How do you control the molecular weight of radical polymerization?
Control of radical polymerization in order to get a polymer with lower average molecular mass can be done by one of these ways:
- Increase the amount of initiator relative to monomer (i.e. double or triple the amount).
- Use a chain transfer agent such as a thiol or mercaptan (R-S-H).
How do you control molecular weight in step growth polymerization?
In irreversible step-growth polymerization, the molecular-weight distribution (MWD) of the polymers produced can be controlled via the reaction path. In this paper, the effect of intermediate monomer feed on MWD in batch reactors or continuous plug flow reactors is investigated using a kinetic approach.
How do you find the degree of polymerization from the molecular weight?
Divide the molecular weight of the polymer by the molecular weight of the monomer unit to calculate the degree of polymerization. If the molecular mass of tetrafluoroethylene is 120,000, its degree of polymerization is 120,000 / 100 = 1,200.
What is the significance of molecular weight distribution MWD?
Molecular weight distribution is a key item of information in tailoring polymer structures for different end uses. Manufacturers offer very many different grades of commodity polymers like poly(vinyl chloride), polyethylenes and polystyrenes. These grades differ significantly between themselves.
How can the control of the molecular mass of the resulting polymer be done?
We can control the average molecular mass of the resulting polyester. After mixing a diol or triol with a dicarboxylic acid, we can inject little monocarboxylic acid (e.g. acetic acid) to the reaction flask. This small acid will cause chain termination ~~~~~~~~O-CO-CH3 upon reacting with the accessible alcohol groups.
What happens when styrene polymerizes?
Styrene readily polymerizes to polystyrene by a relatively conventional free radical chain mechanism. Either heat or initiators will begin the polymerization. Initiators thermally decompose, thereby forming active free radicals that are effective in starting the polymerization process.
What is step-growth polymerization explain the steps involved in this process?
A step growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers form first dimes, then trimers, oligomers and eventually long chain polymers. The polymer is dissolved in solution with dimethylacetamide (CH3C(O)N(CH3)2) and dope is then dry spun.
How do you find theoretical molecular weight of a polymer?
Generally. the total molecular weight of any polymer is calculated by Degree of polymerization multiplied by molecular weight of monomer.
How is the molecular weight distribution in polymers explained?
Polymer molecular weight is defined as a distribution rather than a specific number because polymerization occurs in such a way to produce different chain lengths. Weight average molecular weight (MW) and number average molecular weight (MN) are two ways we can characterize the polymer molecular weight.
How does molecular weight affect polymer properties?
The lower the molecular weight, lower the transition temperature, viscosity, and the mechanical properties. Due to increased entanglement of chains with increased molecular weight, the polymer gets higher viscosity in molten state, which makes the processing of polymer difficult.
What do you understand by molecular weight and degree of polymerization of polymer?
The degree of polymerization (DP or Xn) is defined as the number of monomer units in the polymer. It is calculated as the ratio of molecular weight of a polymer and molecular weight of the repeat unit. Number average DP and weight average DP are the two main types used for measuring the DP.
What determines molecular weight of a polymer?
Molecular weight is determined by multiplying the mass of each subsequent repeating unit in the polymer chain, before adding the mass of either end group. This provides a range of values that are used to establish the molecular weight distribution of the material.
How radicals are used in polymerization?
The free radical uses one electron from the pi bond to form a more stable bond with the carbon atom. The other electron returns to the second carbon atom, turning the whole molecule into another radical. This begins the polymer chain.
What is step-growth polymerization explain with example?
In step-growth polymerization, one or more types of monomers can be involved, and each monomer should have at least two sites for bonding. For polymerization with more than one type of monomers, for example, involving A and B monomers, A–B step-growth polymerization or A–A/B–B step-growth polymerization can occur.
What is molecular weight of step polymer?
b) Step polymerization involving monomers of 120 and 130 g/mol, allowed to undergo sixteen polymerization steps. c) Step polymerization involving monomers of 100 and 105 g/mol, allowed to undergo ten polymerization steps, producing a condensation product with molecular weight 15 g/mol.
What is the molecular weight of polymer?
A polymer’s molecular weight is the sum of the atomic weights of individual atoms that comprise a molecule. It indicates the average length of the bulk resin’s polymer chains. All polymer molecules of a particular grade do not have exactly same molecular weight. There is a range or distribution of molecular weights.
How do you find the molecular weight of a distribution?
The average molecular weight is determined by summing the weights of all the chains and then dividing by the total number of chains. The average molecular weight is an important method of characterizing polymers.
What is molecular weight as applied to a polymer?
A polymer’s molecular weight is the sum of the atomic weights of the individual atoms that comprise a molecule. It indicates the average length of the bulk resin’s polymer chains.