PVC reacts with Polystyrene.

I'm no expert, however here is the listing of reactivities of these chemicals according to NIOSH

PVC is incompatible with: Copper, oxidizers, aluminum, peroxides, iron, steel [Note: Polymerizes in air, sunlight, or heat unless stabilized by inhibitors such as phenol. Attacks iron & steel in presence of moisture.]

Styrene is incompatible with : Oxidizers, catalysts for vinyl polymers, peroxides, strong acids, aluminum chloride [Note: May polymerize if contaminated or subjected to heat. Usually contains an inhibitor such as tert-butylcatechol.]

Hello I know of these things it is the chemistry of why such a commonly used product should be so very reactive. I had a plastic bin bag sitting on a sheet of polystyrene and in only a week or so the bottom of the bag had disintegrated and the contents spilled out. The polystyrene had a hole melted into it. The sheet was 2" thick and the hole an inch deep by approx 4" wide. I knew about the PVC issues from long ago. That why all PVC mains leads are wrapped in polythene when the goods are packed using polystyrene foam. It is also a problem that cause some fires when used as an insulating material by the building trade and as cavity wall insulation. Power cables could come into contact and their insulation would suffer. Before RCD's were widely used.

They also require different solvents for welding.

Whereas polystyrene will solvent-weld to itself with a range of ketones, such as butan-2-one [AKA 'MEK': methyl ethyl ketone], ketones won't touch PVC (or ABS, for that matter). PVC and ABS can be joined to each other, and polystyrene to itself, using a different, PVC-compatible solvent.

you said :

methyl ethyl ketone], ketones won't touch PVC ? Please tell me what is the solvent for PCV to weld to itself?

(or ABS, for that matter). PVC and ABS can be joined to each other, and polystyrene to itself, using a different, PVC-compatible solvent.

Without immediate access to the bottle with which to look it up, PVC pipework can be joined by solvent-welding, and bottles of the correct stuff may be found at home improvement stockists and plumbers' merchants quite widely. It resembles thick wallpaper paste in consistency though, being an organic solvent rather than water-based, it is very pungent and highly flammable.

tetrahydrofuran as a window manufacture at one time we dissolve scrap to make glue to glue to seams

Beg to differ - MEK will attack PVC and ABS - if you don't believe it, take a scrap piece of material you don't care about and observe the gloss level (the glossier start the better). Apply a little MEK to to a rag using the appropriate personal protective equipment and watch the material surface move towards 'dull' - you are attacking the material. Acetone is even more aggressive.

In the surface repair process of ABS, it is common practice to take shavings and slowly disolve them in MEK building up an adhesive paste that can can be spread on and into to repair a surface crack and once the MEK vapor dissipates can be machined -

Go to your local plumbing centre and ask for plastic pipe cement.

Interpreting the Wiki notes on PVC it seems that it is the plasticiser in PVC used to make it supple that causes the posted problem with polystyrene; it is relatively easy to dissolve the polystyrene with the residual PVC plasticiser.

As there is a difference between PVC and uPVC, the u standing for 'unplasticised' and being a more rigid material, there ought not to be a difficulty between uPVC and polystyrene as the plasticiser is absent.

I am asking about the reative chemistry! The "u" is for UV treated.

a plasticizer is not reactive, but it does work it's way between the molecules of various platics and changes them from brittle to flexible. It will also expand polymers and they are thus weakened, paint it stripped and loses adhesion.

http://www.google.com/search?hl=en&q=%22phthalate+plasticizers%22+%2Bpaint

Hmmmmmm. Here's a possibility: PVC plasticiser denatures/decomposes/evaporates on exposure to UV light and the thermal effects of sunshine, the PVC thereby losing suppleness? Unplasticised PVC, being more rigid, suffers much less.

How about that?

PVC react quite happily in the dark.

it is the DOP (Plasticizer) leaching out of the PVC that is reacting with the PS

if you are trying to construct items where it is important to have these two products in contact with each other, you need to work with material vendors who are familiar with using 'non-migrating' pvc compounds - these are special formulations designed to overcome the aromatic difficulties you are experiencing. While being extremely compatible with PVC these special plasticizers have very low affinity for ABS and polystyrene resins and therefore can be used in applications where plasticized PVC comes in contact with these other resins.

good luck

did you end up getting enough information? Jim