure 3. Also, the density of the block copolymers was found to be linearly dependent on butadiene content (see Figure 4). The linear additivity of density (specific volume) has been observed by other workers for incompatible block copolymers of styrene and butadiene indicating that very little change in density from that of pure components has occurred on forming the block copolymers.(32) While the above statement is somewhat plausible, these workers have utilized the small positive deviation from the linear additivity law to estimate the thickness of the boundary in SB block copolymers.(32)... 

Comparison of Polymer Architectures from Living Polymerization,... 

R.D. McCullough, R.D. Lowe, M. Jayaraman, and D.L. Anderson, Design, synthesis, and control of conducting polymer architectures structurally homogeneous poly(3-alkylthiophenes), J. Org. Chem., 58 904-912, 1993. 

FIGURE 5.7 Schematic Representation of typical, (partially) electroluminescent LC polymer architectures. (a) Rodlike structure, (b) Hairy-rod structure, (c) Combined main-chain-side-chain system, (d) Semiflexible segmented structure, (e) Semiflexible segmented structure with disklike mesogen. (After Weder, C. and Smith, P., Main-chain liquid-crystalline polymers for optical and electronic devices, in Encyclopedia of Materials Science and Technology, Buschow, K.H., Cahn, R.W., Flemings, M.C., Ilschner, B., Kramer, E.J., and Mahajan, S., Eds., Elsevier Science, New York, 2001.)... 

We use polystyrene-Z>-polybutadiene block copolymers as the starting material with preformed polymer architecture. These polymers are comparatively cheap and easily accessible.1 For the present problems a series of narrowly distributed polystyrene-6-polybutadiene block copolymers with rather different molecular weights were synthesized via anionic polymerization (Figure 10.4, Table 10.1). As a test for the modification of technological products, a commercial triblock copolymer was also used. 

Synthetic polyisoprene, 9 559 Synthetic polymer architectures, 26 786 Synthetic polymeric micelles, 20 482 Synthetic polymers... 

Since that time, synthetic chemists have explored numerous routes to these statistically hyperbranched macromolecular structures. They are recognized to constitute the least controlled subset of structures in the major class of dendritic polymer architecture. In theory, all polymer-forming reactions can be utilized for the synthesis of hyperbranched polymers however, in practice some reactions are more suitable than others. 

Variations in the graft polymer architectures are possible by controlling the... 

After the appearance of the seminal 1985 paper from the Tomalia group, there was an enormous amount of intrinsic interest in dendritic polymer architecture. On the other hand, there was substantial resistance to accepting research results for publication by many of the major scientific journals, some of the reasons cited by the critics of that period included the following ... 

Freed et al. [42,43], among others [44,45] have performed RG perturbation calculations of conformational properties of star chains. The results are mainly valid for low functionality stars. A general conclusion of these calculations is that the EV dependence of the mean size can be expressed as the contribution of two terms. One of them contains much of the chain length dependence but does not depend on the polymer architecture. The other term changes with different architectures but varies weakly with EV. Kosmas et al. [5] have also performed similar perturbation calculations for combs with branching points of different functionalities (that they denoted as brushes). Ohno and Binder [46] also employed RG calculations to evaluate the form of the bead density and center-to-end distance distribution of stars in the bulk and adsorbed in a surface. These calculations are consistent with their scaling theory [27]. 

Table 4. The R Rfj=p-iatio and parameter C in Eq. (14) for various polymer architectures. The C-parameter gives information on the internal flexibility (C=0 inflexible particles, C= 0.2 flexible chain behavior) ...

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