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Preparation and stress‐strain properties of aba block copolymers of α‐methylstyrene and butadiene
Author(s) -
Cunningham Robert E.
Publication year - 1978
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1978.070221017
Subject(s) - copolymer , materials science , thermoplastic elastomer , polymer chemistry , monomer , polystyrene , polymer , elastomer , solvent , ultimate tensile strength , thermoplastic , benzene , composite material , chemistry , organic chemistry
ABA‐type “tapered” block copolymers of α‐methylstyrene (monomer A) and butadiene were prepared using four commercially available dilithio initiators. Polymerizations were run at 25°C in benzene solvent, or at 40°C with butadiene dissolved in neat α‐methylstyrene. Although α‐methylstyrene has a rather low ceiling temperature, triblock copolymers could be made at these temperatures by using α‐methylstyrene concentrations well in excess of the [ M ] e values at the respective temperatures. Its concentration was such that molecular weights of at least 15,000–20,000 for the A blocks could be attained. The course of the copolymerization at 40°C was followed, showing that copolymers containing about 40% α‐methylstyrene could be formed in 4–8 hr, depending on the initiator used. They showed the usual behavior of triblock thermoplastic elastomers, with tensile strengths > 3000 lb/in. 2 at 24°C. However, because of the high T g of poly(α‐methylstyrene) (172°C), they also had tensiles of several hundred lb/in. 2 at 100°C, unlike comparable polymers with polystyrene end blocks, which have practically no strength at this temperature. Microstructures of polybutadienes made with these initiators are also given.