Lactides thermodynamics

In some but not so rare cases, however, reactivity of macromonomers was found to be apparently reduced by the nature of their polymer chains. For example, p-vinylbenzyl- or methacrylate-ended PEO macromonomers, 26 (m=l) or 27b, were found to copolymerize with styrene (as A) in tetrahydrofuran with increasing difficulty (l/rA is reduced to one half) with increasing chain length of the PEO [41]. Since we are concerned with polymer-polymer reactions, as shown in Fig. 3, the results suggest that any thermodynamically repulsive interaction, which is usually observed between different, incompatible polymer chains, in this case PEO and PSt chains, may retard their approach and hence the reaction between their end groups, polystyryl radical and p-vinylbenzyl or methacrylate group. Such an incompatibility effect was discussed in terms of the degree of interpenetration and the interaction parameters between unlike polymers to support the observed reduction in the macromonomers copolymerization reactivity [31,40]. Similar observations of reduction of the copolymerization reactivity of macromonomers have recently been reported for the PEO macromonomers, 27a (m=ll) with styrene in benzene [42], 27b with acrylamide in water [43], and for poly(L-lactide), 28, with dimethyl acrylamide or N-vinylpyr-rolidone in dioxane [44]. 

B. Gander, P. Johansen, H. Nam-Tran, and H.P. Merkle, Thermodynamic approach to protein microencapsulation into poly(D,L-lactide) by spray drying. International Journal of Pharmaceutics, 129, 51-61 (1996). 

Caprolactone and L-lactide are medium strained cyclic esters and the thermodynamic parameters for polymerization of these have been determined and are listed in Table 3. 

Duda, A., and Penczek, S., 1990, Thermodynamics of L-Lactide Polymerization. Equilibrium Monomer Concentration. Macromolecules, 23 1636... 

The heat capacities and enthalpies of combustion were measured to analyze the thermodynamics of polymerization of n- and L-lactides into their polymers. The enthalpies and entropies of the lactide pol3mierization determined from these data are as follows AHp = —27.0 kj mol and ASp = —13.0 J moP K at 400 K, indicating an exothermic reaction. The kinetics of ROP of lactide have also been studied with various catalysts,... 

The above thermodynamic analysis of the polycondensation reveals that PLIAs having high molecular weights may be produced when the condensed water is efficiently removed to a level of 1 ppm from the polymerization system without evaporation of the L-lactide monomer present in equilibrium. The ordinary reaction conditions that may allow the effective removal of the water may involve (1) a temperature range of 180-200 °C (2) a low pressure below 5 torr and (3) a long reaction time in the presence of an appropriate catalyst and, in some cases, azeotropic solvent for removing water efficiently. ... 

High pressure fluid phase equilibrium data of poly (L-lactide) in carbon dioxide and dichloromethane Data extract from Landolt-Bornstein VIII/6D3 Polymers, Polymer Solutions, Physical Properties and their Relations I (Thermodynamic Properties Equilibria of Ternary Polymer Solutions) ... 

Like poly(p-dioxanone) homopolymer, copolymers of PDO and lactide can be prepared by several conventional polymerization means. The most commercially viable method relies upon melt polymerization. Since a thermodynamic equilibrium between the monomer (p-dioxanone) and the polymer [poly (p-dioxanone) ], results during polymerization (Bezwada et al, 1987, 1990) in conversions ranging from... 

In a related study, Pitt and others (1979a) reported release rates of various steroids from monolithic films and capsules made from homopolymeric PCL, poly (D,L-lactide), and copolymers of caprolactone and D,L-lactide (in both 60/40 and 90/10 caprolactone/D,Lrlactide acid ratios), and copolymers of glycolic acid with D,L-lactide. The release rates of the steroids from the caprolactone-co-lactide polymers were similar to the homopolymeric PCL. However, the release rates from the glycolide-co-lactide polymers were much slower than those observed with PCL. Further data analysis revealed that the obseiv ed release kinetics depended upon the steroid dissolution rate (in the polymer) and the polymer cry stallinity. WTiile it is outside the scope of the current discussion, a good background reference on PCL thermodynamics and crystallinity is given by Lebedev (1979) and Chynoweth Stachurscki (1986). 

Duda, A. Penczek, S. Thermodynamics of L-lactide polymerization. Equihbrium monomer concentration. MacromofecMfe 1990, 23, 1636-1639. 

Witzke DR, Narayan R, Kolstad JJ. Reversible kinetics and thermodynamics of the homopolymerization of L-lactide with 2-ethylhexanoic acid tin(II) salt. Macromolecules 1997 30(23) 7075-85. 

In the design of a modem lactic acid plant, mathematical models are indispensable. For example, the kinetic model of oligomerization of lactic acid and the right thermodynamic model for the gas/liquid equilibria are important in design for the concentration of lactic acid by evaporation as well as for prepolymerization in the lactide route. 

CHEMISTRY AND THERMODYNAMIC PROPERTIES OF LACTIC ACID AND LACTIDE AND SOLVENT MISCIBILITY... 

Thermodynamic properties of lactic acids and lactide, including entropy of fusion (A5), heat of formation (AHf), and heat capacity Cp), have been determined calorimetrically. Table 2.7 summarizes some of the thermodynamic data at... 

Model propagation reactions were computationally investigated and the polymerization of lacOCA was predicted to be about three times more thermodynamically favorable than that of lactide. 

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