POLY(N-ACYLETHYLENIMINE) COPOLYMERS CONTAINING PENDANT PENTAMETHYLDISILOXANYL GROUPS .2. THERMAL-BEHAVIOR AND X-RAY-DIFFRACTION STUDY

Two series of random copolymers of 10-(pentamethyl disiloxanyl) decyl oxazoline (Si) with undecyl (U) (four copolymer compositions) and nonyl (N) (eight copolymer compositions) oxazolines over the whole composition range, with a total degree of polymerization of about 100, were studied by DSC and wide angle X-ray diffraction. All the polymers are crystalline. For the N/Si copolymers, the melting points, normalized DELTA-H and DELTA-S of fusion are almost constant in a broad range of copolymer composition from 10 to 65 mol % of Si. The rationale for this behavior is that the copolymers crystallize two dimensionally, with the crystalline polymethylene plates separated by the bulky flexible pentamethyl disiloxanyl (P) groups. In this range, increasing Si only increases the distance between the plates. With more than 65 mol % Si, the bulky P groups interfere with the packing of the alkyl chains and change the crystallization behavior; the polymers show disordered packing as demonstrated by their X-ray patterns and extremely low DELTA-H. In the U/Si copolymers, since the undecyl side chain has one more carbon than the decyl group to which the P group is attached, the P groups interfere much more strongly with the packing of the side chains than in the N/Si polymers. The copolymer melting points uniformly decrease as the concentration of Si increases. The plateau on the plot of normalized DELTA-H versus polymer composition is only from 10 to 50 mol % of Si. The average long spacings of the annealed polymers increase linearly from 24 angstrom (N/Si polymers) or 28 angstrom (U/Si polymers) to 34.1 angstrom with the increase of Si up to 50%. With more than 50% Si, the polymers have an identical lamellar thicknesses of 34 angstrom, within the experimental error. Copolymers with less than 75 mol % of Si can crystallize from hexadecane solutions forming gels down to polymer concentrations of 2-3 wt %. The long spacings of the gels are almost identical with those of the pure crystalline polymers and independent of the polymer/solvent ratios. When hexamethyl disiloxane is added to the solutions, it can intercalate and the resulting crystalline gels have long spacings larger than those found in the absence of siloxane.