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Final Report: Photocrosslinked Immobilization of Polyelectrolytes for Template Assisted Enzymatic Polymerization of Conjugated Polymers
EPA Grant Number: SU831894Title: Photocrosslinked Immobilization of Polyelectrolytes for Template Assisted Enzymatic Polymerization of Conjugated Polymers
Investigators: Warner, John C. , Hangun-Balkir, Yelda , Kiarie, Cecilia , Kumar, Jayant , Pal, Reshma , Trakhtenberg, Sofia
Institution: University of Massachusetts - Lowell , University of Massachusetts - Boston
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: September 30, 2004 through May 30, 2005
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity, and the Planet (2004)
Research Category: Pollution Prevention/Sustainable Development
Description:
Objective:The electronic industry generates millions of tons of toxic waste, primarily heavy metals and organic solvents, every year. Products from this industry have short useful lifetimes determined by the industry’s growth rate and rapid generation of more advanced technology. They rapidly become obsolete and when disposed of constitute a significant environmental problem due to low biodegradability of its mostly plastic components as well as to high content of heavy metals including lead. Proper disposal of these e-waste is lacking. While we decry the waste generation and its impact on human and environmental health we recognize that prosperity in modem times relies heavily on electronics. Technologies relying on both computers and computerized equipment became an indispensable part of education process, healthcare, academic research, manufacturing, entertainment, etc. The growing demand in consumer electronics thus raises the need for efficient, affordable, environmentally benign and biodegradable substitutes for current technologies.
In response to the need for alternatives to technologies currently used in electronics industry we proposed to investigate the possibility of patterning substrates with conductive polymers in an environmentally benign way.
Recently surface patterning with conjugated polymers has received quite a bit of attention due to their potential applications in a variety of microelectronic and electro-optical devices. The electrical properties of conjugated polymers can be manipulated by controlling the method of preparation or by the addition of secondary materials (dopants) that effect electron transport. The prospect of being able to precisely tailor the physical and electrical properties of conjugated polymers makes them attractive potential alternatives for both metals and semiconductors in various applications.
One of the obstacles that prevents the wide utilization of conjugated polymers is the harsh conditions that the polymerizations require in both bulk and surface processes. However in the last few years an alternative polymerization technique has been developed in the Center for Advanced Materials in UMass Lowell. Conductive polymers based on aniline, phenol and their derivatives are enzymatically synthesized with Horseradish Peroxidase (HRP) under mild conditions, such as room temperature. aqueous media and pH> 4. For this process to generate useful conductive materials, a suitable polyanionic template must be provided in order to align the monomers into growing polymer chains. Sulfonated polystyrene (SPS) was first used as a template for polymerization in aqueous solution.
In order to utilize this technique for surface patterning with conductive polymers, the ability to pattern substrate with polyanionic templates is required. Our interests in Green Chemistry. coupled with our work with thymine based photoresist systems has allowed us to devise a process to pattern various surfaces with sulfonated polystyrene comonomer derivatives containing vinylbenzylthymine (VBT) and vinylphenylsufonate (VPS). These environmentally benign, water soluble photopolymers undergo a 2π + 2π photodimerization reaction of the pendant thymine units when exposed to low levels of ultraviolet irradiation. The photodimers create crosslinked networks in regions of ultraviolet exposure, rendering the polymer significantly less water soluble (virtually insoluble) in those areas. This process leads to an immobilization of the polymer in response to the irradiation (hence a photoresist), allowing removal of the unexposed regions by a simple aqueous wash. The unreacted photopolymeric material can be recovered and reused in subsequent applications.
With this novel expertise to specifically pattern sulfonated polystyrene derivatives on various substrates in hand, we set out to explore the ability of these patterned surfaces to function as a template for the HRP catalyzed polymerization of aniline under mild conditions.
In the P3 proposal the purpose of this project was defined in a following way to synthesize Intrinsically Conductive Polymer films on a polyelectrolyte template ihat is immobilized on a substrate via photocrosslinking”.
Summary/Accomplishments (Outputs/Outcomes):In the first stage the parametric studies were performed to determine the optimal conditions of VBT-VPS coatings preparation. Methylene blue dye was used as a model for monomer adsorption on immobilized VI3T-VPS polyanionic template. UV-vis spectrometry was used to monitor the dye adsorption on VBT-VPS coatings. It was found that
- Higher ultraviolet irradiation doses initially improve the quality of coatings and increase the amount of adsorbed dye but eventually saturation is reached.
- For same irradiation levels amount of adsorbed dye is increasing with increase of VBT content (or VBT:VPS ratio) in VBT-VPS copolymers.
- For same irradiation levels and same VBT:VPS ratio amount of adsorbed dye is higher for VBT-VPS polymers with higher molecular weight.
We assumed that in order for the VBT-VPS copolymer to be a suitable template for conductive polyaniline synthesis it needs to have long VPS sequences uninterrupted by VBT. That required us to use copolymer with relatively low VBT content, namely VBT(VPS)14. To compensate for low VBT content we used a polymer with high molecular weight (260 kDa) and exposed it to relatively high ultraviolet irradiation level (2.4 J/cm2).
