Hydrosilylation as an efficient tool for polymer synthesis and modification with methacrylates

Abstract

Hydrosilylation is a well-established reaction for the preparation of organo-silicon compounds, in which vinyl groups react with silanes (Si–H) usually catalysed by late transition metal complexes, most often Pt(II) complexes. Hydrosilylation of functional methacrylates provides access to functional poly(dimethylsiloxane)s (PDMS), from appropriate hydride terminated and functional PDMS, in very high yielding reactions without the formation of any side products, odour and without the need for labor-intensive purification. Herein, commercially available telechelic PDMS hydrides (h₂PDMS) have been modified with a range of different methacrylates using very low catalytic amounts of commercial Pt(II) catalysts. The products have been characterized by ¹H and ¹³C NMR, SEC, IR and MALDI-ToF MS demonstrating high selectivity and very high reaction yields. The versatility of hydrosilylation has been exploited for the preparation of ABA triblock copolymers using poly(ethylene glycol) methacrylate and more structurally demanding vinyl terminated methacrylic macromonomers as obtained by catalytic chain transfer polymerization (CCTP). ¹H NMR revealed the formation of solely anti-Markovnikov products and the high tolerance of the reaction towards other functionalities, such as epoxides present in glycidyl methacrylate. The specific Si–H signals in ¹H NMR (4.8 ppm) and IR (2126 cm⁻¹) from the Si–H group allow for facile monitoring of the progress of the reaction. SEC and MALDI-ToF MS investigations further highlighted the formation of well-defined polymer systems with near perfectly matching molecular compositions.

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Introduction

Highly efficient organic reactions have been used for many years to modify and alter the properties of materials. In particular, the introduction of the “click chemistry” concept by Sharpless¹ and coworkers in 2001, has inspired researchers to seek new, and rediscover old, efficient reactions, which are, e.g. high yielding, stereospecific, do not generate side products and hopefully do not require purification by chromatography. Numerous reactions have experienced a renaissance as “click-type” reactions and have been demonstrated to be applicable for the fabrication of diverse materials/polymer architectures for applications in material science, biology and medicine.^2–6 Prominent recent examples include thiol–ene,^7–9 Michael-addition and Diels–Alder reactions.¹⁰

A highly efficient reaction, which has not received as much attention in this context as we think it merits, is catalytic hydrosilylation,^11,12 the insertion of an unsaturated vinyl group into a Si–H bond. Poly(organo siloxane)s (POS), silicones,¹³ are exploited as building blocks in many industrial products. Poly(dimethyl siloxanes) (PDMS) are probably the most important member of this polymer class exhibiting some excellent material properties, including high flexibility, excellent thermo-oxidative stability, high moisture resistance, low glass transition temperature (T_g) and non-toxicity.¹³ Due to these unique properties, POS, and in particular PDMS, are used in diverse applications, for example in semiconductor devices, aerospace, decorative coatings, biomaterials, as mold release agents, anti-foam and foaming agents, personal care products, additive materials, high performance elastomers and deformers and are ubiquitous in our homes and lives.^14–16 The first hydrosilylation reaction of trichlorosilane and 1-octene in the presence of acetyl epoxide was reported by Sommer et al. in 1947.¹⁷ Since then, hydrosilylation has become one of the most powerful reactions in silicone polymer and surface chemistry.¹⁸ The mechanism for the late transition metal catalysed hydrosilylation (usually using d⁸ and d¹⁰ metals) was proposed by Chalk and Harrod in 1965 (Scheme 1A).¹² The oxidative addition of a silane to the metal complex is followed by migratory insertion of the alkene into the M–H bond. In a reductive elimination step, the Si–C bond is formed and the metal complex is regenerated.

Scheme 1 Chalk–Harrod hydrosilylation mechanism catalyzed by a late transition metal catalyst (A),¹² and general hydrosilylation reaction of hydride terminated PDMS (h₂PDMA) with methacrylates (B).

