We thank the MIT Department of Chemistry and the MIT Lincoln Labs Advanced Concepts Committee for support of this work.

We first describe the synthesis and purification of PEG-MM B from 3 kDa O-(2-aminoethyl)polyethylene glycol (PEG-NH2) and norbornene-N-hydroxysuccinimidyl (NHS) ester. The former compound can be purchased from Sigma Aldrich Inc., or prepared via anionic polymerization according to literature procedures22,23. The latter compound can be prepared in two steps according to a published procedure21. Next we describe a synthesis of catalyst A</...

<ol>
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Nano. 2, 751-760 (2007).</li><li>Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoscience,+Nanotechnology,+and+Chemistry.">Nanoscience, Nanotechnology, and Chemistry.</a> Small. 1, 172-179 (2005).</li><li>Leitgeb, A., Wappel, J., Slugovc, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+ROMP+toolbox+upgraded.">The ROMP toolbox upgraded.</a> Polymer. 51, 2927-2946 (2010).</li><li>Johnson, J. A., Lu, Y. Y., Burts, A. O., Lim, Y. -. H., Finn, M. G., Koberstein, J. T., Turro, N. J., Tirrell, D. A., Grubbs, R. 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The key advantage of brush-first BASP synthesis is the unique ability to rapidly synthesize nanostructures of diverse size and composition in parallel without need for specialized equipment. In this study, we demonstrate the brush-first synthetic method using a norbornene functionalized PEG macromonomer (B, Figure 1) and a bis-norbornene nitrobenzyl ester crosslinker (C, Figure 1). The PEG chains from B impart ...

Polymeric nanoparticles have been widely studied for their potential use as platforms for drug delivery, supported catalysis, biological imaging, and self-assembly1-3. Modern applications require that nanoparticle syntheses be facile, reproducible, compatible with chemical functionalities, and amenable to diversification4,5. Ring-opening metathesis polymerization (ROMP) of strained olefins is a powerful methodology for the synthesis of functional polymeric nanostructures with controlled sizes and narrow mass distributions1,6-8. For example, norbornene-functionalized poly(ethylene glycol) (PEG) macromonomers (MMs) can be efficiently polymerized via ROMP to generate water soluble bottle-brush polymers. Using this approach, nanostructures that carry multiple releasable drug molecules, fluorophores, and spin-contrast agents can be prepared rapidly and in parallel6,9,10.
ROMP has also been used for the &#34;arm-first&#34; synthesis of star polymers. In the arm-first method, linear polymers are crosslinked with a multi-functional crosslinker to give spherical nanostructures with polymeric arms. Schrock and co-workers reported the first arm-first ROMP synthesis of star polymers via crosslinking of norbornene, dicarbomethoxynorbornadiene, and trimethylsilyl protected dicarboxynorbornene linear polymers with a bifunctional norbornene crosslinker.11,12 Buchmeiser has extended this methodology for the synthesis of materials with a range of applications that include supported catalysis, tissue-engineering, and chromatography13-17. Otani and coworkers have made star polymer nanoparticles with functional surfaces via a related &#34;in-out&#34; polymerization strategy18,19.
Most arm-first polymerizations involve a complex interplay of monomer, polymer, and star coupling reactions. The latter proceeds via a step-growth mechanism that typically leads to broad molecular weight (MW) distributions. To overcome this limitation in related arm-first atom transfer radical polymerization reactions, Matyjaszewski and coworkers performed arm-first crosslinking of preformed polymeric MMs to provide star polymers with very narrow MW distributions20. In this case, the steric bulk of the MMs, and the increased ratio of star arms to initiation sites, inhibited poorly controlled star+star coupling processes, and led to a living, chain growth mechanism.
When we attempted the same strategy in the context of ROMP with a norbornene-terminated PEG-MM and a bis-norbornene crosslinker, star polymers with very broad, multi-modal MW distributions were obtained. This result suggested that in this system the MM alone was not sufficiently bulky to inhibit star+star coupling. To increase the steric bulk of the star arms, and potentially limit this uncontrolled coupling, we attempted to first polymerize the MM to form bottle-brush polymers in the absence of crosslinker and then add the crosslinker. We were pleased to find that under certain conditions, this &#34;brush-first&#34; method provided straightforward access to &#34;brush-arm star polymers&#34; (BASPs) with narrow MW distributions and tunable core and corona functionalities.
We recently reported the brush-first ROMP synthesis of PEG BASPs using Grubbs 3rd generation catalyst A (Figure 1)21. In this work, exposure of PEG-MM B to catalyst A generated a living brush macroinitiator with defined backbone length (B1, Figure 1). Transfer of aliquots of the B1&#160;to vials that contained different amounts of crosslinker C initiated BASP formation. The MW, and therefore the size, of the BASPs increased geometrically with the amount of C added. We provided a mechanistic hypothesis for this geometric growth process and demonstrated that functional, nitroxide core- and corona-labeled BASPs could be readily prepared without the need for post-polymerization modification steps or sequential monomer additions. However, in all of the reported examples, we were concerned about catalyst deactivation; we carried out all reactions under N2 atmosphere inside a glovebox.
Since our initial report, we have found that the brush-first method is very effective for the formation of BASPs from a wide range of norbornene-terminated MMs and functional crosslinkers. We have also discovered that the method can be performed on the benchtop with no special precautions to remove air or moisture.
Herein, a series of three BASPs of differing MWs will be synthesized by the brush-first method under ambient conditions. In brief, 10 equivalents of B will be exposed to 1.0 equivalents of catalyst A (Figure 1a) for 15 min to yield a BI with an average degree of polymerization (DP) of 10. Three aliquots of this batch of BI will be transferred to separate vials that contain 10, 15, and 20 equivalents (N, Figure 1b) of C. After 4 hr, the polymerizations will be quenched via addition of ethyl vinyl ether. The star polymer MWs and MW distributions will be characterized using a gel permeation chromatography instrument equipped with a multi-angle laser light scattering detector (GPC-MALLS).

