Anionic polymerization 1-propiolactone

Slomkowski, S., and Penczek, S., Influence of dibenzo-18-crown-6 ether on the kinetics of anionic polymerization of p-propiolactone, Macromolecules, 9, 367-369, 1976. 

Solvent and Substituent Effects in the Anionic Polymerization of o ,Q -Disubstituted j3-Propiolactones... 

These and related methods allowed us recently to reevaluate the structure of active centers in anionic polymerization of simple, unsubstituted lactones, 5-propiolac-tone. The rationale was put forward in terms of stereo -electronic factors to explain why g-propiolactone propagates on carboxylate and e-caprolactone on alcoholate anions. This is shown in scheme below ... 

In anionic polymerization, B-propiolactone initiated with potassium alcoholate, gives,in initiation,both alco-holate and carboxylate anions. Alcoholate ions in every next step convert partially into carboxylate whereas carboxylate reproduce themselves quantitatively. Thus, after a few steps only carboxylate anions are left (14). Related situation was observed in the polymerization of styrene oxide (15). Here, however, it is only due to the structure of the initiator used. Thus, when in the initiation step both secondary and primary alcoholate anions are formed, due to the low steric requirements, in the next step apparently only the attack on the least substituted carbon atom takes place and already in the second step exclusively secondary alcoholate anions are present. 

In the anionic polymerization there are three monomers only that have been studied in more detail, namely ethylene oxide, propylene sulfide, and B-propiolactone. Some... 

The anionic polymerization of B-propiolactone in CH2CI2 led to the dependence of the ratio of reactivities of macro ions and macroion pairs on the solvating power of the medium (53). For higher proportions in the mixture of the more powerfully ion solvating component (B-propiolactone) the ratio of kp/ki decreased (at 350C kp/ki= =210 and 150 for the systems with 1bPL o=1 and 3 mol l respecively). Moreover, k in this system practically does not depend on the composition of the mixture and the decrease of the ratio is due to the decrease of kp (33)). We found also that the ratio of kp/k decreases also when the temperature is lowered, e.g. in a system with bPL o= =3 mol l" from 150 at 35°C to 5.6 at -20OC. ... 

Assumptions concerning a possible zwitterionic mechanism were made by a number of authors for different cases of anionic and cationic polymerization68-73. This mechanism was well substantiated for the anionic polymerization of diethyl vinyl-malonate under the action of triphenylphosphine68, and 0-propiolactone under the action of trimethylamine69 and betaine70. ... 

Draw a short section of the polymer obtained from anionic polymerization of )S-propiolactone. 

What is the structure of the polymer produced by anionic polymerization /3-propiolactone using NaOH as catalyst ... 

Propiolactone The anionic polymerizations of the P-lactones and s-lactones have been extensively investigated... 

The kinetics of these polymerizations is complex. Both complexed ion pairs and free ions are involved in the propagation reactions and the free ion rate constants depend on monomer concentration. The relative reactivity of complexed ion pairs and free ions is temperature dependent. Above the inversion temperature of —35°C, free ions are more reactive than ion pairs, but below this temperature the ion pairs are more reactive. At 30 °C in DMF, the observed (average) propagation rate constant is 0.13 l/(mol s) [146], The anionic polymerization of a,a-dialkyl-P-propiolactones such as pivalolactone (a,a,-dimethyl-P-propiolactone) initiated with carboxylate anions exhibits the main characteristics of living polymerizations. 

These steps repeat themselves until the chains are built up. Anionic polymerizations can yield optically active polymers. This was observed in formations of poly(a-methyl, a-ethyl-p-propiolactone) [193] that contains asymmetric carbon atoms. 

With j8-propiolactone, an acetyl scission has also been discussed. The anionic polymerization of 8-caprolactone probably also occurs by an acyl ring opening ... 

Rate and Stereochemistry of the Anionic Polymerization of a,a -Disubstituted- fl-propiolactones... 

