Synthesis Characterization And Properties Of Novel Thermoplastic Elastomers Of Polyisobutylene Based Star Block Copolymers PDF Download

Polyisobutylene due to its unique properties, such as exceptional chemical, oxidative and thermal stability, low gas permeability and biocompatibility (bioinert), is a widely used material in applications ranging from oil additives to biomaterials. The objective of this dissertation was to study the copolymerization of alloocimene, a renewable monomer, and isobutylene under the traditional butyl rubber polymerization conditions: H2O/AlCl3 initiating system in methyl chloride solvent at -95 °C. It was our hypothesis that polyalloocimene would lead to improved filler interaction. Our work led to the discovery of the first two-phase (emulsion) living isobutylene polymerization system, solving the problems associated with solution living isobutylene polymerization systems: the use of unique and commercially not available initiators, expensive coinitiator at high concentrations and poor heat transfer due to the high viscosity of the reaction mixture even at low polymer concentrations (15wt%). High molecular weight copolymers, Mn = 200,000 to 400,000 g/mol, with molecular weight distribution of [Uppercase D with a line] = 1.5 to 2.1, were prepared containing 9 to 30 wt% alloocimene at 80 to 90 % conversion. The copolymerization of alloocimene and isobutylene was found to be living up to 40 % conversion, or 6.5 minutes, resulting in a diblock polymer structure, consisting of a polyalloocimene-rich first block and a polyisobutylene second block. Tri- and tetrablock copolymers were prepared by sequential monomer addition technique. Both di- and multiblock structures showed thermoplastic elastomeric properties. This is the first example of a diblock copolymer thermoplastic elastomer. This is also the first copolymerization system allowing the preparation of tri- and tetrablock copolymer polyisobutylene-based thermoplastic elastomers using an inexpensive polymerization system. Diblock copolymers showed outstanding reinforcement with carbon black: the ultimate tensile strength increased from 2-6 MPa to 10-14 MPa at 60 phr (37.5 wt%) loading. The tensile strength of tri- and tetrablock copolymers also increased upon carbon black reinforcement. The ultimate tensile strength of a tetrablock copolymer having Mn = 347,000 g/mol and containing 23.7 wt% alloocimene increased from ~14 MPa to ~22 MPa upon 45 phr (31 wt%) carbon black loading. Silica reinforcement of a triblock (Mn = 205,000 g/mol, 28.2 wt% alloocimene) copolymer increased the ultimate tensile strength by ~50 %, to ~18.5 MPa, using 15 phr (13 wt%) silica loading. The Payne effect in carbon black loaded triblock copolymer compounds was investigated. The dynamic fatigue properties of di-, tri- and tetrablock copolymers and their carbon black composites were investigated using the hysteresis method. The neat diblock copolymers broke premature during the dynamic creep test conducted at 0.51 MPa stress, whereas the tri- and multiblock copolymers showed 144 to 170 % absolute dynamic creep respectively. Reinforcement by carbon black led to a two orders of magnitude decrease in the absolute dynamic creep. Curing of poly(Allo-b-IB) tri- and tetrablock copolymers were investigated using sulfur- and peroxide-based systems. The new thermoplastic elastomers showed similar curing as well as permeability characteristics as halobutyl rubbers. A peroxide curing recipe was developed for poly(Allo-b-IB) multiblock copolymers, indicating no polymer degradation during the curing process.