What are reactivity ratios?
The reactivity ratio is a measure of the tendency for a comonomer to show a preference for insertion into a growing chain in which the last inserted unit was the same, rather than the other comonomer.
What is reactivity ratio in copolymerization?
The reactivity ratios represent the rate at which one type of growing chain end adds on to a monomer of the same structure relative to the rate at which it adds on to the alternative monomer. The copolymer equation can be used to predict chain structure in the three different ways, already mentioned.
What is copolymerization example?
The process of forming polymers from two or more different monomeric units is called copolymerization. Multiple units of each monomer are present in a copolymer. The process of forming polymer Buna-S from 1, 3-butadiene and styrene is an example of copolymerization.
What is meant by copolymerization?
Copolymerisation is a process in which a mixture of more than one monomeric species is allowed to polymerise. The copolymer contains multiple units of each monomer in the chain.
How do you calculate reactivity ratio?
(a) Reactivity ratios are defined by the ratios of the propagation rate constants for adding a monomer (A or B) to a growing chain end of the same identity. rA = kA/kB represents the preference of the A-chain end for similar monomers of type A and likewise rB.
What is monomer ratio?
The reactivity ratio for each propagating chain end is defined as the ratio of the rate constant for addition of a monomer of the species already at the chain end to the rate constant for addition of the other monomer. The copolymer equation is then: with the concentrations of the components in square brackets.
What is graft copolymerization?
Graft copolymer is a type of copolymer in which one or more blocks of homopolymer are grafted as branches onto a main chain, meaning it is a branched copolymer with one or more side chains of a homopolymer attached to the backbone of the main chain.
What are homopolymers and copolymers?
If a polymer consists of only one kind of monomers then it is called a homopolymer, while a polymer which consists of more than one kind of monomers is called a copolymer.
Is copolymer A silicone?
One such silicone copolymer is poly(dimethylsiloxane) (PDMS) based-polyurethane. Silicone oils are widely used in personal care products and they can provide unique properties, such as high lubricity, non-toxicity, excessive spreading and film formation.
What is QE scheme?
Quantitative easing (QE) is a form of unconventional monetary policy in which a central bank purchases longer-term securities from the open market in order to increase the money supply and encourage lending and investment. Instead, a central bank can target specified amounts of assets to purchase.
What is a grafted polymer?
Graft polymerization is a process in which monomers are covalently bonded and polymerized as side chains onto the main polymer chain (the backbone). Grafting is an attractive approach to impart a variety of functional groups to a polymer. 1 (A, B, and C are representing different types of monomers).
Is oligomer a monomer?
In other words, oligomer is a molecule that consists of a few monomer units. Dimers, trimers, and tetramers are, for example, oligomers respectively composed of two, three, and four monomers.
What is the molar ratio of a copolymer?
The molar ratio of each monomer in the polymer is normally close to one, which happens when the reactivity ratios r 1 and r 2 are close to zero, as can be seen from the Mayo–Lewis equation. For example, in the free-radical copolymerization of styrene maleic anhydride copolymer, r 1 = 0.097 and r 2 = 0.001,…
What is the quantity R2 in copolymerization?
The quantity r1 r2 is the ratio of the product of the rate constants for reactions of a radical with a monomer of same kind to the product of the rate constants for the cross reactions. The figure below shows the incremental polymer composition as a function of monomer composition for different reactivity ratios.
How to predict the composition of a copolymer?
To predict the composition of a copolymer based on the reactivity ratios, we introduce two more variables: the mole fraction of unreacted monomer f1and the mole fraction in an increment of copolymer F1formed at a given stage in the polymerization process: f1= [M1] / ([M1] + [M2])= 1 – f2 F1=(r1f12+ f1f2)/(r1f12+ 2f1f2+ r2f22)
What should the reaction pressure be for copolymerization?
A commercial polymer with an overall CTFE-to-ethylene ratio of 1:1 contains ethylene blocks and CTFE blocks in the proportion lower than 10 mol.% each [40]. Reaction pressure is adjusted to give the desired copolymer ratio [41]. Typical pressures during the process are on the order of 3.5 MPa (508 psi).