Molecular weight distribution in step growth polymerization pdf

The effect of thermal history on crystal molecular weight is shown in figure 4. The other process, called stepgrowth polymerization, involves the buildup of molecular weight not in a chainlike fashion but in a stepwise fashion, by the random combination of monomer molecules containing reactive functional groups. Species of different molecular weight oligomers are formed throughout the reaction, with the weight distribution broadening and shifting to higher molecular weight with reaction time. Stepgrowth polymerization method for ultrahigh molecular. Dynamic networks that drive the process of irreversible.

Control of molecularweight distribution in stepgrowth. The molar mass distribution of a polymer sample depends on factors such as chemical kinetics and workup procedure. These polymerization techniques generate many important commodity polymers where their broad range of molecular weight distribution gives rise to important physical properties. Stepgrowth polymerization request pdf researchgate. Robust molecular mass control is therefore a key issue in polymer production. Prediction of molecular weight distribution in chain. Request pdf stepgrowth polymerization stepgrowth polymerization is a very. Pdf this work presents results on the prediction of the molecular weight distributions mwd of chain growth polymerization using. Introduction synthetic polymers are polydisperse to varying degrees in a variety of ways. Polymer chemistry online course video lectures by iit. Polymerization processes are categorized into two broad classes, according to their reaction mechanisms. The chains in a sample may differ in, for example, molecular weight, degree of long or shortchain branching, stereostructure or composition either grossly, as with copolymers, or slightly, as with end group. Nature of chain polymerization and its comparison with step polymerization.

Starting from an abtype monomer, linear homopolymers, diblock copolymers, as well as starshaped polymers were synthesized in an efficient manner. Pdf prediction of molecular weight distribution in chain growth. Ideal stepgrowth polymerization gives a polymer with dispersity of 2. Ashok khanna and anil kumar, an analytical solution of the molecular weight distribution of reversible step growth polymerization in homogeneous continuous flow stirred tank reactors, journal of applied polymer science, 37, 11, 32053226, 2003.

Polymer molecular weight distribution and definitions of. Number distribution and number average molecular weight m n. Stiile colorado state university, fort collins, co 80523 as illustrated in the articles on chain polymerization, a chaingrowth polymerization is one in which each polymer chain, after being started by a free radical initiator, a cationic catalyst or an anionic catalyst, grows rapidly, producing a high molecular weight polymer. Chemical engineering 160260 polymer science and engineering. During propagation, only monomers react to the active site at the end of the growing chain. Molecular weight distribution in equilibrium stepgrowth. By varying t open access articles from polymer chemistry. Control of molecularweight distribution in stepgrowth polymerization. Solomon2 1 centre of research excellence in corrosion, research institute, king fahd university of petroleum and minerals, dhahran 31261, saudi arabia 2 corrosion protection and materials research laboratory, department of chemistry, faculty of science, university of.

This assumption is very reasonable for this initiation mechanism. Stepgrowth polymerization of polyphenylcarbosilane and. Mechanism of stepgrowth polymerization back to index. Step growth polymerization p olymerization mechanism in which bifunctional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Ideal living polymerization results in a dispersity of 1. Feature 3 designed, usually narrow, molecular weight distribution. In this approach, a doublestrainpromoted azidealkyne click reaction dspaac with a reactive intermediate was used as the.

Molecular weight distribution in linear stepgrowth polymers. In step polymerization the molecular weight usually builds up slowly. Features of controlled living radical polymerizations. In a stepgrowth polymerization, the molecular weight of the polymer chain builds up slowly and there is only one re action mechanism for the formation of polymer. Comparison of molecular weight vs conversion plot between stepgrowth and living chaingrowth polymerization. Controlled stepgrowth polymerization ccs chemistry. Molecular weight distribution of linear chains in stepgrowth polymerization under the influence of cyclization reactions article in macromolecular theory and simulations 214 may 2012 with 19. Other articles where stepgrowth polymerization is discussed.

