- 1. Please describe the difference between your Chemilian™ and Forza™ platforms.
The Chemilian™ platform has the general formula wherein any R groups are employed to give a range of properties. The R groups most commonly used and most extensively studied provide homopolymer glass transition temperatures (Tg) from -40°C to >150°C. All the materials in this platform are polymerizable using basic, nucleophilic and free radical initiators. For further information, please reference the Chemilian™ Technical Data Sheet.
The Forza™ subplatform consists of the same polymerizable vinyl group but contains two or more of them within the same molecule. A sample Forza macromer is shown below. The result is a polymerizable material that will produce a cross-linked or highly cross-linked polymer suitable for more demanding applications. Within this category, Sirrus has explored difunctional adducts with a range of properties, such as flexibility and UV resistance, as well as multifunctional adducts that are suitable for demanding coatings applications.
- 2. Please describe stability, solubility and handling of Sirrus monomers in aqueous media.
Our monomers have reasonable pot life when handled in deionized water. Monomers will stay stable for a few hours, enough time to conduct a polymerization or crosslinking reaction, after which a decrease in the alkene functionality due to Michael addition may be observed. Stability up to 12 hours has been observed. Typical polymerizations in water will happen in minutes. Long-term storage in water is not recommended. Monomers will polymerize when mixed with city water. Please see our patents (US Patent 9,249,265 and 9,637,564) on emulsion polymerization, US 9,637,564.
- 3. What storage guidelines are recommended?
Sirrus ships all samples with a stabilizer package intended to maintain room temperature for at least six months. However, it is generally recommended to store Sirrus monomers at cold temperatures (0-5°C 5°C) and allow them to return to room temperature before each use to minimize condensation inside the storage container. Store the samples in plastic. Passivate all glassware with a weak acid solution (0.1% MSA in THF) before conducting desired reactions in glass. Long-term storage in glass is not recommended.
- 4. What inhibitors are used with Sirrus monomers?
We stabilize monomers with 10 ppm of methanesulfonic acid and 100 ppm of BHT. However, Sirrus will work with its development partners and customers to fine-tune the stabilizer package pending the desired application and cure speed.
- 5. What are the safety and handling recommendations for Sirrus monomers?
Please read the SDS sheet prepared for each material before using it. Always use proper ventilation when using Chemilian™ products. Store material away from alkaline substances and in a cool, dark place. Always wear proper PPE when handling Chemilian™ products. Plastic pipettes are recommended for aliquots, and double dipping of the pipette is not advisable as it may have contacted a basic, initiating species. Consult your Sirrus representative if you have further questions.
- 6. In case of anionic polymerization, what kind of material or stimulation can be an initiator?
Sirrus monomers initiate with bases (alkaline materials) and nucleophiles to polymerize anionically. Sodium benzoate and other sodium salts work well. Potassium or calcium benzoates, carbonates, pyruvates and sulphates have also been demonstrated to be initiators. Secondary and tertiary amines will initiate anionic polymerization, although secondary amines may also catalyze Michael addition. Amines like tetramethyl guanidine (TMG) and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) have been demonstrated as some of the fastest nucleophilic initiators in bulk and solution chemistries.
- 7. What are some examples of good Michael addition catalysts?
It is known that acids and bases catalyze Michael addition. Acids will stabilize the anionic polymerization and will only permit Michael addition, which can also happen at room temperature, uncatalyzed, slowly with time. Bases will also be anionic initiators for Sirrus materials, which will compete with Michael addition.
- 8. What is the proposed mechanism of Michael addition with alkenes?
Scroll right to see the full image →
Click to enlarge
- 9. What kind of material or stimulation can be used to initiate free radical polymerization?
Commonly used peroxide-based free radical initiators will initiate free radical polymerization for our family of monomers in the presence of elevated temperatures or UV light in combination with typical photoinitiators.
- 10. How does Sirrus compare the efficacy of different types of amines as a Michael donor?
Primary and secondary amines will Michael add, although subsequent anionic polymerization is possible from the resultant secondary amine formed during the Michael reaction. Secondary amines can Michael add as well as initiate anionic polymerization. Tertiary amines only catalyze anionic or zwitterionic polymerization. Amines like DBU and TMG have been demonstrated to be very strong initiators. We believe that this is related to both nucleophilicity and pKb values. The behavior of initiators when mixed in bulk can often be different from initiators used on a surface. These relationships are more complicated, so please contact your Sirrus representative for details for specific application strategies.
- 11. Do primary amines only result in Michael addition?
Yes. However, the resultant Michael product has a secondary amine forming and subsequently may also initiate polymerization. Typically though, Michael addition is the first reaction.
