Silicones bring added difficulty to the table for formulators and product manufacturers, due to their insolubility in both water and in most organic oils.  This requires them to be pre-emulsified by mixing them with multiple surfactants (usually a nonionic and cationic one) in water to form an aqueous emulsion or micro-emulsion.  The droplets of silicone form an aggregate with the nonionic and cationic surfactants and are suspended inside micelles (tiny spheres) that are dispersed in the aqueous phase of the solution.  The outer shell of these micelles is the hydrophilic portion of the surfactants, which renders these particles soluble in water.  This emulsion can then be added to an aqueous shampoo or conditioning product fairly easily.  To save time and resources at the final production site, oftentimes the raw materials manufacturer will simply provide the materials as a pre-made micro-emulsion.

So, it is important to remember that the PTMPD (and other amine-functionalized silicones) is not water soluble itself, but is grouped with other materials to make it be so for the sake of the product manufacturing process as well as for the  stability of the final product.  Once the product is applied to the hair, the positively-charged silicone and the positively-charged cationic surfactant both separately adhere to various negative sites on the surface of the hair, forming a protective, emollient film, and the nonionic surfactants are washed away.  The micelle cluster no longer exists, and the polymer is completely insoluble in water.

Once applied to the hair, propoxytetramethyl piperidinyl dimethicone is highly substantive due to the ionic bonds formed between itself and the negatively-charged surface of the cuticle. A powerful anionic (negatively-charged) surfactant is necessary to remove this type of polymer form the hair.  Even then, it may be highly resistant to removal. This property is considered to be favorable by most formulators, as it means that the benefits imparted by the ingredient will persist over multiple washings.  It does not build up on itself, and it does not attract organic oils to itself, so those will also not build up on top of it.

However, some users have expressed their belief that this persistent film caused their hair to become dehydrated, frizzy, or unpleasant in texture.  While this experience is not universal, this anecdotal evidence certainly cannot be dismissed or discounted.  One might also speculate whether the anti-oxidant properties diminish over time, or whether the optical properties of the film change and result in a duller appearance to the hair.


In closing, it is clear that amine-functionalized silicones provide many advantageous properties when used in hair care products. Among these are high gloss, lightweight conditioning, fewer tangles, and protection from thermal damage.  This particular polymer, PTMPD, provides even greater benefits in terms of color retention, sun protection, and intensive, targeted conditioning properties for damaged hair.  However, if one ascribes to shampoo-free methods of hair maintenance, this silicone might be too difficult to remove from your hair and could create unpleasant side effects over time.  If you have been displeased with the results of amodimethicone on your hair, this might be another silicone to avoid as well.  However, for most people, products containing PTMPD can be a really nice addition to the hair beautification and protection arsenal.


References

http://www.faqs.org/patents/app/20120178324 (HA info patent)

Urrutia, Adriana, Silicone: The Basis of a Perfect Formulation for Hair Care,

Dow Corning de Mexico S.A. de C.V.