SynopsisMelt crystallization of isotactic polypropylene (iPP), poly(ethy1ene oxide), poly(butene-l), and polycaprolactone in contact with various substrates (mostly polymeric) has been studied by hot stage polarizing microscopy. Nucleating abilities of surfaces have been characterized qualitatively by examining the substrate-induced morphologies of the crystallizing polymer. These morphologies have been classified into three groups, depending on whether the substrate is very active (transcrystallinity), moderately active, or inactive as a nucleating agent. The morphologies observed are temperature-dependent, changing from transcrystalline to spherulitic upon increase of the crystallization temperature. A t intermediate temperatures, mixed surface morphologies (transcrystalline plus spherulitic) are observed.The concentration of titanium and aluminum catalytic residues in isotactic polystyrene (ips) samples can be reduced by two methods, i.e., (a) fractionating the polymer and (b) chelating Ti and A1 with acetylacetone. The high nucleating ability of IPS samples in the crystallization of iPP has been shown to be due to the polymer (ips) itself, and not to Ti and A1 residues. Apart from ips, other polymers (low energy surfaces) have also been found to induce transcrystallinity.From a, survey of 43 substrate-crystallizing polymer pairs, conclusions have been drawn which are relevant to the following potential factors in heterogeneous nucleation processes: (a) chemical structure, (b) crystallographic unit cell type, (c) lattice parameters, (d) crystallinity of substrate, and (e) surface energy of substrate.Summit, New Jersey 07901. chusetts, Amherst, Massachusetts.

SynopsisIn the melt crystallization of isotactic polypropylene, poly(ethy1ene oxide) and poly(butene-1) in contact with substrates, the existence of a fixed number of nucleating sites on the substrate surfaces has been established. When these sites become active successively (the transient in the number of nuclei is long) during crystallization, pseudohomogeneous nucleation on the substrate occurs. Nucleation rates for poly(butene-1) and poly(ethy1ene oxide) on substrates and in bulk have been measured. These data can be used for comparing the nucleating ability of substrates. Estimates of the variation of bulk nucleation rates from one volume element to another as well as for repeated crystallization within a given volume element have been included. Finally, the temperature coefficients of heterogeneous nucleation rates have been combined with the temperature coefficient of spherulitic growth rate of poly(butene-1), to yield values of the interfacial energy parameters appearing in the theory of heterogeneous nucleation. The quantitative characterizetion of the nucleating ability of substrates by this method is an improvement over the mere use of nucleation densities or nucleation rates.

SynopsisIn the initial stage of the development of transcrystallinity, nuclei appear sporadically on the substrate. The growth rate and melting temperature of the transcrystalline region are found to be the same as those of spherulites nucleated in the bulk of the polymer. Nucleation densities n, a t the interface, and nb in bulk, for the crystallization of isotactic polypropylene, poly (ethylene oxide), and poly (butene-1) in contact with various substrates, have been measured by counting the number of spherulites generated. Despite variations in the results from various causes, the quantities n, and ns/nb are useful parameters for characterizing the nucleating ability of various substrates.

The notch sensitivity of high‐density polyethylene (HDPE), polypropylene (PP), and polybutylene (PB) was evaluated using uniaxial tensile deformation and fractographic analysis. Each polyolefin was tested at relatively low and high molecular weights (MW). Only the lower MW HDPE was found to be clearly notch‐sensitive. The lower MW PP exhibited some tendency toward notch sensitivity. The lower and higher MW PB, the higher MW HDPE, and the higher MW PP displayed notch strengthening. Whereas PB showed similar notched tensile performance regardless of molecular weight, both HDPE and PP showed higher susceptibility to notch sensitivity at lower molecular weights (and concomitant higher crystallinity). Tendencies toward notch sensitivity or notch stengthening were evidenced in the failure modes of these materials.

Polybutylene (PB) refers to a series of commercial semicrystalline resins derived from high molecular weight, predominantly isotactic poly(1‐butene) homopolymer or copolymer. 1‐Butene is manufacture by the catalytic oligomerization of ethylene. It can also be manufactured from mixed butylenes streams: acid extraction, the Sorbutene process, and the methyl tert ‐butyl ether process. Isotactic poly (1‐butene) is manufactured by a stereospecific Zeigler‐Natta polymerization. In melt processing of commercial PB resins, two crystal forms are encountered. PB pipe can be fabricated by extrusion, PB film is produced by a blown film process. Other processing systems are also discussed. The most important commercial outlet for PB resins is in pipe with applications that include cold‐water service and cold‐ and hot‐ water plumbing. Some other pipe applications include well piping, heat‐pump piping, and fire‐sprinkler piping. The advantages of PB in pipe applications include flexibility, toughness, resistance to creep, environmental stress cracking, wet abrasion, and chemicals. PB can also be used in seals on containers and packages since it has the ability to peel with controllable force. Data are also given on specifications and analytical methods. 1‐Butene is flammable. It is not toxic at moderate concentrations, higher concentrations cause an anesthetic effect,