Synthesis of Controlled Polymer Nanospheres by a Reversible Addition- Fragmentation Chain Transfer (RAFT) iniemulsion Polymerization Huije Lee, Sang Eun Shim, Byung H. Lee, Soonja Choe* Department of Chemical Engineering, nha University, 253 Yonghyundong, Namgu, ncheon 42-751, S. Korea
Objectives To apply a RAFT agent bearing carboxyl acid group to miniemulsion polymerization To obtain stability-enhanced functionalized polymer nanospheres with narrow PD via RAFT method ntroduction Synthetic methods of functionalized particles Copolymerization with ionic monomers Polymerization with charge endowing surfactants or initiators ulti-step process in which functional groups are introduced after the colloid synthesis Applications Colloidal drug carrier, detoxification Solid-phase supports in biomedical and biochemical fields nformation technology aterials for humidity sensors.
Living Free-Radical Polymerizations LRP ethods Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT) Nitroxide-ediated Polymerization (NP) Atom-Transfer Radical Polymerization (ATRP) Characteristics of LRP Precise control of n & PD Precise control of stereostructure Synthesis of highly functional block copolymers Tailor-made polymer products Advanced materials applicable to T, BT, and NT
Trend in LRPs Timeline of LRP 19 198 82 86 199 95 98 2 Stable Radicals: Gomberg Living Radical Polymerization (niferter( niferter): Otsu NP: Solomon & Rizzardo ATRP: atyjaszewski RAFT: Rizzardo Research nterest in LRPs 1. Homogeneous: Bulk / Solution Heterogeneous: iniemulsion Heterogeneous: Emulsion 2. olecular Design in Homogeneous Polymerization
RAFT Polymerization Generic RAFT Agent Structure X Weak single bond X R R is free radical leaving group (R must also be able to reinitiate polymerization) Reactive double bond Z Z modifies addition and fragmentation rates S C S CH 2 S C S CH 2 (4-Toluic acid) dithiobenzoate, TADB Benzyl dithiobenzoate, BDB
echanism of RAFT Polymerization nitiation nitiator P n Chain transfer P n + S S R Ph K add K -add P n S Ph S R K β K -β P n S Ph S + R Reinitiation R k i R k p P m Chain equilibration P n + S Ph S P n P m S Ph S P n P m S Ph S + P n Termination P n + P m k t dead polymer
RAFT Polymerization Problems in conventional emulsion polymerization Lack of colloidal stability Retardation of polymerization rate Formation of a conspicuous red layer at the beginning of polymerization Broad molecular weight distribution (higher than 1.5) Techniques utilized to overcome the problems Semi-batch process Seeded emulsion polymerization iniemulsion polymerization
Experimental Recipe - Reaction medium : double distilled de-ionized (DD) water - onomer : ethyl methacrylate, Styrene - Surfactant : Sodium dodecyl sulfate (SDS) - Cosurfactant : Hexadecane - nitiator : 2,2 Azobis(isobutyronitrile) (ABN) - RAFT agent : (4-Toluic acid) dithiobenzoate, Benzyl dithiobenzoate Conditions - 6 8 O C, 22 rpm - [RAFT]/[ABN] =, 1, 2, 5 Characterizations - olecular weight measurement : GPC HPLC pump (WATERS 51), Viscometer (Viscotex) - Particle size and Zeta potential : Zetasizer (alvern, Zetasizer 4) - Conductivity measurement : Conductivity meter (KE, G - 115) - Analysis of particle size & morphology : SE (Hitachi, S - 43)
Polymerization Kinetics : Effect of Reaction Temperature ([TADB]/[ABN]=1), PA 1. 3. Fractional Conversion.8.6.4.2 6 o C 7 o C 8 o C Ln{[]/[]} 2.5 2. 1.5 1..5 6 o C 7 o C 8 o C. 2 4 6 8 1 12 14 16 18 Polymerization Time (min). 2 4 6 8 1 12 14 16 18 Polymerization Time (min)
olecular Weight Evolution : Effect of Reaction Temperature ([TADB]/[ABN]=1), PA Number-average olecular Weight 1 9 8 7 6 5 4 3 2..2.4.6.8 1. Fractional Conversion 6 o C 7 o C 8 o C PD 2.8 2.6 2.4 2.2 2. 1.8 1.6 1.4 1.2 1...2.4.6.8 1. Fractional Conversion 6 o C 7 o C 8 o C
