Poly(2-alkyl-2-oxazoline) containing multiphase systems

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Virginia Tech


This research is focused on the polymerization of 2-alkyl-2-oxazoline homopolymers and 2-alkyl-2-oxazoline containing copolymers with well-defined structures. In addition, the potential of selected materials as polymer blend compatibilizers was briefly evaluated. The polymerization of 2-alkyl-2-oxazoline was investigated with regard to the effects of initiator structures on molecular weight control and molecular weight distribution, living characteristics, and mechanisms and kinetics. The structure of initiators was shown to greatly affect the molecular weight control and molecular weight distribution of poly (2-ethyl-2-oxazoline). The living nature of poly (2-ethyl-2-oxazoline) in chlorobenzene initiated by benzyl iodide, benzyl chloride/NaI, or chloroethyl ethyl ether/NaI has been established by Mn-conversion plots and sequential monomer addition experiments. However, the molecular weight distributions of these polymers were not as narrow as Poisson distributions, Mechanistic and kinetic studies of 2-ethyl-2-oxazoline polymerizations suggested that, at very early stages of polymerization, the active species is covalent. After that very early Stage of polymerization, ionic species are present and the overall propagation rates increases. The rate determining step was found to be the initial propagation step(s) using benzyl iodide as the initiator, and initiation and/or the initial propagation step(s) in the case of iodobutane as an initiator. A kinetic study of 2-methyl-2-oxazoline polymerization in CD₃CN also indicated slower initiation than propagation rates using both butyl mesylate and butyl iodide as initiators. Based on the knowledge of 2-alkyl-2-oxazoline homopolymerizations, poly(2-alkyl-2-oxazoline) containing copolymers were prepared using macroinitiator methods, with poly(2-alkyl-2-oxazoline) being either the macroinitiator or the second component synthesized.

Narrow distribution poly(dimethylsiloxane) oligomers terminated with benzyl chloride endgroups were prepared by living anionic ring-opening polymerization of hexamethylcyclotrisiloxane followed by termination with a benzyl chloride containing chlorosilane reagent. Cationic ring-opening polymerization of 2-ethyl-2-oxazoline using these macroinitiators in combination with NaI generated a series of well defined block copolymers.

Poly(butyl vinyl ether) and poly(methyl vinyl ether) oligomers with Poisson distributions and precisely terminated on one end with a chloroethyl ether functional group were prepared by living cationic polymerization of alkyl vinyl ethers using a chloroethyl vinyl ether/HI initiating system with ZnI₂ as catalyst and terminated by lithium borohydride. The chloroethyl ether functional groups were used in conjunction with sodium iodide to polymerize 2-ethyl-2-oxazoline blocks. In order to insure effective initiation and to narrow the copolymer molecular weight and composition distributions, the chloride to iodide conversion was made prior to the addition of monomer. A series of these diblock materials was prepared wherein the molecular weight distributions ranged from 1.3 to 1.4.

The bulk, solution and surface properties of these copolymers were investigated by NMR, DSC, XPS and surface tension measurements. Both types of materials described above are currently being utilized for studying the parameters important for steric stabilization of inorganic particles in polar media.

A less defined series of materials was also prepared. Using poly(butyl vinyl ether-co-chloroethyl vinyl ether) random copolymers as: macroinitiators, 2-methyl-2-oxazoline was polymerized, resulting in poly(butyl vinyl ether-2-methyl-2- oxazoline) graft copolymers. Poly(2-methyl-2-oxazoline-ε-caprolactone) block copolymers were prepared using hydroxyterminated poly(2-methyl-2-oxazoline) as miacroinitiators. Poly(butyl vinyl ether-g-2-methyl-2-oxazoline) (PBVE-g-PMOX) or poly(2-methyl-2-oxazoline-b-ε-caprolactone) (PMOX-b-PCL) were screened as potential blend compatibilizers for poly(ε-caprolactam) (Nylon 6) and isotactic poly(propylene). Analysis of these blends by SEM indicated that PBVE-g-PMOX might function as a blend compatibilizer for Nylon 6/poly(propylene) blend while PMOX-b-PCL would not.