Grafting onto a renewable unsaturated polyester via thiol–ene chemistry and cross-metathesis

European Polymer Journal 49 (2013) 843–852

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Grafting onto a renewable unsaturated polyester via thiol–ene chemistry and cross-metathesis Nicolai Kolb, Michael A.R. Meier ⇑ Karlsruhe Institute of Technology, Institute of Organic Chemistry, Fritz-Haber-Weg-6, Building 30.42, 76131 Karlsruhe, Germany

a r t i c l e

i n f o

Article history: Received 25 August 2012 Received in revised form 22 September 2012 Accepted 27 September 2012 Available online 12 October 2012 Keywords: Olefin cross-metathesis thiol–ene Renewable polyester Methyl 10-undecenoate Malonate Passerini

a b s t r a c t Methyl 10-undecenoate was modified to its corresponding malonate derivative by the reaction with sodium hydride in dimethyl carbonate. This malonate was then polymerized with 1,6-hexanediol, catalyzed by 1.0 mol% titanium (IV) isopropoxide, to a poly(malonate) bearing C9 aliphatic side-chains with terminal double bonds. The double bonds of this poly(malonate) were used for grafting onto reactions by either ruthenium-catalyzed cross-metathesis reactions with acrylates or thiol–ene addition reactions. Several examples are shown for both methods. For the cross-metathesis reactions, 1.0 mol% Hoveyda–Grubbs 2nd generation (HG II) catalyst was used with 10.0 equivalents of the respective acrylate under bulk conditions at 40 °C. The thiol–ene additions were carried out with 1.0 equivalents of the respective thiol in THF with 5.0 mol% 2,2-Dimethoxy-2-phenylacetophenone (DMPA) under UV (365 nm) irradiation. Moreover, we have shown that a carboxylic acid group can be easily installed via thiol–ene addition and that the resulting polymer can be further modified by the Passerini three-component reaction with quantitative conversion. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Considering the decrease of fossil resources, it is one of today’s major challenges of chemistry to develop sustainable alternatives for commodity chemicals. In this context, fatty acids have been proven to be a promising resource for polymer chemistry [1,2]. We have recently presented a method for the selective modification of saturated fatty acid methyl esters (FAMEs) towards malonate derivatives by deprotonation of the FAME in a-position with sodium hydride (NaH) in dimethyl carbonate (DMC) as reactive solvent [3]. Most of the other conversions of fatty acids towards renewable polymers have been reported for unsaturated fatty acids. Thus, the double bond within the aliphatic chain is used for diverse chemical modifications, for example, via thiol–ene addition reactions [4–10], ruthenium-catalyzed olefin-metathesis [11–17] or isomerization

⇑ Corresponding author. Tel.: +49 (0)721 608 48326. E-mail address: [email protected] (M.A.R. Meier). URL: http://www.meier-michael.com. (M.A.R. Meier). 0014-3057/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eurpolymj.2012.09.017

reactions with subsequent modifications [18,19], to only mention some of the more recent examples. The aim of this project is to expand the scope of the fatty-acid derived malonate polymer synthesis to an unsaturated FAME, namely methyl 10-undecenoate, which bears a C11 aliphatic chain with a terminal double bond. The precursor, 10-undecenoic acid, can be synthesized by the pyrolysis of ricinoleic acid, which is the major fatty acid of castor oil [20]. The malonate derivative of this ester and its polyester would still contain a terminal double bond on each side-chain, which allows grafting onto reactions via both the ruthenium-catalyzed cross-metathesis and thiol–ene addition reactions to introduce various functional groups in an efficient manner under mild conditions. Similar modifications have been carried out on different polymers via thiol–ene addition reactions yielding selectively functionalized polymers. For example, it has been shown that polybutadienes [21,22], polystyrenes or polyesters [23] and polyoxazolines [24,25] bearing short aliphatic chains with terminal double bonds can be used for the modification with different thiols. Thereby, various functional groups (e.g. hydroxyl groups, esters, or carboxylic acids) can be