<table border="0" cellpadding="0" cellspacing="0" width="592">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="84" rowspan="2" style="height:84px;width:216px;">Grubbs Second Generation Catalyst</td>
			<td rowspan="2" style="width:91px;">Materia (or Sigma Aldrich)</td>
			<td rowspan="2" style="width:119px;">C848 (Sigma Aldrich: 569747)</td>
			<td style="width:167px;">
			Used as purchased from manufacturer. 
 *Provided as a generous gift.
			</td>
		</tr>
		<tr height="42">
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Pyridine</td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">270970</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">O-(2-aminoethyl)polyethylene glycol 3000</td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">07969</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">PEG-MM</td>
			<td style="width:91px;">N/A</td>
			<td style="width:119px;">N/A</td>
			<td style="width:167px;">Synthesized following reported procedures (Ref. 21, protocol 1)</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">norbornene-N-hydroxysuccinimidyl (NHS) ester</td>
			<td style="width:91px;">N/A</td>
			<td style="width:119px;">N/A</td>
			<td style="width:167px;">Synthesized following reported procedures (Ref. 21)</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Bis-norb-NBOC Crosslinker</td>
			<td style="width:91px;">N/A</td>
			<td style="width:119px;">N/A</td>
			<td style="width:167px;">Synthesized following reported procedures (Ref. 21)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Pentane</td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">158941</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Tetrahydrofuran (HPLC grade)</td>
			<td style="width:91px;">Sigma Aldrich </td>
			<td style="width:119px;">34865</td>
			<td style="width:167px;">Dried and purified over a solvent purification columns </td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Dichloromethane</td>
			<td style="width:91px;">VWR </td>
			<td>BDH1113-4LG</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Acetonitrile (HPLC grade)</td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">34998</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Acetic Acid </td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">A6283</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Sodium sulfate </td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td>239313</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Diethyl ether</td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">673811</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Dimethylformamide (HPLC grade) </td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">270547</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Lithium Bromide</td>
			<td style="width:91px;">Sigma Aldrich</td>
			<td style="width:119px;">213225</td>
			<td style="width:167px;">Used as purchased from manufacturer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">MillQ Biocel A10</td>
			<td style="width:91px;">Millipore</td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Beckmann Coulter HPLC (127p solvent module, 166p detector)</td>
			<td style="width:91px;">Beckmann Coulter</td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Zorbax 300SB-C18 PrepHT reverse phase column </td>
			<td style="width:91px;">Agilent</td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">1260 Infinity Liquid Chromatography </td>
			<td style="width:91px;">Agilent</td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">GPC KD-806M column</td>
			<td style="width:91px;">Shodex</td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dawn Heleos II Light Scatterer</td>
			<td style="width:91px;">Wyatt</td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Optilab T-rEX Refractive Index Detector</td>
			<td style="width:91px;">Wyatt</td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glass Scintillation Vials - 40 ml</td>
			<td style="width:91px;">Chemglass</td>
			<td>CG-4909-05</td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glass Scintillation Vials - 4 ml </td>
			<td style="width:91px;">Chemglass</td>
			<td style="width:119px;">CG-4904-06</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Glass Scintillation Vials (PTFE-lined cap) - 2 ml </td>
			<td style="width:91px;">Agilent</td>
			<td>5183-4518</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Stir-bars</td>
			<td style="width:91px;">VWR</td>
			<td style="width:119px;">5894x</td>
			<td style="width:167px;">various sizes </td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">13 mm 0.45 &#181;m Nylon Syringe filter</td>
			<td style="width:91px;">PerkinElmer</td>
			<td>02542903</td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">13 mm 0.45 &#181;m polytetrafluoroethylene syringe filter</td>
			<td style="width:91px;">PerkinElmer</td>
			<td>02542909</td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">1 ml disposable syringes </td>
			<td style="width:91px;">VWR</td>
			<td style="width:119px;">53548-001</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Swing bucket centrifuge or similar</td>
			<td style="width:91px;"> </td>
			<td style="width:119px;"> </td>
			<td style="width:167px;">Should be able to reach approximately 4,000 rpm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Round bottom flask</td>
			<td style="width:91px;"> </td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fritted glass filter assembly </td>
			<td style="width:91px;"> </td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Rotary Evaporator </td>
			<td style="width:91px;"> </td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Balance </td>
			<td style="width:91px;"> </td>
			<td style="width:119px;"> </td>
			<td style="width:167px;"> </td>
		</tr>
	</tbody>
</table>

