Controlled Surface-Initiated Grafting of Poly(caprolactone)

to Silica Nanoparticles for Oil encapsulationRichard R. Craft1, Christopher B. Keller2, Scott M. Grayson*1Stony Brook University, Stonybrook, NY.2,*Tulane University, New Orleans, LA.

Thanks to the the Scmehl group for the use of theirIR,and the Schantz group for the use of their TGA.Thanks to Chris Keller for guidance.We thank the National Science Foundation for financialsupport through grants DMR-1460637 and IIA-1430280

Overall Goals• To control the grafting density of ε-caprolactone polymer chains grafted from SiO2-GPS

through surface-initiated ring opening polymerization (SIROP). • To determine variation in grafting density produced by functionalizing nanoparticles with

fractions of unreactive OTS , as a blocking agent, in addition to GPS.

Specific Aims• Determination of the mass of grafted poly(caprolactone) by comparison with in-situ

poly(caprolactone)• Calculation of grafting density through mass loss of attached poly(caprolactone)• To achieve high molecular weight poly(caprolactone) with a low dispersity• To produce and quantify variation in number of grafting sites due to OTS

functionalization

Following the work of Dr. Muhammad Ejaz, Silica nanoparticles (SiO2) are functionalized with 3-gylcidoxypropyltriethoxysilane (GPS). Then via surface-initiated ring opening polymerization(SIROP) of ε-caprolactone, poly(caprolactone) (PCL) chains are grafted- from the functionalizednanaparticles . A polar block may be added which allows the grafted particles to act asamphiphilic micelles, as shown by Ejaz et al.2 The amphiphilicity of the particles is controlled, inpart, by the length of the PCL chain which forms the nonpolar region. The pore size of thenanoparticle’s corona would be dependent on the density of caprolactone grafting sites on itssurface. Through comparison of particles functionalized with some ratio of GPS and OTS, andthose with only GPS, information is gained regarding the portion of available sites as well as thedegree of control which can be established through this mechanism

Background

130°C, 7 hours

110°C, 7 hours, 3:1 GPS:OTS

100°C, 7 hours, 1:1 GPS:OTS

In FTIR spectra poly(caprolactone) is characterized by anester peak at 1734 cm-1 and a weak C-H peak at 2914 cm-1 .Anisole appears to suppress the polymerization of ε-caprolactone, at high dilution .Longer reaction times don’t appear to improve this in anyappreciable way.Temperatures as much as 30 °C lower don’t significantlyimpact ε-caprolactone grafting.

60°C, 65 hours

With anisole, 130 °C, 7 hours

MALDI-TOF of free PCL

Introduction

AbstractEjaz et al (2015) demonstrated the potential for silica nanoparticle-based oil dispersants. Incontrast to traditional dispersants, such dispersants maintain emulsion and structural integrity atmuch greater dilution.2 Through control of grafting density and length of the polymer chainsgrafted to the nanoparticle surface, the pore size is altered, potentially affecting its encapsulationability.

With anisole, 130 °C, 24 hours

1Muhammad Ejaz, A. M. A., Scott M. Grayson, Amphiphilic hyperbranched polyglycerol-block-polycaprolactone copolymer-grafted nanoparticles with improved encapsulation properties. Reactive and Functional Polymers 2016, 102, 39-46.2Muhammad Ejaz, A. M. A., Karolina A. Kosakowska, and Scott M. Grayson, Modular amphiphilic copolymer-grafted nanoparticles: "nanoparticle micelle" behavior utility as dispersants. Polymer Chemistry 2015, 6, 7749-7757.

+

SiO2 nanoparticle grafted SiO2 nanoparticle

• Anisole, in the volume used, impedes ε-caprolactone polymerization• Poly(caprolactone) can be grafted at temperatures as low as 60 °C, given an

adequately long time frame• The GPS:OTS ratios used do not allow control over grafting density, suggesting that

relatively few of the available grafting sites are used

• Sonication at various intensities should be applied to the grafted nanoparticles, so that a threshold for their degradation may be established

• Proportionally greater amounts of OTS could be used successively to more exactly estimate the number of grafting sites

• Solvents could be tested as a control mechanism• Hyperbranched poly(ethylene glycol) could be added as a polar block so that the effects

of any polymerization control mechanism could be observed in terms of encapsulation ability and stability (Ejaz et al 2016)1

Pre-SIROP

FTIR Comparison

1000 2000 3000 4000 5000 6000 7000 8000 m/z

3239.7383125.5863011.4502897.368

2783.266

3261.7103147.6223033.4392919.2182805.060

2750 2850 2950 3050 3150 3250

114.102

Average molecule weight of monomerTheoretical: 114.144 g/molExperimental: 114.102 g/mol

Mn = 3359.64 g/molMw = 3398.90 g/molĐ = 1.0144

NMR of Free PCL TGA of grafted particles

Further Research

Conclusions

References

Acknowledgements

Poly(caprolactone) auto-ignites at 204°C, GPS at 231°C. Any mass change which occurs between these temperatures can be wholly attributed to poly(caprolactone).

130°C, 24 hours, anisole, 0.28% mass loss

110°C, 7 hours, 3:1 GPS:OTS, 0.98% mass loss

130°C, 7 hours, 0.92% mass loss

130°C, 7 hours

130°C, 24 hours, anisole

Unpolymerized ε-caprolactone

BC

BF

C

D

EAPeaks associated with poly(caprolactone) have notably higherintegration and greater splitting in the sample which was runfor 7 hours without anisole. (C, F, E, and A)The sample which was run for 24 hours in anisole also showsgreater presence of peaks characteristic of ε-caprolactone (Iand G)

BD

IH

G

DH

FI

EG A