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introduced. So far, the described examples almost exclusively covered non-renewable polymers. On the other hand, we recently introduced a new methodology for a versatile grafting onto unsaturated polymers via olefin-metathesis with acrylates [26]. Here, we would like to demonstrate the great potential of unsaturated fatty-acid derived poly(malonates) as renewable polymers. Since the double bond within the aliphatic side-chain is still available for modifications, it is possible to selectively introduce functional groups and therefore change the thermal and/or physical properties of this renewable polymer. Furthermore, it is of importance that, by the selective introduction of functional groups, well-defined polymeric structures can be easily prepared, which otherwise might be challenging. Thus, these methods allow a straightforward tuning of polymer structure and therefore also polymer properties. 2. Results and discussion 2.1. Preparation of starting polyester (P0) The first step of our investigations was the synthesis of a malonate derivative from unsaturated fatty acids and its polymerization (Scheme 1). We chose the castor oil derived 10-undecenoic acid as the substrate, since it features a terminal double bond, thus offering manifold opportunities for subsequent grafting onto chemistry. For the malonate synthesis we used our recently described procedure [3] with 2.5 equivalents of sodium hydride and 1.0 equivalent DMF in 20.0 equivalents of dimethyl carbonate as reactive solvent. This reaction yields the unsaturated malonate derivative in 80.8% yield on a multiple gram scale. The

polymerization of the resulting malonate monomer was then carried out with 1,6-hexanediol and 1.0 mol% titanium isopropoxide under bulk conditions under high vacuum at 120 °C. The obtained polymer was precipitated in ice-cold methanol. The resulting poly(malonate) had an average molecular weight of 10.2 kDa and was obtained as a yellow, highly viscous oil. Differential scanning calorimetry showed a glass-transition of this polymer at 74.1 °C, which corresponds with our earlier studies on saturated poly(malonates) [3]. 2.2. Cross-metathesis with acrylates We investigated the modification of P0 via rutheniumcatalyzed cross-metathesis with acrylates (type II olefins), which exhibit excellent cross-metathesis selectivity with terminal olefins (Scheme 2) [27]. We chose the Hoveyda– Grubbs catalyst 2nd generation (HG II) catalyst [28], since this catalyst gave best results in our earlier studies on the cross-metathesis of methyl 10-undecenoate with methyl acrylate (MA) [11]. The first experiments were carried out on a 0.5 mmol (155 mg) scale in 1 mL of dichloromethane (DCM) with 1 mol% catalyst loading and 5–10 equivalents of MA. Although we achieved complete conversion of the terminal double bonds, GPC analysis showed coupling of the polymer via self-metathesis (Table 1, entries 1–2). Therefore, we tried to carry out the reaction under bulk conditions with 10 equivalents of MA to avoid DCM as solvent and suppress the polymer–polymer coupling side-reaction yielding complete conversion of the terminal double bond without cross-linking (Table 1, entry 3). With 5 equivalents of MA under bulk conditions, only 67% conversion was achieved and polymer–polymer coupling took

Scheme 1. Synthesis of malonate derivative and starting polymer P0.

Scheme 2. Polymer-functionalization via ruthenium-catalyzed olefin-metathesis.

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N. Kolb, M.A.R. Meier / European Polymer Journal 49 (2013) 843–852 Table 1 Reaction condition screening for cross-metathesis modifications after 2 h reaction time. Entry

HG II (mol%)

DCM (mL)

MA (equivalents)

Conva (%)

Polymer–polymer coupling

1 2 3 4 5

1.0 1.0 1.0 1.0 0.5

1.0 1.0 None None None

5.0 10.0 10.0 5.0 10.0

>99 >99 >99 67 83

Yes Yes No Yes No

a The degree of functionalization was determined by 1H NMR (CDCl3) spectroscopy of the crude samples where the malonic a-hydrogen (3.25 ppm) and ester CH2 (4.05 ppm) signals were taken as references.

place in a considerable amount (Table 1, entry 4). On the other hand, reducing the catalyst loading to 0.5 mol% also resulted in lower conversions of 83% (Table 1, entry 5). Therefore, we decided to use bulk conditions with 10 equivalents of the respective acrylate and 1.0 mol% of the HG II catalyst at 40 °C for the further cross-metathesis modifications employing different reaction times. With the optimized reaction conditions in hand we tested the cross-metathesis of P0 with different acrylates on a 1.0 mmol scale. In addition to MA, we also used t-butyl acrylate (bearing the possibility of simple ester cleavage), 2-hydroxyethyl acrylate (HEA), and PEG acrylate (Mn 480). With methyl- and t-butyl acrylate, the reaction proceeded without coupling and with good to very high conversions after 3 h (Table 2, entries 1 and 2). With HEA, however, the reaction did not proceed as satisfying as with the other acrylates since only 83% conversion was achieved even after 6 h reaction time (Table 2, entry 3). We consider that this is because of the free hydroxyl groups, which can lead to catalyst degradation. [29] However, also with HEA no polymer–polymer coupling was observed. With PEG acrylate on the other hand, the reaction proceeded very fast with complete conversion after only 1 h (Table 2, entry 3). Unfortunately, the double bonds of the a,b-unsaturated ester of the PEG modified polymer P4 tend to cross-link very easily during the work up and drying. Therefore, P4 had to be handled as a solution in THF containing butylated hydroxytoluene as a radical inhibitor. The 1H NMR spectra of P0 and metathesis modified polymers P1–P4 are shown in Fig. 2. It is clear to

