\(2CH_4\xrightarrow[lln]{1500^0C}C_2H_2+3H_2\)
\(2C_2H_2\underrightarrow{t^0,p,xt}CH\equiv CH-CH_2=CH_2\)
\(CH\equiv CH-CH_2=CH_2+H_2\underrightarrow{PbCO_3,t^0}CH_2=CH-CH=CH_2\)
\(nCH_2=CH-CH=CH_2\underrightarrow{t^0,p,xt}\left(-CH_2-CH=CH-CH_2-\right)_n\)