ORIGINAL PAPER Alkylene oxide poylmerizations: identification of side reactions and by-products Muhammad Imran Malik 1 & Muhammad Irfan 1 & Akbar Khan 1 & Sana Rahim 1 & Rubina Abdul-Karim 1 & Jamshed Hashim 1 Received: 7 April 2016 /Accepted: 9 November 2016 # Springer Science+Business Media Dordrecht 2016 Abstract In this study microwave-assisted anionic ring open- ing polymerization (ROP) of alkylene oxides is reported. Low molar mass polymers of propylene oxide (PO), butylene oxide (BO) and hexylene oxide (HO) are synthesized by anionic ring opening using various monohydric alcohols as initiators. The monohydric alcohols and lower molar masses allowed for monitoring of different types of possible unwanted by- products and their sources. Liquid chromatography at critical conditions (LCCC) and liquid adsorption chromatography (LAC) are used to determine the presence of oligomers other than targeted. Finally, MALDI-TOF MS of the products have clearly shown the trends and extents of different types of side reactions that are possible in anionic ring opening of alkylene oxides. Propylene oxide is most vulnerable to chain transfer reactions compared to higher alkylene oxide. Keywords Polyoxyalkylenes . Anionic ring opening polymerization . Microwave-assistedpolymerizations . HPLC of polymers Introduction Polyoxyalkylene are very important class of polymers for nu- merous applications in modern day material science [1–3]. Polyoxyethylenes (PEO) are the lowest member of this group and are very hydrophilic in nature. The higher polyoxyalkylenes have pendant alkyl group and their hydro- phobicity increases with the length of the alkyl group (methyl, ethyl and butyl) on the polymer chain. The solubility of poly- mers is strongly affected by the length of the polymer chains. Fairly high molar masses of Polyoxypropylene (PPO) are in- soluble in water at room temperature. The polymers of higher alkylene oxides such as polyoxybutylene (PBO) and polyoxyhexylene (PHO) are soluble only in non-polar organic solvents and un-conventional solvents like silicon oils [4, 5]. The differences in the polarity of various polymers of alkylene oxides can be exploited for synthesis of polyoxyalkylene block copolymers with completely different physical proper- ties [6]. Different mechanisms reported for polymerization of alkylene oxides in literature are: coordinate-initiated, cationic or anionic [7]. Polymerization of PO has been discussed in detail in literature [8–13]. BO and HO have been polymerized using lithium as counter ion and tert butyl polyiminophosphazene base as complexing agent [4, 14], double metal cyanide (DMC) [15], and potassium alcoholate in combination with crown ethers as useful catalyst systems [5]. The cationic mechanism is not very favorable in the syn- thesis of block copolymers because of ring-chain equilibria (backbiting), which leads to the formation of products with a different architecture (linear and cyclic homopolymers to multiblocks). Coordinate-initiated polymerization is suitable for the production of homopolymers; in the synthesis of block copolymers, however, such catalysts may also yield chains with different functionalities. Anionic ring opening polymerization (ROP) is the most widely employed technique for polymerization of alkylene oxides. Broadly accepted mechanism of anionic ROP of alkylene oxides is shown in Scheme 1. The problems associ- ated with ROP of higher alkylene oxides by coordinate-initi- ated, cationic mechanisms can be avoided by anionic ROP, * Muhammad Imran Malik mimran.malik@iccs.edu 1 H.E.J. Research Institute of Chemistry, International Centre for Chemical and Biological Sciences (ICCBS), University of Karachi, Karachi 75270,, Pakistan J Polym Res (2016) 23:258 DOI 10.1007/s10965-016-1141-z