- 12. What kind of molecular weight control can be obtained under anionic polymerization?
For polymerization in solutions, molecular weights can be controlled by varying the initiator concentration as well as initiator choice. Block copolymers and random copolymers can be built with controlled architecture under lower temperatures. Please reference our Solution Polymer Patent (US Patent 9,279,022).
- 13. Has Sirrus demonstrated the ability to control monomer sequence? For example, AAABBB?
Yes. Typically, sequential addition allows us to control monomer sequence. At low temperatures, chain-transfer side reactions are significantly reduced.
- 14. What polydispersity levels have been obtained under lab conditions?
Sirrus has demonstration PDI as low as 1.05 when polymerization is initiated at low temperatures. Higher PDI is observed at room temperature and above, likely due to chain-transfer reactions.
- 15. What kind of multiblock structures have been demonstrated? What initiators have been used to achieve them?
We have synthesized diblock and triblock copolymers. Initiators used have been TMG type amines, sodium benzoate and alkyl lithium initiators. The best results were demonstrated at temperatures less than 0°C.
- 16. How facile is free radical polymerization? Can typical free radical initiators be used?
Yes. Sirrus has demonstrated free radical polymerization using UV curing initiators. Extensive studies with heat-activated systems have not been conducted, but there is evidence that heat-curing, free radical initiators, such as peroxides, will work with the Sirrus family of monomers. Please let us know if you intend to pursue free radical chemistries for your application. If needed, the level of the radical stabilizer in the samples can be adjusted.
- 17. Has Sirrus demonstrated anionic copolymerization with any other types of anionically polymerizable monomers, such as cyanoacrylates, epoxides, styrene, butadiene, etc.?
Anionic copolymerization with non-malonate monomers at room temperature has proven difficult. It has been demonstrated that hybrid copolymers with other monomer families may have been prepared anionically with alkyl lithium initiators at low temperature. We have also used alkyl lithium initiators to successfully prepare copolymers with other monomer families via free radical polymerization.
- 18. Has Sirrus characterized any products of surface polymerization? Can grafted polymers be well controlled? What are the best surface initiators?
Anionic polymerization can be initiated on a surface in the presence of an initiator. A polymer front is propagated that may be several microns thick. Testing by Sirrus partners has demonstrated best-in-class adhesion for methylene malonates polymerized using surface initiation on responsive (i.e., initiating) substrates. One proposed mechanism is that a covalent bond may be formed with the initiator at the interface.
Glass may be an ideal surface to observe this behavior. Plastics including polycarbonate and ABS demonstrate this type of surface bonding in some adhesive and coating applications. Base coats formulated with amines or anionic surfactants also demonstrate strong surface initiation.
Low-energy substrates like polypropylene are not inherently good initiators for anionic polymerization. Sirrus will test activation on substrates of interest and provide guidance regarding their suitability as anionic initiators.
- 19. Can a coated interface like glass-filled polypropylene affect polymerization?
Yes, the coating of a material has a large impact on the polymerization kinetics. In some cases, it can increase bonding strength via polymerization initiation from the coated substrate.
- 20. Can water or alcohols affect polymerization?
Primary alcohols will Michael add across the double bond, while secondary alcohols will do so much more slowly. Polymerization or Michael addition in the presence of deionized water over short periods of time (approximately 10-12 hours) has not been observed. We do not recommend using monomers in a waterborne system for long-term storage due to the potential for Michael addition with ionized hydroxides. Please reference Sirrus’ emulsion polymerization patent (US 9,249,265). Municipal water and ground water have been found to initiate anionic polymerization, possibly due to the presence of dissolved salts in those water sources.
- 21. What polymerization methods other than anionic are most promising for Sirrus monomers?
UV-initiation and thermal initiation (with and without initiator) are all viable approaches for polymerization. The recommended approach depends on the intended comonomers and application.
- 22. Which monomers should be used to produce hybrid copolymers with acrylic polyols?
We recommend Forza™ macromers to make copolymers with acrylic polyols. Much of the work done by Sirrus on clear coat research has been hybrid cure consisting of Michael addition cure in combination with free radical or anionic cure. For efficient crosslinking using a hydroxyl group, multifunctional materials are needed.
- 23. What other functional groups may be used in a Michael addition reaction with Sirrus monomers?
Primary amines offer the most utility for Michael addition reactions because the competing anionic polymerization is not as rapid. Thiols can also be used for Michael addition across the alkene. Neutralized carboxylic acid functionality (even on polymer backbones) can provide good initiating sites, but mostly for anionic polymerization.
- 24. Can monomers and crosslinkers polymerize without any other chemicals? Can they become homopolymers?
