Copolymerization 956 INDEX

Polymers for improving the viscosity index of the copolymethacrylate type can be made into dispersants by copolymerization with a nitrogen monomer. The utilization of these copoiymers allows the quantity of dispersant additives in the formulation to be reduced. 

T and are the glass-transition temperatures in K of the homopolymers and are the weight fractions of the comonomers (49). Because the glass-transition temperature is directly related to many other material properties, changes in T by copolymerization cause changes in other properties too. Polymer properties that depend on the glass-transition temperature include physical state, rate of thermal expansion, thermal properties, torsional modulus, refractive index, dissipation factor, brittle impact resistance, flow and heat distortion properties, and minimum film-forming temperature of polymer latex... 

Radical copolymerization of diaryl nitrones, such as a-(2-hydroxyphenyl)-A-(2,6-dimethylphenyl) nitrone (HDN), a-(2-hydroxy-4-methacryloyloxyphenyl)-N -(2,6-dimethylphenyl) nitrone (HMDN), and a-(2-hydroxy-4-methacryloyloxy-phenyl)-A-phenylnitrone (HMPN) (Fig. 2.30), with methyl methacrylate leads to copolymers in good yields with considerable quantities of hydroxy substituted diaryl nitrone pendants. The presence of photoactive nitrone pendants in these copolymers allows one to control photochemically the refractive index of polymethyl methacrylate films (468, 700, 701). 

The hnal copolymer was obtained in 90% yield it had a molecular weight of 10,800 and polydispersity index of 2.1. In this case, Diels-Alder copolymerization dominates over the cyclobntane homopolymerization. It means that Diels-Alder addition of the dienophile cation-radical to the diene is substantially faster than the competing addition of the dienophile cation-radical to the nen-tral dienophile. 

Hence, cation-radical copolymerization leads to the formation of a polymer having a lower molecular weight and polydispersity index than the polymer got by cation-radical polymerization— homocyclobutanation. Nevertheless, copolymerization occnrs nnder very mild conditions and is regio-and stereospecihc (Bauld et al. 1998a). This reaction appears to occnr by a step-growth mechanism, rather than the more efficient cation-radical chain mechanism proposed for poly(cyclobutanation). As the authors concluded, the apparent suppression of the chain mechanism is viewed as an inherent problem with the copolymerization format of cation-radical Diels-Alder polymerization. ... 

Propylene and 4-methyl- 1-pentene were copolymerized by Colin et al. (1) using a Ziegler-Natta catalyst and the product characterized as having at least one fraction obtained by that had a block index greater than about 0.3 and up to about 1.0 with a polydispersity greater than 1.3. 

Refractive index matching Precise control of refractive Copolymerization... 

The refractive index must be precisely controlled because it is essential for optical components such as single-mode optical waveguides. This control can be achieved by copolymerization of low- and high-refractive-index polyimides. Birefringence control can be achieved by a film elongation technique using a particular polyimide. 

The photoelastic behavior of nonionized PAAm network and ionized P(AAm/MNa) network prepared by the copolymerization of AAm with MNa ( MNa = 0.05) was investigated in water-acetone mixtures [31]. For a pure PAAm network, the dependences of all photoelastic functions (see Eqs. (15) and (16)), i.e. modulus G, strain-optical function A and stress-optical coefficient C, on the acetone concentration in the mixtures are continuous (Fig. 17). At ac = 54 vol %, the ionized network undergoes a transition which gives rise to jumpwise change in G, A and C also the refractive index of the gel n8 changes discontinuously. While in the collapsed state the optical functions A and C are negative, in the expanded state they are positive. 

Ethylene Polymers. Depending on the polymerization conditions, three major types of polyethylene are manufactured low-density polyethylene (LDPE) by free-radical polymerization, linear low-density polyethylene (LLDPE) by copolymerization of ethylene with terminal olefins, and high-density polyethylene (HDPE) by coordination polymerization. The processes yield polymers with different characteristics (molecular weight, molecular weight distribution, melt index, strength, crystallinity, density, processability). 

Linear low-density polyethylene (LLDPE)440-442 is a copolymer of ethylene and a terminal alkene with improved physical properties as compared to LDPE. The practically most important copolymer is made with propylene, but 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are also employed.440 LLDPE is characterized by linear chains without long-chain branches. Short-chain branches result from the terminal alkene comonomer. Copolymer content and distribution as well as branch length introduced permit to control the properties of the copolymer formed. Improvement of certain physical properties (toughness, tensile strength, melt index, elongation characteristics) directly connected to the type of terminal alkene used can be achieved with copolymerization.442... 

To facilitate a rapid determination of the percentage of styrene in copolymerization products with linseed oil, a graphical method was based on the observation80 that polymerization reactions of pure styrene and pure linseed oil can be represented by two parallel lines in a refractive index (wJJ) vs. density (1d24°) diagram (cf. Fig. 86). 

In conclusion, even though there is the definite correlation between carboxylic group index and minimum in respect to graftability in our system, a detailed work with model compounds would be required to futher elucidate the mechanism of lignin participation in the copolymerization reaction. 

The various data obtained for the kinetics of graft copolymerization onto PTFE films demonstrate that this reaction is complicated by the fact that the rate of diffusion of the monomer may become the controlling factor. It seems interesting at this point to compare and discuss together the results obtained with the different monomers. Table I summarizes the data obtained for autoacceleration indexes (/ ), dose-rate exponents (a), and over-all activation energies E, with styrene, acrylic acid, and vinylpyridine. Several conclusions can be derived from an examination of these data. 

It is worth noting that the above-mentioned expressions (4.5-4.7) contain, as particular cases, the results obtained both for binary [54] and ternary [112] copolymerization. However, the general formulae (4.6) and (4.7) for indexes of sequential homogeneity of multicomponent copolymers with any m were not obtained earlier by the author of Refs. [Ill, 113], who investigated this problem theoretically. The approaches applied in the above papers result in cumbersome formulae and are not needed since Eqs. (4.6) and (4.7) can be immediately obtained [6] from the Markov chain theory. 

In the systems (I) and (III) 2-simplex consists of a sole cell, all the trajectories inside which approach SP corresponding to homopolymer Ms where rs < 1. The systems (I) and (III) topologically are equivalent, since they differ from each other only by the inversion of the monomer indexes therefore their phase portraits are of the same type, too. In the systems (II) and (IV) the azeotropic point separates the simplex into the two cells. However, the system (IV), in which both parameters r, and r2 exceed unity practically is non-realizable [20-24]. That is why the stable binary azeotropes are excluded from the consideration, and the dynamics of the copolymerization of two monomers is exhaustively characterized by only two types (I) and (II) of phase portraits. 

Melville et al. [222] started from the copolymerization scheme (62), extended to include initiation (141) and termination by mutual combination (142), M Ml is a copolymer chain of r monomeric units with an M (or M2) radical at trie end. A chain containing a number of units different from r is designated by the index s. 

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