see that the initial signals for the terminal double bond at 4.9 and 5.7 ppm disappear almost completely, except for HEA-modified polymer P3. Moreover, no polymer– polymer coupling occurs, which would result in signals for internal olefins at around 5.3 ppm. The latter result corresponds to the absence of high molecular weight shoulders in the GPC chromatograms (Fig. 1). 2.3. Thermal properties of olefin-metathesis modified polymers The thermal properties of all olefin-metathesis modified polymers were analyzed by differential scanning calorimetry (Fig. 3). In contrast to the starting polymer P0 with a Tg of 74.1 °C, polymers P1–P3, which were grafted with short acrylates, have slightly higher Tg values. Methyland t-butyl-acrylate modified polymers P1 and P2 have almost similar Tg values of 50.8 °C and 51.2 °C, respectively. HEA-modified polymer P3 has a significantly lower Tg value of 59.2 °C. PEG-modified polymer P4 on the other hand exhibits the expected thermal properties of a semi-crystalline polymer with a Tg value of 59.0 °C, a clear crystallization point at 43.6 °C and the melting transition Tm at 1.9 °C. 2.4. Thiol–ene coupling modifications Having shown the modification possibilities via crossmetathesis, we were also interested in the modification of P0 via thiol–ene addition reactions (Scheme 3). It is long

Table 2 Reaction condition screening for the cross-metathesis with MA. Time (h)

Degree of functionalizationa (%)

Mnb (kDa)

Mw (kDa)

PDI

P1

3

>95

12.4

27.0

2.18

P2

3

>99

13.6

26.8

1.97

P3

6

83

11.4

24.1

2.12

P4

1

>99

24.8

39.6

1.60

Entry

Acrylate

a The degree of functionalization was determined by 1H NMR (CDCl3) spectroscopy of the precipitated polymers by using the malonic a-hydrogen (3.25 ppm) and ester CH2 (4.05 ppm) signals were as references. b Molecular weight distribution from THF-GPC system.

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Fig. 1. GPC traces of olefin-metathesis functionalized polymers P1–P4 after precipitation.

known that thiols can add to terminal double bonds by radical initiation or even initiator-free in an anti-Markovnikov manner [30]. We carried out our first studies on a 0.5 mmol scale in 0.5 mL THF under UV irradiation without any initiator at room temperature for 4 h with various amounts of 2-mercaptoethanol. These initiator-free reactions proceeded very poorly with low conversion for 1–2 equivalents of thiol (Table 3, entries 1–3) and good conversions for a 3-fold excess of thiol (Table 3, entry 4). These results led us to try 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a radical initiator under UV irradiation, also at room temperature. With a loading of 5.0 mol% DMPA the reaction proceeded with quantitative conversion of the double bond after only 1 h without observed polymer–polymer coupling (Table 3, entries 5, 6 and 8). Lowering the concentration of DMPA to 2.0 mol% gave only 60% conversion (Table 3, entry 7). Therefore, we used 5 mol% of DMPA and equimolar amounts of the respective thiol in a 1 M THF solution for further modifications. Similar studies were performed in higher dilutions, with larger thiol-loadings or at higher temperatures and usually re-

Fig. 2. 300 MHz 1H NMR (CDCl3) spectra of olefin-metathesis functionalized polymers P1–P4 after precipitation (see experimental part for details). The regions from 4.8 to 7.1 ppm are enlarged for better analysis of the internal a,b-unsaturated esters.

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847

Fig. 3. DSC analysis of polymers P0–P4 after precipitation.

ysis and GPC data (Fig. 4) led us to the conclusion that polymer–polymer coupling was very low (<5%) and no side-reactions such as the radical-initiated ring-closure of the side-chains occurred. However, it is noteworthy that the GPC results in our THF GPC system showed shoulders for all thiol–ene modified polymers. We believe that this is due to column interactions of the introduced functional groups, since such interactions and shoulders did not occur when DMAC was used as GPC solvent. However, with DMAC it was not possible to analyze polymer P9. Therefore, polymer P9 was analyzed with our THF-GPC system (and thus unfortunately showed shoulders due to column interactions).

Scheme 3. Grafting onto P0 via thiol–ene addition reaction.

Table 3 Reaction condition mercaptoethanol.

