Temperature diblock copolymers

Fig. 23 Phase diagram in the temperature-diblock copolymer plane for the (dPB PS) mixture below the Lifshitz line separating blend like from diblock-like phase behavior. The full dots and the solid line represent the critical points of a two-phase region. The hatched area indicates a crossover from Ising to isotropic Lifshitz critical behavior, and a double critical point DCP is at 7% diblock concentration. The Lifshitz line separates at high and low temperatures the disordered phases and droplet and bicontinuous microemulsion phases ( xE). Its non-monotonic shape near the DCP is caused by the strong thermal fluctuations...

A diblock copolymer, 71% polyisoprene (1) by weight and 29% polybutadiene (B), was blended in different proportions into a 71%-29% mixture of the individual homopolymers. The loss tangent was measured as a function of temperature for various proportions of copolymer. Two peaks are observed ... 

With diblock copolymers, similar behavior is also observed. One component is enriched at the surface and depending on miscibility and composition a surface-induced ordered lamellar structure normal to the surface may be formed. Recent investigations include poly (urethanes) [111], poly(methoxy poly (ethyleneglycol) methacrylate)/PS [112] and PS/PMMA [113, 114]. In particular the last case has been extensively studied by various techniques including XPS, SIMS, NR and optical interferometry. PS is enriched at the surface depending on blockcopolymer composition and temperature. A well ordered lamellar structure normal to the surface is found under favourable conditions. Another example is shown in Fig. 6 where the enrichment of poly(paramethylstyrene), PMS(H), in a thin film of a di-... 

FIGURE 5.17 Temperature versus G —the shear storage modulus at a frequency of 1.6 Hz for diblock copolymer poly(ethylene propylene)-poly(ethylethylene) (PEP-PEE). The order-disorder transition (ODT) calculated to be 291°C 1°C. (From Rosedale, J.H. and Bates, F.S., Macromolecules, 23, 2329, 1990. With permission of American Chemical Society.)... 

A carbazole-functionalized norbornene derivative, 5-CN-carbazoyl methy-lene)-2-norbornene, CbzNB, was polymerized via ROMP using the ruthenium catalyst Cl2Ru(CHPh)[P(C6Hii)3]2 [100]. The polymerization was conducted in CH2C12 at room temperature, to afford products with polydispersity indices close to 1.3. Subsequent addition of 5-[(trimethylsiloxy)methylene]-2-norbornene showed a clear shift of the SEC trace of the initial polymer, indicating that a diblock copolymer was efficiently prepared in high yield. 

Fig. 51 Phase diagram for PS-PI diblock copolymer (Mn = 33 kg/mol, 31vol% PS) as function of temperature, T, and polymer volume fraction, cp, for solutions in dioctyl ph-thalate (DOP), di-n-butyl phthalate (DBP), diethyl phthalate (DEP) and M-tetradecane (C14). ( ) ODT (o) OOT ( ) dilute solution critical micelle temperature, cmt. Subscript 1 identifies phase as normal (PS chains reside in minor domains) subscript 2 indicates inverted phases (PS chains located in major domains). Phase boundaries are drawn as guide to eye, except for DOP in which OOT and ODT phase boundaries (solid lines) show previously determined scaling of PS-PI interaction parameter (xodt

A phase diagram of the symmetric PS-fc-PI blended with PS homopolymer of shorter chain lengths was constructed by Bodycomb et al. [ 174]. The effect of blend composition on the ODT is shown in Fig. 56 along with the results of mean-field calculations. In analogy to MFT the addition of homopolymer decreases the ODT temperature for the nearly symmetric diblock copolymer. 

A number of diblock copolymers of NIPAM and hydrophobic comonomers have been prepared by various groups and assessed in terms of micellar structure, thermosensitivity, and applications. For example, PS-fo-PNIPAM was shown to form either micelles consisting of a PS core and a PNIPAM corona, or vesicles. The assemblies were colloidally stable at elevated temperature [262-266]. 

It is clear from the previous discussion that a proportionality between crystallization temperature and the volume of the crystallizing phase has been found for PEO in many cases (Fig. 4), including AB and ABA diblock copolymers however, there have been reports of exceptions to this trend and they have also been included in the data compilation of Fig. 5, in particular the extensive data reported by Xu et al. [96]. In the case of ABC triblock copolymers a different behavior has also been reported and will be analyzed in detail in Sect. 5. 

