Preparation and Post-Functionalization of Hyperbranched Polyurea

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Preparation and Post-Functionalization of Hyperbranched Polyurea Coatings Fei Xiang, Lia Asri, Oleksii Ivashenko, Petra Rudolf, and Ton Loontjens Langmuir, Just Accepted Manuscript • DOI: 10.1021/la504412v • Publication Date (Web): 11 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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For: Langmuir

Preparation and Post-Functionalization of Hyperbranched Polyurea Coatings

Fei Xiang1, Lia Asri2, Oleksii Ivashenko3,Petra Rudolf2, Ton Loontjens2*

1

Dupont, No. 600, Cailun Road, Zhangjiang Hi-Tech Park, Pudong New District,

Shanghai 201203, P.R.C 2

Zernike Institute for Advanced Materials, Nijenborgh 4, 9747 AG, Groningen, the

Netherlands 3

National Institute for Nanotechnology, University of Alberta 11421, Saskatchewan

Dr., T6G 2M9 Edmonton AB, Canada *Corresponding author: [email protected]

ACS Paragon Plus Environment

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Abstract

Post-functionalizable hyperbranched polyurea coatings were prepared by the bulk polycondensation of AB2 monomers on pre-activated silicon substrates. As shown earlier, AB2 monomers were prepared, comprising a secondary amino group (A) and two blocked isocyanates (B) connected by hexyl spacers, in a single step and in quantitative yields. Covalent anchoring of the coatings on substrates was accomplished by reacting the secondary amino group in the focal point of the polymers with the blocked isocyanates (BIs) of the covalently attached coupling agent. The BIs in the top-layer of the coatings were storage-stable under ambient conditions, but well modifiable with amino- or hydroxyl-functional compounds on heating. Attachment of polyethylene glycol or perfluoro-1-decanol afforded hydrophilic or hydrophobic surfaces. Immobilization and quaternization of polyethyleneimines yielded highly charged surfaces. The coatings were extensively characterized by a number of techniques, such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, ellipsometry and contact angle measurements.

Key words: hyperbranched, polyureas, coatings, hydrophilic, hydrophobic, antibacterial


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Introduction Objects are frequently coated not only for decoration but also to create special surface properties such as corrosion protection, wear resistance, wettability or prevention of biofouling. These functional properties can to a large extent be controlled by the adhesion strength of the coating on a substrate, the mechanical properties of the coating layers and the performance of the top-layer with the environment. Adhesion of a coating on a substrate by only physical interactions is convenient and frequently utilized in commercial applications. However, if a high durability is required a physical bonding may fail.1 Adaptation of the surface of an object by a (electro)chemical pre-treatment and/or by primers results in a substantial improvement of the adhesion forces. Nonetheless, the bonding of the final coating layer hereon might still be mediated only by physical interactions. The durability of organic coatings can be improved by covalently anchoring the layer onto substrates by the “grafting from” polymerization technique. In the “grafting from” approach a living polymerization starts from an immobilized initiator. This approach is well known and frequently reported. Matyjaszewski et al.2 and others3 started the living polymerization of acrylates from a grafted ATRP-initiator. Polyesters have been anchored successfully on a silicon surface by ring-opening polymerization of lactones.4 Tsubokawa et al.5,6 reported on an alternating Michael-addition of methacrylate to immobilized amino groups followed by amidation of the ester moieties with diamines. Bergbreiter et al.7-10 grafted poly(acrylic acid) onto a functionalized polyethylene surface. The maximum thickness of such a grafted coating depends obviously on the length a


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polymer chain can reach, which in turn is determined by the livingness of the polymerization system. Although the livingness of various polymer systems differs, eventually all living polymerization systems will terminate. Hence, the layer thickness obtained from living linear polymer systems can therefore not be larger than the length of a polymer chain (< 100 nm), which is not sufficient for durable coatings.11 In contrast, hyperbranched polymers (HBPs) possess many living end-groups and premature termination of some of them will not limit chain growth. As a result, more robust (thicker) coating layers can be obtained, while still being completely immobilized. Another important advantage of hyperbranched (HB) coatings is that they retain numerous active (“living”) end groups that can be used for post-modification reactions. A common method to prepare HBPs starts from A2/B3 monomer mixtures. This is an attractive route because a large amount of commercial monomers exist. However, the structure of polymers obtained by this technology is ill-defined. In contrast, HBPs prepared from AB2 monomers are well-defined, with one A group in the focal point and many B groups at the periphery of the polymer brushes. By selecting proper B groups, this technology offers a versatile toolbox to prepare a variety of surface properties by post-functionalization reactions on the same coating platform. In spite of these advantages, the use of HBPs prepared from AB2 monomers is still limited due to the lack of convenient synthetic routes to produce these monomers.12-15 Here we describe the utilization of AB2 monomers, prepared in a single-step reaction and in quantitative yields,16 to prepare and apply the corresponding coatings on