2.5. Modification of polymers by multi-component reactions screening

for

the

thiol–ene

addition

of

Entry

2-Mercaptoethanol (equivalents)

DMPA (mol%)

Time (h)

Conv. (%)a

1 2 3 4 5 6 7 8

1.0 1.5 2.0 3.0 1.0 1.0 1.0 1.0

– – – – 5.0 5.0 2.0 5.0

4.0 4.0 4.0 4.0 4.0 2.0 2.0 1.0

55 55 61 90 >99 >99 60 >99

2-

a The conversion was determined via 1H NMR (CDCl3) analysis of the crude reaction mixture taking the malonic a-hydrogen (3.25 ppm) and ester CH2 (4.05 ppm) signals as references.

sulted in quantitative conversions of the double bonds [23–24,31]. We used these conditions for further modifications with different thiols bearing different functional groups, such as hydroxyl groups, esters or carboxylic acids (Table 4). For all thiols used, the reaction proceeded with quantitative consumption of the double bond within one hour as verified by 1H NMR analysis. Further 1H NMR anal-

Since its discovery in 1921 by Mario Passerini, the Passerini multi-component reaction has become a very useful tool in organic chemistry for various purposes [32]. This reaction is well-established in organic chemistry and it was only recently that we have shown that the Passerini reaction can be used for the synthesis of renewable monomers, as a polymerization method, and for grafting onto polymeric structures under very mild conditions and at room temperature. [33] Therefore, we were also interested in this study to broaden the scope of graftingonto via the Passerini reaction. Our aim was to modify our starting polymer P0 via thiol–ene addition with 3-mercaptopropionic acid (P9) and subsequently use the pendant carboxylic acids of the resulting polymer for a Passerini reaction without further purification steps (Scheme 4). For the thiol–ene addition, we employed our already established procedure; subsequently, t-butyl isocyanide and heptanal were added as model substrates since these compounds would lead to characteristic signals in the 1H NMR spectra (CDCl3; d = 1.29 ppm for t-butyl and 0.80 ppm for terminal CH3) and allow a straightforward characterization of the product. Employing 1.0 equivalents

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Table 4 Results of the thiol–ene addition reactions of P0 with various thiol compounds. Degree of functionalizationa (%)

Mn (kDa)

Mw (kDa)

PDI

P5

>99

17.2

30.6

1.79

P6

>99

19.1

33.1

1.73

P7

>99

9.9

14.7

1.48

P8

>99

14.7

22.7

1.55

P9

>99

13.9

29.9

2.14

Entry

Thiol

a The conversion was determined by 1H NMR (CDCl3) analysis of the precipitated polymers taking the malonic a-hydrogen (3.25 ppm) and ester CH2 (4.05 ppm) signals as references.

could be precipitated in cold n-hexane to recover it in >95% yield. Also GPC analysis clearly showed a very efficient reaction proceeding without any noticeable sidereaction (Fig. 5). The presence of the shoulders in the GPC spectra was previously discussed and is most likely due to interactions with the column on the THF-GPC system. It is worth mentioning that the obtained polymer

Fig. 4. GPC traces of thiol–ene modified polymers P5–P8 after precipitation.

of the isocyanide and aldehyde only 80% conversion was achieved after 24 h at room temperature. For 1.1 as well as 1.2 equivalents of isocyanide and aldehyde 88% conversion was obtained under otherwise unchanged conditions. However, complete conversion of the carboxylic acid was achieved using 1.5 equivalents of the reagents, which was verified by 1H NMR analysis. The obtained polymer

Fig. 5. GPC traces in THF of polymers P9 and P10 after precipitation.

Scheme 4. Grafting onto free carboxylic acids via the Passerini multi component reaction.

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Fig. 6. DSC analysis of polymers P5–P10 after precipitation.

P10 has the tendency to cross-link after several weeks when it is stored at room temperature.

fatty-acid derived polymers that still contain the double bond within the aliphatic chain for further reactions.

2.6. Thermal properties of thiol–ene addition modified polymers

4. Experimental 4.1. Materials

The thiol–ene modified polymers P5–P10 exhibit the expected thermal behavior (Fig. 6), as measured with differential scanning calorimetry. Polymers P5 and P6, which bear one and two hydroxyl groups respectively, have a higher Tg value of 54.6 or 46.0 °C than the starting polymer P0 with 74.1 °C. The 1-butanethiol modified polymer P7 showed a clear melting transition at 41.7 °C. These results are in accordance with our findings that longer aliphatic side-chains in the polyesters increase their melting point [3] due to side chain crystallization. Polymers P8 and P9 exhibit Tg values of 63.6 or 40.9 °C, respectively. Finally, the Passerini-modified polymer P10 exhibits the highest Tg value of 29.8 °C. 3. Conclusion In conclusion, we have presented two efficient pathways for the modification of our renewable polyester bearing terminal double bonds in the side-chains, which should be easily applicable to similar polymeric structures. For the cross-metathesis modifications, an excess of acrylate was crucial and the conversion was highly dependent on the functional group of the acrylate. For the thiol–ene addition on the other hand, equimolar amounts of the thiol with 5 mol% of the photoinitiator without the use of transition metal catalysts resulted in complete consumption of the double bond under very mild conditions. Moreover, we have shown that the thiol–ene modified polymer can further be modified by the Passerini reaction in a one-pot reaction with quantitative conversion. These findings demonstrate not only the great versatility of grafting-onto methods, but also clearly demonstrate the potential of

