Confinement copolymers

Within the scope of the original definition, a very wide variety of ionomers can be obtained by the introduction of acidic groups at molar concentrations below 10% into the important addition polymer families, followed by partial neutralization with metal cations or amines. Extensive studies have been reported, and useful reviews of the polymers have appeared (3—8). Despite the broad scope of the field and the unusual property combinations obtainable, commercial exploitation has been confined mainly to the original family based on ethylene copolymers. The reasons for this situation have been discussed (9). Within certain industries, such as flexible packaging, the word ionomer is understood to mean a copolymer of ethylene with methacrylic or acryhc acid, partly neutralized with sodium or zinc. 

For many years use of this material was largely confined to America and it was seldom met in Europe because of the cheaper EVA materials available. In 1980, however, BP initiated production of such materials, whilst in the United States the material is produced by Union Carbide. The Dow company, whose product Zetafin was the most well-known grade, no longer supply the copolymer. 

More definitive evidence of enzymatic attack was obtained with 1 1 copolymers of e-caprolactone and 6-valerolactone crosslinked with varying amounts of a dilactone (98,99). The use of a 1 1 mixture of comonomers suppressed crystallization and, together with the crosslinks, resulted in a low-modulus elastomer. Under in vitro conditions, random hydrolytic chain cleavage, measured by the change in tensile properties, occurred throughout the bulk of the samples at a rate comparable to that experienced by the other polyesters no weight loss was observed. However, when these elastomers were implanted in rabbits, the bulk hydrolytic process was accompanied by very rapid surface erosion. Weight loss was continuous, confined to the... 

If the chains are long, the composition of the copolymer and the arrangement oi units along the chain are determined almost entirely by the relative rates of the various chain propagation reactions. On the other hand, the rate of polymerization depends not only on the rates of these propagation steps but also on the rates of the termination reactions. Copolymer composition has received far more attention than has the rate of copolymerization. The present section will be confined to consideration of the composition of copolymers formed by a free radical mechanism. 

Well-defined nanoclusters (w 10-100 A diameter) of several metals have been prepared via the polymerization of metal-containing monomers. The synthetic approach involves the block copolymerization of a metallated norbornene with a hydrocarbon co-monomer which is used to form an inert matrix. Subsequent decomposition of the confined metal complex affords small clusters of metal atoms. For example, palladium and platinum nanoclusters may be generated from the block copolymerization of methyl tetracyclododecane (223) with monomers (224) and (225) respectively. 10,611 Clusters of PbS have also been prepared by treating the block copolymer of (223) and (226) with H2S.612 A similar approach was adopted to synthesize embedded clusters of Zn and ZnS 613,614... 

The mean-field SCFT neglects the fluctuation effects [131], which are considerably strong in the block copolymer melt near the order-disorder transition [132] (ODT). The fluctuation of the order parameter field can be included in the phase-diagram calculation as the one-loop corrections to the free-energy [37,128,133], or studied within the SCFT by analyzing stability of the ordered phases to anisotropic fluctuations [129]. The real space SCFT can also applied for a confined geometry systems [134], their dynamic development allows to study the phase-ordering kinetics [135]. 

Analyzing theoretically the thermodynamic behavior of the melt of a proteinlike copolymer, authors of work [39] did not confine themselves to the construction of its phase diagram. They also calculated the temperature dependencies of amplitudes and periods of mesophases, as well as their volume fractions in two-phase regions on these diagrams. This permitted them to reveal some important distinctions in the thermodynamic behavior of melts of Markovian and proteinlike heteropolymers. 

Kim et al. have introduced silicon atoms in PPV block copolymers to confine the conjugation length and achieve blue EL materials. Copolymers 188-190 [215] and 191 [216] have been synthesized by Wittig-Horner and Knoevenagel condensation, respectively. The emission band in this series can be tuned between 410 and 520 nm, and ITO/polymer/Al PLEDs with turn-on voltages 7 V have been reported (Chart 2.41). 

The above approaches used the idea of conjugation length control in PTs by distorting the polymer backbone with bulky substituents as side groups. Hadziioannou and coworkers [509,510] demonstrated PL and EL tuning via exciton confinement with block copolymers... 

G.G. Malliaras, J.K. Herrema, J. Wildeman, R.H. Wieringa, R.E. Gill, S.S. Lampoura, and G. Hadziioannou, Tuning of the photo- and electroluminescence in multi-block copolymers of poly[(silanylene)-thiophene]s via exciton confinement, Adv. Mater., 5 721-723, 1993. 

Strongly segregated systems, Todt > Tc < Tg with hard confinement. A strictly confined crystallization within MDs has been observed for strongly segregated diblock copolymers with a glassy amorphous block [29-42]. 

Figure 1 shows the DSC cooling scan of iPP in the bulk after self-nucleation at a self-seeding temperature Ts of 162 °C (in domain II). The self-nucleation process provides a dramatic increase in the number of nuclei, such that bulk iPP now crystallizes at 136.2 °C after the self-nucleation process this means with an increase of 28 °C in its peak crystallization temperature. In order to produce an equivalent self-nucleation of the iPP component in the 80/20 PS/iPP blend a Ts of 161 °C had to be employed. After the treatment at Ts, the cooling from Ts shows clearly in Fig. 1 that almost every iPP droplet can now crystallize at much higher temperatures, i.e., at 134.5 °C. Even though the fractionated crystallization has disappeared after self-nucleation, it should also be noted that the crystallization temperature in the blend case is nearly 2 °C lower than when the iPP is in the bulk this indicates that when the polymer is in droplets the process of self-nucleation is slightly more difficult than when it is in the bulk. In the case of block copolymers when the crystallization is confined in nanoscopic spheres or cylinders it will be shown that self-nucleation is so difficult that domain II disappears. 

