Diblock double-crystalline

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. 

There have been relatively few reports dealing with double-crystalline diblock copolymers [102-110,197-200]. The particular case of ABC triblock copolymers with two semicrystalline blocks will be presented in a separate section. Works pertaining to one of the most studied systems PCL-fo-PEO have already been previously reviewed [43]. Recently, probably the most comprehensive studies on double-crystalline diblock copolymer systems were performed on poly(p-dioxanone)-fc-PCL diblock copolymers, PPDX-fr-PCL, and therefore several important aspects of these works [102,103,107] will be summarized in this section. 

In a related double-crystalline PE-fr-poly(L-lactide), PE-fo-PLLA diblock copolymer (with an approximate 50/50 weight ratio), similar behavior was observed [103]. When the diblock copolymer is cooled from the melt at 10 °C min 1 only one crystallization exotherm is observed, indicating that the L-lactide block is also affected by the molten PE block that is covalently bonded to it [103]. However in this case, the crystallization exotherms can be separated by reducing the cooling rate to 2 °C min-1 [ 106]. 

Another double-crystalline system that has recently been studied is that of PLLA-fo-PCL diblock copolymers [110]. Kim et al. synthesized rather broad molecular weight distribution PLLA-fc-PCL diblock copolymers with polydis-persities ranging from 1.3 to 1.6. They reported that a diblock copolymer with a Mn value of 77 000 and a PCL weight fraction of 0.32 was phase-separated... 

Sun L, Liu YX, Zhu L, Hsiao BS, AvUa-Orta CA (2004) Self-assembly and crystallization behavior of a double-crystalline polyethylene-block-poly(ethylene oxide) diblock copolymer. Polymer 45 8181-8193... 

T, = 66.6°C for a PEO [18], The crystallization process is more complicated in the double crystalline diblock copolymers than in the homopolymeis. In the specific case of PEO-6-PCL diblocks, the crystallization of the first block occurs at supercoolings higher than in the correspondmg PEO homopolymer as a consequence of the diluent effect caused by the homogeneous melt. This effect becomes evident when comparing the crystallization temperature of PEO (Tc = 42.6°C) with that of the PEO block within = 36.2°C) ... 

As can be seen from the results presented above, the study of PEO-6-PCL has made evident the complexity of the crystallization and melting processes in double crystalline diblock copolymers that have the following characteristics their crystallization starts from a homogenous melt, crystallization and melting points of the blocks are very near to each other, and there is an absence of a nucleating effect of each block on the other. 

Another type of remarkable double crystalline materials that have been synthesized and characterized by Balsamo et al. are ABC triblock terpolymers composed of polystyrene, polyethylene and poly(ir-caprolactone) (PS-5-PE-6-PCL or SEC) [51-54,57,63]. The morphology, nucleation and crystallization of such copolymers have been recently reviewed [3]. It is interesting to mention that in such terpolymers the PE block induces an antinucleation effect [3,63] on its covalently bonded neighboring PCL block, a remarkable effect that has only been observed in this tjq >e of triblock terpolymer. Diblock copolymers or triblock terpolymers with two crystallizing blocks can display aU possible effects from the nucleation point of view of one crystallizing block on the other. One block can cause nucleation of the other, or cause no effect, or in the other extreme of behavior induce antinucleation. In addition to the... 

The formation and properties of inclusion compounds of cyclodextrin with double crystalline PLLA-b-PCL diblock copolymers has been extensively discussed in a series of contributions by Tonelli et al. [64-67], where they highlight the changes that can be introduced in the structure and properties of the copolymers when they form these peculiar inclusion complexes. 

Wang W, Liu R, Li Z, Meng C, Wu Q, Zhu F (2010) Synthesis and self-assembly of new double-crystalline amphiphilic polyethylene-h/ock-poly[oligo(ethylene glycol) methyl ether methacrylate] coil-brush diblock copolymer. Macromol Chem Phys 211 1452-1459... 

In this section, two examples of the use of self-nucleation are presented for block copolymers and nanocomposites. The first example shows how self-nucleation can help separate the coincident crystallization of a double crystalline diblock copolymer. In the second example, the efficiency scale based on self-nucleation helps to define supernucleation. 

Hamley IW, Parras P, Castelletto V, Castillo RV, Muller AJ, PoUet E, Dubois P, Martin CM. Melt structure and its transformation by sequential crystallization of the two blocks within poly(L-lactide)-WocA -poly(e-caprolactone) double crystalline diblock copolymers. Macromol ChemPhys 2006 207 941-953. 

Li S, Myers SB, Register RA. Sohd-state structure and crystallization in double-crystalline diblock copolymers of linear polyethylene and hydrogenated polynorbomene. Macromolecules 2011 44 8835-8844. 

Albuerne J, Marquez L, Muller AJ, Raquez JM, Degee P, Dubois P, Castelletto V, Hamley IW. Nucleation and crystallization in double crystalline poly(p-dioxanone)-b-poly( -caprolactone) diblock copolymers. Macromolecules 2003 36 1633-1644. 

Salim NV, Hanley T, Guo Q. Microphase separation through competitive hydrogen bonding in double crystalline diblock copolymer/homopolymer blends. Macromolecules 2010 43(18) 7695-7704. 

Crystallization within Strongly Segregated Double-Crystalline Diblock Copolymers and Triblock Copolymers, 355... 

Polyethylene-fi-poly(ethylene oxide) diblock copolymers (PE-6-PEO) represent an interesting double-crystalline diblock copolymer system since both blocks are strongly segregated and at the same time they have a marked tendency to crystallize in view of their highly flexible linear chains [20]. Hillmyer et al. [271] synthesized PE-6-PEO block copolymers of 2.1 and 2.8 kg/mol from hydroxyl terminated poly(l,4-butadiene) catalytically... 

Fig. 535 Avrami plots showing the growth of the relative degree of crystallinity (

---