To date, several studies on the modification of end-functional hydride PDMS (h₂PDMS) and copoly(dimethyl)(methyl-hydrogen)siloxane have been reported.¹⁹ The latter approach was used for the preparation of acrylate containing²⁰ and fluorinated PDMS, respectively.²¹ Hydrosilylation of h₂PDMS systems was demonstrated as a technique for the introduction of (meth)acrylic acid,^22,23 amine and epoxy terminal end groups.²⁴ The addition of Si–H can be favorably compared with thiol–ene chemistry (addition of S–H) which has been the focus of many publications in recent years.^7,9 Hydrosilylation has the advantage of having starting materials with little or no odor which are extremely stable other than to react very selectively with vinyl groups in the presence of appropriate catalysts. Thus, we decided to investigate the utility of this reaction seeking in particular a way of functionalising macromonomers as prepared by catalytic chain transfer polymerisation (CCTP) as this sterically hindered vinyl group has proved difficult to functionalise in a high yielding and efficient way.

Herein, hydrosilylation is used as a highly efficient reaction for modification with different methacrylates demonstrating a high tolerance towards a range of functionalities in combination with high yields. In this study, linear telechelic h₂PDMS is transformed with methacrylates bearing different groups including methyl, hydroxyl and glycidyl using platinum-divinyltetra-methyldisiloxane (Pt(dvs)) as catalyst at relatively low temperature (37 °C) (Scheme 1B) whereas this type of reaction is often performed at elevated temperatures. Characterisation of the products has been carried out with ¹H NMR and FTIR spectroscopy, size exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-ToF MS). Based on these results, hydrosilylation of methacrylate-based materials and in particular oligomers derived from CCTP is demonstrated as a tool for the synthesis of block copolymers from CCTP products.

Results and discussion

Modification of hydride terminated PDMS with methacrylates

Hydrosilylation was employed as a versatile and efficient method for the synthesis of functional telechelic PDMS (Scheme 1B). PDMS with hydride α,ω-end groups (h₂PDMS; average M_n 580 g mol⁻¹) was modified with different methacrylates (Scheme 2), including methyl methacrylate (MMA), 2-hydroxylethyl methacrylate (HEMA), glycidyl methacrylate (GMA), lauryl methacrylate (LMA), 2-ethyl hexyl methacrylate (EHMA), butyl methacrylate (BMA) and diethylene glycol methyl ether methacrylate (DEGMEMA).

Scheme 2 Hydrosilylation of methacrylate monomer and h₂PDMS hydride terminated, R represents a function same as another end.

Firstly, MMA was used in order to optimise the reaction conditions with regard to temperature and reaction time. Surprisingly within 60 min at 37 °C the reaction was found to be complete, as determined by ¹H NMR (Fig. S1†). The characteristic Si–H signal at 4.8 ppm was used to follow the progress of the reaction (Fig. 1). The insertion of the methacrylic alkene functionality into the Si–H bond results in the formation of a Si–C bond and loss of the Si–H group. After 60 min at 37 °C the Si–H signals disappeared whilst new signals between 0.5 and 1 ppm appeared, which can be assigned to the newly formed CH₂ group. A high-field shift of the methacrylate methyl group is observed, characteristic for the transition from an sp² to an sp³ neighboring group. Further evidence of the success of the reaction was obtained by IR spectroscopy (Fig. 2) with the disappearance of the characteristic Si–H band at 2126 cm⁻¹ and the appearance of the ester band at 1750 cm⁻¹.

Fig. 1 ¹H NMR spectra of the feed mixture of MMA and h₂PDMS (A) and the product MMA-PDMS-MMA (B) in CDCl₃.

Fig. 2 IR spectroscopy of h₂PDMS and MMA-PDMS-MMA.

Hydrosilylation is a catalytic addition reaction and both the Markovnikov and the anti-Markovnikov products are possible. Previously, it has been reported that hydrosilylation catalysed by rhodium and rhenium complexes follow the anti-Markovnikov rule.^25,26 Due to the asymmetric substitution of the methacrylates used in this study, valuable and conclusive information is obtained from the ¹H NMR spectrum of the final product (Fig. 1 bottom). A product according to the Markovnikov rule would result in the formation of a quaternary carbon substituted with two methyl groups, whereas an anti-Markovnikov product would contain CH₂ and CH₃ groups (Scheme S1†). ¹H NMR spectroscopy revealed the formation of the anti-Markovnikov product; the quartet of triplets at 2.5 ppm corresponds to a CH group neighbouring a CH₂ and CH₃ group, and the two signals between 0.5 and 1 ppm originate from the CH₂, which couples to the protons of the vicinal chiral carbon atom. Thus, the conditions applied in this study favour an anti-Markovnikov product, most likely due to the lower steric hindrance of the intermediate state. All modifications in this study were complete after 60 min at 37 °C with quantitative conversions and close to 100% yields after work-up. The formation of anti-Markovnikov products was observed for all methacrylate additions as evidenced by the corresponding NMR spectra (Fig. S2–S14†).

