LLDPE, HDPE, PET, PP, AC, HIPD, GPPS, EPS, PE, PVC, E/P
A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their broad range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function.
Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals
CHAIN LENGTH
The physical properties of a polymer are strongly dependent on the size or length of the polymer chain. For example, as chain length is increased, melting and boiling temperatures increase quickly. Impact resistance also tends to increase with chain length, as does the viscosity, or resistance to flow, of the polymer in its melt state.[21] Melt viscosity is related to polymer chain length Z roughly , so that a tenfold increase in polymer chain length results in a viscosity increase of over 1000 times.
Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass transition temperature (Tg)[citation needed]. This is a result of the increase in chain interactions such as Van der Waals attractions and entanglements that come with increased chain length[citation needed]. These interactions tend to fix the individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures[citation needed].
Degree of Polymerization
common means of expressing the length of a chain is the degree of polymerization, which quantifies the number of monomers incorporated into the chain.As with other molecules, a polymer’s size may also be expressed in terms of molecular weight. Since synthetic polymerization techniques typically yield a polymer product including a range of molecular weights, the weight is often expressed statistically to describe the distribution of chain lengths present in the same.
Common examples are the number average molecular weight and weight average molecular weight.The ratio of these two values is the polydispersity index, commonly used to express the “width” of the molecular weight distribution.A final measurement is contour length, which can be understood as the length of the chain backbone in its fully extended state.
The flexibility of an unbranched chain polymer is characterized by its persistence lenght.