Semicrystalline thermoplastics polymerization

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

D nidon A semicrystalline thermoplastic formed by polymerization of 1 -butene... 

Definition A semicrystalline thermoplastic formed by polymerization of 1-butene Empincal (C4Hs)x Formula [CHzCHCCzHsjjn Properties Colorless vise, liq. misc. with min. oil insol. in water m.w. 500-75,000 dens. 0.910 pour pt. -60 to 50 C... 

Polycaprolactone Poly-e-caprolactone (PCL) is a semicrystalline, thermoplastic, linear aliphatic polyester synthesized by the ring-opening polymerization of e-caprolactone and is produced commercially by Union Carbide-Dow (Midland, MI) and Rhone-Poulenc (Collegeville, PA). This polymer has a melhng point of approximately 62°C and a glass transihon temperature of approximately -60°C. PCL is readily degraded and mineralized by a variety of microorganisms [45] ... 

Poly (etheretherketone) or PEEK, the structure of which is shown in Fig. 16.2, was originally developed primarily for composite applications. It is produced by the step-growth polymerization process of dialkylation of bisphenolate salts. PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained at high temperatures. It has a glass transition temperature or Tg at about 143 °C and melts around 343 °C. It is highly resistant to thermal... 

Shear yielding in a form of homogeneous bulk process can contribute substantially to the crack resistance of a polymeric solid. On the other hand, however, localized shear yielding in the form of shear microbands is believed to be a precursor of brittle fracture in many semicrystalline thermoplastics. Localized shear yielding is thus a major contributor to the initiation of cracks along with crazing, which, however, is believed not to operate in semicrystalline thermoplastics. 

The final mechanism of stress relief is the thermomechanically activated chain scission. Primary bond breakage can be homolytic, ionic, or by a degrading chemical reaction. It is worthwhile to note that the relative slippage of chains, microfibrils, and fibrils reduces or prevents the mechanical scission of chains in quasi-isotropic polymeric solids. In other words, chain scission is an important mode of fracture only in highly oriented semicrystalline thermoplastics. 

Polyacetals, also referred to as polyoxymethylenes (POMs) or polyfonnalde-hydes, are a semicrystalline engineering thermoplastic polymerized as a homopolymer and copolymer. The homopolymer and copolymer have somewhat different molecular structures and performance values. The difference between performance values is narrowing with new formulations (compounds). Polyacetal engineering thermoplastics were introduced to the world in 1956 with the potential of replacing metals, aluminum, brass, and cast zinc, which polyacetals continue to do. 

Polyethylene is a semicrystalline, thermoplastic material classified as a synthetic organic polymer. Depending on manufacturing process conditions, polyethylene melts between approximately 110-135°C to form a non-Newtonian hquid that may be molded into a wide variety of shapes utilizing various fabrication techniques. One of the first questions many scientists and engineers ask when beginning a career in the polyethylene industry is How can such a simple polymer, represented by the formula -(CH -CH ) -, result in such a complex business The answer lies in the enormous variety of molecular structures that are possible in the polymerization and, more importantly, copolymerization of ethylene with a wide variety of other 1-olefins. 

Polypropylene (PP) is a semicrystalline commodity thermoplastic produced by coordination addition polymerization of propylene monomer [197]. Most frequently, stereospecific Ziegler-Natta catalysts are used in industrial processes to produce highly stereospecific crystalline isotactic (iPP) and syndiotactic (sPP) polymer with a small portion of amorphous atactic PP as a side product. Polymerization of non-symmetrical propylene monomer yields three possible sequences however, the steric effect related to the methyl side group highly favors the head-to-tail sequence. The occurence of head-to-head and tail-to-tail sequences produces defects along the PP chain [198]. Presence of such defects affects the overall degree of crystallinity of PP. 

Block copolymers were developed rapidly in the 1960s when living anionic polymerization was first utilized to synthesize triblock thermoplastic elastomers or elastoplastics. At the same time, step or condensation polymerization to produce thermoplastic polyurethanes, urea-urethane spandex fibers, and later more specialized materials, such as the semicrystalline polyester-polyether copolymers were developed [10]. Imide block or segmented copolymers utilizing... 

