Harry R. Allcock – A True Pioneer in the Field of Inorganic and Organometallic Polymers
Selected highlights of the career of Professor Harry R. Allcock are presented. The theme of the interplay of fundamental and applied chemistry, a hallmark of Dr. Allcock’s research program, is exemplified by discussions of the mechanistic and synthetic studies of phosphazene polymerization followed by applications in the areas of biomedical materials and solid state conductivity.
KeywordsPhosphazenes polyphosphazenes biomedical materials ionic conductivity
It is most fitting that the Journal of Inorganic and Organometallic Polymers and Materials should devote this issue to honor the long, productive and high impact career of Professor Harry Allcock. If Inorganic Polymers were first established as an important area of basic and applied research by Rochow, then Harry Allcock has been the prime mover in establishing the breadth and depth the area over the past 40 years of his still highly productive career at the Pennsylvania State University. This productivity has been manifested in three single authored monographs [1, 2, 3], two coauthored text books, (one in three  editions, the other in two editions ) as well as edited  and two co-edited [7, 8] volumes, well over 500 peer reviewed articles, reviews and chapters and 57 patents.
In order to provide some insight into the nature of Allcock’s scientific and technical contributions, I will start by showing how Allcock’s early ground breaking investigations took a chemical curiosity and transformed it into a major area of current research. Following this I will focus on three areas of Allcock’s research program which demonstrate the range of fundamental and applied chemistry. These studies while based on the poly(phosphazene) platform have much broader implications for Polymer and Materials Science.
Allcock has always maintained a dual approach of fundamental and applications driven research to his studies. An area that maintains an on going appeal to him in this regard is that of biomedical applications. This work involves the synthesis and property evaluation of poly(phosphazenes with bioactive side groups such as amino acid esters [31, 32], steroids , anesthetics , heparin , glyceryl , oligopeptides , glycolic and lactide esters [38, 39] (biodegradible materials) and hydroxyapatite composites . Certain of these materials as well as the paracarboxyphenoxy phosphazene serve as effective microencapsulations hydrogels [41, 42, 43]. In a process in which the elegance is matched by conceptual simplicity, the carboxylate salts of +1 cations are soluble in aqueous solutions but may be cross-linked to form hydrogels simply by addition of a divalent cation . The resulting microspheres can encapsulate reagents and even whole cells (and allow for cellular integrity and function to continue), which are present in the solution where then ionic cross-linking process occurs. Enzyamatic immobilization within poly(phosphazenes) hydrogels with polyether side chains has also been explored . The design of poly(phosphazenes) with certain of the side groups described above for control release of bioactive materials has also been accomplished [45, 46, 47]. Other biomedical targets which have been explored include skeletal tissue regeneration [48, 49], antibacterial activity and mutagenicity , tissue engineering  and bone repair studies [52, 53]. In addition to the broad and exciting range of biomedical applications noted above, this work shows a signature aspect of the Allcock research program i.e. the use of the poly(phosphazene) platform as a spring board into seemingly distant but crucially important areas of science and technology.
As a last, of many possible, example of the transformation of fundamental work involving the poly(phosphazene) platform to the production and characterization of new materials with significant applications potential, I will move to the area of Materials Science. The specific focus will be in the area of solid polymer electrolytes. The core concept was to exploit the stability and low glass transition temperature of the poly(phosphazene) backbone along with metal ion, specifically lithium, bind capacity of polyether side chains such as the ethoxyethoxymethoxy (MEEP) entity [54, 55, 56, 57, 58, 59, 60]. The synthetic work focused on stubstituent and additive control of the conductivity and increased dimensional stability needed for long term integrity of devices obtained from these electrolytes. Further work in the synthetic domain explored additional poly(phosphazenes) such as gels , organic polymers with pendant cyclophosphazenes containing polyether substituents [62, 63, 64, 65], and phosphazene-ethylene oxide block coplymers  as lithium carrier solid electrolytes. Typical of the Allcock approach synthesis is only one part of a multifaceted approach to polymer science. In the polymer electrolyte work, numerous publications explore studies of conductivity, transport properties and mechanisms of conductivity in these materials [67, 68, 69, 70, 71, 72].
The choice of topics for this snapshot of the diversity and creativity exhibited by the output from Allcock’s laboratory is by necessity brief and idiosyncratic with the author. One could have treated each of these in more depth and looked at other topics such as organometallic phosphazenes, phosphazene clathrates, radiation chemistry, phosphazene membranes, electrical/optical materials, and phosphazene surface modification. He has been recognized by important institutional appointments, the Evan Pugh Professorship is the Pennsylvania State University’s highest academic honor, a Guggenheim Fellowship, visiting scientist at Stanford, Imperial College of Science and Technology, London and the IBM Almaden Laboratories as well as numerous endowed lectureships. His work has lead to major honors by professional organizations including the Chemical Pioneer Award of the American Institute of Chemists and three of the American Chemical Society major awards: the National Award in Polymer Chemistry (1984), National Award in Materials Chemistry (1992), the Herman Mark Award in Polymer Chemistry (1994) and most recently, the Award in Applied Polymer Science (2007). So inclusion I will return to where I started by saying that it is most fitting and proper that the Journal exclusively focused on Inorganic and Organometallic Polymers and Materials should dedicate this issue to a true pioneer and continuing significant contributor to this fascinating and important area of science.
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