The thermodynamic properties of a polymer chain with a length of N=100 near an adsorbed surface

modeled by a self-avoiding walk on the simple cubic lattice in addition to both the vertex-plane interaction energy ε1 and the vertex-vertex interaction energy ε2

were calculated by means of the multiple Markov chains method．These two interaction energy terms ε1 and ε2 were related to the vertex-plane interaction parameter α and the vertex-vertex interaction parameter β．The statistical physical quantities obtained by Mont Carlo simulations include the free energy FN(α

β)

the heat capacities а2FN(α

β)／а2 α and а2 FN (α

β)／а2 β

the mean number of visits per edge m〉／N．the mean number of contacts per edge〈n〉／N and the mean square z-component Rz2 of the end-to-end distance．It suggests a new method to eonstruct the α-β phase diagram by structure parameters〈m〉／N

〈n〉／N and RZ2

which is very similar to that obtained by the traditional method using peaks of the heat capacity．The α-β phase diagrams indicated that there are four regions of phases

which are desorbed-expanded (DE)

adsorbed-expanded (AE)

desorbed-compact (DC) and adsorbed-compact (AC)．In both expanded phase and compact phase

there were adsorption transitions as the surface interaction increased．In both desorbed and adsorbed phases

there were collapse transitions as the nearest-neighbor interaction increased．It is also found that there are two triple points in the α-β phase diagram

which represent the coexistance of the three phases AE-AC-DC and AE-DE-DC

respectively．and AE-DE-DC

respectively．