2ND VIRIAL-COEFFICIENT OF ISOTACTIC OLIGO(METHYL METHACRYLATE)S AND POLY(METHYL METHACRYLATE)S - EFFECTS OF CHAIN STIFFNESS AND CHAIN-ENDS

The second viral coefficient A(2) was determined for isotactic poly(me thyl methacrylate) (i-PMMA) over a wide range of weight-average molecu lar weight M(W) from 7.89 x 10(2) to 1.93 x 10(6) in acetone at 25.0 d egrees C, for M(W) greater than or equal to 1.55 x 10(5) in chloroform at 25.0 degrees C and in nitroethane at 30.0 degrees C, and for M(W) = 6.88 x 10(5) in acetonitrile at 35.0, 45.0, and 55.0 degrees C. (Som e of the data had already been obtained in the previous work.) It is s hown that the observed dependence of A(2) on M(W) in the oligomer regi on may be quantitatively explained by the Yamakawa theory that takes a ccount of the effect of chain ends, The values of the effective excess binary-cluster integrals beta(1) and beta(2) associated with the chai n End beads are then found to be 66 and 360 Angstrom(3), respectively, in acetone at 25.0 degrees C by taking the repeat unit as a single be ad. The analysis shows that the effect of chain ends remains even for relatively large M(W) in the good solvent as in the cases of atactic p olystyrene (a-PS) and atactic poly(methyl methacrylate) (a-PMMA). The results for the true interpenetration function Psi in A(2) without the effect of chain ends indicate that the two-parameter theory breaks do wn completely, as found previously for a-PS and a-PMMA; the observed P si as a function of the cubed gyration-radius expansion factor alpha(s )(3) depends separately on M(W) and on the reduced excluded-volume str ength lambda B. It is found that the values of Psi for i-PMMA are appr eciably smaller than those for a-PMMA in the same solvent, i.e., for t he same value of the binary-cluster integral beta, while the former va lues almost coincide with the latter for the same lambda B. The Yamaka wa theory that takes account of the effects of chain stiffness and loc al chain conformation on the basis of the helical wormlike chain may e xplain satisfactorily the observed behavior of Psi and also the remark able difference in it between i-PMMA and a-PMMA, the effects appearing in Psi through both lambda B and the mean-square radius of gyration [ S-2].