The Synthesis And Properties Of The Low-Molecular-Weight Styrene-α-Methylstyrene Copolymer

Aromatic hydrocarbon oil is the best choice for processing aids in the rubber industry because of its excellent properties.However,as it has been pointed out in more and more studies that polycyclic aromatic hydrocarbons are highly carcinogenic,it is urgent to find a new processing aid to replace aromatic oils in tire formulations for the sake of health,safety and environmental protection.Styrene oligomers with similar air tightness and damping properties to rubber then attracted widespread attentions.At present,the synthesis methods of styrene oligomers include free radical polymerization,anionic polymerization and cationic controlled polymerization.Studies have shown that the free radical synthesis process is cumbersome and it requires severe reaction conditions;the anion polymerization synthesis process is difficult to control and the molecular weight is too high.Focusing on the above problems,the author of this paper prepared styrene-α-methylstyrene block oligomer（St-co-AMS）with cationic controlled polymerization method and researched the impact of synthesis conditions like the choice of initiator,the amount of initiator,polymerization temperature on the polymerization reaction.The author of this paper also studied the effect of styrene-α-methylstyrene oligomer on the wet skid resistance and mechanical properties of tread rubber composites.The results showed that St-co-AMS could significantly improve the wet skid resistance of tread rubber but had little effect on the mechanical properties of the tread rubber.The innovation points of this experiment are as follows:1.A series of low molecular weight styrene-α-methylstyrene oilgomer were synthesized by cationic polymerization method using activated clay Maghnite-H⁺as the initiator,methylene chloride as the reaction medium,and styrene andα-methylstyrene as raw materials.The number-average molecular weight oilgomer was 800-2500 g/mol,and the yield to 88%.The experimental results showed that reaction temperature,time,monomer concentration,initiator treatment method and dosage all have an effect on the yield;and the yield was the highest when the addition amount of activated clay was 5%,the reaction temperature 0℃,the reaction time 4h,and the ratio between m（St-co-AMS）and m（CH₂Cl₂）was 1:1.The oilgomer structure was characterized by infrared spectroscopy（FTIR）,nuclear magnetic resonance spectroscopy（NMR）,gel permeation chromatography（GPC）,etc.;and its thermodynamic properties was measured by thermogravimetric analyzer（TGA）,differential scanning calorimetry Instrument（DSC）,etc.It was proved by FTIR and NMR characterization that the low molecular weight oilgomer was of copolymer structure and it had good thermal stability and a suitable glass-transition temperature.2.The role of St-co-AMS in rubber composites and its working mechanism was researched by using rubber as the base material.St-co-AMS and rubber composites,were prepared by open blending method.The rubber composite material used in this experiment was a reactive resin.FTIR analysis results showed that a certain cross-linking reaction occurred in the blending preparation process of St-co-AMS and rubber composite material.The vulcanization condition experiment showed that the addition of St-co-AMS could improve the overall vulcanization performance of the rubber composite;dynamic mechanical tests showed that an addition of 5 phr St-co-AMS could increase the dynamic performance of the rubber material by 64%at 0°C,and the anti-wetting effect was obvious.At 60℃,the tanδof the rubber with oligomer was slightly higher than that of the blank rubber composite,which proved that adding oligomer would not adversely affect the rolling resistance of rubber.The mechanical test showed that the low added parts of St-co-AMS could improve the mechanical property of thread rubbers to a certain extent,as well as the tensile strength,tear strength and elongation at break.Water contact angle and scanning electron microscopy tests further confirmed that St-co-AMS could improve the dispersion of silica in rubber.At the same time,St-co-AMS had good compatibility with rubber composites.Its low molecular weight made its plastificating effect and its adhesion with rubber materials better,thus elevating the dynamic property of rubbers as rubber processing aids.