Future Industries Institute, University of South Australia , Mawson Lakes, South Australia 5095, Australia.
School of Engineering, University of South Australia , Mawson Lakes, South Australia 5095, Australia.
ACS Appl Mater Interfaces. 2016 Jun 29;8(25):16493-502. doi: 10.1021/acsami.6b04477. Epub 2016 Jun 15.
We report a systematic study of the plasma polymerization of ethyl α-bromoisobutyrate (EBIB) to produce thin film coatings capable of serving as ATRP initiation surfaces, for which they must contain α-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 α-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.
我们报告了乙基α-溴代异丁酰溴(EBIB)的等离子体聚合的系统研究,以生产能够作为原子转移自由基聚合(ATRP)引发表面的薄膜涂层,为此它们必须含有α-溴代异丁酰基官能团。在等离子体聚合沉积聚合涂层时,通常会在等离子体中发生前体(“单体”)分子的大量碎裂;并且保留较大的结构元素具有挑战性,特别是当它们本身具有化学不稳定性时。通常利用低等离子体功率和低压力等经验原则。然而,我们表明,α-溴代异丁酰基结构部分在等离子体气相中和在低气压等离子体条件下是不稳定的,在碰撞阈值以下,保留的很少。相比之下,在较高的压力下,这种结构基序的碎裂似乎大大减少,并且获得了用于 ATRP 引发的有用涂层。等离子体相组成的质谱分析表明,如果将等离子体条件引导到前体分子的离子上,则可以通过等离子体保留所需的结构部分。而在低压力下,等离子体聚合物主要由各种中性(自由基)碎片组装而成,在较高的压力下,沉积是由超热离子发生的,其中质子化的完整分子离子是最丰富的。在较高的压力下,大量离子具有低的动能,导致“软着陆”,从而减少了碎裂。这项研究表明,如果阐明并控制等离子体相中的化学和物理过程,使期望的较大结构元素在薄膜沉积中发挥关键作用,那么前体分子中相对复杂的结构基序可以在等离子体聚合中保留。