Copolymer crystallization

Keywords ABC triblock copolymers Block Copolymers Crystallization Homogeneous nucleation... 

Examples of all these cases can be found in Table 1, where a thorough fisting of most references dealing with block copolymers crystallization in the past decade is presented along with salient features of the systems that have been studied. 

Since excellent reviews on block copolymer crystallization have been published recently [43,44], we have concentrated in this paper on aspects that have not been previously considered in these references. In particular, previous reviews have focused mostly on AB diblock copolymers with one crystal-lizable block, and particular emphasis has been placed in the phase behavior, crystal structure, morphology and chain orientation within MD structures. In this review, we will concentrate on aspects such as thermal properties and their relationship to the block copolymer morphology. Furthermore, the nucleation, crystallization and morphology of more complex materials like double-crystalline AB diblock copolymers and ABC triblock copolymers with one or two crystallizable blocks will be considered in detail. 

Lotz and Kovacs [93] reported n = 0.5 many years ago when their PS-b-PEO diblock copolymers crystallized at very large supercoolings (i.e., homogeneous nucleation was assumed to take place). However, the origin of this result was not explained. 

Contributions to the subject of ABC triblock copolymer crystallization are listed in Table 1, where some characteristics of the triblock copolymers involved are reported with the corresponding references. 

The modification of PET with low levels of naphthalate comonomer increases the Tg and enables optimally oriented articles (films, fibers, containers, etc.) to resist higher temperatures without shrinkage. Heat setting under tension may be applied to further extend thermal stability. In addition, when retention of optical transparency is required, such copolymers crystallize less readily than PET, and may readily be quenched from the melt to the transparent, amorphous state. Thus,... 

The system consisting of copolymers of styrene and />-fluoro styrene (case b), instead, is characterized by isodimorphism. For the whole range of copolymer compositions the system exhibits crystallinity. The crystal structure is that of the homopolymer deriving from the predominant comonomer. Up to >-fluoro styrene, contents of about 50% by moles the copolymers crystallize in the threefold helix structure of iso-... 

Copolymers show chemical resistance generally similar to that of polystyrene and terpolvmers similar to that of ABS (acrylonitrile-butadiene-styrene). Neither type is recommended for use in strongly alkaline environments. All impact versions have good natural color and products are available in a wide range of colors. Copolymer crystal grades have good clarity and gloss. 

The orientation of crystalline stems with respect to the lamellar interface in block copolymers is a subject of ongoing interest and controversy. In contrast to homopolymers, where folding of chains occurs such that stems are perpendicular to the lamellar interface, the parallel orientation has been observed for block copolymers crystallized from the heterogeneous melt. It is not yet clear whether this is always the preferred orientation, or whether chains can crystallize perpendicular to the lamellar plane, for example when crystallization occurs from the homogeneous melt or from solution. 

Thermal Properties. The DPP portion of block copolymers crystallizes on heating at 290°C and then melts at 480°C. The DMP portion of block copolymers does not crystallize thermally but can be caused to crystallize by treatment with a suitable solvent, such as a mixture of toluene and methanol the crystallized DMP then melts at 258°C. The glass-transition temperatures of the homopolymers are too close (221°C for DMP, 228° for DPP) to permit observation of separate transitions, either in block copolymers or blends of the homopolymers. 

In a similar manner, the ethylene-octene copolymer crystallized directly via the orthorhombic phase without the intervention of the anticipated hexagonal phase as would be anticipated in linear polyethylenes at these high pressures and temperatures (at approximately 3.8 kbar and around 200 °C). At 100 °C, see Fig. 15, the d values for (110) and (200) orthorhombic reflections are 4.08 A and 3.71 A. When the sample is cooled below 100 °C, a new reflection adjacent to the (110) orthorhombic peak appears at 80 °C. The position of the new reflection is found to be 4.19 A and so corresponds to a new phase. No change in the intensity of the existing (110) and (200) reflections is observed, however the intensity of the amorphous halo decreases, which suggests that the appearance of the new reflection (d = 4.19 A) is solely due to the crystallization of a noncrystalline component. On cooling further as the new reflection intensifies, the (110) and (200) orthorhombic reflections shift gradually. However, at 50 °C, the (100) monoclinic reflection appears with a concomitant decrease in the intensity of the (110) orthorhombic reflec-... 