In addition, the products were investigated by size exclusion chromatography (SEC) (Fig. 3). Unmodified h₂PDMS showed a monomodal trace with a dispersity (Đ) = 1.23. Upon modification a shift to higher molar mass was observed, while retaining narrow molar mass distributions for all hydrosilylation products, except HEMA-PDMS-HEMA. The reaction with HEMA resulted in a rather broad molar mass distribution (Đ = 1.71). Presumably, this could be the result of interactions with the column material and a non-suitable solvent system employed for the amphiphilic product obtained. However, ¹H NMR demonstrated quantitative conversion of the Si–H groups without the formation of any side products. To further elucidate the products formed, MALDI-ToF MS measurements were conducted.

Fig. 3 SEC elution traces of h₂PDMS and methacrylate (x) modified PDMS (x–PDMS–x; SEC eluent: CHCl₃ + 2% TEA).

Analysis of the MALDI-ToF MS spectra of the MMA hydrosilylation product revealed the molecular composition of the product with distributions, which are in agreement with the expected composition (Fig. 4). The products were analysed using dithranol as matrix and sodium iodide to improve the ionization. The molar mass increments (74.02 g mol⁻¹) were assigned to the DMS repeating units (Fig. 4 inset). End group analysis proved the successful introduction of MMA groups into the polymer, with chemical composition calculated according to (C₂H₆SiO)_n(C₇H₁₅SiO₂)₂O + Na⁺. No further distributions and thus side products were observed indicative of the high yields and selectivity of this reaction. The same observations were made for modifications with the other methacrylates (Fig. S15–S21†).

Fig. 4 MALDI-ToF MS spectrum of MMA-PDMS-MMA with the molecular composition (C₂H₆SiO)_n(C₇H₁₅SiO₂)₂O + Na⁺, where n represents the repeating unit of PDMS.

Synthesis of ABA triblock copolymers

Hydrosilylation was further employed for the synthesis of ABA triblock copolymers (Scheme 3). Poly(ethylene glycol)methacrylate (PEGMA; average M_n 300 g mol⁻¹) was selected as a methacrylate terminated polyether. The reaction was conducted according to the protocol established for the small organic methacrylates. Full conversion of h₂PDMS was reached within 90 min, as indicated by the disappearance of the corresponding Si–H signal (4.80 ppm) in the ¹H NMR spectrum (Fig. 5). In addition, even for the reaction with PEGMA exclusively the anti-Markovnikov product was obtained.

Fig. 5 ¹H NMR spectrum of PEG₆-b-PDMS₆-b-PEG₆ triblock copolymer in CDCl₃.

Scheme 3 Synthesis of ABA triblock copolymers using PEGMA and CCT oligomer, respectively.

SEC analysis further demonstrated the quantitative conversion of the starting materials (Fig. 6). A complete shift of the SEC trace to higher molar mass was observed following the reaction. The absence of the PEGMA signal proved the high efficiency of the hydrosilylation modification. A well-defined ABA triblock copolymer was obtained as suggested by the narrow molar mass distribution (M_n = 2200, Đ = 1.19).

Fig. 6 SEC elution traces of h₂PDMS, PEG₆MA and PEG₆-b-PDMS₆-b-PEG₆ triblock copolymer (SEC eluent: THF + 2% TEA).

