polymers Review Polyolefins, a Success Story Dominique W. Sauter, Mostafa Taoufik and Christophe Boisson * Université de Lyon, Univ Lyon 1, CPE Lyon, CNRS, UMR 5265, C2P2 (Chemistry, Catalysis, Polymers & Processes), Bat. 308F, 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France; [email protected] (D.W.S.); [email protected] (M.T.) * Correspondence: [email protected]; Tel.: +33-472-431-780 Academic Editor: Zhibin Ye Received: 21 April 2017; Accepted: 21 May 2017; Published: 24 May 2017 Abstract: This paper reports the principal discoveries which have played a major role in the polyolefin field and have positioned polyolefins as the most produced plastics. The early development of polyolefins covering the production of LDPE (Low density polyethylene) at ICI (Imperial Chemical Industries) and the discovery of Phillips or Ziegler-Natta catalysts are highlighted in the first section. In the second part, the impact of the implementation of molecular catalysts on the research in polyolefins is discussed together with the most recent advances leading to high-performance tailor-made resins. Keywords: polyolefins; coordination catalysis; specialty polymers; high-performance resins; macromolecular engineering; tailor-made polymers; history of science 1. Introduction Polyolefins, in particular polyethylene (PE) and isotactic polypropylene (i-PP), are widely used in our everyday life for an extremely wide range of applications; indeed, they account for more than 50% in weight of the produced polymers. More than 300 grades of commercially available polyolefins provide a wide range of mechanical properties [1]. With more than 178 million tons having been produced in 2015 [2,3], polyolefins remain at the top of the global production of synthetic polymers [4]. From the point of view of cost, PE and i-PP rank as the least expensive polymers to produce, and stand out because they are far less toxic compared to many other commodity plastics [5]. As discussed by Mülhaupt et al. [6], polyolefins meet the requirements of sustainable development and green polymer chemistry [7,8]. The development of solvent-free catalytic processes, the design of lightweight engineering plastics, the recyclability and the low carbon footprint of polyolefins are the main arguments for this statement. Polyethylene is the simplest polyolefin, its general formula is (–CH2–CH2–)n, and it is generally composed of a mixture of interconnected crystalline and amorphous parts which can exhibit short and long chain branching. Even if polyethylene seems to be an unsophisticated material in a first glance, it turns to be possible to tailor the polymer to include elaborate structures based on the organization of the three basic groups, methyl, methylene and methine. This also includes the preparation of blends. Polyolefins are either produced by a free radical process (Low density polyethylene: LDPE) or using coordination catalysis (Low linear density polyethylene: LLDPE, high density polyethylene: HDPE, and i-PP). The present paper highlights the chronology of the development of the polyolefin production and the recent advances leading to performance polyolefins available today (Scheme1). Polymers 2017, 9, 185; doi:10.3390/polym9060185 www.mdpi.com/journal/polymers Polymers 2017, 9, 185 2 of 13 Polymers 2017, 9, 185 2 of 13 SchemeScheme 1. 1.Major Major advances advances inin polyolefinspolyolefins development. 2. Polyolefins, the Beginning of the Story: How Does It All Start? 2. Polyolefins, the Beginning of the Story: How Does It All Start? Although the first trace of polyethylene was reported at the end of the 19th century as a side productAlthough formed the during first trace the ofthermal polyethylene decomposition was reported of diazomethane at the end [9], of it thewas 19th only century identified as later a side productas a polymer. formed during the thermal decomposition of diazomethane [9], it was only identified later as a polymer.In the 1920s Hermann Staudinger set the basis for a new field of chemistry by introducing the conceptIn the of 1920s high Hermann molar mass Staudinger macromolecules, set the basis and defining for a new the field polymerization of chemistry process by introducing as linking the concepttogether of highindividual molar small mass monomer macromolecules, molecules and by the defining formation the polymerizationof covalent bonds process [10–12]. as It linking was togetheronly a individual few years small later, monomer in 1933 moleculesat the Imperial by the Chemical formation Industries of covalent (ICI) bonds site [10 in–12 Winnington]. It was only a few(Northwich, years later, UK) in that 1933 Fawcett at the Imperialand Gibson Chemical discovered Industries the overnight (ICI) site formation in Winnington of a small (Northwich, amount UK)(about that Fawcett1 g) of an and unexpected Gibson discovered white powder the overnightwhile running formation some ofcondensation a small amount experiments (about 1with g) of an unexpectedhighly pressurized white powderethylene whileand benzaldehyde running some [13,14] condensation. When Fawcett experiments and Gibson with tried highly to repeat pressurized this ethyleneexperiment and benzaldehyde without benzaldehyde, [13,14]. When the Fawcettreactor expl andoded. Gibson It triedtook totwo repeat additional this experiment years to finally without benzaldehyde,repeat the production the reactor of polyethylene, exploded. It tookand yet two agai additionaln, the success years of to the finally test was repeat obtained the production by chance. of polyethylene,Indeed, while and repeating yet again, this the successexperiment, of the one test of was their obtained autoclaves by chance. had a Indeed,leak which while allowed repeating some this experiment,traces of oneoxygen of their to contaminate autoclaves hadthe aethylene leak which batch. allowed At high some temperatur traces ofe, oxygen the molecular to contaminate oxygen the ethylenedecomposed batch. Atto provide high temperature, free radicals the thereby molecular enabling oxygen the decomposed formation of topolyethylene provide free [15]. radicals In this thereby free radical process, intra- and intermolecular chain transfer led to the formation of LDPE containing enabling the formation of polyethylene [15]. In this free radical process, intra- and intermolecular chain short and long chain branching. A process employing high temperature (200 to 300 °C) and high transfer led to the formation of LDPE containing short and long chain branching. A process employing pressure (1000 to 4000 bars) was patented by ICI in 1937 [16], and the first factory production plant high temperature (200 to 300 ◦C) and high pressure (1000 to 4000 bars) was patented by ICI in 1937 [16], started operating in 1939 with a capacity of 100 ton/year [14]. Nowadays, LDPE is still widely and the first factory production plant started operating in 1939 with a capacity of 100 ton/year [14]. produced with conditions close to those elaborated by Fawcett, Gibson and Perrin, and largely used Nowadays,in the food LDPE industry is still widelybecause produced it combines with conditionsexcellent mechanical close to those properties elaborated and by Fawcett,food friendly Gibson andadvantages Perrin, and (non-toxic largely used and inmetal the free food materials). industry because it combines excellent mechanical properties and foodTechnological friendly advantages advances (non-toxic continued andduring metal the free 1940s; materials). several groups developed some efforts in orderTechnological to find a catalytic advances process continued for the duringproducti theon 1940s;of polyethylene. several groups Mayo developedat U.S. Rubber some Company efforts in orderand to Fischer find a catalyticat BASF AG process produced for the HDPE. production The U.S. of polyethylene.Rubber company Mayo did at not U.S. believe Rubber in CompanyHDPE’s andcommercial Fischer at potential BASF AG [17], produced while BASF HDPE. AG The showed U.S. interest Rubber in company Fischer’s did catalysis not believe work involving in HDPE’s commercialtitanium tetrafluoride potential [17 and], while aluminum BASF powder AG showed [13]. However, interest in during Fischer’s this catalysistroubled period, work involving Fischer titaniumwas asked tetrafluoride to refocus andhis research aluminum in order powder to participate [13]. However, in the war during effort this by developing troubled period, new types Fischer of wasfuel asked for the to refocusarmy. This his considerably research in order slowed to participatedown his advances in the war in polyolefin effort by developingcatalysis, but new finally types his of fuelcatalytic for the system army. This was considerablypatented in 1953, slowed ten years down after his advancesits discovery in polyolefin[18]. catalysis, but finally his catalyticIt systemwas in was the patentedearly 1950s in 1953,that two ten yearsmajor after breakthroughs its discovery happened [18]. in the field of catalytic polymerization of olefins. These discoveries enabled to run polymerization under milder Polymers 2017, 9, 185 3 of 13 It was in the early 1950s that two major breakthroughs happened in the field of catalytic polymerization of olefins. These discoveries enabled to run polymerization under milder temperature and pressure conditions than those previously used for LDPE production. The first major progress concerned the work done by Hogan and Banks at Phillips Petroleum Company, in Bartlesville, Oklahoma. Hogan and Banks research focused on the conversion