MORPHOLOGIES OF MICROPHASE-SEPARATED CONFORMATIONALLY ASYMMETRIC DIBLOCK COPOLYMERS

The equilibrium morphological behavior of a series of conformationally asymmetric linear diblock copolymers is characterized via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). T he linear diblock molecules of polyisoprene and poly(t-butylmethacryla te) (PtBMA) are prepared anionically over a range of PtBMA volume frac tions 0.17 to 0.85. Solution light-scattering experiments are performe d on PtBMA homopolymer at theta conditions, and the results were compa red with PI data in the literature in order to characterize the degree of conformational asymmetry between the respective blocks. This confo rmational asymmetry is quantified by an epsilon of 0.75. The experimen tal results are compared with morphological behavior calculated utiliz ing self-consistent mean field theory for a diblock system with epsilo n = 0.75. At middle to high PtBMA volume fractions, phi(PtBMA) > 0.30, the experimental morphological behavior agrees well with the calculat ed behavior; the microphase boundaries are slightly shifted to higher volume fractions of the PtBMA block due to its larger Kuhn length. At phi(PtBMA) < 0.30, however, discrepancies are found in the volume frac tion dependence of experimentally determined morphological behavior an d that calculated theoretically. Interestingly, extremely well-ordered cylindrical microstructures were observed for PI cylinder domains emb edded in PtBMA matrices; these samples were prepared by solvent castin g with no treatment, such as shearing, to enhance long-range order. Th ese well-ordered cylinder structures contrast with PtBMA cylinders in a PI matrix on the opposite side of the phase diagram that have very p oor long-range order. (C) 1997 John Wiley & Sons, Inc.