MALDI-ToF MS spectrum showed a peak pattern typical for (block) copolymers with molar mass increments corresponding to both the DMS (74.02 g mol⁻¹) and EG (44.03 g mol⁻¹) repeating units (Fig. 7). The chemical composition was confirmed by the isotopic pattern. End group analysis revealed the formation of solely PEGMA modified PDMS with the chemical formula C₇H₁₅SiO₃(C₂H₄O)_m(C₂H₆SiO)_n(C₂H₄O)_oC₇H₁₅SiO₂ + Na⁺, where n, m and o represent the number of repeating units of DMS, EG and EG, respectively. For a detailed analysis, the peak at 931.48 m/z was selected corresponding to the formula C₇H₁₅SiO₃(C₂H₄O)₄(C₂H₆SiO)₃(C₂H₄O)₄C₇H₁₅SiO₂Na⁺. For a more comprehensive evaluation, the peaks in the inset in Fig. 7 are assigned with the corresponding number of repeating units. Thus, MALDI-ToF confirms that simple hydrosilylation can be used to synthesize amphiphilic copolymers containing silicone hydrophobic middle blocks.

Fig. 7 MALDI-ToF MS spectrum of PEG₆-b-PDMS₆-b-PEG₆ with the molecular composition C₇H₁₅SiO₃(C₂H₄O)_m(C₂H₆SiO)_n(C₂H₄O)_oC₇H₁₅SiO₂ + Na⁺, where n, m and o represent the number of repeating units of DMS, EG and EG, respectively.

To further demonstrate the versatility of the hydrosilylation reaction for transformation of a relatively unreactive vinyl group, structural demanding vinyl end-functionalized CCT macromonomers^27,28 (CCTP MMA dimer) were employed for the preparation of ABA triblock copolymers (Scheme 3). In contrast to the hydrosilylation reactions described in this study so far no reaction occurred at 37 °C, which is attributed to the steric hindrance of the substituents of the vinyl groups of CCT macromonomers. Thus, the reaction was conducted at elevated temperatures (100 °C) with a higher h₂PDMS-to-CCTP MMA dimer ratio. After 24 h full conversion of the Si–H groups was observed by ¹H NMR (Fig. S29†) and IR spectroscopy (Fig. S30†) by the disappearance of the Si–H signal at about 4.7 ppm and Si–H band at 2100 cm⁻¹, respectively. In addition, a shift of the SEC trace to higher molar mass was observed (Fig. S31†). This opens the way for formation of triblock copolymers from any CCTP product.

Conclusions

Seven different small organic methacrylates have been used to modify terminal hydride substituted PDMS via hydrosilylation in the presence of a commercial platinum(II) catalyst (Pt(dvs)). It was demonstrated that the reactions proceed to very high conversions over 60 min under mild reaction conditions. According to ¹H NMR spectroscopy and MALDI-ToF MS investigations, 100% conversions without the formation of side products were obtained for all methacrylates. ¹H NMR revealed the synthesis of anti-Markovnikov products. Moreover, hydrosilylation is described as an alternative approach for the synthesis of block copolymers. Well-defined block copolymers were obtained by modification with PEGMA, as proven by ¹H NMR spectroscopy, SEC and MALDI-ToF MS. Furthermore, adjustment of the reaction conditions enabled the synthesis of ABA triblock copolymers with sterically demanding vinyl terminated CCT macromonomers.

In summary, hydrosilylation represents a powerful tool for the fabrication of functional PDMS materials, including end-functional PDMS and triblock copolymers. The addition of Si–H can be compared to thiol–ene, S–H, chemistry which has found extensive use in polymer and materials synthesis.^7,9 The vast variety of commercially available hydride substituted PDMS and functional methacrylates in combination with the beneficial characteristics of the reaction, such as quantitative conversion at mild conditions, high selectivity and high tolerance towards various functionalities, makes hydrosilylation of methacrylates interesting for a broad range of applications. In particular, the combination of CCTP and hydrosilylation will give access to new exciting polymer systems and functionalization opportunities.

