Polycaprolactone (PCL)
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Polycaprolactone is a biodegradable thermoplastic polymer derived from the chemical synthesis of crude oil. Although not produced from renewable raw materials, it is fully biodegradable.
Preparation:-
It can be prepared by ring opening polymerization of ε-caprolactone using a catalyst (a hydroxyl functional initiator) such as stannous octanoate. Unlike standard glycol-adipate polyester polyols which are formed by an acid-catalyzed condensation reaction, polycaprolactone polyols are formed in a manner that is easy to control.
Ring opening polymerization of ε-caprolactone to polycaprolactone
Impurities
The major impurities in the medical grade are toluene (<890 ppm, usually about 100 ppm) and tin (<200ppm).
CHARACTERISTICS
A biodegradable polyester with a low melting point of around 60°C and a glass transition temperature of about −60°C.
Polycaprolactone has good water, oil, solvent and chlorine resistance. PCL has been known to become brittle, lose its tensile strength and fall apart after several months so is not suitable for permanent or critical applications. Additionally, since polycaprolactones are not formed by an acid-catalyzed reaction, they have significantly improved hydrolysis resistance in comparison to glycol-adipate polyesters.
Finally, polycaprolactone polyls retain all of the performance benefits of polyester polyols. In comparison to polyether polyols, polycaprolactone polyols have enhanced:
· Chemical resistance
· UV resistance
· Cut and Tear strength
· Abrasion resistance
· Narrow molecular weight distribution
· Controlled functionality
· All primary hydroxyl groups
Chemical properties:-
| Polymer | Inherent Viscosity (dL/g) | Crystalline Melt Transition (°C) | Glass Transition Temp (°C) | Solubility (at 5% w/w) | Approx. Resorption (months) |
| · Solvents (partial listing only) 1 = dichloromethane 2 = tetrahydrofuran 3 = ethyl acetate 4 = chloroform 5 = hexafluoroisopropanol 6 = acetone | |||||
| PCL | 1.00 - 1.30 | 58-63 | (-65) - (-60) | 1 4 5 | >24 |
Physical Properties:-
| Polymer | Density (g/mL) | Tensile Strength (psi) | Elongation (%) | Modulus (psi) |
| PCL | 1.11 | 3000 - 5000 | 300 - 500 | 3 - 5x104 |
Uses:-
As Implantable Biomaterial
PCL is degraded by hydrolysis of its ester linkages in physiological conditions (such as in the human body) and has therefore received a great deal of attention for use as an implantable biomaterial. In particular it is especially interesting for the preparation of long term implantable devices, owing to its degradation which is even slower than that of polylactide.
As drug delivery device
PCL is an Food and Drug Administration (FDA) approved material that is used in the human body as (for example) a drug delivery device, suture , or adhesion barrier. It is being investigated as a scaffold for tissue repair via tissue engineering, GBR Membrane. It has been used as the hydrophobic block of amphiphilic synthetic block copolymers used to form the vesicle membrane of polymersomes.
A variety of drugs have been encapsulated within PCL beads for controlled release and targeted drug delivery which have been peer reviewed.
In dentistry
In Odontology or Dentistry is used in root canal filling. It performs likegutta-percha, has the same handling properties, and for re-treatment purposes may be softened with heat, or dissolved with solvents like chloroform. Similar to gutta-percha, there are master cones in all ISO sizes and accessory cones in different sizes available.
Other uses
It also serves to make stiffeners for shoes and orthopedic splints, and fully biodegradable compostable bags, sutures, and fibres.
References
· Sinha et al., Int. J. Pharm., 278, 2004
· http://www.tri-iso.com/Newsletters/17_Polyurethane_and_PUR_Corner_-_January_2007.html
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