Measurement of Diffusion Coefficients of Oligomeric Penetrants in Rubbery Polymer Matrixes

Abstract

The diffusion coefficients of oligomeric radicals in monomer-polymer systems have a major influence on properties such as polymerization rates and molecular weight distributions. The present work reports the results of an extensive set of studies of diffusion coefficients of rubbery ternary systems comprising polymer, diluent, and oligomer, determined by pulsed-field-gradient NMR, at 25 and 40°C. Oligomers of methyl methacrylate (MMA) and of butyl methacrylate (BMA) were synthesized by using a catalytic cobalt chain transfer agent to produce macromonomers with a terminal double bond. Where necessary, these were fractionated by preparative GPC to obtain samples ranging from dimeric to decameric; typical polydispersities were 1.08. Pulsed-field gradient NMR is facilitated by being able to monitor the proton NMR of the CH 2 hydrogens on the double bond. Matrixes used were high molecular weight polyMMA and polyBMA, the weight fraction of polymer (wp) being varied by adding appropriate amounts of diluent (the saturated equivalents of MMA and BMA, viz., methyl isobutyrate and butyl isobutyrate). Above c* (the concentration at which chains start to overlap), all data for diffusion coefficients Di of an oligomer of degree of polymerization i could be fitted with acceptable accuracy by D1(wp)/Di(wp) ) i 0.664 + 2.02w p , for both BMA and MMA oligomers in both MMA and BMA matrixes; the same relation also fits earlier data on styrene oligomers in polystyrene. If more accurate scaling parameters are obtained experimentally for smaller oligomers, these can be used to predict data for higher oligomers with even better reliability. For MMA monomer in pMMA, where free-volume parameters are available, the predicted dependences of monomer diffusion coefficient on w p and temperature are in accord with experiment.

Reaction–diffusion model for the preparation of polymer gratings by patterned ultraviolet illumination

“…19 Considering the grating prepared from the F-diacrylate and Cl-monoacrylate monomers, it is interesting to note that for the simulations with the dynamic model, the obtained values of K 1 ϭ0.21 and K 2 ϭ0 indicate that the diffusion coefficients drop by 1 order of magnitude, going from 0% polymer to 50% polymer. This corresponds nicely with the behavior of MMA in PMMA and PBMA, which also drops by 1 order of magnitude: 31,32 DϷ2ϫ10 Ϫ9 m 2 /s ͑0% conversion͒ and DϷ3ϫ10 Ϫ10 m 2 /s ͑50% conversion͒. The value of K 1 is lower for the system of the Si-dimethacrylate and the F-diacrylate (K 1 ϭ0.16), which indicates a steeper decrease for increasing polymer volume fraction.…”

“…For comparison, the diffusion coefficients of methylmethacrylate ͑MMA͒ in polymethylmethacrylate ͑PMMA͒ and polybutylmethacrylate ͑PBMA͒ are Dϭ2 ϫ10 Ϫ9 m 2 /s ͑0% conversion͒ and 3ϫ10 Ϫ10 m 2 /s ͑50% conversion͒, 31,32 respectively. For high conversion, the diffusion coefficient of MMA in PMMA is 2ϫ10 Ϫ14 m 2 /s at T ϭ150°C.…”

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

“…Therefore this is the first parameter that will be scrutinized. [31] n-butyl methacrylate (BMA), [31] 2-hydroxyethyl methacrylate [47] and styrene [32] have been carried out by pulsed-field-gradient NMR and have resulted in power-law exponents of -0.66, -0.66, -0.66 and -0.51, respectively, in dilute solution. To the best of our knowledge the literature contains no such chain-length-dependent diffusion coefficients for acrylate oligomers.…”

“…[18] Further, these values of α s are consistent with the power-law exponents found in measurements of D i as a function of i for oligomers. [31,32] Given all this it seems reasonable to say that chain-length-dependent termination at low conversion may now be regarded as well understood for methacrylates and styrene polymerization.…”

Bimolecular radical termination: New perspectives and insights

“…The linear increase in the a gel profiles for all polymers was consistent with self-diffusion measurements. 79,80 Comparison of these polymers indicated that a gel was largest for PMMA and smallest for PMA, and decreased in the order a gel(PMMA) > a gel(PSTY) > a gel(PVAc) > a gel(PMA) . It is believed that termination in concentrated solutions may be controlled by reptation, 23,25 which predicts that a gel is conversion independent in the concentrated regime and close to 1.5 25 or 2.…”