Page 41 - Engineering Plastics Handbook

Chemistry of Polymerization 15

“sides.” More ring sides have more ring strain, so a three-member ring
has less strain, while a seven-member ring such as ε-caprolactam used
to polymerize polyamide-6 has greater ring strain, which facilitates
polymerization [3, 6, 13]. Polyamide-6 can be produced by ring-opening
chain-growth ionic polymerization of caprolactam. It can be produced by
hydrolytic bulk polymerization of ε-caprolactam in the presence of water,
acid, alkali (ionic polymerization), or alcohol, which breaks the capro-
lactam ring. Polyamide-12 is produced by ring-opening polymerization
of laurolactam. Poly(ethylene-imine) (PEI) and aliphatic polyesters can
be polymerized by ring-opening mechanisms [4].
Aromatic engineering thermoplastics are produced from macrocyclic
oligomer precursors by ring-opening polymerization without by-product
formation during polymerization [6]. Selection of amine catalysts such
as Et N (triethylamine) is a factor in getting high cyclic oligomers and
3
low linear oligomer yields [13].
Macrocyclic oligomer precursors of polycarbonates, PET, polymers of
amides, etherketones, and ethersulfones are candidates for further
study of macrocyclic oligomer polymerization thermodynamics [6].
Research extends to cyclic arylates (cyclic aryl-aryl esters) and cyclic
alkyl aryl esters going back to isolating a cyclic trimer of poly(ethylene-
terephthalate) in 1954 [13]. Much of the work on macrocyclic oligomers
as precursors to high-MW macromolecules starts with spiro(bis)indane
(SBI) biphenyl monomer to produce macrocyclic carbonates.
The 80,000-MW polyethersulfone was produced by heating an SBI-
based cyclic oligomer mixture at 380 to 400°C (716 to 752°F) in the melt
with 1.0 mol % bisphenol A disodium salt [6]. In 1990, an etherketone
macrocyclic mixture was prepared by an aryl-aryl coupling; and nickel(0)
catalyzed aryl coupling of selected bis-arylchlorides can produce about
40% cyclic etherketones by applying pseudodilution methods [13].
Macrocyclic aramids (aryl-aryl aramids) have been prepared from SBI-
based diamines and other starting materials. Findings with gel perme-
ation chromatography were used to analyze macrocyclic oligomers [13].
GPC is used to determine polymer properties and kinetic data. Together
with light-scattering detection, GPC offers more precise MW determi-
nations than alternative methods [11].
Reaction conditions needed to form selective cyclics include mainte-
nance of the right hydrolysis, condensation ratio, and the right amine
catalyst [13].
Structural characterizations of macrocyclic aromatic sulfide oligomers
were studied jointly at Guangzhou Institute of Chemistry and McGill
University Department of Chemistry. The studies used matrix-assisted
laser desorption and ionization time of flight mass spectroscopy (MALD
ITF-MS), which the researchers said was a powerful tool to analyze the
macrocyclics [13].