Polymerization Kinetics : Effect of [TADB]/[ABN], 8 o C PA Fractional Conversion 1..8.6.4.2 1 2 5 Ln{[]/[]} 3. 2.5 2. 1.5 1..5 1 2 5. 2 4 6 8 1 12 Polymerizaion Time (min). 2 4 6 8 1 12 Polymerization Time (min)
olecular Weight Evolution : Effect of [TADB]/[ABN], 8 o C PA Number Average olecular Weight 1 9 8 7 6 5 4 3 2 1..2.4.6.8 1. Fractional Conversion 1 2 5 PD 5. 4. 2. 1 2 1.8 5 1.6 1.4 1.2 1...2.4.6.8 1. Fractional Conversion
GPC Traces & SE Photograph of PA : 2hr, 8 o C [TADB]/[ABN] 1 2 5 5 1 15 2 25 Retention Time (min) [TADB]/[ABN]=1, 9nm
Synthetic echanism a d H 2 O b Stirring c Heating COO- COO- H 2 O COO - ore H 2 O H 2 O onomer Surfactant nitiator RAFT agent (TADB)
Particle Size Distribution of PA Latex : 2hr, 8 o C 52 1 [TADB] / [ABN] = [TADB] / [ABN] = 1 [TADB] / [ABN] = 2 [TADB] / [ABN] = 5 12 11 1 ntensity Size (nm) 9 8 7 6 5 1 2 3 4 5 6 Size (nm) 4 1 2 3 4 5 [TADB] / [ABN]
Zeta Potential & Conductivity of PA Latex : 2hr, 8 o C -2 3. ntensity 5 2 1 [TADB] / [ABN] = [TADB] / [ABN] = 1 [TADB] / [ABN] = 2 [TADB] / [ABN] = 5 Zeta potential (mv) -25-3 -35-4 -45 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 Conductivity (ms/cm) -7-6 -5-4 -3-2 -1 1 2 3 4 5-5 2. 1 2 3 4 5 6 Zeta potential (mv) [TADB] / [ABN]
Polymerization Characteristics : Effect of carboxyl acid [RAFT]/[ABN] = 1.3, 8, PS Ln{[] /[]} 2. 1.8 1.6 1.4 1.2 1..8.6.4.2 TADB BDB. 1 2 3 4 5 6 7 8 n 9 8 7 6 5 4 3 2 1 TADB BDB..1.2.3.4.5.6.7.8 PD 2.6 2.4 2.2 2. 1.8 1.6 1.4 1.2 TADB BDB..1.2.3.4.5.6.7.8 Reaction Time (hr) Fractional Conversion Fractional Conversion TADB : S C S CH 2 BDB : S C S CH 2
nfluence of RAFT agents : Particle size, Zeta potential, and Conductivity (8hr), PS [RAFT]/[nitiator] = 1.3 TABD BDB Particle Size (nm) Zeta potential (mv) Conductivity (ms( ms/cm) 125.1 135.7-48.2-44.5 2.6 2.48 SE images
Polymerization Characteristics : Effect of [TADB]/[ABN], 8, PS Ln{[] o /[]} 1.6 1.4 1.2 1..8.6.4.2. 1 2 3 4 5 6 7 8 Reaction Time (hr) 1 2 3 Number Average olecular Weight 12 1 8 2 15 1 5 1 2 3..1.2.3.4.5.6.7.8 Fractional Conversion PD 3.5 1 2 3 3. 2.4 2.2 2. 1.8 1.6 1.4 1.2 1...1.2.3.4.5.6.7.8 Fractional Conversion
Average Particle Size & SE Photographs of PS : 8hr, 8 o C 13 Average Particle Size (nm) 12 11 1 9 [TADB]/[ABN]=, 9nm 1 2 3 4 [TADB]/[ABN] [TADB]/[ABN]=3, 125nm
Zeta Potential & Conductivity of PS Latex : 8hr, 8 o C -48 4.3 Zeta Potential (mv) -49-5 -51-52 -53-54 Conductivity (ms/cm) 4.2 4.1 4. 3.9 3.8 3.7 3.6 3.5-55 1 2 3 3.4 1 2 3 [TADB]/[ABN] [TADB]/[ABN]
Conclusions A linear increase in n with respect to the conversion is observed, indicating the nature of living (controlled) radical polymerization. The PA-system - The higher the temperature, the faster conversion, the lower n and PD are obtained. - As the ratio of [TABD]/[ABN] increases, the conversion, molecular weight, molecular weight distribution, and particle size decrease. - With the ratio of [TABD]/[ABN], the zeta potential & conductivity increase, i.e. the stability of the PA latex is enhanced.
Conclusions The PS-system - A BDB (w/o carboxyl acid functionalized)-added system leads to slower conversion, similar n and PD, and larger particle size, however, decreases the zeta potential and conductivity. - As the ratio of [TABD]/[ABN] increases, the conversion, molecular weight, and molecular weight distribution decrease, however, particle size increases. - With the ratio of [TABD]/[ABN], the zeta potential & conductivity increase, i.e. the stability of the PS latex is enhanced. The polymer nanospheres functionalized with carboxylic acid group can be prepared by a novel mechanism.