Block copolymers birefringence

BICARBONATE, 105 135 BICYCLE, 167 BINARY BLEND, 5 BINARY SYSTEM, 134 BIREFRINGENCE, 218 BLENDING, 11 28 368 BLISTER PACKAGING, 454 BLOCK COPOLYMER, 31 101 107 178 252 368 BLOW EXTRUSION, 19 74 79 BLOW MOULDING, 34 35 95 140 193 263 312 420... 

The evolution of microstructural orientation in block copolymers was studied in real time by Kornfield and co-workers using birefringence measurements on diblocks sheared in situ (Gupta et al. 1995 Kannan and Kornfield 1994). The birefringence of the polymer in two orthogonal planes was measured using laser light... 

Figure 10.11 Birefringence multiplied by the cosine of twice the orientation angle of a PS/ PBD star block copolymer as a function of temperature.

M. J. Folkes and A. Keller, The birefringence and mechanical properties of a single crystal from a tri-block copolymer, Polymer, 12,222 (1971) M. J. Folkes and A. Keller, Optical and swelling properties of macroscopic single crystals of an S-B-S copolymer. I. Samples possessing a lamellar morphology, J. Polym. Sci., Polym. Phys. Ed., 14, 833 (1976). 

Until now we have considered the basic origin of birefringence and some of the general techniques used for determining this optical parameter. It is necessary, however, to discuss certain limitations when interpreting this parameter. Until now no mention has been made of two or multiphase systems such as semicrystalline polymers, amorphous block copolymers or even plasticized or filled polymers. In such systems the measured birefringence can be expressed as... 

As an alternative to holographic experiments, the photoinduced birefringence can also be measured by the response of the material to polarized light. Its value depends on the concentration of the photoactive chromophores, which decreases with increasing amount of the homopolymer. Normalizing the results to the azobenzene content yields very similar results for each series of blends in which the same block copolymer is used (see Fig. 37). This also confirms that the photoresponse is independent of the homopolymer content. 

Thus, each individual phase i contributes to the birefringence according to its volume fraction (f>i and birefringence Am. These different phases can, for example, be the amorphous and crystalline phases of partially crystalline polymers, aggregates in block copolymers, fillers, or plasticized regions. 

Recently, Folkes and Keller showed that all the observed birefringence in an extruded cylinder of an ABA block copolymer was due to... 

The sonic technique suffers from one of the same difficulties as the birefringence method in that only an average orientation of the total system is obtained. Thus, if one has a multicomponent system (e.g. semicrystalline, block copolymer. etc.X one cannot separate component orientation by this technique alone. It is noteworthy that the orientation measured by the sonic method can be correlated directly with birefringence data on the same material.This ease of correlation has been suggested to lead to values of the intrinsic birefringence by extrapolation of the sonic data to perfect orientation. 

PLLA generally form non-banded spherulites from the melt that exhibit negative birefringence. Banding can appear after special annealing conditions or in blends and block copolymers. 

Balsara, N. P. Perahia, D. Safmya, C. R. Tirrell, M. Lodge, T. P. (1992) Birefringence Detection of the Order-to-Disorder Transition in Block Copolymer Liquids, Macromolecules 25, 3896-3901. 

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