Experimental

Materials

Hydride terminated PDMS (h₂PDMS; average M_n 580 g mol⁻¹), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, toluene, methyl methacrylate (MMA), 2-ethyl hexyl methacrylate (EHMA), glycidyl methacrylate (GMA), lauryl methacrylate (LMA), butyl methacrylate (BMA), diethylene glycol methyl ether methacrylate (DEGMEMA), poly(ethylene glycol methyl ether) methacrylate (PEGMA, average M_n 300 g mol⁻¹), dithranol, sodium iodide and THF were purchased from Sigma-Aldrich and used as received. 2-Hydroxylethyl methacrylate (HEMA) was obtained from Sigma-Aldrich and purified by deionized water/hexane extraction. Platinum-divinyltetramethyldisiloxane (Pt(dvs)) was purchased from Gelest. The MMA macromonomer was synthesized according to literature procedure.²⁹

Instruments

IR spectra were recorded on a Bruker Vector 22 FTIR spectrometer. OPUS software was used to analyse absorbance data. Size exclusion chromatography measurements were performed on an Agilent 1260 Infinity Multi-Detector GPC system. ¹H NMR and ¹³C NMR were recorded on a Bruker DPX-300 and Bruker AC-250, with CDCl₃ as the solvent. The chemical shifts are given in ppm relative to the signal from residual non-deuterated solvent. For the MALDI measurements an Autoflex TOF/TOF apparatus (Bruker Daltonics, Bremen, Germany) was used.

Kinetic studies of hydrosilylation of methyl methacrylate

Hydrosilylation was performed at 100 °C, 70 °C and 37 °C. In all cases, up to 10 vials with each H₂PDMS (1 g, 1.72 mmol, 1 eq.), methyl methacrylate (0.36 g, 3.59 mmol, 2.1 eq.) and 11 μL of Pt(dvs) were prepared and stirred for a maximum of 120 min. At different time points samples were taken and the conversion of the Si–H bond was determined by ¹H NMR spectroscopy.

General procedure for the hydrosilylation of methacrylates

H₂PDMS (1 g, 1.72 mmol, 1 eq.), methacrylate (3.59 mmol, 2.1 eq.) and 11 μL of Pt(dvs) were added into a glass vial and stirred for 60 min at 37 °C. The brownish product was isolated by removal of excess monomer under reduced pressure.

Synthesis of methyl methacrylate functionalized PDMS (MMA-PDMS-MMA)

¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.65 (m, Si–CH₂), 0.93 (m, Si–CH₂), 1.20 (d, CH₃), 2.5 (sex, CH), 3.60 (s, O–CH₃) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 19 (Si–C), 22 (C–C), 30 (C–C), 50 (C–O), 175 (C=O) ppm. IR (cm⁻¹): 2961, 1768, 1257, 1196, 1013, 790, 702 cm⁻¹. GPC (CHCl₃): M_n = 690 g mol⁻¹, Đ = 1.42. MALDI-ToF MS (m/z): C₇H₁₅SiO₃(C₂H₆SiO)_nC₇H₁₅SiO₂·Na⁺, 579.30 (n = 3), 653.34 (n = 4), 727.38 (n = 5), 801.42 (n = 6), 875.46 (n = 7), 949.50 (n = 8), 1023.54 (n = 9).

Synthesis of 2-hydroxylethyl methacrylate functionalized PDMS (HEMA-PDMS-HEMA)

¹H NMR (CHCl₃): δ = 0.00 (s, Si–CH₃), 0.75 (m, Si–CH₂), 1.10 (m, Si–CH₂), 1.25 (m, CH₃), 2.58 (sex, CH), 3.94 (m, CH₂–OH), 4.25 (m, O=C–O–CH₂) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 19 (Si–C), 23 (C–C), 30 (C–C), 55 (C–O), 64 (C–O), 175 (C=O) ppm. IR (cm⁻¹): 2962, 1721, 1258, 1161, 1013, 790, 701. GPC (CHCl₃): M_n = 1200, Đ = 2.00. MALDI-ToF MS (m/z): C₈H₁₇SiO₄(C₂H₆SiO)_nC₈H₁₇SiO₃·Na⁺, 639.24 (n = 3), 713.26 (n = 4), 787.28 (n = 5), 861.30 (n = 6), 935.32 (n = 7), 1009.33 (n = 8).