All solvents and chemicals were used as received. Sodium hydride (NaH, 60 wt.% dispersion in mineral oil), 10-undecenoic acid (98%), 2,2-Dimethoxy-2-phenylacetophenone (DMPA, 98%), (1,3-bis-(2,4,6-trimethylphenyl)2-imidazolidinylidene)dichloro(o-isopropoxyphenylmethylene)ruthenium (HG II, 97%), 2-mercaptoethanol (>99%), thioglycerol (97%), methyl thioglycolate (97%), 3-mercaptopropionic acid (99%), 1-butanethiol (98%), methyl acrylate (99%, contains 6 100 ppm monomethyl ether hydroquinone), t-butyl acrylate (98%, contains 10–20 ppm monomethyl ether hydroquinone), 2-hydroxyethyl acrylate (96%, contains 200–650 ppm monomethyl ether hydroquinone), PEG acrylate (average Mn 480, contains 100 ppm BHT), heptanal (95%) and tert-butyl isocyanide (98%) were purchased from Sigma Aldrich. N,N-Dimethylformamide (DMF, 99.8%, extra dry), Ti(OiPr)4 (98%), 1,6-hexanediol (97%) and dimethyl carbonate (DMC, 99%) were from Fisher Scientific. Methyl 10-undecenoate was synthesized from 10-undecenoic acid using standard procedures. 4.2. General methods All cross-metathesis reactions were carried out using a Radleys Carousel™ 12 Plus (RR98072, 55 Radleys Discovery Technologies, UK). The thiol–ene addition reactions were performed in Radleys Carousel™ reaction tubes with UV irradiation from a BENDA NU-6 KL UV lamp (2  6 W, 365 nm). Nuclear magnetic resonance (NMR) measurements were performed on a Bruker AVANCE DPX system operating at 300 MHz for 1H NMR. The chemical shifts (d) are

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given in ppm relative to tetramethylsilane (TMS, d = 0.00 ppm) as the internal standard. Polymer molecular weight (GPC) analysis was performed on two different systems. The THF-GPC was a LC20A system from Shimadzu in THF with a flow rate of 1 mL/min at 50 °C which was equipped with an SIL-20A autosampler and an RID-10A refractive index detector. The analysis was performed on the following column system: PLgel 5 lm MIXED-D column (Varian, 300 mm  7.5 mm, 10,000 Å) with a SDV gel 5 lm pre-column (PSS, 50  8.0 mm). The DMC-GPC was a Polymer Laboratories PL-GPC 50 Plus Integrated System equipped with an autosampler and a differential refractive index detector running in N,N-dimethylacetamide (DMAc) containing 0.03 wt.% lithium bromide at a flow rate of 1 mL/min at 50 °C. The analysis was performed on the following column system: PLgel 5 lm MixedC column (300  7.5 mm) with a PLgel 5 lm bead-size guard column (50  7.5 mm). The THF-GPC was calibrated with linear poly(methyl methacrylate) standards ranging from Mp 102–981000 Da, the DMAC-GPC was calibrated with linear poly(styrene) standards with molecular weights ranging from 160 to 6,000,000 Da. Both calibration standards were obtained from PSS (Polymer Standard Service). Differential scanning calorimetry (DSC) experiments were carried out under a nitrogen atmosphere starting at 90 °C with a heating rate of 5 °C/min using a DSC821e (Mettler Toledo) calorimeter up to a temperature of 200 °C and a sample mass in the range of 20–30 mg. The data from second heating scans are reported. 4.3. Synthesis of dimethyl 2-(non-8-en-1-yl)malonate 22.3 mL methyl 10-undecenoate (0.10 mol) were mixed with 7.70 mL DMF (1.0 equivalents) and 10.0 g sodium hydride (60 wt.% dispersion in mineral oil, 0.25 mmol, 2.5 equivalents) in 170 mL DMC (2.0 mol, 20 equivalents). The suspension was stirred at 60 °C for 8 h. To stop the reaction, the suspensions were added slowly to 200 mL diluted hydrochloric acid. The organic phase was isolated and concentrated under reduced pressure. Distillation under high vacuum gave the product as a colorless oil with 80.8% yield (20.7 g). 1H NMR (300 MHz, CDCl3) d 5.71 (ddt, J = 16.9, 10.2, 6.7 Hz, 1H, CH2@CHR), 4.95–4.77 (m, 2H, CH2@CHR), 3.65 (s, 6H, COOCH3), 3.28 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 1.95 (dd, J = 13.4, 6.4 Hz, 2H, CH2@CH–CH2R), 1.83 (m, 2H, CH2), 1.26 (m, 10H, chain); 13C NMR (75 MHz, CDCl3) d 169.73 (COOCH3), 138.86 (CH2@CHR), 114.06 (CH2@CHR), 52.17 (COOCH3), 51.54 (CH3OOC–CHR–COOCH3), 33.62 (CH2), 28.82 (CH2), 27.18 (CH2); MS (EI): m/z = 256.2 ([M], calc. 256.17). 4.4. Preparation of the starting poly(malonate) (P0) Dimethyl 2-(non-8-en-1-yl)malonate (25.6 g, 0.10 mol) was mixed with 11.8 g 1,6-hexanediol (0.10 mol) in a 100 mL Schlenk flask. The mixture was heated to 120 °C, then 295 lL Ti(OiPr)4 (284 mg, 1.0 mol%) was added. Afterwards the reaction was heated at 120 °C for 1 h with a stream of argon and afterwards high vacuum was applied for 23 h. After 24 h reaction time the polymer was