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substrates and to modify the surfaces of these coatings. The AB2 monomers were designed in such a way that the HBPs comprised an amino group (A-group) in the focal point and many blocked isocyanates (BIs) as end-groups (B-groups). In addition, an appropriate coupling agent for silicon substrates was developed which allowed the chemical fixation of the HBPs hereon. The resulting HB-coatings were subsequently modified with hydrophilic, hydrophobic or antibacterial moieties, as these are the three main options to combat bacteria. All coatings were analyzed with a number of techniques.

Results and discussion Preparation and application of the coupling agent (1) To achieve a covalent coupling of the HB-coatings onto silicon (and e.g. metals17) substrates (Figure 8) , a coupling agent containing a siloxane and blocked isocyanate (BI) group was prepared. In earlier work we showed that primary amines could be converted into the corresponding caprolactam blocked isocyanates (CBIs) via a reaction with carbonyl biscaprolactam (CBC).1-20-22 By using this technology, the caprolactam blocked isocyanate based on 3-aminopropyl triethoxy silane (APS) was obtained in high yields by heating APS and CBC at 80 oC for 6 h (Figure 1). 19 According to 1H-NMR the reaction proceeded quantitatively, while producing only caprolactam as a side product (Figure 1). The signals at 1.6, 2.1 and 3.0 ppm were assigned to caprolactam. Removal of caprolactam in this stage was not appropriate due to the formation of a larger quantity of caprolactam during the polymerization of


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the AB2 monomers (vide infra) .

Caprolactam APS-monomer

Toluene

9

8 3

4

6+2 5

1

7

CBC

APS 10

9

8

7

6

5

4

3

2

1

0 ppm

Figure 1. The scheme to prepare (1) and the 1H-NMR spectra of APS, CBC and the mixture of caprolactam and (1). (300 MHz, recorded in CDCl3).

The peak of CO-NH (peak 4) at 9.3 ppm is characteristic for the caprolactam blocked isocyanate group. The ratio of integration of peak 1 (CH2CO) to peak 5 (NHCH2) was close to 1, supporting the complete conversion of APS. The CH2 group next to the amino group of APS shifted from 2.5 to 3.1 ppm, demonstrating the participation of the primary amine in the reaction. Hence the 1H-NMR results allow to conclude that APS reacted quantitatively with CBC, forming the corresponding CBI.

Application of (1) on silicon substrates Before applying the coupling agent (1) the silicon surfaces were cleaned and oxidized


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to afford silanol groups. The oxidation, carried out with either UV-ozone or with a piranha solution at 75 oC for 1 h, performed equally well. After the oxidation step, the Si wafers were rinsed with milli-Q water and sonicated with methanol and toluene. Due to oxidation the water contact angle of the silicon surfaces decreased from 50o to less than 15o. To avoid the inevitable deactivation of these activated surfaces over time, the samples were immediately immersed in a 3 % (v/v) solution of (1) in ethanol. After drying, the samples were heated at 110 oC for 2 h to drive the coupling reaction to completion. The non-covalently bound compounds were removed by an ultrasonic washing step with ethanol, yielding a smooth surface with a root mean square (RMS) roughness of 0.6 nm as determined by atomic force microscopy (AFM). The Fourier Transform Infrared (FT-IR) spectra of a silicon substrate collected in transmission before and after modification with (1) were very similar due to the diminutive thickness of layer of (1). Subtracting the spectrum of the pristine surface from that of the treated surface, revealed indeed the characteristic IR absorption bands of (1). The fingerprint of BIs was clearly visible. The carbonyl stretching mode of caprolactam at 1705 cm-1, the carbonyl stretching mode from urea at 1650 cm-1, the C-N deformation at 1540 cm-1 as well as the C-N stretching and CH2 scissoring modes of caprolactam between 1400 cm-1 and 1440 cm-1 were well detectable. The X-ray photoemission (XPS) spectrum of the silicon surface after the UV-ozone treatment showed only the presence of Si and O. After modification with (1), signals in N 1s (6.6±0.8 at. %) and C 1s (34.9±1.5 at. %) regions appear, as well as a change in the O 1s region with concomitant decrease in Si/O ratio down to 0.8 (Figure 2). In