particles without a box: brush-first synthesis of photodegradable peg star polymers under ambient conditions

Convenient methods for the rapid, parallel synthesis of diversely functionalized nanoparticles will enable discovery of novel formulations for drug delivery, biological imaging, and supported catalysis. In this report, we demonstrate parallel synthesis of brush-arm star polymer (BASP) nanoparticles by the &#34;brush-first&#34; method. In this method, a norbornene-terminated poly(ethylene glycol) (PEG) macromonomer (PEG-MM) is first polymerized via ring-opening metathesis polymerization (ROMP) to generate a living brush macroinitiator. Aliquots of this initiator stock solution are added to vials that contain varied amounts of a photodegradable bis-norbornene crosslinker. Exposure to crosslinker initiates a series of kinetically-controlled brush+brush and star+star coupling reactions that ultimately yields BASPs with cores comprised of the crosslinker and coronas comprised of PEG. The final BASP size depends on the amount of crosslinker added. We carry out the synthesis of three BASPs on the benchtop with no special precautions to remove air and moisture. The samples are characterized by gel permeation chromatography (GPC); results agreed closely with our previous report that utilized inert (glovebox) conditions. Key practical features, advantages, and potential disadvantages of the brush-first method are discussed.

Figure 2 shows GPC traces for a variety of BASPs prepared from B1, B2, and B3. In all cases, the data illustrate that increasing the equivalents of crosslinker (N) leads to an increase in the size of the BASP. As was observed in our previous report, 10 equivalents of crosslinker is not sufficient to achieve uniform BASPs; the N = 10 sample shows a clearly multi-modal GPC trace with a large amount of residual b...

Watch this Scientific Journal Video about Particles without a Box: Brush-first Synthesis of Photodegradable PEG Star Polymers under Ambient Conditions at JoVE.com

Particles without a Box: Brush-first Synthesis of Photodegradable PEG Star Polymers under Ambient Conditions

Poly(ethylene glycol) (PEG) brush-arm star polymers (BASPs) with narrow mass distributions and tunable nanoscopic sizes are synthesized in via ring opening metathesis polymerization (ROMP) of a PEG-norbornene macromonomer followed by transfer of portions of the resulting living brush initiator to vials containing varied amounts of a rigid, photo-cleavable bis-norbornene crosslinker.

Convenient methods for the rapid, parallel synthesis of diversely functionalized nanoparticles will enable discovery of novel formulations for drug ...

particles-without-box-brush-first-synthesis-photodegradable-peg-star

Research

JoVE Journal

Chemistry

39.6K visualizações.  Massachusetts Institute of Technology.  Poli (etileno-glicol) (PEG) escova do braço estrela polímeros (BASPs) com distribuições estreitas de massas e tamanhos nanoscopic sintonizáveis ​​são sintetizados através de abertura de anel na polimerização de metátese (ROMP) de um macromonómero de PEG-norborneno seguido por transferência de porções da vida, resultando escova iniciador para frascos contendo quantidades variadas de uma superfície rígida, foto-cliváveis ​​bis-norborneno reticulado...