The Aggregation Behaviour of Polyisoprene Pluronic Graft Copolymers in Selective Solvents

Transcription

1 The Aggregation Behaviour of Polyisoprene Pluronic Graft Copolymers in Selective Solvents Shirin Alexander *,, Terence Cosgrove, *, Wiebe M de Vos,,ʂ Thomas C. Castle, and Stuart W. Prescott, School of Chemistry, University of Bristol, Bristol, BS8 1TS, United Kingdom and Revolymer (U.K.) Ltd, 1 New Tech Square, Zone 2, Deeside Industrial Park, Deeside, Flintshire, CH5 2NT, United Kingdom School of Chemical Engineering, UNSW Australia, UNSW Sydney 2052, NSW, Australia ʂ Membrane Science and Technology, University of Twente, the Netherlands College of Engineering, Swansea University, Swansea, SA2 8PP, UK Characterisation of modified Pluronics Nuclear magnetic resonance spectroscopy (NMR) & heteronuclear single-quantum correlation spectroscopy (HSQC) The 1 H NMR and HSQC spectra of the samples were measured on a Varian 400 MHz spectrometer with sample concentration of 5 w/v % in CDCl, unless mentioned otherwise. HSQC experiment correlates a hydrogen atom that is directly bound to a carbon atom (of a CHx complex) and therefore facilitates the interpretation of the structure. Data are shown in Figure S1. -CH signals of the PPO block (12) occur at δ ~ 1.1 ppm and -CH2 signals at δ ~.-.6 ppm. -CH peak of the end group (5) appears at. ppm which overlaps with the methylene group signals. The signal related the methyl end group is located at. and 59.1ppm which shown by a circle in the HSQC spectrum. As the methyl peak at. ppm overlaps with the -CH2 peaks of the PEG blocks, it is difficult to accurately identify the methyl proton in the spectrum. Due to the low ratio of the end group (-CH) to the PEO-PPO blocks, the signal has a very low intensity but it demonstrates the presence of the methyl group. The methyl group of the PPO block (12 at δ ~ 1.05 ppm) was used to assess the degree of methylation of the polymer. However, obtaining the precise percentage of methylation using * Corresponding authors. terence.cosgrove@bristol.ac.uk, s.alexander@swansea.ac.uk 1

2 1 H NMR was not possible because this peak overlaps with the end group peaks attributed to the -CH2 peaks. The integrals of these protons can be compared with the integrals from the protons of the PEG block at δ~.6 ppm in order to gain a value for the molecular weight of the polymers. The molecular weights of the unmodified and modified P10, and P12 were calculated by NMR and the values are 5046, and 5872 g.mol -1 for the unmodified polymers and 5064, and 5909 g.mol -1 for the products respectively. R5(M10).esp M01(m,,2,6,7,9,10) H 11 O 10 O 8 CH O CH 12 O 1 2.0(5) 1.05(12) Chemical Shift (ppm) sk1476_r1_ghsqc_001.fid.esp F1 Chemical Shift (ppm) F2 Chemical Shift (ppm) Figure S1. 1 H NMR and HSQC spectrum of modified Pluronic P

3 MALDI-TOF mass spectrometry All measurements were carried out using an Applied Biosystems 4700 Proteomics Analyzer (TOF), with a 200 Hz Neodinium YAG laser, operating at 55 nm. The spectrometer was operated in positive ion mode. Reflector mode measurements were used. Each sample was prepared by dissolving polymer sample (20 mg) in chloroform (1 ml). Dithranol was dissolved in THF (1 ml) was used as the matrix, and NaCl (10 mg) in deionised water was used as the counter-ion (unless stated otherwise). The molecular weights of the unmodified and modified Pluronics were determined using MALDI. For the methylated Pluronics a single broad peak was observed with a similar molecular weight distribution to the unmodified Pluronics but shifted to slightly higher molecular weight. The MALDI data showed addition of 161 and 245 g mol -1 to the molecular weight of the Pluronic P10 and P12 respectively. An overlay of the MALDI spectra of the Pluronic P12 and the modified P12 is shown in Figure S2. As the spectra of theses copolymers are very broad, it was not possible to identify the expected un-functional (f=0), mono-methylated (f=1) and unreacted bi-functional (f=2) species individually P12 Me-P %Intensity Mass(m/z) Figure S2: MALDI spectrum of unmodified Pluronic P12 which is centred at g mol -1 and modified P12 centred at g mol -1 with PDI = Characterisation of Pluronic Graft Copolymers The NMR of the product is shown in Figure S. The peaks corresponding to the chains and the backbone are presented in the spectrum. -CH peak of the polyisoprene (1, 21) is located

4 at δ ~ 1.6 ppm while -CH2 (16, 27) and =CH (26, 22) signals are at δ ~ 2.0 and 5.1 ppm respectively. 4

5 R4 after dialysis.esp H C H C a 2 H C CH b O O 20.62(,2,6,5,9,8) 19 O 29 CH 0 O 10.6(5a) 2.02(16,27) 1.66(1,21) 1.10(1) 9 8 O 7 6 O 1 5 m n 2 H C 1 O 4 m CH 5a 5.10(26,22) Chemical Shift (ppm) Figure S: 1 H NMR spectra of the PIP-graft-Pluronic P12 in CDCl. Determination of grafting efficiency by NMR Determination of total number of Pluronic chains per PIP backbone The key peak at δ ~ 1.1 ppm is from the CH group of the PPO, which has protons per propylene oxide unit, and the peak at δ ~ 5.1 ppm is from the C=CH of the polyisoprene backbone; this has only one proton per isoprene unit and is the most distinct polyisoprene peak. As it shown in Figure S4, both free and grafted Pluronic chains are present in the product despite purification an attempt to remove them by reprecipiation and dialysis. Using NMR, the total ratio of Pluronic chains (grafted and ungrafted) to polyisoprene (PIP) backbone can be determined. 5