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the N 1s core level region (Figure 2a) only one component at 399.8 eV was observed, attributed to nitrogen atoms of urea moieties. C 1s core level region was fitted with three components related to aliphatic carbon at 285 eV, C-N and C=O of urea moieties at 286.1 eV and 286.6 eV respectively (Figure 2b). The O 1s peak at 532.2 eV originated from the overlap of the oxygen of the urea moieties and of SiO2 layer on the substrate (Figure 2c) accounting for 33 at. %..

Figure 2. X-ray photoemission spectra of a Si wafer modified with (1): (a) N 1s core level region; (b) C 1s core level region, fitted with three components – aliphatic C, and C-N and C=O from urea moieties; (c) O 1s core level region containing C=O and oxygen from SiO2 substrate. Ellipsometry measurements of silicon wafers indicated a SiO2 layer with a thickness of 2.0±0.2 nm. The thickness of the layer of (1) was 1.8±0.2 nm, based on a refractive index of 1.58 for (1), as obtained by the software of the equipment. After modification with (1), the water contact angle increased from 15o±2o to 75o±2o, due to the hydrophobic nature of (1). The FT-IR, XPS, ellipsometry and contact angle results clearly demonstrated the presence of a thin layer of (1) on the silicon surface. As the layer was not removable by sonication in ethanol, it was concluded that the covalent anchoring of (1) was successfully accomplished.


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Model reaction The HBPs comprise a secondary amino group in the focal point of the polymer (vide

infra), which could be used for anchoring purposes. However, it was analytically not feasible to prove that a covalent coupling reaction between these secondary amino groups with the BIs of (1) took place, due to the masking effect of the polymer layer. Therefore, di-butyl amine (DBA) was chosen as a low molecular weight model compound as it has a similar secondary amino group as the HBPs. DBA was spin-coated onto the silicon sample covered with (1) and heated subsequently for 4 h at 145 oC in a nitrogen atmosphere (Scheme 1). The sample was then washed in an ultrasonic bath with ethanol to remove the unreacted DBA and the possibly released caprolactam. Scheme 1. Substitution of caprolactam by di-butyl amine (DBA).

The FT-IR spectra of the silicon substrates before reaction with DBA showed the carbonyl stretching mode at 1700 cm-1 and the CH2 scissoring mode at 1440 cm-1 of caprolactam, which disappeared after reaction (not shown). An additional peak at 1050 cm-1, was attributed to the CH2 scissoring mode of DBA. It is further noteworthy that no IR bands of free isocyanate groups were observed (at 2200 cm-1), meaning that caprolactam was substituted and not vanished by dissociation of the BIs.


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The XPS spectrum of the surface after modification with DBA is shown in Figure 3. In the N 1s region a peak at 399.8 eV was observed, which is at the same position as for (1) on the Si surface (Figures 3a and 2a). In the C 1s line (Figure 3b) three contributions can be distinguished, namely a main component at 285.0 eV due to C-C bonds. The signals of C-N and C=O components at 286.1 eV and 288.6 decreased remarkably as compared to the spectrum of the surface before reaction (Figure 2b) with concomitant increase in overall carbon content to 37.5±4 at. %. The decrease of the C-N and C=O components indicate indeed that caprolactam was substituted by DBA. As expected, no change in the O 1s core level spectrum was observed (Figure 3c).

Figure 3. X-ray photoemission spectra of reaction product of DBA with (1) on silica surface: (a) N 1s core level region;(b) C 1s core level region, fitted with three components – aliphatic C, and C-N and C=O from urea moieties; (c) O 1s core level region containing C=O and oxygen from SiO2 substrate.