dissolved in 30 mL THF and precipitated in 500 mL ice-cold methanol and kept at 4 °C for 2 h. After carefully decanting of the solvent, the polymer was washed twice with icecold methanol. The pure polymer was obtained with 22.3 g (71.9% yield) as a yellow, highly viscous material. 1H NMR (300 MHz, CDCl3) d 5.73 (ddt, J = 16.9, 10.2, 6.7 Hz, 1H, CH2@CHR), 4.97–4.78 (m, 2H, CH2@CHR), 4.05 (t, [email protected] Hz, 4H, RCOOCH2R), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 1.96 (dd, J = 13.7, 6.8 Hz, 2H, CH2@CH–CH2R), 1.81 (m, 2H, CH2), 1.57 (m, 4H, COOCH2–CH2–R), 1.26 (d, J = 20.2 Hz, 14H, chain). 4.5. Acrylate cross-metathesis 4.5.1. Condition screening with methyl acrylat 155 mg polymer P0 (corresponds to 0.50 mmol repeating units) were dissolved in various amounts of methyl acrylate and optional DCM as solvent. Afterwards, various amounts of HG II catalyst were added and the mixture was stirred at 40 °C. After 2 h the reaction was quenched by addition of 10 lL ethyl–vinyl ether. The crude reaction mixture was analyzed by 1H NMR and THF-GPC. The conversion was calculated by 1H NMR integration. 4.5.2. General procedure (A) for cross-metathesis modifications 310 mg polymer P0 (1.00 mmol) were dissolved in 10 equivalents of the respective acrylate and HG II (6.2 mg, 1 mol%) was added. The mixture was stirred at 40 °C for various times. Afterwards, the reaction was stopped by addition of 20 lL ethyl–vinyl ether and analyzed by 1H NMR and THF-GPC. 4.5.3. Cross-metathesis with methyl acrylate (P1) Following the general procedure (A), 310 mg P0 were dissolved in 900 lL methyl acrylate and stirred at 40 °C for 3 h. After the reaction was stopped, the crude polymer was precipitated in ice-cold MeOH (271 mg, 73.6% yield). 1 H NMR (300 MHz, CDCl3) d 6.89 (dt, J = 15.5, 6.9 Hz, 1H, acrylate b-H), 5.74 (d, J = 15.7 Hz, 1H, acrylate a-H), 4.05 (t, J = 6.7 Hz, 4H, RCOOCH2R), 3.65 (s, 3H, COOCH3), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 2.18–2.05 (m, 2H, acrylate c-CH2), 1.79 (m, 2H, CH2), 1.57 (m, 4H, COOCH2– CH2–R), 1.23 (m, 14H, chain). 4.5.4. Cross-metathesis with t-butyl acrylate (P2) Following the general procedure (A), 310 mg P0 were dissolved in 1.45 mL t-butyl acrylate and stirred at 40 °C for 3 h. After the reaction was stopped, the crude polymer was precipitated in ice-cold MeOH (141 mg, 34.4% yield). 1 H NMR (300 MHz, CDCl3) d 6.78 (dt, J = 15.4, 6.9 Hz, 1H, acrylate b-H), 5.65 (d, J = 15.6 Hz, 1H, acrylate a-H), 4.05 (t, J = 6.6 Hz, 4H, RCOOCH2R), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 2.08 (m, 2H, acrylate c-CH2), 1.81 (m, 2H, CH2), 1.57 (m, 4H, COOCH2–CH2–R), 1.41 (s, 9H, COOC(CH3)3), 1.26 (m, 14H, chain). 4.5.5. Cross-metathesis with 2-hydroxyethyl acrylate (P3) Following the general procedure (A), 310 mg P0 were dissolved in 1.15 mL 2-hydroxyethyl acrylate which resulted in a turbid mixture that was stirred at 40 °C for

