Blends diblock copolymer, Polymer

Nojima S, Wang D, Ashida T. Ringed spheruhte in binary blends of poly(e-caprolactone) and e-caprolactone-butadiene diblock copolymer. Polym J 1991 23 1473-1482. 

The structure factor for the polymer blend-diblock copolymer system is described within the random phase approximation by [54-56]... 

Figure B3.6.5. Phase diagram of a ternary polymer blend consisting of two homopolymers, A and B, and a synnnetric AB diblock copolymer as calculated by self-consistent field theory. All species have the same chain length A and the figure displays a cut tlirough the phase prism at%N= 11 (which corresponds to weak segregation). The phase diagram contains two homopolymer-rich phases A and B, a synnnetric lamellar phase L and asynnnetric lamellar phases, which are rich in the A component or rich in the B component ig, respectively. From Janert and Schick [68].

Block copolymers are closer to blends of homopolymers in properties, but without the latter s tendency to undergo phase separation. As a matter of fact, diblock copolymers can be used as surfactants to bind immiscible homopolymer blends together and thus improve their mechanical properties. Block copolymers are generally prepared by sequential addition of monomers to living polymers, rather than by depending on the improbable rjr2 > 1 criterion in monomers. 

Characterization and control of interfaces in the incompatible polymer blends were reported by Fayt et al. [23]. They used techniques such as electron microscopy, thermal transition analysis, and nonradiative energy transfer (NRET), etc. They have illustrated the exciting potentialities offered by diblock copolymers in high-performance polymer blends. 

When dealing with polymer blends or blockcopolymers, surface enrichment or microstructures may be observed as already discussed in Sect. 3.1. Quite similar effects may be expected for buried interfaces e.g. between polymer and substrate where one component may be preferentially enriched. In a system of PS, PVP and diblock copolymer PS-6-PVP it has been shown by FRS that the copolymer enrichment is strongly concentration dependent [158]. In a mixed film of PS(D) and end-functionalized PS on a silicon wafer the end-functionalized chains will be attached to the silicon interface and can be detected by NR [159],... 

Using the random phase approximation (RPA), the coherent scattering intensity Icoh(Q, t) of a polymer blend/solvent or a diblock copolymer/solvent system can... 

Homogeneous and Heterogeneous Rubbery-Rubbery Diblock Copolymers and Polymer Blends A Unified View... 

Figure 2. Schematic three-dimensional plot showing various planes of AB polymer/polymer composition. From left to right homopolymer blends blends containing 50 weight percent diblock copolymer diblock copolymers. 

As an example of blends with attractive interactions, Fig. 65 shows a superstructure in which interactions between methacrylic acid groups and pyridine side groups of a polystyrene-fc-polybutadiene-fo-poly(f-butyl methacry-late-staf-methacrylic acid) (PS-b-PB-b-P(MAA-sfaf-fBMA)) triblock quater-polymer and a PS- -P2VP diblock copolymer lead to a wavy lamellar structure with cylinders from mixed P2VP and P(MAA-sfaf-fBMA) blocks [194],... 

Xu S, Chen B, Tang T, Huang B. Syndiotactic polystyrene/thermoplastic polyurethane blends using poly(styrene-l)-4-vinylpyridine) diblock copolymer as a compatibilizer. Polymer 1999 40 3399-3406. 

Xu S, Zhao H, Tang T, Dong L, Huang B. Effect and mechanism in compatibilization of poly(styrene-l)-2-ethyl-2-oxazoline) diblock copolymer in poly(2,6-dimethyl-1,4-phenylene oxide)/poly(ethylene-ran-acrylic acid) blends. Polymer 1999 40 1537-1545. 

One can have the same type of situation in a blend of two mutually immiscible polymers (e.g., polymethylbutene [PMB], polyethylbutene [PEB]). When mixed, such homopolymers form coarse blends that are nonequilibrium structures (i.e., only kinetically stable, although the time scale for phase separation is extremely large). If we add the corresponding (PEB-PMB) diblock copolymer (i.e., a polymer that has a chain of PEB attached to a chain of PMB) to the mixture, we can produce a rich variety of microstructures of colloidal dimensions. Theoretical predictions show that cylindrical, lamellar, and bicontinuous microstructures can be achieved by manipulating the molecular architecture of block copolymer additives. 

In fact, even in pure block copolymer (say, diblock copolymer) solutions the self-association behavior of blocks of each type leads to very useful microstructures (see Fig. 1.7), analogous to association colloids formed by short-chain surfactants. The optical, electrical, and mechanical properties of such composites can be significantly different from those of conventional polymer blends (usually simple spherical dispersions). Conventional blends are formed by quenching processes and result in coarse composites in contrast, the above materials result from equilibrium structures and reversible phase transitions and therefore could lead to smart materials capable of responding to suitable external stimuli. 

It is a routine SFM experiment to investigate the heterogeneous structure of polymer blends and composites containing micrometer sized domains [69]. A less trivial problem is to resolve and characterise the features on the nanometer scale (around 10 nm), which are comparable to the tip size and the contact area. Typical systems, which demonstrate microheterogeneous structures, are block copolymers consisting of chemically different and physically incompatible blocks, e.g. A and B. As a result of the interconnectivity of the blocks, block copolymers undergo microphase separation, where the size of the microdomains is restricted to the molecular dimensions. One can distinguish between AB diblock copolymers and triblock copolymers (ABA and ABC). 

The supramolecular structure of block co-polymers allows the design of useful materials properties such as polarity leading to potential applications as second-order nonlinear optical materials, as well as piezo-, pyro-, and ferroelectricity. It is possible to prepare polar superlattices by mixing (blending) a 1 1 ratio of a polystyrene)-6-poly(butadiene)-6-poly-(tert-butyl methacrylate) triblock copolymer (SBT) and a poly (styrene)-Apoly (tert-butyl methacrylate) diblock copolymer (st). The result is a polar, lamellar material with a domain spacing of about 60 nm, Figure 14.10. 

Figure 14.10 TEM image of blend containing 75 wt. % of a SBT triblock copolymer and 25 wt. % st diblock co-polymer. The non-centrosymmetric supramolecular structure of this blend is schematically illustrated in the diagram that assigns the different phases observed in the marked part of the micrograph (Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced by permission).

Khandpur AK et al. (1995) Compatibilizers for A/B blends A-C-B triblock versus A-B diblock copolymers. Polyblends 95, SPE Regional Technical Conference on Polymer Alloys and Blends. Boucherville, Quebec, Oct 19-20, pp 88-96... 

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