Tereshatov V.V., Makarova М.А., Slobodinyuk А.I., Vnutskikh Z.А., Volkova Е.R., Senichev V.Yu., Krasnoselskikh S.F.

Institute of technical chemistry of Ural Branch of Russian Academy of Sciences,. Russia

Frost-resistant polyetherurethane on the base of oligotetramethyleneoxide diol

Frost resistance is one of the most important characteristics of elastomers. Their glass transition temperature Tg determines the possibility of their using at low temperatures [1]. Physical modification of crosslinked one-phase elastomers based on various rubbers by plasticizers can significantly reduce the glass transition temperature. The strength of such materials is significantly reduced due to the weakening of interchain interaction at plasticization. Microphase segregation of soft and hard blocks plays a significant role in reinforcement of polyurethanes with block structure - segmented polyurethanes (SPUs). The hard phase in the material plays a role of reinforcing filler. An appropriate choice of the plasticizer, in our opinion, can assist to develop frost-resistant elastic SPU with high values of the tensile strength and the strain at break.

This work was performed using polyetherurethane based on oligotetramethileneoxide diol PTMO (Mn≈2000 g×mol^-1), 4,4¢-dicyclohexyldiisocyanate HMDI and 1,4-butanediol as chain extender. Di-(2-ethylhexyl)-sebacate (DEHS) with the glass transition temperature equal to -107°C [2] was used as a plasticizer. DEHS influences the microphase segregation of SPUs in a low degree [2-4]. Polyurethane samples were obtained by two-step synthesis using the prepolymer with terminal NCO-groups.

Mechanical properties of SPUs were determined using an universal testing machine INSTRON-3365: engineer tensile strength σ_k; engineer modulus E₁₀₀ – stress value at 100% elongation; ε_k -relative critical strain at break. Tests were carried out at different stretching rates, v. The temperature of the soft phase structural glass transition T_g^s was determined using DSC 822e device of METTLER-TOLEDO company. The values of T_g^s and mechanical properties of SPUs at v=500 mm/min and 25 °C are listed in Table 1.

Table 1 –Properties of SPUs

DEHS content, % mas.	σк, MPa	Е100, MPa	eк, %	Tg^s, ^оС
0	28.3	2.0	635	-74
25	27.1	1.6	710	-90
40	18.7	1.2	772	-98

The results show that the T_g^s values of SPUs reduce significantly as a result of plasticization: from - 74 to - 90°C when introducing of 25% DEHS into the material and to - 98°C at 40% DEHS.
The strength of the SPUs was almost unchanged at 25% content of DEHS.
The high amount of a plasticizer significantly affects the strength of the material. However, the strength level of SPUs remains high - 18.7 MPa. Critical strain value e_k naturally increases with decrease in the conditional modulus that has a positive effect on the operability of the material.
The tensile strength of plasticized SPU changes in a wide range of strain rates (Table 2) in a lower degree. This relates with increasing degree of hard segments orientation in their domains in the direction of stretching, as shown in [4].
It was found that a high level of relative critical strain of plasticized DEHS, more than 400%, did not change at temperatures down to -60 ÷ -70 ° C at the strength values more than 35 MPa.

Table 2 – Mechanical properties of SPUs at 25 °С and various stretching rates.

v, mm/min	Without plasticizer			25% plasticizer
	sk, MPa	Е100, MPa	ek, %	sk, MPa	Е100, MPa	ek, %
1000	17.8	2.4	648	25.9	1.6	721
500	28.3	2	635	27.1	1.6	710
300	34.1	1.9	619	28.9	1.6	742
100	34.6	1.9	609	34.9	1.5	718
50	35.4	1.8	629	33.6	1.5	751
10	36,9	1.8	634	29.8	1.5	726

Thus, SPU plasticized with DEHS based on PTMO, HMDI and 1,4-butanediol has excellent frost resistance at high strength and elasticity.

This work was supported by the Russian Foundation for Basic Research (projects 15-03-02221a and 13-03-96000a).

References

1. Prisacariu C. Polyurethane elastomers: from morphology to mechanical aspects. – Springer Science & Business Media, 2011.

2. Wypych G. Handbook of plasticizers. – ChemTec Publishing, 2004.

3. Tereshatov V.V., Tereshatova E.N., Makarova M.A., Tereshatov S.V. Influence of Chemical Structure and Composition of Mixed Soft Segments on the Properties of Elastomers with Urethane–Urea Hard Blocks. Polymer Science. Series A, Chemistry, physics. 2002, V.44, 275-281.

4. Tereshatov V. V. et al. Interrelationship between ultimate mechanical properties of variously structured polyurethanes and poly (urethane urea) s and stretching rate thereof. Colloid and Polymer Science. 2012, V. 290, 641-651.