Molecular weight distribution of stepgrowth polymers. Chaingrowth polymerizations require the presence of an initiating molecule that can be used to attach a monomer molecule at the beginning of the polymerization. Molecular weight control in emulsion polymerization by. Molecular weight distribution of linear chains in step. Example r71 determining the concentrations of polymers for step polymerization determine the concentration and mole fraction of polymers of chain length j in terms of initial concentration of arb, m o. Although this feature is often desirable, it is not necessarily the result of a controlled polymerization, which only requires the absence of chain transfer and termination, but ignores the effect of rate of initiation, exchange and depropagation. Spontaneous synthesis of a homogeneous thermoresponsive. Chaingrowth polymerization has been successfully performed for many decades through conventional free radical, anionic, or cationic polymerization.

One needs to determine the probability of finding a chain containing x monomer units and a single unreacted a or b group at time \ t \ for a polymerization reaction of aa and bb. Step polymerization reactions typically yield values of mwmn of around 2. All molecules present monomer, oligomer, polymer can react with any other molecule. Light scattering, for example, only yields the weightaverage molecular mass.

Control of molecular weight distribution in polycondensation. Stepgrowth polymerization an overview sciencedirect. Controlled radical polymerization guide sigmaaldrich. Controlling molecular weight and polymer architecture. Molecular weights that are important in determining polymer properties are the numberaverage.

Since the molecularweight distribution of commercial polymers is normally a continuous function, molecularweight averages can be determined by integration if the appropriate mathematical form of the molecular. Chemistry 328n the carothers equation high molecular weights are hard to get this way if there are n o molecules at time 0 and n remaining at time t. Stepgrowth polymerization and stepgrowth polymers rro. In irreversible stepgrowth polymerization, the molecularweight distribution mwd of the polymers produced can be controlled via the reaction path. The weight chain length distribution in a linear stepgrowth polymerization functionality 2 can be given by. Figure 41 molecular mass distributions in step growth polymerization. Using statistical methods derived by paul flory, the molecular weight distribution in step polymerization can be related to the reaction conversion. Number distribution and number average molecular weight mn. Herein, a unique homogeneous stepgrowth polymerization method was developed to prepare various uhmw polymers. From these sets is possible to obtain the molecular weight distribution of.

Uhmw is always a challenge for homogeneous stepgrowth polymerization. Following a comparison of chaingrowth and stepgrowth polymerization, focuses on the latter process by describing requirements for high molecular weight, stepgrowth polymerization kinetics, synthesis and molecular weight distribution of some linear stepgrowth polymers, and threedimensional network stepgrowth polymers. The number distribution a is shown for three different extents of reaction, the mass distribution b shows a single narrow peak which progressively broadens and shifts to high molecular mass as. The molecular weight distribution according to the number. For reducing the disadvantages of bulk polymerization, the process can be carried out in a solution. Chemical engineering 160260 polymer science and engineering lecture 3 molecular weight averages and distributions january 22, 2001 reading.

Polymer molecular weight distribution and definitions of mw averages technical overview introduction polymers consist of repeat units monomers chemically bonded into long chains. At the same time, the number chain length distribution can be calculated with. Molecular weight control, molecular weight determination in. The reaction produced linear polymers with low number. Molecular weight control in emulsion polymerization by catalytic chain transfer aspects of process development iii summary the molecular weight distribution mwd, amongst others, governs the end use properties of polymeric materials, e.

The molecular weight distribution mwd had been derived by flory by a statistical approach based on the. To determine the molecular weight distribution of the polymeric species that form at any given. A new approach to control the molecular weight and polymer architecture using the passerini threecomponent stepgrowth polymerization is described. The preparation of polymers with an ultrahigh molecular weight 106 gmol. Spontaneous synthesis of a homogeneous thermoresponsive polymer network composed of polymers with a narrow molecular weight distribution.