Transport Coefficients of Isotactic Oligo- and Poly(methyl methacrylate)s in Dilute Solution

Abstract

The intrinsic viscosity [ ] was determined for 25 samples of isotactic oligo-and poly(methyl methacrylate)s (i-PMMA), each with the fraction of racemic diads ft -0.01, in the range of weight-average molecular weight Afw from 3.58 x 102 (trimer) to 1.71 x 10® in acetonitrile at 28.0 °C ( ). The translational diffusion coefficient D was also determined from dynamic light scattering measurements for 12 of them in the range of Afw from 6.58 x 102 (hexamer) to 9.46 x 10® under the same solvent condition. It is found that [77] is proportional to Af"1/2 for Afw £ 5 x 104 and its deviation from this asymptotic behavior is small even for smaller Afw, while D is inversely proportional to AfwV2 except for Aíw á 2 x 103. Such apparent Gaussian behavior of [77] and D over a wide range of Afw is the result expected from that previously obtained for the mean-square radius of gyration (S2). From an analysis of these transport coefficients on the basis of the helical wormlike (HW) chain model, it is shown that the above Mv dependences of [77] and D may be well explained by the HW theories with the values of the model parameters consistent with those previously determined from (S2). A comparison is also made of the present results for [ \ and D for i-PMMA with the previous ones for atactic (a-) PMMA with fT = 0.79. This leads to the confirmation of the previous conclusion derived from (S2) concerning the fT dependence of the chain stiffness and local chain conformation of PMMA. That is, the i-PMMA chain is of weaker helical nature than the a-PMMA chain that retains rather large and clearly distinguishable helical portions in dilute solution.

Dynamic Depolarized Light Scattering and Nuclear Magnetic Relaxation Studies of Isotactic Oligo- and Poly(methyl methacrylate)s in Dilute Solution

“…Materials. All the i-PMMA samples used in this work are the same as those used in the previous studies of 〈 S 2 〉, the intrinsic viscosity, the translational diffusion coefficient (in ϑ and good solvents), ,− the scattering function, the second virial coefficient, and the mean-square optical anisotropy, i.e., the fractions separated by preparative gel permeation chromatography (GPC) or fractional precipitation from the original samples prepared by living anionic polymerization, following the procedure of Ute et al They are sufficiently narrow in molecular weight distribution and have a fixed stereochemical composition (the fraction of racemic diads f r ≃ 0.01) almost independent of the weight-average molecular weight M w . The values of M w , the weight-average degree of polymerization x w , and the ratio of M w to the number-average molecular weight M n are summarized in Table .…”

Adsorption of stereoregular poly(methyl methacrylates) on ?-alumina: Spectroscopic analysis

“…This behavior is confirmed by light scattering measurements of the PMMA radius of gyration in solvents. 22,23 However, in athermal solvents, the difference between the chain dimensions of the two isomers is smaller, 21 meaning that the chain expansion of s-PMMA is higher than that of i-PMMA in good solvents.…”

Mean-Square Electric Dipole Moment of Oligo- and Poly(methyl methacrylate)s in Dilute Solution

“…All the a-PMMA samples used in this work are the same as those used in the previous studies of the mean-square radius of gyration 〈 S 2 〉 (in ϑ and good solvents), , the intrinsic viscosity [η] (in ϑ and good solvents), , the mean-square optical anisotropy 〈Γ 2 〉, the scattering function P s , the translational diffusion coefficient D (in ϑ and good solvents), , and the second virial coefficient A 2 . , They are the fractions separated by preparative gel permeation chromatography (GPC) or fractional precipitation from the original samples prepared by group-transfer polymerization and have a fixed stereochemical composition ( f r = 0.79) independent of x , possessing hydrogen atoms at both ends of the chain. All the i-PMMA samples used are the same as those used in the previous studies of 〈 S 2 〉 (in ϑ and good solvents), , [η] (in ϑ and good solvents), , 〈Γ 2 〉, P s , 13 , D , 14,27 , and A 2 , i.e., the fractions separated by preparative GPC or fractional precipitation from the original samples prepared by living anionic polymerization or from the commercial sample 9011-14-7 from Scientific Polymer Products, Inc. They possess a tert -butyl group at one end of the chain and a hydrogen atom at the other except for the sample iMMc6 and have a fixed stereochemical composition ( f r ≃ 0.01) independent of x .…”

“…b M w 's of OM6b, OM8b, MM7, and MM12 had been determined from light-scattering (LS) measurements in acetonitrile at 44.0 °C. , c M w 's of OM12 through MM2a had been determined from LS in acetone at 25.0 °C. ,, d M w 's of iOM3 through iOM7 had been determined by 1 H NMR and GPC , f M w of sMMc4 had been determined from LS in acetonitrile at 45.0 °C …”

“…In a series of recent systematic experimental studies of dilute-solution behavior of polymers in the unperturbed (ϑ) state, we have been analyzing the data obtained for equilibrium conformational and steady-state transport properties on the basis of the helical wormlike (HW) chain model . The polymers investigated so far are atactic polystyrene with the fraction of racemic diads f r = 0.59, − atactic poly(methyl methacrylate) (a-PMMA) with f r = 0.79, − and isotactic (i-) PMMA with f r ≃ 0.01 − as asymmetric polymers and polyisobutylene and poly(dimethylsiloxane) (PDMS) , as symmetric ones. Then valuable information about the chain stiffness and local chain conformation for them has been obtained from the values of the HW model parameters determined.…”