Another remarkable character of this class of Ni complexes is their tendency to promote living polymerization of a-oleftns at low temperatmes and with low concentrations of the monomer. Thus, the low-temperatme polymerization of propylene leads to a material whose number average molecular weight (Mn) increases almost linearly as a function of time and propylene consumption, reaching values ofM = 160 000 Daltons and polydispersities of ca. 1.13. This character allows these Ni catalysts to produce A-B-A type block copolymers composed of semicrystalline and amorphous segments, which is used to prepare thermoplastic elastomeric polymers. The Ni catalysts can also polymerize internal cyclic... 

The living nature of the nickel-catalyzed a-olefin polymerizations coupled with the propensity for chain straightening of longer a-olefins can be utilized to prepare block copolymers with well-defined architectures. For example, the synthesis of a-olefin A—B—A block copolymers where the semicrystalline A blocks are made up of poly(l-octadecene) and the B block is composed of a more highly branched, amorphous, random copolymer of propylene and 1-octadecene enabled the preparation of thermoplastic elastomeric polyolefins. ... 

PIT is a semicrystalline polymer synthesized by the condensation of PDO with either terephthalic acid or dimethyl terephthalate, followed by polymerization. Studies of PTT had never gone beyond academic interest until recent years because one of its raw materials, PDO, was very expensive and available only in a small volume. PTT received less attention compared with PET and PBT. However, recent breakthroughs in PDO synthesis made PTT available in industrial quantities, thus offering new opportunities in carpet, textile, film, packing, and engineering thermoplastics markets. 

There are many kinds of bio-based and biodegradable polymers, among which one of the most promising is poly(lactic acid) (PLA), a biocompatible thermoplastic aliphatic polyester. PLA is a linear thermoplastic polyester produced by the ring-opening polymerization of lactide. Ln general, commercial PLA grades are copolymers of poly(L-lactic acid) and poly(D,L-lactic acid), which are produced from L-lactides and D,L-lactides, respectively. The ratio of L-enantiomers to o,L-enantiomers is known to affect the properties of PLA, i.e. if the materials are semicrystalline or amorphous. Until now, most of the efforts reported in order to improve the properties of PLA have been focused on the semicrystalline material. ... 

Polybutadiene-type resins n. Unsaturated, thermosetting hydrocarbons cured by a peroxide-catalyzed, vinyl-type polymerization reaction, or by sodium-catalyzed polymerization of butadiene or blends of butadiene and styrene. Liquid systems, curable in the presence of monomers, are used for casting, encapsulation, and potting of electrical components, and in making laminates. Molding compounds, often containing fillers and modified with other resins or rubbers, may be compression or transfer molded. Syndiotactic 1,2-butadiene, introduced in 1974 in Japan, is thermoplastic, with semicrystalline nature, with good transparency and flexibility without plasticization. In the presence of a photosensitizer such as p,p -tetramethyl... 

Polypropylene (PP) is a thermoplastic material that is produced by polymerizing propylene molecules, which are the monomer units, into very long polymer molecules or chains. There are a number of different ways to link the monomers together, but PP as a commercially used material in its most widely used form is made with catalysts that produce crystallizable polymer chains. These give rise to a product that is a semicrystalline solid with good physical, mechanical, and thermal properties. Another form of PP, produced in much lower volumes as a byproduct of semicrystalline PP production and having very poor mechanical and thermal properties, is a soft, tacky material used in adhesives, sealants, and caulk products. The above two products are often referred to as isotactic (crystallizable) PP (i-PP) and atactic (noncrystallizable) PP (a-PP), respectively. 

The two principal types of polymerization for thermoplastics including engineering thermoplastics are polycondensation polymerization and chain-growth polymerization. Both types can usually produce hnear, branched, crosslinked amorphous and semicrystalline aromatic and aliphatic polymers [14]. 

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