In order to study the overall crystallization kinetics of the PCL block within PPDX-fo-PCL diblock copolymers, Muller et al. [ 103] first crystallized the PPDX block until saturation by performing a special thermal procedure (it consisted of first cooling from the melt as in Fig. 6 to allow both blocks to crystallize, then the sample was heated to 62 °C and annealed at that temperature for 70 min, a temperature at which the PCL is molten, before quenching to a Tc where the PCL block isothermal crystallization was followed by DSC). With the use of such a procedure the overall isothermal crystallization of only the PCL block was determined in the diblock copolymers where the PPDX block was already crystallized. 

Calorimetric measurements and morphological observations showed that PS-fr-PCL, PB-fr-PCL and PS-fc-PB-fc-PCL copolymers exhibit microphase separation and crystallization if the molecular weight is high enough. Only in PS-fc-PCL diblock copolymers, a shift of the PS glass transition to lower temperatures has been observed. In PS-fo-PB-fo-PCL, the crystallizable block (i.e., PCL) is covalently linked to a rubbery block and it has a free end. For these reasons there is no significant reduction in the melting temperature and... 

As mentioned in Sect. 3, for PEO it has been found that the crystallization temperature is often a function of the MD volume. The examples quoted in Sect. 3 referred to PEO dispersed in droplets or to PEO that was a component within diblock copolymers. For other block copolymer components like PCL the variation in Tc encountered upon MD size increase is not as pronounced. Nojima et al. [22] found that the variation of Tc for PB-fo-PCL block copolymers with spherical PCL MDs of increasing sizes, ranging from 10.3 to 17.4 nm, was of about 5 °C for crystallization at very large supercoolings (Tc fluctuated between - 50 and - 45 °C approximately). For ABC triblock copolymers, Muller et al. [29], Schmalz et al. [101,119] and Balsamo et al. [118] found, by studying copolymers with minority components of PEO or PCL blocks linked to a rubbery block, that the Tc associated with fractionated... 

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. 

Chen et al. [92] also performed self-nucleation experiments by DSC in PB-fr-PEO diblock copolymers and PB/PB-b-PEO blends. The cooling scans presented in their work showed that a classical self-nucleation behavior was obtained for PEO homopolymer and for the PB/PB-b-PEO blend where the weight fraction of PEO was 0.64 and the morphology was lamellar in the melt. For PB/PB-fr-PEO blends with cylinder or sphere morphology, the crystallization temperature remained nearly constant for several self-seeding temperatures evaluated. This observation indicates that domain II or the self-nucleation domain was not observable for these systems, as expected in view of the general trend outlined earlier. 

The micellization behavior of copolymers containing two hydrophobic blocks, or double-hydrophobic block copolymers, has been shown to be mainly controlled by the solvent and its interaction with the copolymer blocks. It is thus possible to tune the micellization of these copolymers by changing the organic solvent. In this respect, large differences in Z, i h, Rc, etc. are expected whenever the interaction parameter between the polymer and the solvent is varied. This is illustrated by, e.g., the work of Pit-sikalis et al. [87] for PS-PSMA diblock copolymers dissolved in either ethyl-or methylacetate. The effect of temperature has been studied by Quintana et al. [88,89], who have clearly shown that CMC decreases with increasing temperature for PS-PEB copolymers in alkanes. 

The most simple diblock copolymers are linear chains, in which one part of the chain consists of one type of monomer, say polystyrene (PS), and the other one of another type, say polybutadiene (PB), as illustrated in Figure 14. PS and PB usually phase separate at low temperatures however, because of their chemical connectivity, block copolymers cannot unmix on a macroscopic scale. They can only phase separate on a microscopic scale, the size of which is determined by the length of the polymers. 

Fig. 6.6 Variation of the static structure factor S(Q) measured on hPE-dPEE diblock copolymer chains (sample IV) as a function of the wave number Q. Temperature closed star 393 K, closed circles 403 K, closed square 413 K, inverted triangle 423 K, closed star 433 K, open triangle 433 K, open circle 453 K, open square 463 K. Solid lines represent the fit with a two-component static RPA approach (Eq. 6.12). (Reprinted with permission from [44]. Copyright 1999 American Institute of Physics)...

Fig. 4 Dependence of the advancing water contact angle on annealing temperature for PS-based diblock copolymer brush layers (filled squares) Si/Si02//PS- -PHFA, (filled triangles) Si/Si02//PS- -PPFA, (filled diamonds) Si/Si02//PS- -PPFS. Lines added as guide for the eye...

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