6 Figure S4: Schematic of a grafted product which illustrates free and grafted chains. Number of Pluronic chains per backbone (nc) = nsc/nbb (1) where nsc is the total number of Pluronic side chains and nbb the total number of the backbone and nc n n sc bb N bb N sc CH CH (2) where NSC is the number propylene oxide units per Pluronic chain, as the mass of each propylene oxide unit is 58 gmol -1, the average Mn of the Pluronic (e.g P12) is 6000 gmol -1, and PPO unit has 70% of the total weight of the Pluronic, so NSC = 72. Nbb is the number of isoprene units per polyisoprene chain: isoprene unit has a mass of 68 gmol -1 and the backbone has Mn of 25,000 gmol -1. So Nbb = 48 (taking into consideration that the backbone has 10 MA groups with Mn = 11 gmol -1 ). The ratio of the integrals at 1.1 ppm (CH) and 5.1 ppm (CH) can be obtained from the NMR spectrum. Determination of number of grafted Pluronic chains per PIP backbone The number of Pluronic chains grafted onto a single backbone (ng), can be calculated using Pulsed Field Gradient Stimulated Echo NMR (PFGSE-NMR). PFGSE-NMR measurements were carried out at 298K on a Bruker DSX-00MHz spectrometer with a Diff 0 field gradient probe using a 5 mm 1 H/ 2 H coil insert. The gradient pulse duration ( δ ) was set to 1-2 ms and the magnetic field gradient (G) was increased from 0.05 to 10 T m -1. The diffusion time (Δ) was set to 150 ms. Calibration of the 6

7 instrument was carried out using a water/methanol reference sample. The stimulated-echo signals were Fourier-transformed and the resulting spectra (signal area as a function of gradient strength) were used to calculate the diffusion coefficients (D / m 2.s -1 ) for each chemically distinct species. The data can be fitted to 2 or diffusion ceofficients, which then can be related to each component (as they have different sizes) and the fraction of that component in the system can be obtained. The smaller component typically has the same diffusion coefficient as the ungrafted Pluronic (large diffusion coefficient), whereas the larger component corresponds to the Pluronic chains which are grafted to the backbone (small diffusion coefficient). The diffusion coefficient of the grafted Pluronic is comparable with the diffusion coefficient of the backbone. So in this case the CH of the grafted Pluronic was termed as CHb: CH CH b slow fraction () By substituting Equation () into Equation (2), the number of grafts can be obtained: ng n n sc bb N bb N sc CH b CH (4) The diffusion data for grafted P10 and P12 was fitted to three distinct diffusion coefficients: one corresponds to the ungrafted Pluronics that have the largest diffusion coefficient (small component), one is due to the grafted Pluronics that have the same diffusion coefficient as the grafted backbone, and the third one (smallest diffusion coefficient), could be due to partially cross-linked backbone as is shown in Table S1. Table S1: Grafting efficiency of the two Pluronics into the PIP backbone. Sample Equivalents of Plu /MA % Crosslinked Plu Total Pluronic chains / PIP Grafted Pluronic chains / PIP PIP-g-P PIP-g-P

8 Gel Permeation Chromatography (GPC) The measurements were carried out by Smithers Rapra Technology Limited, using a Viscotek TDA model 01 refractive index detector. Analysis of all of the polymers was carried out using THF as the solvent at a flow rate of 1.0 ml/min and at a constant temperature of 0 C, with a 5 μm, 0 cm PLgel guard and 2 mixed bed-d columns. All the samples were prepared to give concentration of 2 mg/ml. The solutions were filtered through a 0.2 μm polyamide membrane, prior to the chromatography. Figure S5 shows an overlay of the computed molecular weight distribution for the starting materials and the grafted sample obtained using GPC. Analysis of the Pluronic P12 revealed the presence of a significant proportion of a lower molecular weight component, that could be diblock poly(propylene oxide-block-ethylene oxide) copolymer generated during the commercial manufacture of the triblock poly(ethylene oxide-block-propylene oxide-block-ethylene oxide) copolymer. Analysis of the AGC sample (shown in pink in Figure S5) suggests the desired graft copolymer was formed, though a significant proportion of ungrafted Pluronic was present matching the PFGSE-NMR data. There is shoulder on the AGC peak which is believed is to be an artefact due to a small proportion of the sample being of a higher molecular weight than intended for analysis by GPC column used resulting in a distortion of the shape of the graph. The higher molecular weight portion of the AGC sample is likely to be lightly cross-linked material formed by the reaction of Pluronic that was not methyl functionalised (f=2) present as an impurity in the graft.. Pluronic Backbone AGC Chain-Extended AGbackbone Figure S5: Overlay of molecular weight distribution of polyisoprene backbone ( ), modified P12 ( ) and the PIP-g-P12 ( ). 8

9 A similar molecular weight distribution was obtained for AGC samples with Pluronic P10 grafts. 9