Preparation of Polystyrene with Higher Tg Based on Triple Hydrogen Bond Interactions

1.2.1 General description

When a polymer is made by linking only one type of small molecule, or monomer, together, it is called a homopolymer. When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer. Two monomers A and B can be made into a copolymer in many different ways.

When the two monomers are arranged in an alternating fashion, the polymer is called an alternating copolymer:

In a random copolymer, the two monomers may follow in any order:

In a block copolymer, all of one type of monomer are grouped together and all of the other are grouped together. A block copolymer can be thought of as two homopolymers joined together at the ends:

When chains of a polymer made of monomer B are grafted on to a polymer chain of monomer A we have a graft copolymer:

Styrene, also known as vinyl benzene is an organic compound with the chemical formula C₆H₅CH=CH₂. Under normal conditions, this aromatic hydrocarbon is an oily liquid. It evaporates easily and has a sweet smell, although high concentrations confer a less pleasant odor. Styrene is the precursor to polystyrene, an important synthetic material. Styrene Monomer is the raw material for polystyrene and EPS, accounting for approximately two thirds of total styrene monomer production. The remaining styrene monomer is used as a feedstock in the production of SAN, ABS and the unsaturated polyester resins, SBR and polymer latex. Major downstream styrene markets (polystyrene and ABS) are under pressure as a result of oversupply and interpolymer competition, although rationalization of older, smaller styrenics units should help balance out the market.

Maleimide is the chemical compound with the formula H₂C₂(CO)₂NH. This unsaturated imide is an important building block in organic synthesis. The name is a contraction of maleic acid and imide, the -C(O)NHC(O)- functional group.

Fig1 Molecule of Maleimide

Maleimide and its derivatives are prepared from maleic anhydride by treatment with amines followed by dehydration. A special feature of the reactivity of maleimides is their susceptibility to additions across the double bond either by Michael additions or via Diels-Alder reactions.

A Copolymer is a polymer chain made up of two monomers units, say A and B. When produced by copolymerization, the copolymer chain will comprise a distribution of sequence lengths (S)which will depend upon the monomer feed ratio [A]/[B] and the reactivity ratio (r_A and r_B)which reflect the inherent tendencies of a radical to react with its own monomer relative to the co-monomer.

Therefore, because of the feed ratio, the polymerization of two or more monomers will result either to random copolymers, alternating copolymer and block copolymers ^[6,7].

If a feed ratio of is taken, then the reactivity ratios will indicate the inherent tendency of a system to produce particular sequence length distributions and hence the characteristic average sequence lengths. As an example, for a perfectly alternating copolymer, r_A=r_B=0 and the monomers alternate along the chain. Alternatively, for a completely random copolymer r_A=r_B=1 and S_A=S_B=2

One of the most common and useful reaction for making polymers is free radical polymerization.

It is used to make polymers from vinyl monomers, that is, from small molecules containing carbon-carbon double bonds. Polymers made by free radical polymerization include polystyrene, poly (methyl methacrylate), poly (vinyl acetate) and branched polyethylene.

Copolymerization of maleimide with styrene monomers results in a polymerization mechanism occurring via a charge-transfer complex or via the penultimate model, but it is obvious that polymerization of an electron rich monomer (styrene) with an electron poor monomer (maleimide) leads to a, predominantly, alternating copolymer [8,9].

Fig 1-1 charge transfer complex during the polymerization of styrene-maleimide copolymer

Fig 1-2 Styrene-Maleimide Copolymers