These investigations are continuing to more fully verify the solvent effects observed, and in addition, similar studies are in progress on the effect of substituent size as well as reaction solvent on the anionic polymerization of a series of a-methyl-a-alkyl-6-propiolactones. An equivalent series of B-propiolactam monomers was recently investigated in this laboratory with the surprising result that the rates of propagation within this series increased with increasing size of the a-alkyl substituent (6). 

It has been known for approximately 15 years that the homogeneous, anionic polymerization of a racemic mixture of a chiral g,g-disubstituted-crystalline polymers (1,2), as shown in Equation 1. 

Figure 2 (1). Thirdly, it was recently shown in the polymerization of a-ethyl-a-pheny1-3-propiolactone that the racemic monomer mixture, on the one hand, and the optically-actlve monomer, on the other, gave polymers with entirely different crystalline properties in these homogeneous anionic polymerization reactions ( ).

In the anionic polymerization there are three monomers only that have been studied in more detail, namely ethylene oxide, propylene oxide (methyloxirane), and p-propiolactone (propano-3-lactone). In the anionic active species, like alcoho-late anions, the negative charge (in contrast to onium cations) is localized almost exclusively on one atom. Therefore, dissociation constants are much lower and the differences in reactivity of ions and ion pairs are much more pronounced (Table 9). 

A recent example of the initiation method involves the living anionic polymerization of y-propiolactone initiated by potassium methacrylate in which the potassium cation is complexed with dibenzo-18-crown-6 (DB18C6) (equation 14). Because the growing chain end is a car-boxylate anion, no side reactions occur at the initiator s double bond. 

Epoxides readily undergo anionic copolymerization with lactones and cyclic anhydrides because the propagating centers are similar—alkoxide and carboxylate [Aida et al., 1985 Cherdron and Ohse, 1966 Inoue and Aida, 1989 Luston and Vass, 1984]. Most of the polymerizations show alternating behavior, with the formation of polyester, but the mechanism for alternation is unclear. There are few reports of cationic copolymerizations of lactones and cyclic ethers other than the copolymerizations of [5-propiolactone with tetrahydrofuran and... 

Lactones are easily polymerized by both cationic and anionic initiators, and in fact they (particularly /3-propiolactone) are known to polymerize explosively and unpredictably without addition of any initiators. Inhibitors, such as trialkylborates, have been used to prevent undesired polymerization (73GEP2255194). 

More recently Teyssie determined the rate constants in the polymerization of e-caprolactone (eCL) initiated with aluminium alkoxides, believing that the covalent species are the only ones responsible for propagation [4]. For the same monomer Yamashita estimated tentatively rate coefficients of propagation using an anionic initiator [ ]. Lenz in his studies of substituted g-propiolactones (gPL) observed peculiar influence of structure on reactivity that can have its origin in the multiplicity of ionic structures involved [fi]. 

Photopolymerization of acrylamide by the uranyl ion is said to be induced by electron transfer or energy transfer of the excited uranyl ion with the monomer (37, 38). Uranyl nitrate can photosensitize the polymerization of /S-propiolactone (39) which is polymerized by cationic or anionic mechanism but not by radical. The initiation mechanism is probably electron transfer from /S-propiolactone to the uranyl ion, producing a cation radical which propagates as a cation. Complex formation of uranyl nitrate with the monomer was confirmed by electronic spectroscopy. Polymerization of /J-propiolactone is also photosensitized by sodium chloroaurate (30). Similar to photosensitization by uranyl nitrate, an election transfer process leading to cationic propagation has been suggested. 

T7177>. Ring-opening polymerization can proceed by two mechanisms depending on the initiator used the coordination-insertion mechanism or the anionic mechanism. While most studies focused on the synthesis of poly(/3-hydroxy butyrate), alternative PHAs were synthesized from a-methyl-/3-pentyl-/3-propiolactone... 

D Hondt and Lenz polymerized optically active a-phenyl-a-ethyl-/ --propiolactone anionically a racemic and an isotactic product were formed [99]... 

By comparison unsubstituted lactones such as propiolactone (G) polymerize more slowly and molecular weights are lower. The authors believe propagation is slower, the carboxylate anion formed from pivalolactone ring opening being more nucleophilic because of the inductive effect of the two methyl substituents. 

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