chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, a ladder polymer is a type of double stranded

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

with the connectivity of a ladder. In a typical one-dimensional polymer, e.g.

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...

and polysiloxanes, the monomers form two bonds, giving a chain. In a ladder polymer the monomers are interconnected by four bonds. Inorganic ladder polymers are found in synthetic and natural settings. Ladder polymers are a special case of

cross-link In chemistry and biology, a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...

ed polymers because the crosslinks exist only with pairs of chains. According to one definition, a ladder polymer, adjacent rings have two or more atoms in common.

Organic ladder polymers

Organic ladder polymers are of interest because they can exhibit exceptional thermal stabilities and the conformation of the subunits is constrained. Because they are less flexible, their processing can be challenging. An early example was derived from condensation of the 1,2,4,5-tetraaminobenzene with naphthalenetetracarboxylic dianhydride. Poly(benzimidazobenzophenanthroline) (BBL) is a conjugated ladder polymer. Its backbone is composed of aromatic rings and the ladder structures enable the uninterrupted polymer chains with periodic linkages. However, conjugated ladder polymers additionally contain pi conjugation via strong pi-pi stacking interactions and charge transport. Traditionally, p-typed doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is used as conductive polymers, but BBL doped with poly(ethyleneimine) (PEI) can provide a n-type doped conductive properties for fabricating high-performance organic electronic devices. BBL's glass transition temperature (Tg) is estimated to be around 500 C based on differential scanning calorimetry (DSC) measurements. BBL is stable at higher temperatures. In addition to this, the stress-strain curves of BBL fibers were observed to be very high compared to other semiconductor fibers with a value around 105.8 MPa with the highest BBL polymer concentration.

Inorganic and organometallic ladder polymers

Some polysilicates are ladder polymers. One example is provided by the mineral

tremolite Tremolite is a member of the amphibole group of silicate minerals with composition Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz, and occurs in two distinct forms, crystals and fib ...

. In the area of

coordination chemistry A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

, the ladder structure is seen in some

coordination polymer Coordination may refer to: * Coordination (linguistics), a compound grammatical construction * Coordination complex, consisting of a central atom or ion and a surrounding array of bound molecules or ions ** A chemical reaction to form a coordinat ...

s. Illustrative is the polymer uI(2-picoline">2-picoline.html" ;"title="uI(2-picoline">uI(2-picolinesub>n. When the 2-picoline is replaced by a tertiary phosphine, it forms a tetrameric cubane-type cluster, [CuI(PR₃₄ (R = organic group_. In both cases, the Cu(I) centers adopt tetrahedral molecular geometry.{{cite journal , doi=10.1021/cr100160e , title=One-Dimensional Coordination Polymers: Complexity and Diversity in Structures, Properties, and Applications , date=2011 , last1=Leong , first1=Wei Lee , last2=Vittal , first2=Jagadese J. , journal=Chemical Reviews , volume=111 , issue=2 , pages=688–764 , pmid=20804195 CuXLstructures

References

Polymer chemistry