Heats of fusion, melting transitions, and the derived entropies of fusion were obtained by differential scanning calorimetry for examples from three homologous series of homopolymers having long side chains. Homopolymers having side‐chain lengths between 12 and 22 carbon atoms were chosen from the poly(n‐alkyl acrylates), the poly(N‐n‐alkyl‐acrylamides) and the poly(vinyl esters). The data demonstrated that only the outer paraffinic methylene groups were present in the crystal lattice. This was concluded because phase diagrams obtained for mixtures of structurally different monomers and homopolymers, as well as for selected copolymers, showed only isomorphism in the polymeric examples. In addition, scanning curves, reflecting the distribution of crystallite sizes, became narrower as the side chains became longer. The critical chain length required to maintain a stable nucleus in the bulk homopolymers was a constant value for each homologous series. It varied between 9 to 12 carbon atoms. When heats of fusion were determined in the presence of methanol, main‐chain restraints were freed, thus permitting more methylene groups to enter the crystal lattice. Hence, the heats of fusion, the crystallinity, and melting points increased above that of the bulk state. The magnitude of the contribution to the heats of fusion by each methylene group indicated that the hexagonal paraffin crystal modification prevailed in these homopolymers, in agreement with x‐ray data from the literature.

synopsisThe heats of fusion and the melting transitions of the crystallinity present in the side chains were determined for selected copolymers incorporating n-octadecyl acrylate or vinyl stearate. A major purpose of this investigation was to ascertain the effect of INTRODUCTIONMuch interest has centeredl8.2 on the crystallization phenomenon in copolymers in which one co-unit of the main chain is capable of crystallizing. The Flory theory of the equilibrium crystallization of polymers3 required that sequence length distribution, and not the chemical nature of the amorphous component, determbed the melting point depression. A very broad distribution of crystal sizes and lowered crystallinities were 3349 0

synopsisHeats of fusion and melting temperatures were obtained for selected monomeric n-alkyl acrylates, N-n-alkylacrylamides, and vinyl esters. The correspoqding thermodynamic parameters for homopolymers, derived from these monomers, had been reported previously from this laboratory. The a-hexagonal crystal modification was indicated near the melting point for the higher n-alkyl acrylates, but a B form was stable at low temperatures for the entire series. The magnitude of the heats of fusion indicated @ polymorphs for vinyl esters in support of x-ray diffraction analysis from the literature. Because hexagonal crystal geometry prevailed in all reported homopolymers having long side chains, greater emphasis was placed on thermodynamic data for monomers exhibiting this crystal modification. Accordingly, a convergence temperature was estimated ststistically for the a-hexagonal crystal modification of these systems and appropriate literature values of the n-alkanes and ethyl esters. The convergence temperature was computed to be 135OC, uncorrected for the entropy of disorientation. The anomalously large interfacial end-packing-defect energy of the poly(n-alkyl acrylates) and the poly-N-n-alkylacrylamides was shown to be associated with a high energy barrier to molecular transport in the melt as the vitreous state was approached. In support of this conclusion, similarity of the glass and melting transition temperatures of these homopolymer homologs occurred near their critical side-chain lengths, below which the homopolymers are amorphous. A special critical requirement of nucleus length was not indicated from rough estimations of nucleation parameters for the poly(n-alkyl acrylates). These findings lent increased, but still not unqualified, support to an x-ray diffraction study frpm the literature. The latter had specified the inclusion of the entire side chain and the main-chain units in the crystal lattires of the higher poly(n-alkyl acrylates).