[arnau.castillo]

Hello everyone,
this is my first post, so excuse me If I don't comply strictly to the forum rules.

I'm a Mechanical Engineer without a background in Organic Chemistry, and I just ran into a project where I need some help. Explanation:

As a structural filler, we use the copolymer Paraloid B72, from Rohm and Haas (an EMA Copolymer). Different people uses different types of Solvents (Toluene, Xylene, Acetone or ShellSol A100) to solve this Copolymer, to make it flow into the desired filling areas(usually, solution of 5-20% w/w of Copolymer).
The issue, is that the cast material after solving the original Paraloid, has different properties. I would like to know, If there's any reaction between the copolymer and the described solvents above, what is the reaction mechanisms, how the final material structure will be (how affects to the copolymer chains), and how each of those solvents affects to the theoretically non variant properties.

I hope I have described the issue properly. Thank you in advance for all your help.

[kriggy]

There should be no reaction betweel solvent and the polymer, One of the most important features of solvent in given process is that it doenst interfere with the reaction.
Just to be clear: you dissolve the copolymer in one of those solvents and then you fill some mold and then the mold has different properties than before the addition of the copolymer?
 

[arnau.castillo]

Thanks Kriggy for answering.
Yes, I thought that solvents were actually non reactant. About your clarification:yes, it is exactly what you described.
I read that chains can enlarge (plastification), or contract, thermodinamical properties change,etc.; all of it, opposite to what I knew until now. That's why I need your help, It is too far from my chem knowledge.
Thanks again

[kriggy]

Ok what material is your cast from? Did you try one from different material? Which solvent did you use? Did you try different one?
My knowledge in this area is very limited but maybe your cast dissolved in the solvet by some extent? 

[Enthalpy]

Hi all,

In a polymer, not only the properties of individual long molecules matter, but also the way they organise together. The molecules can be streched mechanically by the fabrication process, for instance to draw a yarn or roll a film. They can be aligned nicely parallel to an other or not. And so on and so forth.

If you dissolve a polymer and then evaporate the solvent, I expect the molecules to crimp and to organise in a poorly ordered way. This should - not an observation from my side, beware - make the polymer lighter, less strong, more permeable and so on.

[arnau.castillo]

Hi Kriggy and Enthalpy,
I casted Paraloid B72 (EMA Copolymer), solved in acetone, toluene, xylene and A100; in an aluminium mold. There's no reaction with the mold (except for the thin, thin layer in contact with the mold).

What I read is that when a polymer is in a solution where the solvent has a greater attraction for segments of the polymer than the polymer segments have for each other, the chain length is extended. Conversely, contraction will occur when a polymer is in a solvent in which the solvent-polymer attraction is less than the polymer-polymer attraction. Solvents for a particular polymer have been denoted “good” if the chain extension is promoted and “poor” if the chain extension is contracted. Good solvents dissolve a larger amount of polymer; if the solvent is too poor, the polymer will not dissolve. The basis for studying solution properties of polymers is that the effects from certain conformations of the polymer chain will persist in the cast deposited from such solutions, with resulting variations in physical properties of the polymeric cast. However, the solvent “type” describes only the thermodynamic quality of the solution and is not necessarily connected with “good” or “bad” properties of the resultant polymer film for a specific use in the conservation of an object.

So, I would like to know how the solvents affects to the polymer chain and other properties and If it can be calculated. Thanks again!!!

[orgopete]

I would say no reaction occurs between the solvent(s) and Paraloid B-72 (according to Wikipedia).

[arnau.castillo]

Hi Orgopete,
it has to react in some how, no? If not, how we could explain the change in Tg and physical properties of the cast Paraloid? In the below article (with PVAC films) it proves the thermodynamic change and the change in mechanical properties, regardless of solvent retention. Maybe it does not change composition but structure? Or both?

http://cool.conservation-us.org/jaic/articles/jaic30-02-008.html]http://cool.conservation-us.org/jaic/articles/jaic30-02-008.html]http://cool.conservation-us.org/jaic/articles/jaic30-02-008.html

thanks

[orgopete]

Okay, I'll have to take that back. I was thinking of a (covalent) bond forming reaction. If you dissolve sodium chloride in water, sodium chloride will have different properties in water than as the solid. Chemists don't normally regard dissolving NaCl in water as forming a bond (though obviously some weak interactions must be present).

Dissolving the polymer in a solvent will reduce or remove the inter or intrapolymeric interactions that give the polymer its properties after vaporization. In that way, I don't think the solvent contributes to the properties of the polymer itself. The solvents may affect the kind of interactions the polymer may be able to adopt, like snowflakes vs ice cubes. It may affect its adherence by altering the surface to which it is applied.

[Enthalpy]

Once the solvent is gone (provided you get completely rid of it!) the polymer's properties depend just on how it has organized back. As the solvent evaporates or goes away somehow, the polymer molecules reorganize and may perfectly forget what their shape was when they were dissolved.

So it's more a question of crystallinity and other details. Dissolution and precipitation should make the solid less ordered, unless it's done very slowly, and should result in a softer and less dense solid. Also, a deposited film is strained by the evaporation as it would shrink but the underlying material prevents it.

Getting completely rid of the solvent isn't easy. Many polymers keep a significant amount of liquids, for instance 13% water in PA66, which swells and softens them. Baking in vacuum improves that, but for thick parts it may take too long.

Maybe perhaps... Methyl methacrylate, the monomer of PMMA (Plexiglas etc) is a liquid that polymerizes under UV light. Your Paraloid B-72 is just a copolymer of methyl and ethyl methacrylate
http://en.wikipedia.org/wiki/Paraloid_B-72
so if you find the monomer, cast it in the mold, and irradiate with UV (mercury lamp or just any fluorescent tube), you get the parts without any solvent. Beware MMA vapour is nasty to the eyes, and MMA is quite sensitive to UV including sunlight and fluorescent tubes.

In case your goal is to deposit a conformal polymer film, different compounds have been developed for that purpose, like parylene
http://en.wikipedia.org/wiki/Parylene