Study On Properties Of Polyurethane Elastomer Based On Polyhydroxy Polybutadiene

Polyurethane elastomer prepared from hydroxyl terminated polybutadiene（HTPB）had excellent hydrolysis resistance,but its mechanical properties were not good.In this paper,pre-isoenol was grafted onto the HTPB molecular chain to synthesize polyhydroxy polybutadiene（PHPB）by graft modification.The increase in the number of hydroxyl groups on the molecular structure of PHPB increased the polarity.With the increase of hydrogen bonding units and intermolecular cohesive force,the prepared PHPB polyurethane elastomers had excellent hydrolysis resistance and good mechanical properties,which broaden the application field of polyurethane elastomers.PHPB was prepared from HTPB with hydroxyl value of 1.1mmol·g^-1 and the effects of solvent type（reaction temperature）,initiator type and dosage,and isopentenol dosage on the viscosity and hydroxyl value of PHPB were investigated.The optimal synthesis schemes selected by experiments were:HTPB,prenyl alcohol as raw material,petroleum ether as solvent,benzoyl peroxide（BPO）as initiator,raw material ratio W（HTPB）:W（oil Ether）=1:1,W（HTPB）:W（prenyl alcohol）=100:3（n（HTPB）:n（prenyl alcohol）=3.16:1）,W（prenyl alcohol）:W（BPO）=1:0.05,and the reaction was carried out for 4 hours at reflux temperature to prepare PHPB having a hydroxyl value of 1.21 mmol·g^-1.The synthesized PHPB was characterized by infrared（FT-IR）,gas chromatography-mass spectrometry（GC-MS）and nuclear magnetic resonance spectroscopy（HNMR）:the-OH peak in the FT-IR of PHPB was increased,the isoprene peak disappeared in the GC-MS and the-CH3 peak appeared in the HNMR spectrum.The above characterizations indicated that the pre-pentenol was successfully grafted onto the HTPB molecular chain to synthesize PHPB.HTPB or PHPB was used as raw material to synthesize HTPB polyurethane elastomer and PHPB polyurethane elastomer by one-step method and prepolymer method.The mechanical properties of elastomers synthesized by different molecular weight polyols,curing parameters（R）,chain extenders and NCO%were investigated.Comparing PHPB polyurethane elastomers with HTPB polyurethane elastomers and polyether polyurethane elastomers,it was found that the mechanical properties of PHPB polyurethane elastomers were obviously higher than that of HTPB polyurethane elastomers,and slightly higher than that of polyether polyurethane elastomers.Using PHPB and MDI as raw materials and TMP as chain extender,the PHPB polyurethane elastomer was prepared by prepolymer method under the condition of NCO%of 12.Its hardness was 95HA,the tensile strength was 12.6MPa and the elongation at break was 64.9%.Under the same conditions,the hardness of the HTPB elastomer was 94.7 HA,the tensile strength was 7.28 MPa and the elongation at break was 51.1%.The synthesized polyurethane elastomers were characterized by infrared,DSC and TG.The PHPB type polyurethane elastomer had a glass transition temperature of-8.45°C and a thermal decomposition temperature of212°C,which were higher than that of the HTPB type elastomer of-29.65°C and195°C.It exhibited high thermal stability.Hydrolysis resistance of HTPB polyurethane elastomers and PHPB polyurethane elastomers synthesized by different molecular weight polyols,curing parameters,chain extenders and NCO%was studied.Compared with the polyether elastomer,the results showed that the hydrolysis resistance of the PHPB polyurethane elastomer was much higher than that of the polyether polyurethane elastomer and comparable to the HTPB type elastomer.Among them,the hydrolysis retention rate of mechanical properties of HTPB elastomer and PHPB elastomer was generally above 85%,which was much higher than that of polyether elastomer（60%-70%）.