On the Quantitative <i>Click</i> Conjugation of Molecular Weight Distributions: What Can Theoretically Be Expected?

Barner‐Kowollik, Christopher

doi:10.1002/marc.200900316

Cited by 35 publications

(48 citation statements)

References 32 publications

(19 reference statements)

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“…As proposed by Barner-Kowollik, the number average molecular weight (M n ) serves as sensitive indicator of the success of the conjugation reaction. [30] As expected, the molecular weight of the block-copolymer (3-b-6) (PMMA-equivalent: M n ¼ 11 400 g Á mol À1 ) effectively is the sum of the molecular weights of the individual building blocks (3) (M n ¼ 3 800 g Á mol…”

mentioning

confidence: 89%

“…It is known however, that SEC results need to be judged with some care when accessing the efficiency of polymer-polymer conjugations. [30] Especially in the current case where two polymers of differing polydispersity and molecular weight are reacted, SEC may draw a skewed picture. As proposed by Barner-Kowollik, the number average molecular weight (M n ) serves as sensitive indicator of the success of the conjugation reaction.…”

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confidence: 98%

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Rapid UV Light‐Triggered Macromolecular Click Conjugations via the Use of o‐Quinodimethanes

Gruendling

Oehlenschlaeger

Frick

et al. 2011

Macromol. Rapid Commun.

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104

120

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Shining a light on click chemistry: The use of UV-radiation as trigger signal provides a facile means to obtain spatial and temporal control over polymer conjugation reactions in addition to providing a further means of achieving orthogonality in click transformations. In the current contribution, UV-radiation was employed to induce a highly efficient Diels-Alder conjugation of polymeric building blocks via the photo-induced in situ formation of highly reactive cis-dienes from a 2-methylbenzophenone precursor.

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confidence: 89%

mentioning

confidence: 98%

Rapid UV Light‐Triggered Macromolecular Click Conjugations via the Use of o‐Quinodimethanes

Gruendling

Oehlenschlaeger

Frick

et al. 2011

Macromol. Rapid Commun.

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104

120

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“…46 For observation of changes in polymer endgroups and conjugation points, no better analytical method exists to this date. This characterization approach is also especially useful for the present study where the macromonomers are conjugated via multi-thiol core molecules (see Scheme 2), thus leading to the formation of homopolymers with distinct topology.…”

Section: Synthesis Of Butyl Acrylate Macromonomermentioning

confidence: 99%

Limitations of radical thiol‐ene reactions for polymer–polymer conjugation

Koo

Stamenović

Ramaswamy

et al. 2010

J. Polym. Sci. A Polym. Chem.

238

228

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In the current work, we report our findings on the use of radical thiol-ene chemistry for polymerpolymer conjugation. The manuscript combines the results from the Preparative Macromolecular Chemistry group from Karlsruhe Institute of Technology (KIT) and the Polymer Chemistry Research group from Ghent University (UGent), which allowed for an investigation over a very broad range of reaction conditions. In particular, thermal and UV initiation methods for the 2 radical thiol-ene process were compared. In the KIT group, the process was studied as a tool for the synthesis of star polymers by coupling multi-functional thiol core molecules with poly(nbutyl acrylate) macromonomers (MM), employing thermally decomposing initiators. The product purity and thus reaction efficiency was assessed via electrospray ionization mass spectrometry. Although the reactions with 10 or 5 equivalents of thiol with respect to macromonomer were successful, the coupling reaction with a one-to-one ratio of MM to thiol yielded only a fraction of the targeted product, besides a number of side products. A systematic parameter study such as a variation of the concentration and nature of the initiator and the influence of thiol to ene ratio was carried out for a one-to-one ratio of MM to thiol content.Further experiments with poly(styrene) and poly(isobornyl acrylate) containing a vinylic end group confirmed that thermal thiol-ene conjugation is far from quantitative in terms of achieving macromolecular star formation. In parallel, the UGent group has been focusing on photo-initiated thiol-ene chemistry for the synthesis of functional polymers on the one hand and block copolymers consisting of poly(styrene) (PS) and poly(vinyl acetate) (PVAc) on the other hand.Various functionalization reactions showed an overall efficient thiol-ene process for conjugation reactions of polymers with low molecular weight compounds (~90% coupling yield). However, while SEC and FT-IR analysis of the conjugated PS-PVAc products indicated qualitative evidence for a successful polymer-polymer conjugation, 1 H NMR and elemental analysis revealed a low conjugation efficiency of about 23% for a thiol-to-ene ratio equal to one. Blank reactions using typical thiol-ene conditions indicated that bimolecular termination reactions 3 occur as competitive side reactions explaining why a molecular weight increase is observed even though the thiol-ene reaction was not successful. The extensive study of both research groups indicates that radical thiol-ene chemistry should not be proposed as a straightforward conjugation tool for polymer-polymer conjugation reactions. Head-to-head coupling is a major reaction pathway, which interrupts the propagation cycle of the thiol-ene process.