In the second stage the VBT(VPS)14 coatings were prepared on polyethylene terephthalate (PET) substrate. Their properties were studied by AFM and FTIR ATR. It was found that
- Coating thickness was 90 nm ± 10 nm.
- Results of spectroscopic (FTIR ATR) and microscopic (AFM) studies were in agreement with each other.
Then PET substrate was patterned with VBT(VPS)14 via irradiation with ultraviolet light through opaque mask and subsequent aqueous rinse. This patterned substrate was exposed to aniline, hydrogen peroxide and horseradish peroxidase in aqueous buffer media, at pH 4.2, at room temperature for 1 hour. This resulted in
- Polyaniline selectively forming on VBT(VPS)14 pattern.
- Polyaniline layer was green which indicated that it is conductive doped emeraldine salt form of polyaniline.
- Polyaniline layer could be dedoped by exposing it to NaOH solution, which caused the green polyaniline layer to become violet indicating the transition of conductive emeraldine salt to insulating emeraldine base form of polyaniline.
- UV-vis spectra were taken for both doped and dedoped polyaniline layers and the results were comparable with previously reported spectra of enzymatically synthesized conductive polyaniline.
- FTIR ATR spectrum of doped polyaniline layer was taken and its features were similar to those exhibited by previously reported FTIR spectra of enzymatically synthesized conductive polyaniline
- Profilometry measurements indicated that the thickness of Pani/VBT(VPS)14 layer was 260nm±5Onm.
- Optical microscopy and profilometry imaging were used to assess the quality of Pani coatings.
In order to further characterize the properties of Pani obtained on VBT(VPS)14 template via enzymatic polymerization in aqueous media we prepared I g of Pani/VBT(VPS)14. We demonstrated that
- Bulk conductivity of doped Pani/VBT(VPS)14 complex was measures by the 4-point probe method and found to be 5x10-5 S/cm. This places the Pani we obtained in a class of conductive polymers.
- Redox behavior of Pani/VBT(VPS)14 complex was further characterizes by cyclic voltammetry. It was found that similar to the previously described Pani/SPS complex, it has two sets of redox peaks at about 0.4 V and 0.8V. This provides clear evidence for the presence of electroactive Pani in the complex.
- Reversible dedoping and doping of Pani/VBT(VPS)14 complex in aqueous solution was demonstrated using UV-vis spectrometry. Here again the results were similar to previously reported for Pani/SPS complex. This is an additional indication that incorporation of photocrosslinkable VBT comonomer into polyanionic template did not have deleterious influence on Pani conductive properties.
- FTIR spectra of Pani/VBT(VPS)14 complex were taken in transmission mode. It was demonstrated that they exhibit the features characteristic for conductive Pani.
- Thermal stability of Pani/VBT(VPS)14 complex was investigated using TGA method. It was found that the complex is stable until about 260 °C, where the thermal degradation occurs.
- It was also found possible to pattern the substrate with Pani by exposing PET substrate patterned with VBT(VPS)14 to aqueous solution of Pani/VBT(VPS)14 complex, however the image was less sharp than when aniline polymerization occurred on immobilized VBT(VPS)14 template.
A unique environmentally benign route for surface patterning with conductive polyaniline is developed.
- It was demonstrated by various methods that photocrosslinkable VBT(VPS)14 polymer provides a suitable template for environmentally friendly enzymatic synthesis of conductive polyaniline. The incorporation of VBT groups (necessary for photocrosslinking) does not hinder the conductivity of synthesized polyaniline.
- We achieved surface patterning with conductive polyaniline in an environmentally friendly way using photocrosslinkable VBT(VPS)14 teplate by two different methods.
- We fulfilled the purpose of the project by synthesizing intrinsically conductive polymer films [Panil on a polyelectrolyte template [VBT(VPS)14] that was immobilized on a substrate [PET] via photocrosslinking.
Proposed Phase II objectives and strategies:
- to make a prototype of an environmentally friendly printed circuit board utilizing the technology established in Phase I;
- to perform life-cycle analysis for the proposed technology;
- to develop undergraduate lab module based on the enzymatic template assisted polymerization in aqueous media
- to optimize substrate patterning for variety of substrates including biodegradable polymers for environmentally friendly printed circuit board applications and silicon wafers for possible integrated circuits applications
No journal articles submitted with this report: View all 8 publications for this project
Supplemental Keywords:conductivity, polymer, photoresist, biodegradable, green chemistry, conductive polyani line,
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TREATMENT/CONTROL, Sustainable Industry/Business, Scientific Discipline, RFA, Technology for Sustainable Environment, Sustainable Environment, Technology, Environmental Engineering, Environmental Chemistry, environmental sustainability, environmentally friendly printed circuit boards, printed circuit boards, clean technologies, lead replacement, polymeric materials, alternative materials, biodegradable materials, environmentally friendly green products, environmentally conscious design, pollution prevention, environmentally benign alternative
Relevant Websites:
http://www.greenchemistry.uml.edu/ 
http://www.uml.edu/centers/cam/
http://www.uml.edu/centers/cam/greentea/
Progress and Final Reports:
Original Abstract