Synthesis of glycidyl methacrylate functional PDMS (GMA-PDMS-GMA)

¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.70 (m, Si–CH₂), 1.10 (m, Si–CH₂), 1.20 (d, CH₃), 2.55 (sex, CH), 2.80 (m, O–CH₂), 3.20 (sex, O–CH), 3.95 (m, O=C–O–CH₂), 4.45 (m, O=C–O–CH₂) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 19 (Si–C), 22 (C–C), 35 (C–C), 44 (C–O), 49 (C–O), 63 (C–O) 178 (C=O) ppm. IR (cm⁻¹): 2961, 1741, 1435, 1258, 1203, 1015, 791, 701. GPC (CHCl₃): M_n = 1400, Đ = 1.18. MALDI-ToF MS (m/z): C₉H₁₇SiO₄(C₂H₆SiO)_nC₉H₁₇SiO₃·Na⁺, 589.37 (n = 2), 663.39 (n = 3), 737.41 (n = 4), 811.43 (n = 5), 885.45 (n = 6), 959.47 (n = 7), 1033.49 (n = 8).

Synthesis of lauryl methacrylate functionalized PDMS (LMA-PDMS-LMA)

¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.65 (m, Si–CH₂), 0.93 (m, Si–CH₂), 0.80 (t, CH₃) 1.20 (d, CH₃), 1.30 (m, CH₂) 2.5 (sex, CH), 4.00 (t, O=C–O–CH₂) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 9 (Si–C), 20, 22, 25, 30, 35 (C–C), 60 (C–O), 175 (C=O) ppm. IR (cm⁻¹): 2959, 2925, 2854, 1736, 1460, 1258, 1197, 1149, 1016, 793. GPC (CHCl₃): M_n = 1500, Đ = 1.12. MALDI-ToF MS (m/z): C₁₈H₃₇SiO₃(C₂H₆SiO)_nC₁₈H₃₇SiO₂·Na⁺, 813.58 (n = 2) 887.60 (n = 3), 961.62 (n = 4), 1035.64 (n = 5), 1109.60 (n = 6), 1183.69 (n = 7), 1257.70 (n = 8).

Synthesis of 2-ethyl hexyl methacrylate functionalized PDMS (EHMA-PDMS-EHMA)

¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.75 (m, Si–CH₂), 0.90 (t, CH₃) 1.00 (m, Si–CH₂), 1.20 (d, CH₃), 1.35 (m, CH₂) 2.55 (sex, CH), 4.00 (d, O=C–O–CH₂) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 9 (Si–C), 12, 19, 25, 35 (C–C), 63 (C–O), 175 (C=O) ppm. IR (cm⁻¹): 2960, 1735, 1461, 1258, 1196, 1148, 1016, 792. GPC (CHCl₃) g mol⁻¹: M_n = 1300, Đ = 1.16, MALDI-ToF MS (m/z) (g mol⁻¹): C₁₄H₂₉SiO₃(C₂H₆SiO)_nC₁₄H₂₉SiO₂·Na⁺, 627.41 (n = 1) 701.43 (n = 2) 775.45 (n = 3), 849.48 (n = 4), 923.50 (n = 5), 997.52 (n = 6), 1071.54 (n = 7).

Synthesis of butyl methacrylate functionalized PDMS (BMA-PDMS-BMA)

¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.75 (m, Si–CH₂), 0.90 (t, CH₃) 1.00 (m, Si–CH₂), 1.20 (d, CH₃), 1.42 (sex, CH₂), 1.55 (quin) 2.55 (sex, CH), 4.00 (t, O=C–O–CH₂) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 11 (Si–C), 20, 23, 28, 30 (C–C), 60 (C–O), 175 (C=O) ppm. IR (cm⁻¹): 2961, 1736, 1257, 1015, 791. GPC (CHCl₃): M_n = 1100, Đ = 1.17. MALDI-ToF MS (m/z): C₁₀H₂₁SiO₃(C₂H₆SiO)_nC₁₀H₂₁SiO₂·Na⁺, 589.33 (n = 2) 663.36 (n = 3), 733.38 (n = 4), 811.40 (n = 5), 885.43 (n = 6), 959.45 (n = 7), 1033.48 (n = 8).