K-Resin SB Copolymer/Crystal Polystyrene Sheet Property Modification with High Impact Polystyrene, Plastics Technical Center Report 409, Chevron Phillips Chemical Co., Bartlesville, OK. 

In summarizing the results from the last three sections, one can conclude that the systematic variation of microhardness under strain performed on (a) homo-PBT (Section 6.2.1), (b) its multiblock copolymer PEE (Section 6.2.2) and (c) on blends of both of these (this section) is characterized by the ability of these systems to undergo a strain-induced polymorphic transition. The ability to accurately follow the strain-induced polymorphic transition even in complex systems such as polymer blends allows one also to draw conclusions about such basic phenomena as cocrystallization. In the present study of a PBT/PEE blend two distinct well separated (with respect to the deformation range) strain-induced polymorphic transitions arising from the two species of PBT crystallites are observed. From this observation it is concluded that (i) homo-PBT and the PBT segments from the PEE copolymer crystallize separately, i.e. no cocrystallization takes place, and (ii) the two types of crystallites are not subjected to the external load simultaneously but in a sequential manner. 

Keywords Block copolymers, Crystallization, Chain folding... 

As shown in Fig. 21.1, the melting point of P(3HB-co-3HV) is depressed rapidly as the 3HV content increases from 0 to 40mol%. This behavior cannot be predicted by the Flory equation [48, 50], which was derived based on the assumption that copolymer crystals are composed of only one kind of comonomer component and the others exist only in the noncrystalline region. The analysis of the crystalline structure of P(3HB-co-3HV) samples with 3HV content up to 30 mol% indicate that only a small fraction of the 3HV units are included in the P(3HB) crystalline lattice as defects [51, 52]. 

The theory also predicts that the content of the minor comonomer units in the crystalline phase decreases with a rise in the crystallization temperature [61]. To confirm this prediction, the contents of comonomer units in the crystalline as well as in the amorphous phases were again measured by high resolution solid-state NMR spectroscopy for the P(3HB-co-3HV) copolymers crystallized at various temperatures [54]. The copolymer samples used were quenched from the melt into the crystallization temperature and left for 5 days at this temperature and then left at room temperature for more than 5 days. For the copolymer with a 3HV content as a whole of 18.3%, in which the 3HV unit is the minor component and this copolymer was crystallized in the P(3HB) lattice, the 3HV content in the crystalline phase (Xc) was found to decrease from 7.6 to 7.2% and the melting point... 

Taking all the fact presented in this section into account, together with the synthesis method and fractionation results, we conclude that the purified copolymer separated from reaction products is an iPS-fo-iPP diblock copolymer consisting of iPS and iPP blocks it is definitely not a simple blend of homopolymers. On the other hand, the distinctive characteristics of the copolymers crystallization kinetics also indicate that, compared with homopolymers and the iPS-iPP blend, the purified copolymer is a true iPS-fo-iPP diblock copolymer (23). 

Atomistic simulations can be used to estimate defect free energies which can then be used as input parameters in thermodynamic models for copolymer crystallization. Recent work by Wendling et al [167-170] has demonstrated the utility of this combined approach conclusively. It is anticipated that such investigations will become increasingly more common in the future. 

Iwata and coworkers ° ° also investigated enzyme adsorption to copolymer single crystals, and reported that PHA depolymerase adsorbed randomly on the surfaces of single crystals. However, the concentrations of adsorbed enzjune on the surface of copolymer single crystals are lower than that for P(3HB) homopolymer single crystals. PHA depolymerase molecules cannot bind tighdy to the irregular surface of copolymer crystals since the copolymer chains with second monomer units have loose loop folds. 

Figure 6.10. Models of (a) single and (b) double folded chain lamellae in PEO/PS block copolymers. (Crystal et ai, 1970.)...

Sect. 7.2. The main reference for this part of the course is Wunderlich B (1976,1980) Macromolecular Physics, Volume II, Crystal Nucleation, Growth, Annealing, and Volume III, Crystal Melting. Academic Press, New York (look for the chapters on copolymer crystallization and melting). 

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