(1974).The crystalline conformation of polypivalolactone was determined by analysis of the chain conformational energies and it was found that the minimum energy corresponds to a planar tmrzs conformation for the ester group. The result was con~pared to published X-ray data based on fiber diffraction which show a significant deviation from trans planarity. This difference is discussed in terms of the relative energies involved and by comparison with literature crystallographic results of low molecular weight carboxylic esters. It is stressed that because of the paucity of information in fiber diffraction, internal energy considerations are important for assigning internal rotation angles. Crystallographic results for low molecular weight compounds show that deviations greater than 10" from trans planarity are rare for ester groups.J. COR~IBERT, N. V. MIEN, F. BRISSE et R. H. MARCHESSAULT. Can. J. Chem. 52,3742 (1974). On a determine la conformation cristalline de la polypivalolactone par analyse des energies conformationnelles de chaines; on a trouve que l'tnergie minimum correspond a une conformation trans coplanaire pour le groupe ester. Ce rCsultat est compare avec les donnees de rayons-)< publiees, basees sur la diffraction de fibre, qui montrent une deviation notable de la planarite trans. On discute de cette difference en termes d'knergies relatives impliquees et par comparaison avec les resultats cristallographiques rapportes dans la litterature pour des esters carboxyliques de faible poids moleci~laire. On fait remarquer que, dd ail peu d'information de la diffraction des fibres, la consideration d'energie internee est importante pour attribuer les angles de rotation interne. Les resultats cristallographiques pour des composes de bas poids moleculaires montrent que des deviations plus grandes que 10' par rapport a la planarite traits sont rares dans les groupes esters.[Traduit par le journal]

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A series of samples of poly(/j-hydroxy butyrate) in solution in 2,2,2-trifluoroethanol have been studied by means of light scattering. From asymptotic behavior of the angular scattering, results can be interpreted in terms of a relatively rigid rodlike particle with a linear density larger than that of the crystallographic helix. This implies a folding of helical segments leading to a model which is self-consistent with the hydrodynamic data in the same solvent.

AB and ABA block copolyesters based on racemic poly(α‐methyl‐α‐n propyl‐α‐propiolactone) (PMPPL) as a “soft” or elastomeric segment and polypivalolactone (PPL) as a “hard” or crystallizable segment have been synthesized and compared with random copolymers of the same composition. X‐ray studies show the coexistence of polymorphic crystal forms for a given polymer in a given sample. Thermal and dynamic mechanical properties give clear evidence of heterophase structure corresponding to segregation of PPL and PMPPL. The crystalline phase clearly provides thermally reversible crosslinking in the ABA block copolymers. On stretching, the planar zigzag form of PMPPL is observed. Because of the domain structure, moduli of ABA samples are higher than those of PMPPL and their tensile strengths are similar to those of comparable styrene‐butadiene block copolymers. The polymer synthesis was achieved by sequential monomer addition with tetrahexyl ammonium benzoate as initiator. For the ABA polymers the diammonium salt of sebacic acid provided a di‐functional initiator. The agreement between calculated and observed molecular weights testify to the “living” character of this polymerization reaction.