Polyesters semicrystalline polymers, properties

Aliphatic polyesters are low-melting (40-80°C) semicrystalline polymers or viscous fluids and present inferior mechanical properties. Notable exceptions are poly (a-hydroxy acid)s and poly (ft -hydroxy acid)s. 

Wholly aromatic polyesters, in which both R1 and R2 are aromatic, are either high-7 amorphous polymers or veiy high melting semicrystalline polymers that often exhibit liquid crystalline properties. 

The presence of crystalline regions tends to rednce the level of light transmission, and pnre semicrystalline polymers in moderate thickness are generally translucent. They include the polyolehns, polyamides, and thermoplastic polyesters. However, several crystallizing polymers can be made into highly transparent, relatively thick prodncts. They are polymethylpentene and polyethyleneterepthalate. Films of many crystallizing polymers, particnlarly oriented hhns, can also be transparent See also optical properties. 

Functionalization of more polar hydroxytelechelic polymers with the synthon resulted in comparably spectacular changes in material properties. Functionalized polyether is a material with a broad rubber plateau in DMTA, and a storage modulus of 10 MPa, whereas the starting material is a viscous liquid. The properties of functionalized polyester and functionalized polycarbonate are those of semicrystalline polymers, whereas the starting materials are very brittle. 

The incorporation of impermeable clay particles into PET (which is a semicrystalline polymer) can improve the barrier properties of PET nanocomposites towards gases and water vapor. This, in turn, results in outstanding property improvements in terms of a decreasing water permeability for food packaging and an increasing flame resistance. When a new system of saturated polyesters... 

Properties of semicrystalline thermoplastics are normally enhanced via reinforcing filler. However, the type and amount of such fillers would complicate any comparison. Hence, properties of various unfilled semicrystalline resins are compared shown in Tables 1.1-1.3. For comparison two commodity semicrystalline polymers, high density polyethylene (HDPE) and polypropylene (PP), are included in Table 1.1. Table 1.1 summarizes properties of HDPE, PP, POM, and polyesters. Table 1.2 contains properties of polyamides and SPS. Table 1.3 lists properties of the highly aromatic, semicrystalline polymers. Clearly, semicrystalline ETPs exhibit very broad performance enhancements over commodity semicrys-talhne polymers. 

Table 1.1 Properties of Semicrystalline Polymers HOPE, PR POM, and Polyesters...

Polylactide is a kind of biodegradable polyester that possesses many desirable properties such as non-toxicity, hydrolyzability and biocompatibility for use for varied biomedical purposes such as sutures, fracture fixation, oral implant and drug delivery microspheres.It is popularly synthesized by the ringopening polymerization of lactide monomers which are the cyclic dimers of lactic acid. Polymerization of racemic D,L-lactide typically results in atactic, amorphous polymers named poly(D,L-lactide) (rg 60 °C), whereas polymerization of L-lactide or D-lactide results in isotactic, semicrystalline polymers called poly(L-lactide) or poly(D-lactide) (7" 180 PLA fractures... 

Polymers containing unsatmated rubber and semicrystalline polymers are often effectively stained using OSO4. What about materials that do not show such differential staining Two examples will be described where reactive (unsaturated) materials are included into the polymer to provide reaction sites. Inclusion of a stainable unsaturated polymer was shown for cellulosics [179] and synthetic fibers [202]. The initial work focused on improvement of the properties of cellulosics by inclusion of an elastomer between the microfibrils. OSO4 staining revealed that a lamellar sheet structure was present. Marfels and Kassenbeck [202] used a similar method with polyester and nylon fibers. 

There are many fibers of S3mthetic origin, most of them spun or extrusion-drawn semicrystalline polymers (e.g., polyolefins, polyamides, polyesters), which are not used as fillers for polymers. The main reason is that, for a material to play a potential reinforcement role as a filler for polymer, large differences in certain key properties must exist between the filler and the polymer matrix. It follows that only three types (or classes) of fibrous products can be considered as valid short synthetic fibers candidates for polymer reinforcement glass fibers, carbon fibers and aramid fibers. 

The above-mentioned results of the SSP of PET can be generally applied to other semicrystalline polyesters, such as poly(butylene terephthalate) (PBT), poly(tri-methylene terephthalate) PTT), polyethylene naphthalate) (PEN) or any other kind of semicrystalline co-polyester, as a result of their similar reaction behaviors. Most of the studies have been focused on PET and PBT due to their industrial importance. Meanwhile, the popularity of PEN is growing on account of the outstanding properties of this particular polymer. 

Mecking showed an efficient way to produce a,G>diesters from fatty acid esters yielding excellent monomers for semicrystalline polyesters [63], Some part of the diesters was hydrogenated to diols and was transesterified with the diesters from the hydroesterification of methyl oleate into long-chain polyesters (Scheme 24). The properties of this thermomorphic polymer are related to those of polyethylene. 

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