Supplementary Material

Zwitterionic Polymer-Grafted MicrospheresPrepared by RAFT Polymerization

Hiromi Kitano,a* Ken-ichiTokuwa,aHarukaUeno,aLifu Li,a Yoshiyuki Saruwatarib

aDepartment of Applied Chemistry, Graduate School of Science and Engineering, University of Toyama, Toyama 930-8555, Japan

bR & D Laboratory, Osaka Organic Chemical Industry Ltd., Kashiwara 582-0020, Japan

S1. Effect of NaCl on the-potential and hydrodynamic diameter of MSs.

(a) (b)

Figure S1ζ-Potential and Dhvalues of polymer-modified microspheres at various concentrations of NaCl and 25 oC. (a) PSSNa-MSand (b) PMOETAC-MS. [PSSNa-MS] =0.01 wt% and [PMOETAC-MS] = 0.01 wt%. [NaCl] = 0, 10, 20, 40, 60, 100 and 150 mM.

S2. Effect of NaCl and proteins on relative hydrodynamic diameter of MSs.

(a) (b)

(c) (d)

FigureS2 Relative Dhvalues of PMOETAC-MS and PSSNa-MS in the presence of BSAand lysozyme at 25 oC.PMOETAC-MS (0.01 wt%) in the presence of (a) BSA and (b) lysozyme. PSSNa-MS (0.01 wt%) in the presence of (c) BSA and (d) lysozyme. [NaCl] = 0.10 M. [BSA] = 4.5 mg/mL. [Lysozyme] = 4.5 mg/mL. The Dh values of microspheres were normalized by that without any additives. The symbol, *, denotes the Dh after incubation inthe indicated solution for 1 h.

S3. Refractive index of polymer-graftedmicrospheres.

At first, the surface density of PCMB graft chain (brush) on the PBAmicrosphere(PCMB-MS) was determined. The DP value of PCMB-CTA was determined to be 87 by GPC. The elemental analyses of the PCMB-MS indicated that thePCMB-PBAblock copolymer was composed of 87 residues of CMB and585 residues of BA. Therefore, the molecular weight of PCMB and PBA blocks were 2.1104 and 7.5104, respectively.

The hydrodynamic radius of PCMB-MS was estimated to be 65.5 nm by theDLS measurements. It was previously reported that the length of PCMB brush on the silica micro-particle was 63.6 % of full-stretching[S1]. Taking account of the length of vinyl group (0.254 nm), the length of PCMB brush(DP = 87; full-stretched length, 22.1 nm) in the corona of microspherewas assumed to be 13.9 (= 22.10.636) nm. Consequently, the volume of corona (PCMB brush layer) on theMS (vcorona) was estimated to be 6.0x10-16 mL using equation (S1).

vcorona = (4/3)  (r23-r13) (S1)

wherer2 and r1 are the hydrodynamic radii of PCMB-MS (65.5 nm) and PBA core((65.5–13.9 =) 51.6 nm), respectively (Figure S3).

The volume of core composed of PBA (vcore) was given as equation (S2), where X is the number of block copolymer in the microsphere.

(7.5104X)/ NAPBA= (4/3)r13 (S2)

The density of PBA core (PBA) was 1.087 g/cm3, and NA is the Avogadro number. Therefore, X and thegraft density of PCMB were estimated as 5.0103and 0.15 chain/nm2, respectively, and the volume of the core (vcore) was calculated to be 5.810-16mL.

The weight of one microsphere (w) was determined to be 8.010-16 g using equation (S3).

w = (2.1104 + 7.5104)5.0103 / NA (S3)

Since the dispersion was 18.1 weight%, the number of microspheres in 1 mL of thedispersion (N) was determined to be 2.31014.

The volume of PCMB brush in themicrosphere (vPCMB) was estimated to be 1.310-16 mL using equation (S4), where the density of PCMB was assumed to be the same as that of PMPC (1.30 g/cm3)[S2].

vPCMB= 2.1104 5.0103 / (NA 1.30) (S4)

Therefore, the volume of water in the corona (vwater) was given as

vwater = vcorona - vPCMB= 6.010-16– 1.310-16 = 4.710-16mL. (S5)

Consequently, the total volume of microspheres in 1 mL of dispersion (V) was determined as

V = (vcore + vwater + vPCMB) N = 0.28 mL. (S6)

Assuming that the refractive index of the corona (ncorona) is simply the volume-proportional summation of the refractive indices of water and polymer chains (S7), the ncorona value could be determinedto be 1.372.

ncorona = (vwaternwater+ vPCMBnPCMB)/vcorona (S7)

By the similar assumption, the average refractive index of the polymer-modified microsphere (nav) (S8) could be determined to be 1.418.

nav = (nPBAvPBA + ncoronavcorona)/vPCMB-MS (S8)

where the nwater, nPCMB and nPBA values are 1.333, 1.49 (n value for poly(methylmethacrylate))[S3] and 1.466, respectively. The apparent refractive index of the dispersion (np) is given as

np = nav (VPCMB-MS /V) + ns[1- (VPCMB-MS /V)] = nav+ ns (1-) (S9)

whereVand VPCMB-MS denote the total volume of the dispersion and microspheres, respectively, in 1 mL of thedispersion.

The volume fraction of thePCMB-modified MS (VPCMB-MS / V) was 0.28 (S6). Therefore, the np value was approximated to be 1.35.Consequently, the Dobs was estimated as 174 nm using equation (S10), where the peak wavelength (p)was 384 nm (Figure S4).

Dobs = (3/8)0.5 (p/np) (S10)

In a similar manner, the average refractive index (np) of PMA-MS dispersion was estimated to be 1.336 at 4.16 weight%. The peak wavelength (p) was 579 nm (Figure 5 (b) in the text) and,therefore, the Dobs value for thePMA-MS dispersion was determined to be 265 nm using equation (S10).

[S1]Suzuki H, Murou M, Kitano H, Ohno K, Saruwatari Y (2011)ColloidsSurf. B: Biointerfaces 84:111-116.

[S2] Iwata R, Suk-In P, Hoven VP, Takahara A, Akiyoshi K, Iwasaki Y (2004)Biomacromolecules5: 2308-2314.

[S2]Brandrup J, Immergut EH, Grulke EA, Abe A, Bloch D, Polymer Handbook, 4th Edition,Wiley-Interscience, 2003.

Figure S3Image ofvcorona, vcore, vPCMB and vH2O.

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