Efficiency of the copolymers

The efficiency of the copolymers, either block or graft, acting as the compatibilizer depends on the structure of the copolymers. One of the primary requirements to get maximum efficiency is that the copolymer should be located, preferentially at the blend interface (Figs. 2a, b, and c). There are three possible conformations, as shown in the figure. Many researchers [10-12] found that the actual conformation is neither fully extended nor flat (Fig. 2c). A portion of the copolymers penetrates into the corresponding homopolymer and the rest re-... 

There was a continuous increase in the second order rate constant (k at) from 20- to 100-fold at pH 9.15 through the Sn series. The nearly equivalent catalytic efficiencies of the copolymer and homopolymer grafts suggest that the major hydro-phobic interaction involved the N-acylimidazole intermediate. However, throughout this series, the copolymers were still better catalysts than the homopolymer. 

These authors suspected that the slightly increased efficiency of the copolymer is due to the cooperative contribution of hydrogen bonding and the electrostatic interaction. Subsequently, the same authors studied the hydrolysis of amylose and sucrose by some copolymers containing ilfonic acid and carboxylic acid groups 28 (41), Again, the polymer catalyst was not particularly effective compared with its small-molecule counterparts. 

Effect of Compatibilizer Concentration. The compatibilizing efficiency of the copolymers is, besides the architecture, a function of their concentration. The effect of a compatibilizer concentration has been quantitatively characterized by the emulsification curve—the dependence of the average particle diameter of the minor dispersed phase on copolymer concentration (70). The particle diameter decreases with increase of copolymer concentration until a constant value is obtained. For most systems, this value is achieved if the copol5uner amount is 15—25% of the dispersed phase. There are systems where saturation was detected only at substantially higher concentration of a copolymer (181). 

Syndiotactic polypropylene can be used as an impact modifier. Indeed, the addition of s-PP to i-PP can improve impact characteristics over pure i-PP [222-225]. When s-PP is blended with i-PP, the resulting resin has a processability better than that of i-PP and impact and transparency properties better than those of pure i-PP. As an impact modifier to a controlled rheology i-PP copolymer, s-PP does not crosslink or affect the peroxide efficiency of the copolymer while improving the Izod notched impact and maintaining the similar processability of the copolymer. 

At this point, more experiments are needed to know how the distribution of the reactive groups along multifunctional chains affects the compatibilization efficiency of the copolymer formed at the interface. 

The amount of the copolymer to be added into a binary blend depends on several factors. Since the copolymer preparation is an expensive process, it should be used to its maximum efficiency. The amount of copolymer (w) required to saturate a unit volume of blend is given by ... 

The composition of the copolymer determines its electroluminescence efficiency. Optimal efficiency (0.3%) was achieved in system 34 when the feed ratio of monomer 4 to monomer 34 was 9 1. This represents a 30-fold improvement in luminescence efficiency relative to PPV in the same device configuration (AlALOj/polymer/Al) 58, 62. Copolymer 33 has found uses as waveguides and... 

Rate of Formation of Primary Precursors. A steady state radical balance was used to calculate the concentration of the copolymer oligomer radicals in the aqueous phase. This balance equated the radical generation rate with the sum of the rates of radical termination and of radical entry into the particles and precursors. The calculation of the entry rate coefficients was based on the hypothesis that radical entry is governed by mass transfer through a surface film in parallel with bulk diffusion/electrostatic attraction/repulsion of an oligomer with a latex particle but in series with a limiting rate determining step (Richards, J. R. et al. J. AppI. Polv. Sci.. in press). Initiator efficiency was... 

This molecular weight response clearly indicates that chain-shuttled ethylene-octene block copolymers, rather than blends, are formed upon introduction of DEZ. The Mn can also be used in conjunction with the DEZ feed and polymerization rate to calculate the number of chains produced per Zn molecule. The low DEZ level of sample 4 results in the production of ca. 12 chains/Zn. However, the reaction is practically stoichiometric at higher DEZ (no H2), with production of sample 6 resulting in 1.9 chains/Zn (or ca. one chain per Zn-alkyl moiety). This example indicates that nearly every polymer chain exited the reactor bound to the CSA, with very little chain termination, demonstrating the efficiency of the chain shuttling reaction. 

Burn and coworkers [173] synthesized copolymer 143, containing a similar electron deficient moiety (triazole) incorporated in the PPV backbone. They have reported an efficient blue emission from this polymer (APL = 466 nm (solution), 486 nm (film), PL = 33% (film)) although the efficiency of the PLED fabricated as ITO/PPV/143/A1 was not very high (CT>j ) reached 0.08% at a luminance of 250 cd/m2). 

Yellow to orange emission was observed in another series of fluorene-phenylene copolymers with CN groups in the vinylene fragment 324-326 (Scheme 2.48) [409]. The PLQY of the copolymers was relatively low (from 3.5% for 326 to 14.7% for 325) and the best results in PLED testing were achieved for copolymer 325. The device ITO/PEDOT/325/A1 showed a turn-on voltage of 5.0 V and a maximum brightness of 7500 cd/m2 at 20 V, with a maximum luminance efficiency of 0.21 lm/W at 6.7 V. 

Copolymer 459, prepared by Stille coupling of dibromophenylene with 2,5-Mv(tributyl-stannyl)thiophene, represents another example of a phenylene-u/t-thiophene backbone, where the substituted phenylene unit forms an oligophenylene vinylene fragment that is not in the main conjugation chain [561]. A PLED fabricated with this polymer (ITO/459/A1) emitted green light (520 nm) with a turn-on voltage of ca. 9.5 V, but no other data on luminance or efficiency of the device were reported (Chart 2.111). 

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