The ring-opening polymerization and copolymerization of e-caprolactone, e-methyl-e-caprolactone, ß, -methyl-e-caprolactone (mixed isomers), and L-lactide using aluminum isopropoxide as initiator were investigated. The chain propagation proceeds through a living anionic type coordinated insertion mechanism. The kinetic features of this process are reported. The experimental monomer reactivity ratios indicate that e-caprolactone and its methyl derivatives yield random copolyesters. However, the e-caprolactone/L-lactide pair exhibits a departure from randomness with the preferred incorporation of L-lactide units. The thermal properties of the copolymers were investigated by differential scanning calorimetry. It was found that the crystallization of e-caprolactone units is limited, in all cases, to copolymers which are rich in this sort of unit. At the same time, the crystallization of L-lactide units was observed in copolymers with high concentrations of this comonomer.Analysis of the melting point depression data of the copolymers indicates that the L-lactide units are almost completely rejected from the caprolactone crystals, whereas about 50% of the e-methyl-ecaprolactone and , -methyl-e-caprolactone comonomer units are incorporated into the e-caprolactone crystals due to an obvious structural similarity. Finally, poly(c-caprolactone-co-e-methyl-e-caprolactone) samples are miscible with poly (vinyl chloride) (PVC) whatever the composition of the copolymer and the composition of the blend, whereas poly(e-caprolactone-co-L-lactide) samples are miscible with PVC uniquely for copolymer L-lactide contents equal to or smaller than 40 wt %. In all cases where miscibility was found, a negative thermodynamic interaction parameter was computed.

The miscibility of polymer blends is often assessed by the measurement of a single glass transition temperature (Tg) as a function of composition. Tg-composition data are generally expressed with equations which predict a monotonic variation of Tg, and any deviation of the results from the linear behavior is then considered as a measure of the strength of the interactions involved. However, an examination of the Tg data of polymer mixtures reveals that several systems exhibit a cusp as a function of composition. In the framework of the free volume theory, this behavior was shown several years ago by Kovacs to occur. According to this theory, if the free volume of the high-Tg polymer goes to zero at a critical temperature T" above the Tg of some of the blends, Kovacs's equation can be used; above Tc, the classical Tg-composition equations can be used. This sort of analysis was applied to a series of blends made of poly (e-caprolactone) with chlorinated polymers, with a good agreement with the experimental results and good predictions of Tc and 4>c, the critical volume fraction. Interaction parameters between this polyester and chlorinated polymers were then determined.

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The miscibility of blends of poly(viny1 chloride) (PVC) with polylactones of the @-propiolactone series (poly(a-methyl-a-n-propyl-@-propiolactone) (MPPL), poly(a,a-dimethyl-P-propiolactone) or polypivalolactone (PPL), and poly(a-methyl-a-ethyl-@-propiolactone) (MEPL)) has been studied by measurements of specific heat, mechanical relaxation, and density. These measurements indicate that there is extensive mixing between the segments of the two components of each blend since a single glass transition temperature and a decrease in melting point have been observed. From the depression in the melting point data, the interaction parameter xlz has been shown to be equal to -0.29 and -0.05 for PVC/MPPL and PVC/PPL blends, respectively.Even if it is well known that poly(ecapro1actone) (PCL) is miscible with a large number of polymers,' it is not clearly understood why this is so. However, it has often been suggested that specific interactions can be the driving force toward the formation of blends. For example, Olabisi2 has concluded that the PCL/poly(vinyl chloride) (PVC) blends are a result of the proton donating character of the a-hydrogens of PVC combined with the proton accepting character of the carbonyl groups of PCL. On the basis of this conclusion, one can rationalize why PCL is generally miscible with polymers containing hydrogens with a proton donating character, or hydroxyl groups, as for example poly(hydroxy ether), poly(epichlorohydrin), and poly (3,3-bis(chloromethyl)oxacyclobutane) (penton). Similar specific interactions have been suggested in blends of poly(buty1ene terephthalate)/poly(hydroxy ether of Bisphenol A) (31, Nylon G/ethyleneacrylic acid ~opolymer,~ poly(viny1 chloride)/ethylene-vinyl acetate-SOz terp o l y m e r~,~ poly(hydroxy ether of Bisphenol A)/poly(cyclohexylenedimethylene tere/i~ophthalate),~ poly(caprolactone)/poly(hydroxy ether of Bisphenol A),3 poly(viny1 chloride)/poly(butylene terephthalate),'j poly(styrene)/ poly(pheny1ene oxide) ,7 poly(viny1idene fluoride) /poly-(methyl acrylate),8 poly(viny1idene fluoride)/poly(ethyl acrylate),8 poly(viny1idene fluoride)/poly(vinyl a~e t a t e ) ,~ poly(viny1idene fluoride)/poly(methyl methacrylate),1° poly(viny1idene fluoride) /poly(ethyl methacrylate),'O and poly(methy1 methacrylate)/styrene-acrylonitrile copo1ymers.l'Following Olabisi's proposal, blends of PVC with common polyesters are expected to be thermodynamically miscible. In order to check this hypothesis, we have chosen polyesters derived from 6-propiolactone substituted in a,a. This series of polymers presents a wide range of physical properties including degrees of crystallinity ranging from 10 to 80% and melting points ranging from 25 to 240It is then the purpose of the present paper to study the degree of miscibility of PVC/polylactone blends by measurements of glass transition temperature ( T J , melting point ( T J , density, and mechanical relaxation. These blends will be shown to be thermodynamically miscible at all compositions in agreement with Olabisi's proposal. These res...

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