Structural Reasons for Restricted Backbone Motion in Poly(n‐alkyl methacrylates): Degree of Polymerization, Tacticity and Side‐Chain Length

Abstract

Summary: The complex dynamics of poly(n‐alkyl methacrylates) is studied by advanced 13C NMR spectroscopy as well as mechanical and dielectric relaxation. Extended backbone conformations are identified as the molecular units involved in structural relaxation. From the variation in the degree of polymerization and a comparison with the presence of stereoregular sequences in the sample, the length of the extended units is determined to involve about five, at most ten monomeric units. Syndiotactic and isotactic sequences behave similarly. These findings are indicative of locally structured polymer melts. magnified image

Self- and Collective Dynamics of Syndiotactic Poly(methyl methacrylate). A Combined Study by Quasielastic Neutron Scattering and Atomistic Molecular Dynamics Simulations

“…It was interpreted as the genuine mechanism for the structural relaxation. [15][16][17] We note at this point that the interchain collective dynamics, which have been measured by NSE techniques at the first maximum of S(Q) in different polymers, was always interpreted as the actual structural R-relaxation. 34 At Q ) 1.9 Å -1 , with the exception of the MC/SG and MC/ MC correlations, basically all the relaxation times are within a factor of 2.…”

“…7,8 Furthermore, other subglass and glass relaxation processes in PMMA have been studied for a long time mainly by dynamic mechanical analysis, dielectric spectroscopy, and advanced NMR spectroscopy. [9][10][11][12][13][14][15][16][17] Especially in the temperature range close to and above the glass-transition temperature (T g ≈ 400 K), PMMA exhibits a complicated dynamics. A complexsand likely cooperativessecondaryrelaxation has been reported, which masks the pure R-process when techniques such as mechanical or dielectric spectroscopy (e.g., ref 13) are used.…”

Investigation of Chain Dynamics in Poly(n‐alkyl methacrylate)s by Solid‐State NMR: Comparison with Poly(n‐alkyl acrylate)s

“…[7,[19][20][21][22] From 1 H or 13 C NMR measurements in CDCl 3 , all samples have a high tendency to syndiotacticity [(65 AE 7)% of syndiotactic triads]. [7,[20][21][22] The glass transition temperatures T g are shown in the Supporting Information. The apparent average molar masses were obtained from size-exclusion chromatography (SEC, also commonly named gel-permeation chromatography, GPC) in tetrahydrofuran (THF) with poly(methyl methacrylate) (PMMA) standards.…”

“…[2,3] Advanced solid-state NMR [4] and temperature-dependent X-ray investigations have recently revealed conformational memory and quantified a specific isotropization process. [5][6][7][8] We recently developed a new solid-state NMR method to quantify chain dynamics in polymers with weak dynamic contrast: the NOE experiment with dipolar filter. [9] The principle of nuclear Overhauser effect (NOE) had been previously used differently in other solid-state NMR experiments to study miscibility in polymer blends [10][11][12] and chain dynamics in polymer melts, [13][14][15] or to differentiate chain length of branches in polyethylene.…”

“…[18] The dynamic processes quantified by the NOE experiment with dipolar filter are compared to relaxation data obtained earlier by independent solid-state NMR, dielectric and mechanical spectroscopy techniques. [6,7] Furthermore, they are interpreted together with the one detected previously in poly(ethyl methacrylate). [9] Finally the PnAMA and the PnAA families are compared in terms of dynamics and local structure.…”