Copolymerization of lactide and glycolide

Table 10 Comparison of the copolymerization of lactide and glycolide in bulk by SnOct2 and BiHexs...

Poly(lactide-co-glycolide) (PLGA) was obtained from copolymerization of lactide and glycolide, and its structure is shown in Scheme 12.4. The product exhibits better properties than PLA and PGA. Compared to PGA, PLGA usually exhibits lower crystallinities and I m values. 

Fig. 48 Formation of poly(lactide-co-glycolide) by copolymerization of lactide and glycol-ide...

As with PG and PL homopolymers, the copolymers of lactide and glycolide are also subject to biodegradation because of the susceptibility of the aliphatic ester linkage to hydrolysis. However, biodegradation of the copolymers is normally faster than the homopolymers because copolymerization reduces the overall crystallinity of the polymer, thus giving the polymer a more open macrostructure for easier moisture penetration. 

As stated, glycolide and lactide maybe copolymerized or copolymerized with a variety of other monomers. The final ratio of monomers incorporated into a copolymer of lactide and glycolide is determined by proton nuclear magnetic resonance spectroscopy ( H NMR) in deuterated chloroform. The ratio of the methylene protons adjacent to the oxygen in glycolide is compared against that of the methyne protons in the lactide. The ratio is expressed as lactide to glycolide. 

One approach is the copolymerization of caprolactone with other cyclic monomers that nndergo ROP, namely, lactide, glycolide [70], or fnnctionalized epoxides [62,63]. In these systems, the second monomer is considered to bear the desired functionality or chemical moiety, and therefore, a wide range of novel functionalities and polymer properties are accessible. Statistical copolymers of caprolactone with lactides and glycolides are discussed earlier [70]. Beside these commonly used polyester monomers, a variety of other functional cyclic esters are described. Cyclic esters... 

The ratio of lactide to glycolide used to prepare the prepolymer must be acljusted so that the resulting prepolymer structure is amorphous. The amount of amorphous lactide/glycolide prepolymer used to prepare the terpolymer can vary over a wide range, and will depend to a great extent on the physical and absorption properties desired. Typically, an amount from 5 to 50 percentby weight of the composition of the polyester is acceptable. This is important to facilitate the successful copolymerization of the prepolymer with p-dioxanone. 

The pol) merization details are given for a small scale laboratory polymerization and a larger pilot scale polymerization of PCL homopolymer. A general description for laboratory copolymerization th lactide or glycolide is also given. 

A wide variety of high-purity monomers are available commercially for copolymerization with e-caprolactone. high-purity L-lactide, D-lactide, DL-lactide, and glycolide monomers may be obtained from either PURAC America of Lincolnshire, Illinois or BI Chemicals of MonUule, New Jersey. 

Copolymerization of D,L-lactide and glycolide in supercritical CO2 with stannous octoate as catalyst 132... 

Mazarro R, de Lucas A, Gracia I, Rodriguez JF. Copolymerization of D,L-lactide and glycolide in supercritical carbon dioxide with zinc octoate as catalyst. J Biomed Mater Res Part B Appl Biomaterials 2008 85B 196—203. 

The features of the copolymers depend on the type, number, length and sequence of the monomer combinations. The most common monomer used in the ring-opening copolymerization process of lactide is glycolide and it can be randomly distributed in... 

Lactide is also copolymerized with e-caprolactone monomer to produce biomaterials for the manufacture of surgical implants and drug carriers. The copolymeiization of lactide—caprolactone follows a similar reaction path as lactide—glycolide. The preference is for a random copolymer comprising of 55—70 mol% of lactide and 30—45 mol% of caprolactone for application as a pharmaceutical carrier (Bezwada, 1995). 

The 2,5-morpholinedione derivatives that have functional protected groups at the 3-position but are unsubstituted at the 6-position, can be homopolymerized, but with only low to moderate yields. Copolymerization with lactide, glycolide or e-caprolactone allows a variation of the number of pendant functional groups diblock copolymers are readily available by sequential polymerization of lactide and 2,5-morpholinedione derivatives. The initiation of lactide polymerization by... 

These representative aliphatic polyesters are often used in copolymerized form in various combinations, for example, poly(lactide-co-glycolide) (PLGA) [66-68] and poly(lactide-co-caprolactone) [69-73], to improve degradation rates, mechanical properties, processability, and solubility by reducing crystallinity. Other monomers such as 1,4-dioxepan-5-one (DXO) [74—76], 1,4-dioxane-2-one [77], and trimethylene carbonate (TMC) [28] (Fig. 2) have also been used as comonomers to improve the hydrophobicity of the aliphatic polyesters as well as their degradability and mechanical properties. 

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