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6 h. After the reaction was stopped, the crude polymer was precipitated in ice-cold n-hexane (278 mg, 69.8% yield). 1H NMR (300 MHz, CDCl3) d 6.94 (dt, J = 15.5, 6.9 Hz, 1H, acrylate b-H), 5.78 (d, J = 15.7 Hz, 1H, acrylate a-H), 4.20 (s, 2H, COOCH2CH2OH), 4.05 (t, J = 6.5 Hz, 4H, RCOOCH2R), 3.78 (s, 2H, COOCH2CH2OH), 3.25 (t, J = 7.4 Hz, 1H, CHR(COOMe)2), 2.13 (m, 2H, acrylate c-CH2), 1.81 (m, 2H, CH2), 1.57 (m, 4H, COOCH2–CH2–R), 1.26 (m, 14H, chain). 4.5.6. Cross-metathesis with PEG acrylate (P4) Following the general procedure (A), 310 mg P0 were dissolved in 4.4 mL PEG acrylate and stirred at 40 °C for 1 h. After the reaction was stopped, the crude polymer was precipitated in ice-cold diethyl ether. The exact weight of polymer could not be measured since it tended to polymerize upon complete drying. 1H NMR (300 MHz, CDCl3) d 6.91 (dt, J = 15.3, 6.9 Hz, 1H, acrylate b-H), 5.77 (d, J = 15.6 Hz, 1H, acrylate a-H), 4.25–4.14 (m, 2H, COOCH2CH2OR), 4.04 (t, J = 6.6 Hz, 4H, RCOOCH2R), 3.68–3.64 (m, 2H, COOCH2CH2OR), 3.58 (s, 28H, PEG CH2), 3.50–3.45 (m, 2H, PEG CH2), 3.31 (s, 3H, PEG-OCH3), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 2.12 (m, 2H, acrylate cCH2), 1.81 (m, 2H, CH2), 1.57 (m, 4H, COOCH2–CH2–R), 1.36 (m, 2H, chain), 1.29 (m, 4H, chain), 1.23 (m, 8H, chain). 4.6. thiol–ene addition 4.6.1. Condition screening with 2-mercaptoethanol 155 mg P0 (0.50 mmol) were dissolved in 0.5 mL THF with optional DMPA as photoinitiator and various amounts of 2-mercaptoethanol. The mixtures were then stirred for different times at room temperature and continuously analyzed by 1H NMR. The conversion was determined by 1H NMR integration of the terminal double bonds. 4.6.2. General procedure (B) for thiol–ene additions 620 mg P0 were dissolved in 2 mL THF with 25.6 mg DMPA (5 mol%) and 1.0 equivalent of the respective thiol. The mixtures were stirred at room temperature under UV irradiation (365 nm) for 1 h. 4.6.3. thiol–ene addition of 2-mercaptoethanol (P5) Following the general procedure (B), 620 mg P0 were dissolved in 2 mL THF with 25.6 mg DMPA and 140 lL 2mercaptoethanol and stirred under UV irradiation for 1 h. Afterwards, the polymer was precipitated in ice-cold nhexane (550 mg, 70.9% yield). 1H NMR (300 MHz, CDCl3) d 4.05 (t, J = 6.6 Hz, 4H, RCOOCH2R), 3.65 (t, J = 6.0 Hz, 2H, RCH2SCH2–CH2OH), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 2.66 (t, J = 6.0 Hz, 2H, RCH2SCH2–CH2OH), 2.45 (t, J = 7.3 Hz, 2H RCH2SCH2–CH2OH), 2.11 (s, 2H, CH2), 1.82 (m, 2H, CH2), 1.57 (s, 6H, chain), 1.25 (m, 16H, chain). 4.6.4. thiol–ene addition of thioglycerol (P6) Following the general procedure (B), 620 mg P0 were dissolved in 2 mL THF with 25.6 mg DMPA and 173 lL thioglycerol and stirred under UV irradiation for 1 h. Afterwards, the polymer was precipitated in ice-cold n-hexane (627 mg, 68.2% yield). 1H NMR (300 MHz, CDCl3) d 4.05 (t, J = 6.5 Hz, 4H, RCOOCH2R), 3.74–3.63 (m, 2H, HOCH2–