The thickness of layer (1) did not change during the modification with DBA, as measured by ellipsometry (1.9±0.2 nm). This indicated that the coupling agent layer was not damaged by the treatment with DBA. The water contact angle of the DBA modified layer increased slightly from 75o±2o to 81o±3o, a change which was


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attributed to the substitution of caprolactam by the slightly more hydrophobic DBA. FT-IR, XPS, ellipsometry and contact angle measurements indicated that the secondary amino groups of DBA indeed substituted caprolactam of the BIs of surfaces coated with (1). It was thus reasonable to expect that the secondary amino group of the AB2 monomers would react in a similar manner.

Preparation of AB2 monomers In a previous study we have described a convenient one-step method to synthesize AB2 monomers.16 In short, the AB2 monomers were obtained in quantitative yields by heating stoichiometric amounts of bis(hexamethylene) triamine (BHMTA) and CBC at 80 oC for 6 h in toluene (Scheme 2).

Scheme 2. Preparation AB2 monomers from bis(hexamethylene) triamine and carbonyl biscaprolactam.

During this reaction, only the primary amino groups of BHMTA reacted with CBC. Caprolactam, the only side product, was easily removed by an aqueous extraction. After separation of the organic and aqueous layers, organic solvent was removed by distillation. The AB2 monomers were obtained in high yields (>98%) and in a purity


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that appeared to be high enough to perform directly polymerizations.16

Application of HB-coatings The AB2 monomers were spin-coated on the pre-activated silicon substrates (5 and 20 wt %, in DMF or ethanol) and polymerized in bulk at 145 oC under nitrogen atmosphere for 2 h (Figure 4). After the polymerization the samples were ultrasonically washed with ethanol for 30 min to remove the non-covalently bound species. The coupling agent (1) appeared to be indispensable under these conditions. Coatings applied without the coupling agent were nearly completely removed during the sonication step in ethanol.

d. Continued growth HB-coating AB2

AB2

a. Coupling agent (1)

b. Initial HB-coating

c. Modified coating

Figure 4. Schematic representation of the polymerization of AB2 monomers on pre-treated silicon substrate and the modification thereof. Transmission FT-IR spectra of the covalently coupled coating showed strong IR bands, demonstrating the presence of a thick layer (Figure 5).

23

The coatings prepared from


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the ethanol solution were thicker than those prepared from DMF solutions, probably because ethanol evaporates faster than DMF during the spinning process. As a result, less of the monomer (solution) was removed during the spinning process. According to the intensity of the corresponding IR bands, the coating layer obtained by spin coating of the 20 wt % ethanol solution was the thickest, what matched with the profilometry data (vide supra) (Figure 5). 0 .7

0 .6 Absorbance Units

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H B P M 6 -2 h -5 % D M F H B P M 6 -2 h -2 0 % D M F H B P M 6 - 2 h -5 % E th a n o l H B P M 6 - 2 h - 2 0 % E th a n o l

0 .5

0 .4

0 .3

0 .2 3600 3400 3200 3000 2800

1800

1600

1400

-1

W a ve n u m b e r (c m )

Figure 5. Transmission FT-IR spectra of HB-coatings on silicon wafers obtained by the spin coating from ethanol or DMF. The XPS spectra of N 1s, C 1s and O 1s core level regions of the HB-coating are shown in Figure 6. The N 1s was fitted with one component at 399.8 eV, similarly to the product obtained by modifying the silicon substrate that was covered with (1) by DBA (Si-1-DBA). In the C 1s core level region the components at 286.1 eV and 288.7 eV increased in intensity as compared to Figure 3b, which is consistent with growth of polymer branches containing urea and caprolactam moieties, demonstrating the similarity of the chemical structure of (1) and the HB-coating. Similarly to Si-1-DBA, the O 1s line showed a single peak at 532.5 eV.


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Figure 6. X-ray photoemission spectra of HB-coating on a silica substrate: (a) N 1s core level region; (b) C 1s core level region, fitted with three components – aliphatic C, and C-N and C=O from urea moieties; (c) O 1s core level region containing C=O and oxygen from SiO2 substrate. The thickness of the coatings was determined with a stylus profiler by measuring the depth of scratches made by a razor blade. The thickness of coatings from a 20 wt % DMF solution was 0.45±0.05 µm and from a 20 wt % ethanol solution 0.99±0.06 µm. Thicker coatings could be obtained by spinning an additional amount of AB2 monomers on top of the first layer and polymerizing it by heating. These additional layers were immobilized as well as they were not removable by sonication in ethanol. In a representative sample the thickness increased from 0.99±0.06 to 1.40±0.05 µm upon sequential coating procedures. In principle this procedure could be repeated many times. The water contact angle of the HB-coating was very similar to the one of the surface covered by (1), due to the similarity in chemical structure. The surfaces were smooth, as indicated by the RMS roughness (as determined by AFM) of 0.4 nm for the coating deposited from a 20 wt % ethanol solution and 0.8 nm for the one deposited from a 20 wt % DMF solution.


