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Extramural Research

2000 Progress Report: Nonionic Surfactants for Dispersion Polymerizations in Carbon Dioxide

EPA Grant Number: R826115
Title: Nonionic Surfactants for Dispersion Polymerizations in Carbon Dioxide
Investigators: DeSimone, Joseph M.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Karn, Barbara
Project Period: November 1, 1997 through October 31, 2000
Project Period Covered by this Report: November 1, 1999 through October 31, 2000
Project Amount: $370,000
RFA: Technology for a Sustainable Environment (1997)
Research Category: Nanotechnology , Pollution Prevention/Sustainable Development

Description:

Objective:

More than 30 billion pounds of organic and halogenated solvents are used world-wide each year as process aids, cleaning agents, and dispersants, and solvent-intensive industries are considering alternatives that can reduce or eliminate the negative impact that solvent emissions can have on the environment. Recently, the design and synthesis of surfactant molecules that are active in CO2 has enabled a variety f new processes that will reduce hazardous waste production and emission. With this innovation, we have demonstrated that CO2 can be used as a replacement for more hazardous volatile organic compounds (VOCs) and chlorofluorocarbons (CFCs) that are traditionally used as solvents in the polymer industry. The key feature of this work has been the rational design and utilization of surfactants, or soaps, which are amphiphilic and interfacially active in a CO2 continuous phase. It is apparent that the widespread use of CO2 by industries will depend strongly on the design and efficient synthesis of effective surfactants (amphilphilic macromolecules that act as soaps in CO2) for a variety for applications. This pursuit is the main focus of this proposal.

Progress Summary:

A block copolymer composed of CO2-phobic polyvinylacetate (PVAc, 10.3 kDa) and a CO2-philic fluorinated octyl acrylate (PFOA, 43.1 kDa) of average effective molecular weight 90.4 kDa has been studied by time of flight small angle neutron scattering (SANS) in supercritical CO2(sc-CO2) at 65?C [1-3]. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of sc-CO2 by profiling pressure, so that the block copolymer, in a semidilute solution, finds sc-CO2 a good solvent at high pressure and a poor solvent at low pressure. At high pressures, the copolymer is in a monomeric state with a random coil structure. However, on lowering the pressure, aggregates are formed with a structure similar to aqueous micelles? the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of the micelle. This unimer-aggregate transition is driven by the gradual elimination of CO2 molecules solvating the hydrocarbon segments of the polymer. Comparison of these results with related data on the same polymer at different temperatures indicates that the transition is critically related to the density of the solvent. This suggests the definition of a critical micellization density. Mathematical modeling of the data in terms of core-shell micelle structures permits a detailed description of the structure and the degree of swelling (penetration) of the solvent into the different regions of the aggregates throughout this unimer-aggregate transition [2].

In parallel with SANS studies of the structure of polymer aggregates in CO2, we have begun to characterize the molecular dynamics of a PS (polysytrene)-b-PFOA copolymer by medium-resolution quasi-elastic neutron scattering (QENS). Line shapes are dominated by localized diffusive modes and segmental dynamics of the anchored, finite-length PFOA chains. For Q # 0.6 ?-1, we obtain effective diffusion coefficients of approximately 0.8 x 10-6 cm2/s. At higher Q, a single component is not sufficient as shown by excess intensity on the flanks. For Q ?1.5 ?-1, the wings reflect contributions due to a distribution of faster, more localized chain modes.

This PS-b-FOMA copolymer has been utilized as the stabilizer in the dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) in CO2 continuous phase [4]. HEMA was effectively emulsified in CO2 with the amphiphilic diblock copolymer surfactant. Spherical particles in the submicrometer range were obtained with relatively narrow particle size distributions. The initial pressure and concentrations of stabilizer have substantial effects on the size of the colloidal particles.

Future Activities:

This is the last annual report to be prepared for this grant.


Journal Articles on this Report : 5 Displayed | Download in RIS Format

Other project views: All 21 publications 15 publications in selected types All 15 journal articles

Type Citation Project Document Sources
Journal Article Shiho H, DeSimone JM. Dispersion polymerization of 2-hydroxyethyl methacrylate in supercritical carbon dioxide. Journal of Polymer Science Part A - Polymer Chemistry 2000;38:3783-3790. R826115 (2000)
R826115 (Final)
not available
Journal Article Triolo A, Triolo F, Lo Celso F, Betts DE, McClain JB, DeSimone JM, Wignall GD, Triolo R. Critical micellization density: A small-angle-scattering structural study of the monomer-aggregate transition of block copolymers in supercritical CO2. Physical Review e 2000;62(4):5839-5842 R826115 (2000)
R826115 (Final)
not available
Journal Article Triolo F, Triolo A, Triolo R, Londono JD, Wignall GD, McClain JB, Betts DE, Wells S, Samulski ET, DeSimone JM. Critical micelle density for the self-assembly of block copolymer surfactants in supercritical carbon dioxide. Langmuir 2000;16(2):416-421 R826115 (2000)
R826115 (Final)
not available
Journal Article Triolo R, Arrighi V, Triolo A, Migliardo P, Magazu S, McClain JB, Betts D, DeSimone JM, Middendorf HD. QENS from polymer aggregates in supercritical CO2. Physical Review B 2000;276-278, 386-387. R826115 (2000)
R826115 (Final)
not available
Journal Article Triolo R, Triolo A, Triolo F, Steytler DC, Lewis CA, Heenan RK, Wignall GD, DeSimone JM. Structure of diblock copolymers in supercritical carbon dioxide and critical micellization pressure. Physical Review E 2000;61(4):4640-4643. R826115 (2000)
R826115 (Final)
not available
Supplemental Keywords:

carbon dioxide, VOC, CFCs, alternatives, innovative technology, waste reduction, waste minimization, environmentally conscious manufacturing., RFA, Scientific Discipline, Sustainable Industry/Business, cleaner production/pollution prevention, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Economics and Business, Chemistry and Materials Science, cleaner production, non-ionic surfactants, environmentally benign solvents, dispersion polymerization, emission controls, green process systems, carbon dioxide, plastic, chlorofluorocarbons, pollution prevention, source reduction, Volatile Organic Compounds (VOCs), polymer design, green chemistry, solvents, polymeric coatings

Relevant Websites:

http://www.unc.edu/depts/chemistry/faculty/desimone/resact.htm Exit EPA icon
http://www.nsfstc.unc.edu Exit EPA icon
http://www2.ncsu.edu:80/champagne/ Exit EPA icon

Progress and Final Reports:
Original Abstract
1999 Progress Report
Final Report

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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