Synthesis of diethylene glycol methyl ether methacrylate functionalized PDMS (DEGMEMA-PDMS-DEGMEMA)

¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.75 (m, Si–CH₂), 1.00 (m, Si–CH₂), 1.18 (d, CH₃), 2.55 (sex, CH), 3.40 (s, O–CH₃), 3.5 (t, O–CH₃), 3.60 (m, O–CH₃) 4.12 (t, O=C–O–CH₂) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 19 (Si–C), 22, 30 (C–C), 58, 62, 78, 70, 72 (C–O), 175 (C=O) ppm. IR (cm⁻¹): 2961, 1736, 1456, 1258, 1198, 1014, 791. GPC (CHCl₃): M_n = 1500, Đ = 1.15. MALDI-ToF MS (m/z): C₁₁H₂₃SiO₅(C₂H₆SiO)_nC₁₁H₂₃SiO₄·Na⁺, 681.33 (n = 2), 755.31 (n = 3), 829.31 (n = 4) 903.33 (n = 5), 977.35 (n = 6), 1051.37 (n = 7).

Synthesis of PEG₆-b-PDMS₆-b-PEG₆ triblock copolymer

H₂PDMS (1 g, 1.72 mmol, 1 eq.) and PEGMA (1.04 g, 3.46 mmol, 2.01 eq.) were dissolved in 1.5 mL toluene and 11 μL of Pt(dvs) were added into a glass vial and stirred for 60 min at 37 °C. Subsequently, toluene was evaporated under reduced pressure and 45 mL water were added and the solution was centrifuged for 12 min (7800 rpm). The supernatant was removed and the precipitate was dissolved in THF, the organic phase was dried over MgSO₄, filtered and the volatiles were removed under reduced pressure to give the ABA triblock copolymer. ¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.70 (m, Si–CH₂), 1.05 (m, Si–CH₂), 1.20 (d, CH₃), 2.55 (sex, CH), 3.46 (s, O–CH₃), 3.58 (m, O–CH₂), 4.25 (m, O=C–O–CH₂) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 18 (Si–C), 22 (C–C), 30 (C–C), 55, 60, 65, 70 (C–O) 175 (C=O) ppm. IR (cm⁻¹): 2960, 2876, 1734, 1455, 1258, 1199, 1015, 792. GPC (THF): M_n = 2200, Đ = 1.19. MALDI-ToF MS (m/z) (g mol⁻¹): C₇H₁₅SiO₃(C₂H₄O)_m(C₂H₆SiO)_n(C₂H₄O)_oC₇H₁₅SiO₂·Na⁺, 857.46 (m = 4, n = 2, o = 4), 901.49 (m = 5, n = 2, o = 4), 931.48 (m = 4, n = 3, o = 4), 945.52 (m = 5, n = 2, o = 5), 975.52 (m = 4, n = 3, o = 5), 1005.51 (m = 4, n = 4, o = 4), 1019.55 (m = 5, n = 3, o = 5), 1049.54 (m = 5, n = 4, o = 4), 1329.67 (m = 6, n = 6, o = 6).

Synthesis of PMMA₂-b-PDMS₆-b-PMMA₂ triblock copolymer

H₂PDMS (5 g, 8.6 mmol, 1 eq.), MMA macromer (4.3 g, 21.5 mmol, 2.5 eq.) and 33 μL of Pt(dvs) were added into a glass vial and stirred for 24 h at 100 °C. The product was isolated by removal of excess monomer under reduced pressure at 137 °C. ¹H NMR (CHCl₃): δ = 0.00 (m, Si–CH₃), 0.72 (m, Si–CH₂), 0.85 (m, Si–CH₂), 1.44 (d, CH₃), 1.67 (m, CH₂), 2.08 (m, CH₂), 2.51 (m, CH), 3.60 (s, O–CH₃) ppm. ¹³C NMR (CHCl₃): δ = 0.00 (Si–C), 21 (Si–C), 23 (C–C), 33 (C–C), 39 (C–C), 50 (C–O), 177 (C=O) ppm. IR (cm⁻¹): 2980, 1700, 1250, 1180, 1003, 790, 70 cm⁻¹. GPC (THF): M_n = 1400 g mol⁻¹, Đ = 2.10.

Acknowledgements

NR gratefully acknowledges the Thai Royal Government (DPST) for financial support DMH is a Wolfson/Royal Society Fellow and equipment used in this research was parted funded through Advantage West Midlands (AWM) Science City Initiative and part funded by the ERDF.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: ¹H and ¹³C NMR, IR, MALDI-ToF MS spectra. See DOI: 10.1039/c4ra14956d

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