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“…[7] In CuCAAc a polymer a-functionalized with an azide and another polymer chain carrying an v-alkyne can readily be reacted to generate block copolymers. [8] An alternative pericyclic method of conjugating two polymer chains is connecting them via a Diels-Alder or hetero DielsAlder reaction. [9][10][11][12][13] For the present study, however, the method of ligation is of no concern-as long as the reaction is rapid on the time scale of potential diffusion effects-as we will assume an ideal process, where two polymer chains react immediately and quantitatively with their a-and v-ends as soon as they meet.…”

Section: Introductionmentioning

confidence: 99%

“…Earlier, we have demonstrated that the conjugation of two mono-modal initial size-exclusion chromatography (SEC) distributions can lead to multi-modal conjugated distributions depending on their initial number average M n , weight average M w , and thus PDI. [8] The simulations of the convolutions were carried out under statistical conditions, i.e., each and every single polymer chain was able to react with another with identical rates no matter how many monomer units these chains carried. The motivation for the present study stems from the fact that the polymerpolymer ligation reaction displays similarities to the bimolecular termination process in free-radical polymerization (FRP)-a diffusion controlled process.…”

Section: Introductionmentioning

confidence: 99%

The Influence of a Potential Diffusion Control on the Outcome of Modular Polymer–Polymer Click Conjugations

Preuss

Barner‐Kowollik

2011

Macro Theory & Simulations

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The only reliable factors for assessing if a polymer–polymer click conjugation is successful are an assessment of the number average $\overline {M} _{{\rm n}} $ of the resulting molecular weight distribution (MWD) and the shape of the number, respectively, concentration distribution as was demonstrated earlier. The present contribution explores if a potential chain length dependence (CLD) of the conjugation reaction—caused by a potential diffusion control—can affect the outcome of the polymer–polymer click ligation process. The CLD of the click rate coefficient, $k_{{\rm click}}^{{\rm i},{\rm j}} $, was implemented via a geometric mean approximation for chain length dependent termination, employing α‐values from 1.0 to 0.2. The number averages $\overline {M} _{{\rm n}} $ and weight averages $\overline {M} _{{\rm w}} $ (and thus the PDIs) of the initial distributions were varied widely to explore under which conditions CLD effects have the largest impact. The present study clearly demonstrates that—if diffusion effects and thus a CLD of $k_{{\rm click}}^{{\rm i},{\rm j}} $—play a role in polymer–polymer ligation, the MWDs generated through conjugation display a marked conversion dependence, i.e., $M_{{\rm n}}^{{\rm click}} (x)$, with the maximum $M_{{\rm n}}^{{\rm click}} $ being reached at quantitative conversions. While the $\overline {M} _{{\rm n}} $ reached at quantitative conversions coincides with the $\overline {M} _{{\rm n}} $ obtained under CL‐independent conditions, the final $\overline {M} _{{\rm w}} $ of both the CLD and non‐CLD differs significantly. While the present theoretical study cannot replace the actual experiment, it unambiguously demonstrates that polymer–polymer click conjugations can be influenced by CLD effects. Given the larger α‐values for smaller chain length, broad distributions in the range up to approximately 3 000 Da are especially affected.magnified image

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On the Quantitative Click Conjugation of Molecular Weight Distributions: What Can Theoretically Be Expected?

Cited by 35 publications

References 32 publications

Rapid UV Light‐Triggered Macromolecular Click Conjugations via the Use of o‐Quinodimethanes

Rapid UV Light‐Triggered Macromolecular Click Conjugations via the Use of o‐Quinodimethanes

Limitations of radical thiol‐ene reactions for polymer–polymer conjugation

The Influence of a Potential Diffusion Control on the Outcome of Modular Polymer–Polymer Click Conjugations

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