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CHOH–CH2SCH2R), 3.56–3.46 (m, 1H, HOCH2–CHOH–CH2SCH2R), 3.26 (t, J = 7.4 Hz, 1H, CHR(COOMe)2), 2.68–2.51 (m, 2H, HOCH2–CHOH–CH2SCH2R), 2.51–2.42 (m, 2H, HOCH2–CHOH–CH2SCH2R), 1.80 (m, 2H, CH2), 1.57 (m, 6H, chain), 1.25 (m, 16H, chain). 4.6.5. thiol–ene addition of n-butanethiol (P7) Following the general procedure (B), 620 mg P0 were dissolved in 2 mL THF with 25.6 mg DMPA and 215 lL nbutanethiol and stirred under UV irradiation for 1 h. Afterwards, the polymer was precipitated in ice-cold MeOH (493 mg, 61.6% yield). 1H NMR (300 MHz, CDCl3) d 4.05 (t, J = 6.7 Hz, 4H, RCOOCH2R), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 2.43 (t, J = 8.6 Hz, 4H, RCH2SCH2R), 1.79 (m, 2H, CH2), 1.65–1.47 (m, 8H, chain), 1.42–1.18 (m, 18H, chain), 0.85 (t, J = 7.2 Hz, 3H, CH3). 4.6.6. thiol–ene addition of methyl thioglycolate (P8) Following the general procedure (B), 620 mg P0 were dissolved in 2 mL THF with 25.6 mg DMPA and 179 lL methyl thioglycolate and stirred under UV irradiation for 1 h. Afterwards, the polymer was precipitated in ice-cold MeOH (528 mg, 61.4% yield). 1H NMR (300 MHz, CDCl3) d 4.05 (t, J = 6.7 Hz, 4H, RCOOCH2R), 3.67 (s, 3H, COOCH3), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 3.16 (s, 2H, SCH2COOMe), 2.61–2.48 (m, 2H, CH2), 1.79 (m, 2H, CH2), 1.53 (m, 6H, chain), 1.25 (m, 16H, chain). 4.6.7. thiol–ene addition of 3-mercaptopropionic acid (P9) Following the general procedure (B), 620 mg P0 were dissolved in 2 mL THF with 25.6 mg DMPA and 175 lL 3mercaptopropionic acid and stirred under UV irradiation for 1 h. Afterwards, the polymer was precipitated in icecold n-hexane (415 mg, 49.9% yield). 1H NMR (300 MHz, CDCl3) d 10.53 (s, 1H, COOH), 4.05 (t, J = 6.4 Hz, 4H, RCOOCH2R), 3.26 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 2.70 (m, 2H, RCH2SCH2CH2COOH), 2.59 (t, J = 7.2 Hz, 2H, RCH2SCH2CH2COOH), 2.46 (t, J = 6.8 Hz, 2H, RCH2SCH2CH2COOH), 1.80 (m, 2H, CH2), 1.65–1.45 (m, 8H, chain), 1.25 (m, 16H, chain). 4.7. Passerini reaction of P9, heptanal and t-butyl isocyanide (P10) For the Passerini reaction the crude reaction mixture resulting from the preparation of P9 was taken and mixed with 340 lL t-butyl isocyanide (3.0 mmol, 1.5 equivalents) and 417 lL heptanal (3.0 mmol, 1.5 equivalents). The mixture was stirred at room temperature for 24 h. Afterwards the polymer was precipitated in ice-cold n-hexane (1.18 g, 96.2% yield). 1H NMR (300 MHz, CDCl3) d 6.02 (s, 1H, NH), 5.01 (t, J = 6.0 Hz, 1H, CHR3), 4.05 (t, J = 6.6 Hz, 4H, RCOOCH2R), 3.25 (t, J = 7.5 Hz, 1H, CHR(COOMe)2), 2.83– 2.68 (m, 2H, RCH2SCH2CH2COOR), 2.63 (t, J = 6.4 Hz, 2H, RCH2SCH2CH2COOR), 2.47 (t, J = 7.3 Hz, 2H, RCH2SCH2CH2COOR), 1.79 (m, 4H, 2 CH2), 1.54 (m, J = 3.3 Hz, 6H, chain), 1.33–1.18 (m, 33H, RC(CH3)3 + chain), 0.79 (t, J = 6.0 Hz, 3H, CH3).

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