Yes, all the materials in the Sirrus platform will copolymerize to form random copolymers. Block copolymers can be created. Please reference our Solution Polymer Patent (US Patent 9,279,022). We can also make homopolymers of individual mono-functional monomers.
- 25. What is the mechanism of cure for the Forza™ platform in coatings when applied of waterborne base coatings?
Inherently basic substrates or base coatings provide nucleophilic sites for anionic initiation. The result is substrate initiation, which provides high levels of adhesion.
The remainder of the coating likely polymerizes due to a combination of free-radical cure and propagating anionic cure from the substrate below.
We have conducted experiments to help prove this hybrid system in which each mechanism is separately inhibited. The resulting coating does not exhibit the same properties or does not cure at all. For these reasons, we believe the system depends on both mechanisms of cure.
Sirrus suggests that partners try these experiments with the desired substrate. First, inhibit free radical polymerization by adding 1000 to 5000 ppm BHT to the system and repeat the cure. If the material does not cure or cures poorly, the polymerization was predominately free radical. Second, inhibit anionic polymerization by adding 500 ppm of methanesulfonic acid and repeat the cure conditions. If the material does not cure or cures poorly, the polymerization was predominantly anionic. Conduct experiments at room temperature to ensure the cure was not entirely anionic polymerization initiated by the substrate.
- 26. What free radical curing conditions are recommended?
We have demonstrated free radical cure using conventional free radical initiators in 2-3% by weight amounts using a mercury, broad spectrum UV lamp. Cure with LED lamps has also been observed, but the photoinitiators must be matched appropriately with the wavelength of the LED lamp. Please contact a Sirrus representative for more information on free radical polymerization techniques.
- 27. Are Chemilian™ and Forza™ monomer curing mechanisms different?
No, the crosslinkers, macromers and monomers will all polymerize anionically and free radically.
- 28. Is it possible to chain terminate polymerization?
Yes. In Sirrus monomers, polymerization will end when all functionality is consumed or a vitrification point is reached. For anionic polymerization, chain termination can be achieved with acids. We have used trifluoroacetic acid and methanesulfonic acid, as well as pyruvic acid, for chain termination in solution polymerization work.
- 29. What is the highest obtainable Tg polymer?
We have synthesized poly(fenchyl methyl methylene malonate) with a measured homopolymer Tg of over 150°C, and have measured as high as 190°C with controlled synthesis. Additional high Tg homopolymers may be possible using cyclohexyl side groups.
- 30. What is the lowest obtainable Tg polymer?
We have synthesized poly(dihexyl methylene malonate) with a measured homopolymer Tg of approximately -40°C. Lower Tg homopolymers may be possible.
- 31. What is the preferred method of measuring Tg for Sirrus homopolymers?
We polymerize materials in solution to a very high molecular weight (50,000->1,000,000 Daltons). The polymer is precipitated out of solution, filtered and dried. Differential Scanning Calorimetry (DSC) is typically used for Tg measurement, and the midpoint of the transition is selected as the Tg. An example of a typical DSC curve is shown below. The same sample preparation technique may be used for Thermogravimetric Analysis (TGA).
- 32. What types of esters have been demonstrated? Are they possible?
We have had success changing the R group on the diesters. Both symmetric and asymmetric diesters have been successfully synthesized and characterized as part of the Chemilian™ family of monomers. We have also demonstrated the synthesis of ketoesters and difunctional and multifunctional oligomeric macromers in the Forza™ family of monomers.
- 33. Are there ways to utilize Sirrus monomers for surface functionalization by grafting?
Our monomers have been used for surface functionalization on responsive surfaces.
- 34. Can PEGs be used to functionalize Sirrus materials?
We have prepared several “PEGylated” monofunctional and multifunctional monomers via transesterification.
- 35. Which methylene malonate compounds have hydrophilic properties?
We have tested various “PEGylated” monomers and found them to be hydrophilic when applied as a coating on a substrate.
- 36. Which methylene malonate compounds are available for sampling?
We will commercialize monomers in two phases. Four commercial materials will be produced in the first phase:
Diethyl methylene malonate (DEMM) for use as a chemical intermediate.
A polyester macromer of DEMM and butane diol having an average molecular weight of 1,000 Daltons.
A high Tg monomer that can produce a homopolymer Tg of ~140°C and molecular weight >250 Daltons.
A low Tg monomer that can produce a homopolymer Tg of ~ -40°C and molecular weight >250 Daltons.
The second phase is part of Sirrus Next, with monomers designed exclusively for partners. Please contact us for more information about Sirrus Next.
- 37. Which coating procedure (spraying, dipping, etc.) is preferred for methylene malonates?
