# Poly-(3-ethyl-3-hydroxymethyl)oxetanes--Synthesis and Adhesive Interactions with Polar Substrates
## 1 Introduction  
Hyperbranched polyoxetanes (POXs) are a relatively new class of polymers. The first syntheses were independently reported by [PERSON]'s and [PERSON]'s groups in 1999 [1; 2]. However, co-polymerizations of monomers with both oxetanyl and styryl groups were already reported by [PERSON] et al. in 1989 [3]. POXs are classified as branched polyethers and are synthesized from oxetanes--four-member cyclic ethers bearing hydroxymethyl groups. In the literature, most reports are focused on the polymerization or co-polymerization of 3-ethyl-3-(hydroxymethyl)oxetane (EHO) [4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. The monomer for this process is easily available from trimethylloprone. The main synthetic approach to polyoxetanes goes via cationic ring-opening polymerization, as an anionic mechanism was found to be less effective due to either a low molar mass (ca. 500 g/mol) or broad dispersities (\(M_{\mathrm{w}}\)/\(M_{\mathrm{n}}\) = 4.0-5.5) and a low degree of branching of the products [15; 16]. Investigations on the mechanisms of polymerizations revealed that they undergo an active chain end mechanism (ACE) or an activated monomer mechanism (AMM) [17]. The ACE mechanism is more efficient, as cyclization reactions do not occur.  
Polyoxetanes are not paid sufficient attention, though their chemical properties like the ease of side chain functionalization or grafting make them versatile and valuable scaffolds in many fields of material science. Reports on the applicability of functionalized polyoxetanes cover, among others, liquid crystals [18], polymer electrolytes with lithium ion coordination abilities [19; 20], fluorine-containing hydrophobic materials [21], amphiphilic block copolymers with poly(ethylene oxide) [22], hybrid networks of fluorine-bearing polyoxetane and inorganic phases [23], hybridfluorine-polyoxetane-polyurethane coatings [24], and hyperbranched polyoxetanes in drug delivery systems [25; 26; 27]. [PERSON] and co-workers also used functionalized polyoxetanes to incorporate telechelics in polyurethanes [28; 29].  
As the number of papers on polyoxetanes is relatively low, the number of works on the adhesive properties of POXs is even lower. Hardly any reports on polyoxetane-based adhesives can be found in the literature.  
[PERSON] at al. described a catechol-containing polyoxetane as a platform for an adhesive curable with FeCl\({}_{3}\)[30]. The investigated adhesives exhibited relatively good strengths on such substrates like metals (3.7-4.9 MPa), poplar wood (2.7 MPa), and glass (2.10 MPa). Further research in that group demonstrated that merging catechol with phosphoric acid and a POX backbone might induce adhesion in humid environments, which may give way to the design of biomimetic adhesives [31]. Reports on photocurable adhesive systems based on epoxides and oxetanes can be also found in the literature [32; 33].  
In 2016, we made a patent application on the use of poly(hydroxy)oxetanes as hot-melt adhesives in wood bonding [34]. This study presents the synthesis and molecular characteristics of poly-(3-ethyl-3-hydroxymethyl)oxetanes of different molar masses and their adhesive interactions with polar substrates. According to our best knowledge, the present study is the first to discuss POX-lignocellulosic adhesive interactions.  
In our approach, POXs were synthesized from 3-ethyl-3-(hydroxymethyl)oxetane by using 1,1,1-tris(hydroxymethyl)propane (TMP) as a core molecule. Such protocol allows for the yield of polymers of a lower dispersity when compared to homopolymerization and easier molar mass control [35].