An Apparent Size-Exclusion Quantification Limit Reveals a Molecular Weight Limit in the Synthesis of Externally Initiated Polythiophenes
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Bibliographic record
Abstract
We report the linear and nonlinear regions of the relationship between number average molecular weight determined by gel permeation chromatography (GPC) and 1 H NMR end-group analysis for a series of o -tolyl-initiated poly(3-hexylthiophene)s (P3HTs). For conjugated polymers with chains that are 39–138 repeat units in length (6.5–23 kDa), GPC systematically overestimates the number average molecular weight ( M n ) by a factor of 1.3 ± 0.1 (standard error), and GPC and 1 H NMR end-group analysis correlate in a linear manner. For chains 138–1130 (23–188 kDa) repeat units in length, we observe a nonlinear relationship between GPC and end-group analysis. Static light-scattering experiments confirm that at high molecular weight (>70 kDa) decreasing the catalyst loading does not appreciably increase the polymer chain length. Thus, we conclude that there is a molecular weight limit in the synthesis of externally initiated polythiophenes and a propensity for the growth of nonexternally initiated chains which increases as a function of M n . This is significant as external initiation has been reported to result in nearly 100% externally initiated chains as well as reduce the possibility of chain–chain coupling in a typical synthesis. Our data show that 100% external initiation only holds true for polymers that are less than 40 kDa and encourages caution when determining M n by NMR using this synthetic methodology at high molecular weights.
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| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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