The technique of self-nucleation can be very useful to study the nucleation and crystallization of block copolymers that are able to crystallize [29,97-103]. Previous works have shown that domain II or the exclusive self-nucleation domain disappears for systems where the crystallizable block [PE, PEO or poly(e-caprolactone), PCL] was strongly confined into small isolated MDs [29,97-101]. The need for a very large number of nuclei in order to nucleate crystals in every confined MD (e.g., of the order of 1016 nuclei cm 3 in the case of confined spheres) implies that the amount of material that needs to be left unmolten is so large that domain II disappears and annealing will always occur to a fraction of the polymer when self-nucleation is finally attained at lower Ts. This is a direct result of the extremely high number density of MDs that need to be self-nucleated when the crystallizable block is confined within small isolated MDs. Although this effect has been mainly studied in ABC triblock copolymers and will be discussed in Sect. 6.3, it has also been reported in PS-fc-PEO diblock copolymers [29,99]. 

From this section we can summarize the general behavior of confined crystallizable MDs. These generalizations apply to block copolymers that are in the strong segregation regime and that can crystallize within their specific MD without breakout. When a block copolymer component crystallizes within isolated MD structures like spheres, cylinders or lamellae it may nucleate homogeneously. For homogeneous nucleation to take place, several requirements should be met ... 

Ueda et al. [26] recently investigated a flow-oriented PE-fr-aPP diblock copolymer with Mw = 113 000 (Mn/Mw = 1.1) and a PE volume fraction of 0.48. This diblock copolymer is in the strong segregation regime (i.e., estimated xN = 10.5 and Todt = 290 °C) and has a lamellar morphology in the melt. They found a breakout phenomenon with the formation of spherulites in an intermediate crystallization temperature range 95 < Tc < 101 °C. At crystallization temperatures above 101 °C or below 95 °C spherulites were not formed and the crystallization was confined within the lamellar MD. Ueda et al. report that lamellar MD and spherulites do not co-exist when the material crystallizes from the melt which is separated in lamellar MDs. In other words, in this particular case, breakout or confined crystallization within lamellar MDs depends on the crystallization conditions. 

Several of the ABC triblock copolymers with two crystallizable blocks that have been studied include PE as one of the crystallizable components. The PE block can be found either at the end (PE-fo-PS-b-PCL [94], PE-fr-PEP-fo-PEO [101,119]) or at the center (PS-fr-PE-fr-PCL [98]). When the PE block is located at the center of the copolymer, as is the case in PS-fo-PE-fr-PCL triblock copolymers [94], there are higher constraints on the PE block owing to the absence of free ends. If the PE block is a minor component, confined crystallization with possible homogeneous nucleation is usually encountered. It may be possible that when the PE block does not have free ends, it may be... 

Important differences in crystallization behavior were observed between the two crystallizable blocks within PE-fr-PEP-fr-PEO triblock copolymers. The crystallization of PE occurs without confinement from a homogeneous mixture of PE and PEP segments, but for PEO blocks, the crystallization takes place exclusively at high supercoolings in small isolated MDs. 

The technique of self-nucleation [75] can be very useful to study the nucleation and crystallization of block copolymer components, as already mentioned in previous sections. In block copolymers, factors like the volumetric fraction and the degree of segregation affect the type of confinement and therefore modify the self-nucleation behavior. In the case of semicrystalline block copolymers, several works have reported the self-nucleation of either one or both crystallizable components in PS-fc-PCL, PS-b-PB-b-PCL, PS-b-PE-b-PCL, PB-fr-PIB-fr-PEO, PE-fr-PEP-fr-PEO, PS-fc-PEO, PS-h-PEO-h-PCL, PB-b-PEO, PB/PB-fc-PEO and PPDX-fc-PCL [29,92,98,99,101-103,134] and three different kinds of behavior have been observed. Specific examples of these three cases are given in the following and in Table 5 ... 

Several block copolymer systems have shown only domains I and III upon self-nucleation. This behavior is observed in confined crystallizable blocks as PEO in purified E24EP57EO1969 [29]. Crystallization takes place for the PEO block at - 27 °C after some weak nucleating effect of the interphase. Domain II is absent and self-nucleation clearly starts at Ts = 56 °C when annealed crystals are already present, i.e., in domain III (Fig. 17b). The absence of domain II is a direct consequence of the extremely high... 

Floudas et al. [135] also studied the isothermal crystallization of PEO and PCL blocks within PS-b-PEO-h-PCL star triblock copolymers. In these systems the crystallization occurs from a homogeneous melt Avrami indexes higher than 1 are always observed since the crystallization drives structure formation and does not occur under confined conditions. A reduction in the equilibrium melting temperature in the star block copolymers was also observed. 

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