Shielding Effects in Polymer‐Polymer Reactions, 6

Eisenhaber, Stephan; Zifferer, Gerhard

doi:10.1002/mats.201300155

Cited by 7 publications

(4 citation statements)

References 43 publications

(68 reference statements)

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“…They found that the efficiency decreased as the initiator density increased and the solvent quality worsened. Monte Carlo simulation technique has also been used to investigate the contact probabilities of polymer chains in surface‐initiated reversible addition–fragmentation chain transfer polymerization …”

Section: Introductionmentioning

confidence: 99%

“…Monte Carlo simulation technique has also been used to investigate the contact probabilities of polymer chains in surface-initiated reversible additionfragmentation chain transfer polymerization. [ 20 ] Kinetic models have also been used as a simple and straightforward approach to investigate the polymer growth in surface-initiated controlled radical polymerization systems. [ 8,[21][22][23][24][25] However, a prior knowledge of grafting density must be assumed when using such approach.…”

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confidence: 99%

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Factors Affecting Grafting Density in Surface‐Initiated ATRP: A Simulation Study

Mastan

Zhu

2016

Macro Theory & Simulations

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studies have reported deceleration in the growth rate of polymer chains as polymerization progressed. [ 5,6 ] There are two schools of theories that could explain this experimental phenomenon, propagation and termination theories. The propagation theory explains this trend through reduction of available monomers in the grafted layer due to crowding. On the other hand, the termination theory justifi es the deceleration through decreased active chain ends due to surface radical termination, which is assisted by radical migration through the reversible activationdeactivation reactions involved in ATRP. These two theories have also been used to offer explanation under which conditions the solution and surface chains possess similar or different properties in a simultaneous solution and surface polymerization. [ 7,8 ] This helps to evaluate whether the properties of free polymer chains formed in solution can be used as an estimate for those of the grafted poly mer brush on surface for calculation of grafting density, as often assumed in experimental studies.The dry thickness of polymer brush ( δ ) and its grafting density ( τ ) are two important parameters of grafted In surface-initiated atom transfer radical polymerization, knowledge of grafting density is of signifi cant interest because it is one of the determining properties of grafted polymer. It is well known that not all of the immobilized initiators can grow into polymer chains. However, little is known about why this happens and what affects the grafting effi ciency. The lack of information is partly due to the diffi culty in experimental determination of grafting density on fl at substrates. To circumvent the problem, Monte Carlo simulation with bond fl uctuation model is used in this study to investigate the effects of various reaction conditions on the grafting density. The simulation results show lower grafting density when less deactivator is present. In systems with lower deactivator concentration, the number of monomer added per activation cycle is higher. Coupling this with close proximity of immobilized initiators results in chains initiated at earlier time to shield their neighboring initiator moieties from adding mono mers, thus lowering the grafting density in such a system. These simulation results also provide an explanation to the seemingly confl icting trend reported in the literatures.

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Factors Affecting Grafting Density in Surface‐Initiated ATRP: A Simulation Study

Mastan

Zhu

2016

Macro Theory & Simulations

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“…e ., without any radical termination. However, they consider crowding from grafted chains, thus starving of monomers in the grafted layer, to affect the kinetics . The chain‐crowded monomer‐starved environment reduces the available monomer molecules for radical chain ends, which are buried inside the polymer layer, thereby reducing the growth rate.…”

Section: Introductionmentioning

confidence: 99%

What Limits the Chain Growth from Flat Surfaces in Surface‐Initiated ATRP: Propagation, Termination or Both?

Mastan

Zhu

2015

Macro Theory & Simulations

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Surface‐initiated controlled radical polymerization, such as ATRP, has been proven to be a powerful method for preparation of well‐controlled functional grafted polymers. There are thousands of experimental works published, by varying polymers, surfaces, and applications. In comparison, theoretical developments are very lacking. Many fundamental questions still remain to be answered. These questions include, but not limited to: What determine the surface initiator efficiency? How many chains per square nanometer can be fully grown? What is the maximum thickness can polymer grow to? If chains are simultaneously grown from surface and solution, which has higher molecular weight? Answers to these questions are most helpful for innovation and further development in this important area. In this work, we employed recently developed theories to explain experimentally observed kinetic profiles of polymer layer thickness growth. What limits the growth of surface chains? Is it the monomer starvation in grafting layer that slow down propagation? Or is it the termination of radicals that stop the chain growth? It was found that no existing models could fully explain the often contradictory experimental observations. It is our hope that this work will provoke further discussions and inspire more effort in resolving the fundamental issues of this area.

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“…In order to investigate the shielding effects in the surface initiated RAFT polymerization, Eisenhaber and Zifferer used a lattice based MC simulation in combination with exact enumeration techniques. To reduce the time‐consuming evaluation of contact probabilities, both chains are embedded in a small‐sized cubic lattice.…”

Section: Monte Carlo and Combined Techniquesmentioning

confidence: 99%