It is important to test all substrates being considered to determine if the substrate will initiate polymerization without an initiator. If the substrate is responsive (i.e., polymerization is initiated), then multiple techniques are available depending on the desired application. Spraying is recommended for coating flat, responsive substrates. In curved substrates, significant non-recyclable overspray waste could be generated with spray techniques.
Little work has been performed on dipping application techniques, as there is concern that placing a responsive substrate in a tank of monomer could lead to bulk polymerization of the vessel. Preliminary experiments using chemical vapor deposition indicate this technique may have significant potential, as contacting the vapor with a responsive substrate would lead to polymerization—effectively converting the vapor into a solid coating.
If the surface is not responsive, other techniques may be explored, including a pre-treatment of the substrate, a two-part spray, brush application or a sequential addition of initiator/monomer or monomer/initiator. Application techniques may also vary depending on the desired thickness of the coating.
- 38. What conditions are recommended for the coating procedure?
Sirrus has developed monomers that can be applied under a wide set of conditions. A key value proposition for many customers is the ability to cure our materials at or below room temperature.
While pure methylene malonate systems do cure at room temperature, combinations of different chemistries, including Michael addition with polyols, may require slightly elevated temperatures to achieve fast cure. Conditions are also dependent on the specific monomer being used, as monomers with higher molecular weight tend to have slower cure speeds than low molecular weight monomers. This may be attributable to steric and mobility hindrances.
- 39. Are bulk polymerizations observed? If so, how can they be avoided?
Yes, bulk anionic polymerization can occur. Acid pre-treatment (passivation) is recommended for all equipment used to process, store and transport methylene malonates to prevent bulk anionic polymerization. Bulk free radical polymerization is also possible. We recommend adding a free radical stabilizer, maintaining reasonable storage temperatures and keeping materials in an oxygen containing atmosphere to prevent unwanted free radical polymerization.
- 40. Are catalysts needed? If so, which type?
The use of catalysts or initiators is recommended for polymerization on nonresponsive substrates or to accelerate cure speeds. Most basic materials can initiate polymerization. For quality control purposes, Sirrus often tests initiation speed with a 0.1-0.5 mol% sodium benzoate solution in reagent alcohol. In certain applications, secondary or tertiary amines can act as anionic polymerization initiators. Many building materials such as concrete and glass are natural initiators.
Free radical polymerization initiators work with methylene malonates. Free radical cure can be initiated by residual radical initiator or stabilizer from synthesis methods. For Michael addition catalysis, copper/zinc triflate has a catalytic effect on Michael addition speed.
- 41. Which solvents can be used for dilution of methylene malonates?
Many Coatings market solvents can be utilized with methylene malonates. We prefer solvents with boiling points slightly below the boiling points of the desired coating materials to enhance film forming properties. Sirrus monomers are low viscosity, so dilution is not required for applications. However, for higher viscosity crosslinkers, we may recommend the solvent to be included in formulations for application purposes. Some solvents used include butyl acetate and glycol ether PM acetate. Alcohols should be avoided as they can readily Michael add across the double bond.
- 42. What is the pot life of methylene malonates?
Most monomers have a very short pot life (<10 minutes) if mixed with an anionic polymerization initiator. Higher molecular weight monomers and crosslinkers may have longer pot life.
- 43. Can pot life be extended by the addition of an inhibitor?
The pot life may be extended, but if the intent is to anionically polymerize the monomers, once the acid stabilizer is titrated away with a basic initiator, the living polymerization is initiated. It can be stopped with the addition of a chain terminator.
In the case of a desired Michael addition with polyols, longer pot life can be obtained with the addition of an acid providing the opportunity to anionically polymerize once the mixture is contacted with a responsive substrate.
- 44. What responsive surfaces may be utilized for grafting?
Any surface that has naturally occurring nucleophilic groups may be used. The properties of the monomers/macromers will need to be adjusted to match the properties of the surface on which they are applied. Please contact Sirrus for further information.
- 45. What pre-treatment methods are recommended for non-responsive substrates?
We recommend nucleophilic primers (such as silanes or amines), corona or plasma treatment that would expose hydroxyl or carboxylate functionality, or sanding in instances where initiators may lie below the substrate surface (e.g., glass filled polypropylene).
- 46. Please comment on surface-initiated adhesion strength versus secondary initiation.
Surface initiation results in much better adhesion versus using a secondary initiator. While both methods will result in curing of the polymerizable composition, a nucleophilic substrate results in surface interactions that produces a higher bond strength. In the case of a secondary initiator, the polymer chain likely has less interaction with the substrate and often results in poor adhesion.
Please contact a Sirrus representative to provide guidance on which application method may be best for your desired surface.