Copolymer backbone, monomer ratio

Free-radical copolymerization of vinyl acetate with various vinyl siloxane monomers was described 345). Reactions were conducted in benzene at 60 °C using AIBN as the initiator. Reactivity ratios were determined. Selective hydrolysis of the vinyl acetate units in the copolymer backbone was achieved using an aqueous sodium hy-droxide/THF mixture. The siloxane content and degree of hydrolysis were determined by H-NMR. 

ADMET copolymerization of 1,9-decadiene and 1,5-hexadiene [26] leading to perfectly random linear PBD-polyoctenamer copolymers was the first demonstration of the viability of this approach. The resulting copolymers contained comonomer ratios consistent with the monomer feed, and NMR analysis confirmed the random nature of the copolymer. Moreover, the same copolymers could be produced by the reaction of one comonomer with the homopolymer of the other comonomer for example, 1,9-decadiene with 1,4-PBD. This result further confirms the interchange reactions known to occur on the double bonds of the ADMET polymer backbone. 

The mole fraction of the monomer units that are cross-linked in the polymer is X,., and nt is Ihe number-average number of atoms in the polymer backbone between cross-links. The temperature should be expressed in absolute degrees in this equation. The constant K is predicted to be between 1.0 and 1.2 it is a function of the ratio of segmental mobilities of cross-linked to uncross-linked polymer units and the relative cohesive energy densities of cross-linked and uncross-linked polymer (88). The theoretical equation is probably fairly good, but accurate tests of it are difficult because of the uncertainty in making the correction for the copolymer effect and because of errors in determining nf. 

Controlling the size, shape and ordering of synthetic organic materials at the macromolecular and supramolecular levels is an important objective in chemistry. Such control may be used to improve specific advanced material properties. Initial efforts to control dendrimer shapes involved the use of appropriately shaped core templates upon which to amplify dendritic shells to produce either dendrimer spheroids or cylinders (rods). The first examples of covalent dendrimer rods were reported by Tomalia et al. [43] and Schluter et al. [44], These examples involved the reiterative growth of dendritic shells around a preformed linear polymeric backbone or the polymerization of a dendronized monomer to produce cylinders possessing substantial aspect ratios (i.e. 15-100) as observed by TEM and AFM. These architectural copolymers consisting of linear random... 

Of great industrial interest are the copolymers of ethene and propene with a molar ratio of 1/0.5, up to 1/2. These EP-polymers show elastic properties and, together with 2-5 wt% of dienes as third monomers, they are used as elastomers (EPDM). Since they have no double bonds in the backbone of the polymer, they are less sensitive to oxidation reactions. As dienes, ethylidenenorbomene, 1,4-hexadiene, and dicyclopentadiene are used. In most technical processes for the production of EP and EPDM rubber in the past, soluble or highly disposed vanadium components are used [69]. Similar elastomers can be obtained with metallocene/MAO catalysts by a much higher activity which are less colored [70-72]. The regiospecificity of the metallocene catalysts toward propene leads exclusively to the formation of head-to-tail enchainments. The ethylidenenor-bornene polymerizes via vinyl polymerization of the cyclic double bond and the tendency to branching is low. The molecular weight distribution of about 2 is narrow [73]. 

In addition to these irregularities, Winey et al. (1996) have found that in random and alternating copolymers of styrene and methyl methacrylate, the sequence distribution of monomers along the backbone of the polymer strongly affects its miscibility with polystyrene and polymethylmethacrylate homopolymers, even when the overall ratio of styrene/methyl methacrylate in the copolymer chain is held constant. A strictly alternating sequence of monomers in the copolymer was found to be more miscible with the ho-miopolymers than is a copolymer with a random sequence distribution. These results... 

Ethylene is used in a considerable number of copolymers. Some of these are binary copolymers, but copolymers of three or even four components also are known. As indicated in Section 2.3, specific monomer reactivity ratios are required for generating a copolymer. However, this requirement is satisfied for a number of monomers. Some common copolymers of polyethylene are indicated in Table 6.1.3. Some of the copolymers listed in Table 6.1.3 are a/f-copolymers. They behave during pyrolysis as homopolymers. More details regarding pyrolysis of several a/f-copolymers are given further in this section for poly(propylene-a/f-ethylene), in Section 6.3 for poly(ethylene-a/f-chlorotrifiuoroethylene), and in Section 6.9 for poly(ethylene-a/f-maleic anhydride). The copolymers in which the backbone chain contains atoms different from carbon, such as oxygen or sulfur, are discussed in sections dedicated to polymers containing that particular atom in the backbone. 

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