Tereshatov V.V., Makarova M.A., Senichev V.Yu.,Vnutskikh Zh.A., Savchuk A.V., Slobodinyuk A.I., Kiselkov D.M.

Federal State Budget Foundation of Science Institute of Technical Chemistry of Ural branch of Russian Academy of Sciences. Perm, Russia

Obtaining and properties of tetrablock-polyurethane ureas with mixed polyether segments and various hard ones

An overwhelming majority of urethane-containing polymers (polyurethanes, polyurethane ureas) consist of soft (SS) and hard (HS) segments (blocks) forming polymer chains [1,2]. The structure of the soft segments is determined by used oligomers. Reaction of diisocyanate and low-molecular-mass diol, or diamine results in formation of hard segments. Some compositions contain cross-linking agents and plasticizers [3]. A difference in polarity of soft and hard segments leads to their microphase separation and formation of soft and of hard nano-dispersed phases. Hard domains are stabilized by hydrogen bonds [2].

Properties of urethane-containing materials are regulated varying the chemical structure, molecular weight, polarity of soft segments, as well as concentration and structure of hard segments. Thus, materials with diverse properties were developed. Usually, segmented polyurethanes (SPUs) and polyurethane ureas (SPUUs) consist of alternating uniform soft SS and hard HS segments (SSHS)_n [1]. Structure and properties of such materials are well-studied. Urethane-containing multiblock-copolymers are much less investigated.

New investigation objects are of significant interest for detecting particularities of behavior for urethane-containing elastomers with a complex structure of the polymer chains. This paper presents results of the synthesis and investigation of thermal, thermo-mechanic, physic-mechanic and other properties of tetrablock-copolymers containing various polyether soft segments and various hard blocks (segments).

Segmented polyurethane ureas (SPUU) with mixed polypropileneoxide (PPO) soft segments and polytetramethyleneoxide (PTMO) ones of various molecular mass (M_n) were investigated. The following compounds were used as initial components for the synthesis of SPUU: 2,4-toluene diisocyanate (TDI) , isophorone diisocyanate (IDI), oligopropylene oxide diol (PPO) Voranol 1010L with M_n=1000 g·mol^-1, oligotetramethylene oxide diol with M_n=1000 g·mol^-1, and 4,4¢-methylene-bis-(2-chloroaniline) (MOCA). The synthesis was performed as a two-step process, with preliminary preparation of prepolymers: TDI- and PPO-based FP-1 and IDI- and PTMO-based FP-2. Prepolymers FP-1 and FP-2 were mixed in the given ratio. Then, the melted MOCA was introduced into the reactor. Hardening of samples was provided within 3 days at 90^oC.

Glass transition temperature () of the soft segments matrix (soft phase) of investigated elastomers was determined with use of the DSC 822^e calorimeter; softening temperature of the hard phase was determined with use of the TMA/SDTA 841^e device. Mechanical tests were conducted at the stretching rates from 0.28 s^-1. Tensile strength (maximal stress value calculated for initial cross-sectional area of samples), relative critical strain value (%), engineer modulus E₁₀₀ (stress value calculated for initial cross-sectional area of samples at 100% relative strain), and true tensile strength, where were determined. Rheological properties of reaction mixes (reaction masses) were investigated with use of Reotest-2 equipped with the «cone-plate» device at 90±0.5°С, and at the share rate of 180 s^-1.

Elastomers based on prepolymer FP-1 and FP-2 blends, contain different quantity of polypropylene oxide SS_PPO and polytetramethylene oxide SS_PTMO soft segments and hard segments of various types:

HS₁ (TDI- and МОСА-based)

HS₂ (IDI- and МОСА-based)

Results of rheokinetic study of compositions on the base of prepolymers FP-1 and FP-2 showed an intensive increase in viscosity at 90°С to be observed within the period less than 15 min for system FP-1 +МОСА, but after 100 min for FP-2+МОСА system. Rheokinetic curves of the compositions based on prеpolymer blends are greatly shifted towards the curve corresponding to the composition based on FP-1 (Fig. 1). Thus, interaction rates of the prepolymers with aromatic diamine are different. The obtained data allow us to suppose that FP-1 in prepolymers blend predominantly reacts with МОСА at the initial stage of polyurethane ureas synthesis. This reaction leads to the formation of hard segments HS₁. Further FP-2 reacts with diamine to form hard segments HS₂ and PTMO soft segments. Taking this into account the structure of multi-block copolymer chains can be represented by the following simplified formula: (SS_PPOHS₁)_m–(SS_PTMOHS₂)_n.

The fragments of SPUU polymer chains consist of different types of hard and soft segments provided that oligodiisocyanate reactivity varies significantly. Molar ratio of PTMO and PPO soft segments is equal to the one of FP-2 and FP-1.

The molar fraction of the hard segments HS2 in the composition of urethane urea segments HS1+HS2 is close to the molar fraction of prepolymer FP-2 in the blend with FP-1. Thus, the composition of soft and hard segments in SPUU corresponds to the composition of FP-1 and FP-2 prepolymer blend, used at the synthesis of the material. The evidence of sole glass transition temperature for soft phase in SPUU indicates the thermodynamic compatibility between PTMO and PPO segments.

Fig.1Rheokinetic curves at 90^oC for compositions with various molar fraction of FP-2 in the mix with FP-1: 1-0, 2-0.3, 3-0.5, 4-0.7, 5-1.0

Thermal and physic-mechanic properties of polyurethane ureas depend on the molar composition of the FP-1-FP-2 prepolymer mix in the non-linear manner, and, correspondingly, on the ratio between polymer chains (SS_PPOHS₁)_m and (SS_PTMOHS₂)_n , where n ≈ x₂ (Table).

An optimal combination of microphase separation and interchain interaction in the soft phase leads to the significant improvement of strength and strain properties of the multiblock-copolymer at the FP-2 molar fraction x₂ ≈ 0.5 in the mix with FP-1. This effect combining with good rheology properties of the reaction mass expands possibilities of new materials application for various technologies.

Table. Properties of SPUUs at the various FP-2 molar fraction x₂ in the mix with FP-1

x2	Tg^s, °C	Th, °C	sk, MPa	ek, %	Е100, МPа	fr, MPa
0	-5	190	38.4	410	16.1	196
0.3	-18	176	42.5	512	8.4	260
0.5	-46	173	57.6	620	6.8	415
0.7	-61	171	52.1	607	5.8	368
1.0	-70	167	48.2	552	5.6	314

Acknowledgments This work was financially supported by the Russian Fund for Basic Research and Government of Permskiy kray (Project 16-43-590647r_a).

References

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