Block amorphous/crystalline

Due to the lack of vinyl monomers giving rise to crystalline segment by cationic polymerization, amorphous/crystalline block copolymers have not been prepared by living cationic sequential block copolymerization. Although site-transformation has been utilized extensively for the synthesis of block copolymers, only a few PIB/crystalline block copolymers such as poly(L-lactide-fc-IB-fc-L-lactide) [92], poly(IB-fr- -caprolactone( -CL)) [93] diblock and poly( -CL-fr-IB-fr- -CL) [94] triblock copolymers with relatively short PIB block segment (Mn< 10,000 g/mol) were reported. This is most likely due to difficulties in quantitative end-functionalization of high molecular weight PIB. 

DiMarzio et al. developed a scaling model for semicrystalline lamellar structures with alternating layers of amorphous and crystalline blocks, with crystalline chains folded perpendicular to the interface [24]. The model system in-... 

Amorphous-Crystalline Donor Acceptor Block Copolymers. 128... 

Scheme 2 Various donor and acceptor monomers can be combined to obtain block copolymers with amorphous or crystalline segments. In the left box, the polymerizable monomers are shown. On the right, the architectures of the resulting two main classes of D-A block copolymers are depicted amorphous-crystalline and crystalline-crystalline block copolymers...

Fig. 8. Schematic design of a spherulite which is formed in the course of polymer crystallization. Spherulites contain blocks of crystalline zones, embedded in an amorphous matrix. The size can be in the pm range and larger...

When one component of an amorphous block copolymer is replaced by a crystalline polymer, the domains or crystalline texture formed by the solvent cast should depend at least on two factors (a) crystallization of the crystalline block segment and (b) microphase separation resulting from the incompatibility of the A and B blocks. The crystalline texture observed in solid film is considered strongly dependent on the relative contributions of the two phase... 

It is obvious that the presence of the PMMA block (amorphous) leads to a decrease in the degree of crystallinity of the PCL block this is more evident in Diblock 1 having 58.6% (w/w) of PMMA, than in Diblock 2 having only 38.3% of PMMA. However, this effect is expected due to the steric overlapping of the PMMA block during the crystallization of the PCL chains the amorphous chains of PMMA influence the chain folding in the PCL block, thus leading to a reduction in crystallinity of the latter. 

For the low temperature [ ) relaxation tan 6 is largest in the 0° direction for the annealed sheet, in the c direction for the b-c sheet, and in the a direction for the a-b sheet. It was in similar directions at the appropriate temperatures that specimens rapidly became more compliant in static loading experiments (Figs. 5 and 6). Reference to the schematic representation of morphology (Fig. 17, Appendix) indicates that blocks of crystalline lamellae are oriented at approximately 45° to the crystallographic axes. The blocks are built of fold molecular chains oriented axially, and thus aligned at approximately 45° to the basal planes of the lamellae. They are separated by relaxed amorphous material and tie molecules. 

Figure 6.21 Model of crystallizable triblock copolymer thermoplastic elastomer. The center block, amorphous, is rubbery, whereas the end blocks are crystalline (64).

Different microphase separated morphologies occur depending on the relative compositions of the different components and the total molecular weight as expressed by the degree of polymerization. In addition, the aggregation state of the blocks (amorphous, liquid-crystalline, or crystalline) or the presence of solvents (formation of micelles, vesicles) largely influences the morphology as well. 

As for ABC triblock copolymers of PFP-PFS-PDMS, the PFP block is amorphous because of its atacticity, whereas the PFS block is crystalline at room temperature. These triblock copolymers form micelles in hexane, a solvent selective for the PDMS block. When the PFP block is very short (DP=1 or 6) the polymer forms flexible wormUke micelles. A triblock copolymer with a longer PFP block (DP= 11) forms starUke spherical micelles. Films show a peak in the WAXS spectrum characteristic of a crystalline PFS block for the wormUke structures. There is no evidence... 

It is widely recognized that amorphous-amorphous diblock copolymers form a variety of microdomain structures when the segregation strength between different blocks is moderately large. When one block is crystalline and the other is amorphous (i.e., crystalline-amorphous diblock copolymers), it is easily supposed that the morphology formation at low temperatures is driven by a close interplay between... 

Due to the lack of vinyl monomers giving rise to crystalline segment by cationic polymerization, amorphous/crystalline block copolymers have not been prepared by living cationic... 

Sakurai K., MacKnight W. J., Lohse D. J., Schulz D. N., and Sissano J. A. (1994) Blends of amorphous-crystalline block copolymers with amorphous homopolymers. 2. Synthesis and characterization of poly(ethylene-propylene) diblock copolymer and crystallization kinetics for the blend with atactic polypropylene. Macromolecules 27 4941-4951. 

Similarly, the random introduction by copolymerization of stericaHy incompatible repeating unit B into chains of crystalline A reduces the crystalline melting point and degree of crystallinity. If is reduced to T, crystals cannot form. Isotactic polypropylene and linear polyethylene homopolymers are each highly crystalline plastics. However, a random 65% ethylene—35% propylene copolymer of the two, poly(ethylene- (9-prop5lene) is a completely amorphous ethylene—propylene mbber (EPR). On the other hand, block copolymers of the two, poly(ethylene- -prop5iene) of the same overall composition, are highly crystalline. X-ray studies of these materials reveal both the polyethylene lattice and the isotactic polypropylene lattice, as the different blocks crystallize in thek own lattices. 

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