What are Polyolefin Polymers?
Polyolefins are macromolecules formed by the polymerization of olefin monomer units. The IUPAC nomenclature term for polyolefins is poly(alkene). The most common polyolefins are polypropylene (PP) and polyethylene (PE). These polymers are prevalent in a wide array of applications depending on the material characteristics of the polymer, most notably consumer plastic. Thus, molecular properties like molecular weight (MW) distribution and branching are fundamental and related to parameters such as material fatigue, impact strength, and resistance to degradation. As a result, these properties routinely inform research and development (R&D) as well as for quality control and assurance (QC, QA).
Common types of polyolefin polymers
Polyolefins polymers are some of the most prevalent plastics used today and come in various types
- Polyethylene (PE) with subgroups
- high-density HDPE
- low-density LDPE
- linear low-density LLDPE
- Polypropylene (PP)
- Ehylene propylene diene monomer (EPDM) rubber
The table below gives a glimpse of the wide-scale distribution of these materials, ranging from everyday household use to specialized industrial applications. Here, most take advantage of the resistance to heat and an array of common solvents. This then makes the materials economical for many tough high wear applications.
|Polymer Type||Symbol||Examples of use|
|HDPE||♴||fuel tanks, bottle caps, plastic bottles,…|
|LDPE||♶||liquid containers, tubing, plastic wrap,…|
|PP||♷||piping, carpet, roofing, hinges, auto parts,…|
|EPDM||seals, electrical insulation, roofing,…|
Polyolefin melting point
Polyolefins are typically dissolved in high-boiling solvents, such as 1,2,4-trichlorobenzene (TCB), 1,2-dichlorobenzene (ODCB) or decahydronaphthalene (decalin), at temperatures from 130 – 160 °C. Here, Molecular Weight characterization needs can sometimes be met with simple Ubbelohde intrinsic viscosity data or melt flow index determinations. For advanced characterization, high-temperature Gel Permeation Chromatography is used to compare different branching agents, to predict performance and to correlate with rheology results. In other words, Molecular Weight (MW), a radius of gyration (RG), and Mark-Houwink constants are often of interest. Some low molecular weight or oligomeric polyolefins may be (partially) soluble in xylenes and other organic solvents which allows for analysis of % monomer or % xylene-soluble fraction. These characteristics have a direct correlation to the physical properties, like flexibility & strength, of the final material.