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Modifications of the HB-coatings Hydroxyl functional compounds Due to numerous blocked isocyanates the coatings offered the possibility to be functionalized with a variety of surface active compounds. Antifouling properties of biomedical implants are for instance an interesting target area. Hydrophobic24 as well as hydrophilic25 or biocidal surfaces can reduce or even prevent bacterial growth.26 Hence, we studied the feasibility to prepare all these types of surfaces, starting from the same HB-coating template. CBIs comprising coatings are stable up to at least 100 oC, even in the presence of hydroxyl or amine functional compounds27. This storage-stability is beneficial as it allows storing without special precautions. At 125 oC compounds comprising hydroxyl-

and

amino

moieties

start

to

react

with

CBIs.

In

case

of

hydroxyl-comprising compounds the presence of a common polyurethane catalyst is preferred to increase the reaction rate. Dibutyl tin dilaurate and tin octanoate (FDA approved) performed equally well. Monomethoxy polyethylene glycol (MPEG, Mn~550 Da) was selected as hydrophilic compound and nonadecafluoro-1-decanol (NFD) was used to obtain a hydrophobic surface (Scheme 3). These compounds were applied by spin coating of 20 wt % solutions in DMF on the HB-coatings. After heating for 2 h at 145 oC, to achieve the coupling, the samples were sonicated in ethanol for 30 min to remove all not covalently attached species.


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Scheme 3. Schematic representation of the modification of a HB-coating layer with 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-nonadecafluoro-1-decanol (NFD, top) and mono-methyl polyethylene glycol (MPEG, bottom).

The FT-IR transmission spectra of HB, HB-MPEG and HB-NFD coatings on the silicon substrate showed, after modification, a strong decrease of the intensity of the caprolactam carbonyl stretching mode at 1705 cm-1 in the spectra of the HB-MPEG and HB-NFD coatings, indicating that a substantial amount of caprolactam was substituted. The characteristic peaks of MPEG or NFD are not visible in the IR spectrum due to overlap with the peaks from HBPs. In the XPS spectra of the HB-NFD coating the fluorine 1s peak was clearly visible (Figure SI 1 in the Supporting Information), proving the presence of NFD. Deconvolution of the C 1s peak of HB-MPEG (Figure SI 2 in the Supporting Information) demonstrated the presence of all the expected C-moieties . The thickness of the HB-MPEG (1.06±0.05 µm) and of the HB-NFD coatings (1.01±0.06 µm) was very similar to the unmodified coating (0.99±0.06 µm), which indicated that the coatings were not damaged during the modification reactions. The


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water contact angle, however, changed substantially from 75o±2o for the HB-coating to 40o±2o for HB-MPEG and 104o±3o for HB-NFD (Figure 7). This demonstrated that the modifications were successfully accomplished and that the hydrophobic / hydrophilic properties of the coating could be varied widely.

(a)

(b)

Figure 7. Photograph of a water droplet deposited on a silicon substrate covered with HB-MPEG (a) or HB-NFD (b) coatings.

Amine functional compounds Amine groups are more reactive towards CBIs than hydroxyl groups and react fast without catalyst. We demonstrated this ability already (vide supra) by the ability to polymerize AB2 monomers and by polymerizing a second layer of AB2 monomers on top of the first one. Besides hydrophobic and hydrophilic surfaces, a third method to combat bacteria is to immobilize biocides. Water soluble quaternary ammonium compounds (quats) are well-known potent biocides, but they are not harmless to human cells.28 A promising approach is to immobilize quats on surfaces, which prevents health issues. In fact, it has been reported that immobilized quats are indeed effective biocides if the charge densities are above a certain threshold.2


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Polyethyleneimines (PEI) were selected as amine functional compounds because they comprise a large number of quaternizable amino groups (Figure 8). 19 Solutions of PEI in methanol were spin-coated onto the HB-coatings. By using an excess of PEI, only a small number of amino groups reacted with blocked isocyanate groups. Hence most of the amino groups were still available for quaternization. Alkylation of the remaining amino groups was performed with hexyl bromide and methyl iodide. The hexyl group had been shown to give a good antibacterial performance.29,30 Due to the small size of the methyl group, methyl iodide allowed for further quaternization (Figure 8). The coatings were subjected to an acetone double rub durability test and withstood 100 rubs.

