Ring-opening Polymerisation of e-Caprolactone

One variation in polyester intermediates that has roused some interest are those prepared by a ring-opening polymerisation of e-caprolactone and methyl-e-caprolactones with titanium catalysts and diol and triol initiators Figure 27.6). 

Poly(e-caprolactone) is prepared by the ring opening polymerisation of e-caprolactone. It has been widely studied as a matrix for controlled-release systems in a range of geometries. Poly( -caprolactone) degrades slower than polyhydroxy acids and is therefore preferred for controlled release devices with a longer life-time (a. 18). More recently an interest has been. shown in poly(e-caprolactone) as a medical device biomaterial (107, a. 19). 

PCL is a semicrystalline flexible polymer produced by the ring-opening polymerisation of e-caprolactone. Union Carbide patented a process which allows achieving a MW as high as 100,000 using stannous octanoate as a polymerisation initiator [51]. 

Knani D, Gutman A L, Kohn D H (1993), Enzymatic polyesterification in organic media. Enzyme-catalyzed synthesis of linear polyesters. I. Condensation polymerisation of linear hydroxyesters. n. Ring-Opening polymerisation of e-caprolactone , J. Polym. Sci. Polym. Chem., 31, 1221-1232. 

Lecomte Ph, Stassin F, Jerome R (2004), Recent developments in the ring-opening polymerisation of e-caprolactone and derivatives initiated by tin(IV) alkoxides , Macromol. Symp., 15, 325-338. 

PCL is produced by ring-opening polymerisation of the relatively cheap petroleum-based monomer — e-caprolactone — and is soluble in a wide range of organic solvents. Due to the slow rate of degradation, PCL was initially investigated as a biodegradable... 

However, ring-opening polymerisation of the lactide, as practised by Cargill, appears more advantageous. The latter is polymerised in the presence of tin/zirconium or titanium catalysts (this technique is also used to polymerise lactones, e.g. caprolactone on the large scale). Lactide, rather like lactic acid, but now possessing two asymmetric carbon atoms within its structure can exist as three stereoisomers L-lactide, D-lactide, and the meso-lactide (see Figure 10.9). 

Following the development of PLGA, poly(e-caprolactone) (PCL) has been synthesised by ring-opening polymerisation and also developed as a degradable polymer. Other synthetic polymers based on hydroxyacids such as malic acid and its derivatives have been proposed. 

Polyamides are now synthesised mainly by ring-opening polymerisation. This is typically the case of polyamide 6, known as Nylon 6, which is prepared by ring opening and polymerisation of 8-caprolactam, the cyclic amide very close to e-caprolactone. 

PCL can be synthesised using two methods, namely by the condensation of 6-hydroxycaproic acid and by the ring-opening polymerisation (ROP) of the cycUc e-caprolactone. This monomer is typically produced by the Baeyer—ViUiger oxidation of cyclohexanone with acetyl hydroxyperoxide (Lecoq et al., 1988). 

In 2006, two NHC-phenoxide chelates 3 were prepared by Shen et al (Figure 7.1). One of them was an active initiator for the ring-opening polymerisation (ROP) of e-caprolactone, albeit with poor control over the chain length and molecular weight distribution. The same group went on with the synthesis of enolate complexes 4, which displayed higher reactivities but equally poor control. ... 

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