Copolymers polydispersity index

Comonomer is exhausted at relatively low conversion (20), but a random copolymer is nevertheless obtained. This is because a very facile transacetalisation reaction allows for essentially random redistribution of the comonomer units (18) and also results in a polydispersity index near 2.0 (21). 

See also PBT degradation structure and properties of, 44-46 synthesis of, 106, 191 Polycaprolactam (PCA), 530, 541 Poly(e-caprolactone) (CAPA, PCL), 28, 42, 86. See also PCL degradation OH-terminated, 98-99 Polycaprolactones, 213 Poly(carbo[dimethyl]silane)s, 450, 451 Polycarbonate glycols, 207 Polycarbonate-polysulfone block copolymer, 360 Polycarbonates, 213 chemical structure of, 5 Polycarbosilanes, 450-456 Poly(chlorocarbosilanes), 454 Polycondensations, 57, 100 Poly(l,4-cyclohexylenedimethylene terephthalate) (PCT), 25 Polydimethyl siloxanes, 4 Poly(dioxanone) (PDO), 27 Poly (4,4 -dipheny lpheny lpho sphine oxide) (PAPO), 347 Polydispersity, 57 Polydispersity index, 444 Poly(D-lactic acid) (PDLA), 41 Poly(DL-lactic acid) (PDLLA), 42 Polyester amides, 18 Polyester-based networks, 58-60 Polyester carbonates, 18 Polyester-ether block copolymers, 20 Polyester-ethers, 26... 

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. 

Number-average molecular weights (M ) of the copolymers are often smaller than the theoretical value calculated from the copolymer yield and the total molar amount of initiator. Nevertheless, the polydispersity indexes (PDIs) are small,... 

Figure 3 shows typical size exclusion chromatographs (SEC) of PMMA-/)-PS-/)-PMMA and multiblock copolymer (PMMA-Z)-PS)n.[35] The polydispersity index (Mw/Mn) of the two... 

The GPC analysis of block copolymers is handicapped by the difficulty in obtaining a calibration curve. A method has recently been suggested to circumvent this difficulty by using the calibration curves of homopolymers. This method has been extended so that the calibration curves of block copolymers of various compositions can be constructed from the calibration curve of one-component homopolymers and Mark-Houwink parameters. The intrinsic viscosity data on styrene-butadiene and styrene-methyl methacrylate block polymers were used for verification. The average molecular weight determined by this method is in excellent agreement with osmometry data while the molecular weight distribution is considerably narrower than what is implied by the polydispersity index calculated from the GPC curve in the customary manner. 

The polydispersity index of the preparation is probably between these two values. The characterization of a block copolymer by MWD deserves careful consideration which is beyond the scope of this paper. 

Living radical polymerizations in miniemulsions have also been conducted by de Brouwer et al. using reversible addition-fragmentation chain transfer (RAFT) and nonionic surfactants [98]. The polydispersity index was usually below 1.2. The living character is further exemplified by its transformation into block copolymers. 

Several additional phases are observed experimentally, but are not thermodynamically stable [13]. Moreover, the synthetic nature of the copolymers implies some heterogeneity in the polymer structure and molecular weight distribution. An excellent review has recently been published [97], and the main conclusion is that the polydispersity index (PDI) influences all aspects of the self-assembly. For example, upon an increase of the PDI of one block, the lattice constant of an ordered structure or the size of microphase-separated domains increases, interfacial thickness increases, and phase transitions may be induced. In addition, macrophase-separation may occur as the PDI is increased at certain compositions and segregation strengths. 

The reaction was carried out at 25-60 °C in different solvents and leads to high molecular weights although with polydispersity indexes higher than 3 based on SEC determinations. Recently, Yamada et al. [75] studied initiators derived from the triphenylverdazyl radical. PS-h-PMMA copolymers are prepared although with low yields. 

One of the most interesting investigations on the stepwise polymerization was performed by Niwa et al. [230, 231] who prepared different diblock copolymers with, very often, a high increase of molecular weight and low polydispersity indexes. As an example of precursor of diblock copolymers, they prepared telechelic 50 as follows ... 

By SEC, we observed that the fnU distribution of PDMS chains shifted to large molar masses, thus proving the good initiation efficiency of snch macroinifator. The final polydispersity index (M /M =1.25) is smaller than the polydispersity index of the PDMS macroinitiator (1.49), another evidence that all PDMS chains were fnnc-tionalized. The final molecular weight obtained by SEC for the triblock copolymer... 

The Step 1 product (8 g) was dissolved in 50 ml of benzene and then treated with 2,2 -azobisisobutyronitrile (14.6 mg) and 13.8 g of vinyl acetate and heated to 60°C for 72 hours. The mixture was cooled, and the polymer was precipitated in heptane. After drying the block copolymer was isolated in 47.8% yield having aM of21,500 daltons and a polydispersity index of 1.6. 

Some characteristics of the homopolymers and copolymers used in this study are shown in Table I percent acid content, percent neutralization, number-average molecular weight (Mn), polydispersity index (Mw/Mn) and the nomenclature used. 

Fig. 1.2 GPC data obtained from an attempt to form a styrene-acrylate diblock copolymer using anionic polymerization. Both the polydispersity index (2.96) and the shape of the curve suggest that the desired homogeneous product has not been formed.

Although in controlled radical polymerisation, termination reactions cannot be excluded completely, they are limited in their extent and consequently the molecular weight is controlled, the polydispersity index is small and functionalities can be attached to the macromolecules. These features are indicative of the realisation of well-defined polymer architectures such as block copolymers, starshaped and comb-shaped copolymers. 

Fig. 43a. Neutron small angle scattering intensity I(q) plotted vs q for three temperatures T above Tmst (main graph), for a polyethylenepropylene(PEP) — polyethylethylene(PEE) diblock copolymer, with f = 0.55, molecular weight Mw — 57.500, polydispersity index Mw/Mn = 1.05. The microphase separation transition occurs for Tmst = 125°C. For further explanations cl Textb Inverse peak intensity I (q ) dotted vs inverse temperature.The full curve is a one-para meter fit to the theoty of Fredrickson and Helfand [58], while Leibler s [43] prediction for the intensity at the transition is marked as mean field theory . From Bates et al. [317]...

Copolymers obtained by this method have low polydispersity indexes (PDK1.3) with various coil length. Unfortunately, due the presence of residual copper in the materials, they have not been used for optoelectronic devices. However, these well-defined model copolymers have been used for the morphological studies. 

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