Figure 8. Schematic representation of a surface coated with hyperbranched polyureas, covalently modified with quaternized polyethyleneimine. XPS measurements afforded information on the composition of the top layer of the coating.19 After alkylation a shoulder appeared of the N 1s core level region in the XPS


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spectrum, so the main peak could be deconvoluted into two peaks, one at 400.3 eV due to nitrogen atoms of the PEI backbone, and a smaller one at a higher binding energy (402.2 eV) (Figure SI 3 in the Supporting Information), which was assigned to quaternary nitrogen atoms. The XPS results showed that the top layer of the coating comprised about 1 at% of nitrogen in a cationic stage.19 Charge densities were measured by a fluorescein adsorption, according to a method described in the literature.31 These measurement showed that the number of surface quats were indeed high (>1015 N+/cm2) and well above the threshold to obtain antibacterial properties. Besides high charge densities, (immobilized) quats have to be hydrophobic. After hexylation, resulting in an increase of the contact angle, the coating became biocidal19.

Conclusion

Covalently fixed hyperbranched polyurea coatings were obtained by polymerizing AB2 monomers in bulk on silicon surfaces, which were pre-treated with a coupling agent. The AB2 monomers were obtained in single-step reaction and in quantitative yields by reacting bishexamethylene triamine with carbonyl biscaprolactam. A coupling agent (1), containing siloxane and blocked isocyanate moieties, was prepared by reacting (3-aminopropyl) triethoxysilane with carbonyl biscaprolactam. The siloxane moiety of (1) was able to react with the hydroxyl groups on silicon surfaces, while the BIs were used for anchoring the HBPs. Micrometer thick,


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covalently fixed coatings were prepared by heating spin-coated solutions of the AB2 monomers on modified silicon substrates. The coupling agent (1) appeared to be indispensable to achieve a firm adhesion. The caprolactam blocked isocyanates (CBIs) of the coatings enabled the anchoring of hydroxyl of amino functional compounds. The CBIs comprising coatings are stable until at least 100 oC, which is beneficial for storage. On heating above 125 oC the coupling with MPEG, NFD and PEIs proceeded smoothly. The water contact angle of the HB-coatings (75o±2o) decreased to 40o±2o with MPEG and increased to 104o±3o with NFD. In the same way PEI amino functional compounds were successfully attached and subsequently quaternized. In summary, the same coating platform allowed the preparation of hydrophilic and hydrophobic surfaces and surfaces with immobilized quaternary ammonium compounds.

Experimental section

Materials All chemicals and reagents were purchased from commercial sources and were used without further purification, unless stated otherwise. Carbonyl biscaprolactam (CBC) was obtained from DSM Innovation Center (> 99 % pure according to HPLC). Silicon wafers (99.5 – 100.5 mm diameter, 1000±15 µm thick, both sides polished, (100) orientation) were obtained from Topsil Semicondctors Materials A/S (Frederikssund, Denmark) and cut into 1 cm × 1 cm samples. Di-n-butylamine (DBA, 99 %)


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Langmuir

potassium hydroxide and dimethylformamide (DMF) were purchased from Acros Organic. Polyethyleneimine (Mw = 750 kDa, 50 wt % in water), iodomethane, 2-methyl-2-butanol,

fluorescein

cetyltrimethylammonium

chloride,

disodium dibutyltin

salt, dilaurate

1-bromohexane (DBTDL,

2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-nonadecafluoro-1-decanol

(NFD,

and

95

%),

98

%),

(3-aminopropyl)triethoxysilane (APS, 99 %) and monomethoxy polyethylene glycol (MPEG, Mn = 550 Da) were obtained from Sigma-Aldrich. Sulfuric acid, hydrogen peroxide and ethanol were obtained from Merck. Methanol and toluene were obtained from Lab-Scan. The water content of toluene was

Preparation and Post-Functionalization of Hyperbranched Polyurea

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