TY - JOUR

T1 - Hyperthermal intact molecular ions play key role in retention of ATRP surface initiation capability of plasma polymer films from ethyl alpha-bromoisobutyrate

AU - Saboohi, Solmaz

AU - Coad, Bryan R.

AU - Michelmore, Andrew

AU - Short, Robert D.

AU - Griesser, Hans J.

PY - 2016/6/29

Y1 - 2016/6/29

N2 - We report a systematic study of the plasma polymerization of ethyl alpha-bromoisobutyrate (EBIB) to produce thin film coatings capable of serving as ATRP initiation surfaces, for which they must contain alpha-bromoisobutyryl functional groups. In the deposition of polymeric coatings by plasma polymerization there generally occurs considerable fragmentation of precursor ("monomer") molecules. in the plasma; and the retention of larger structural elements is challenging, particularly when they are inherently chemically labile. Empirical principles such as low plasma power and low pressure are usually utilized. However, we show that the alpha-bromoisobutyryl structural moiety is labile in a plasma gas phase and in low pressure plasma conditions, below the collisional threshold, there is little retention. At higher pressure, in contrast, fragmentation of this structural motif appears to be reduced substantially, and coatings useful for ATRP initiation were obtained. Mass spectrometry analysis of the composition of the plasma phase revealed that the desired structural moiety can be retained through the plasma, if the plasma conditions are steered toward ions of the precursor molecule. 'Whereas at low pressure the plasma polymer assembles mainly from various neutral (radical) fragments, at higher pressure the deposition occurs from hyperthermal ions, among which the protonated intact molecular ion is the most abundant. At higher pressure, a substantial population of ions has low kinetic energy, leading to "soft landing" and thus less fragmentation. This study demonstrates that relatively complex structural motifs in precursor molecules can be retained in plasma polymerization if the chemical and physical processes occurring in the plasma phase are elucidated and controlled such that desirable larger structural elements play a key role in the film deposition.

AB - We report a systematic study of the plasma polymerization of ethyl alpha-bromoisobutyrate (EBIB) to produce thin film coatings capable of serving as ATRP initiation surfaces, for which they must contain alpha-bromoisobutyryl functional groups. In the deposition of polymeric coatings by plasma polymerization there generally occurs considerable fragmentation of precursor ("monomer") molecules. in the plasma; and the retention of larger structural elements is challenging, particularly when they are inherently chemically labile. Empirical principles such as low plasma power and low pressure are usually utilized. However, we show that the alpha-bromoisobutyryl structural moiety is labile in a plasma gas phase and in low pressure plasma conditions, below the collisional threshold, there is little retention. At higher pressure, in contrast, fragmentation of this structural motif appears to be reduced substantially, and coatings useful for ATRP initiation were obtained. Mass spectrometry analysis of the composition of the plasma phase revealed that the desired structural moiety can be retained through the plasma, if the plasma conditions are steered toward ions of the precursor molecule. 'Whereas at low pressure the plasma polymer assembles mainly from various neutral (radical) fragments, at higher pressure the deposition occurs from hyperthermal ions, among which the protonated intact molecular ion is the most abundant. At higher pressure, a substantial population of ions has low kinetic energy, leading to "soft landing" and thus less fragmentation. This study demonstrates that relatively complex structural motifs in precursor molecules can be retained in plasma polymerization if the chemical and physical processes occurring in the plasma phase are elucidated and controlled such that desirable larger structural elements play a key role in the film deposition.

KW - hyperthermal polyatomic ions

KW - molecular ion

KW - plasma polymerization

KW - ATRP

KW - surface grafting

KW - ethyl alpha-bromoisobutyrate

KW - plasma analysis

KW - TRANSFER RADICAL POLYMERIZATION

KW - CHEMICAL-VAPOR-DEPOSITION

KW - ACRYLIC-ACID

KW - ENERGY

KW - CHEMISTRY

KW - BRUSHES

KW - GROWTH

U2 - 10.1021/acsami.6b04477

DO - 10.1021/acsami.6b04477

M3 - Journal article

VL - 8

SP - 16493

EP - 16502

JO - ACS Applied Materials and Interfaces

JF - ACS Applied Materials and Interfaces

SN - 1944-8244

IS - 25

ER -