The solvent power and low toxicity of DMSO make it useful as a replacement for more hazardous solvents. In many cases DMSO can be used as a direct replacement for solvents which have similar properties, particularly in these cases:
Replacing NMP (N-Methylpyrollidone, CAS [872-50-4]). This solvent is being phased out of many applications due to its reproductive toxicity. NMP is now under evaluation in the European Union as a Substance of very High Concern and NMP-based formulations must be labeled as reproductive toxins (R61).
There is no reproductive toxicity associated with DMSO, but the solvent properties of DMSO and NMP are similar in other ways. Both solvents are very good at dissolving materials which won’t dissolve in anything else. They both have relatively high boiling points and will dissolve completely in water. For a detailed comparison of DMSO and NMP from the perspective of safety, regulatory affairs, and physical properties, click here .
Industries and Specific Applications
In the polymer industry, there are several attractive ways that DMSO can potentially replace NMP. In polymer production, both solvents may be used as a reaction solvent to manufacture engineering resins. In some cases a highly polar solvent like DMSO or NMP is required to produce a polymeric product which has the appropriate molecular weight distribution to impart high solvent resistance. Materials like poly(ether) sulfone and polysulfone resins have been made in both solvents; DMSO use minimizes worker safety concerns.
For a list of DMSO polymer solubility data click here.
DMPA-based Polyurethane Dispersion Coatings
NMP was established as the solvent to dissolve dimethylolpropionic acid (DMPA) during polymer synthesis. The coatings industry is looking for alternatives largely driven by regulatory pressure in the EU.
NMP is used to produce a polyurethane prepolymer which cures upon exposure to atmospheric moisture.
Polymer processing often involves casting a film or membrane from a thermoplastic polymer dissolved in a suitable solvent. Many polymers used will only dissolve in polar solvents such and DMSO. Examples where NMP is used and DMSO might serve as a replacement include:protective coatings based on polymethyl methacrylate (PMMA) or photoresist formulations based on novolac, polyamideimide (PAI) and polyimide (PI) resins.
Solvent Casting of Membranes
Membranes made of Kynar (see Kynar/ DMSO solution viscosity data vs NMP in this resource), polyethersulfone, polysulfone, and poly(ether)ether ketone (PEEK) are solvent cast for reverse osmosis and ultrafiltration applications.
Polymer Cleaning Applications
NMP has been used in photoresist stripping formulations for TFT-LCD fabrication, wafer-level packaging lithography, and other microelectronic device production processes. DMSO is increasingly being adopted in these sophisticated cleaning applications, and formulation guidance can be obtained in this resource.
Although the first generation of safer paint stripping formulations were based on NMP, concerns about the reproductive toxicity of NMP have led formulators to evaluate DMSO as an alternative. It is easy to make DMSO-strippers which are as effective as NMP-based products and which are safer for consumers. Learn more about DMSO in paint stripping applications here.
Advice for NMP Reformulation
The approach to replacing NMP with DMSO is naturally dependent on the specific application. The simplest thing to try is to directly replace NMP with DMSO in your application as a way to quickly gauge relative performance. As NMP was originally chosen in cleaning applications as a way to dissolve difficult materials, another quick test is to make side-by-side solubility comparisons between DMSO and NMP.
If pure DMSO is not sufficiently effective, in some cases formulation with a cosolvent can increase performance. Here are some suggested cosolvents by application:
A popular formulation is based on DMSO and dibasic ester products. There are many brands of dibasic ester to choose from, including DBE (Invista), Estasol (Eastman Chemical), Rhodiasolv (Rhodia), and Santosol DME (Cytec Industries). The VOC content of paint stripping products can be lowered when suitable ‘low vapor pressure’ grades of dibasic ester are chosen. Here is a recommended starting formulation:
57 wt% DMSO
39 wt% Dibasic ester product
1 wt% Thickening agent of choice, such as Methocel OS (Dow Chemical)
1 wt% nonionic surfactant, like Ninol N40-CO
2 wt% d-limonene
General Polymer Processing and Cleaning Applications
Alkanolamines such as monoethanolamine (MEA) and N-methyldiethanolamine (MDEA) have been useful cosolvents to enhance DMSO performance in NMP replacement applications. In some cases, relatively low concentrations (5- 10 wt%) produce the best results. High alkanoamine levels can have an antisolvent effect.
Polymer manufacturing and microelectronic formulation applications are difficult to generalize. In replacing NMP a good understanding of the application is required and this is specialized work.