Slerp / Lerp RotateAround()

I use this script to rotatearound 4 walls at angles of 90,180,270,360. Although this function works good, it stops abruptly. Is there a way to slow down the rotate around towards the end of the rotation. I tried using Time.timeScale but it slowed down the the whole game. Also I tried playing around with physics2d attributes like Drag,Angular Drag, rigidbody2d.AddForce() and rigidbody2d.AddTorque(). But cudnt acheive what I needed.

Just begun learning unity, so I dont know much about it.

Thanks in advance.

Here's my code:

  #pragma strict

  public class mgWallScript extends MonoBehaviour{

     var rotZ: int=0;
    var prefab : GameObject;
    var tprefab : GameObject;
    var thinRingPrefab : GameObject;
    var nextPrefab : GameObject;
    var localPrefab : GameObject;
    var globalWallObj : GameObject;
    var num=4;
   
    public static var radius : float =1.56f; 
    var arr = new Array ();
  
    var rotateTime = 0;
    var rotateSpeed = 10;
    var rotateDegrees =0;
    private var rotating = false;
    public var rotateing = new Array();
    var counterTime:int;
     
    static var globalObj : GameObject;
     
   function Start(){
      counterTime = 0;
      rotateing[0]=false;
      rotateing[1]=false;
      rotateing[2]=false;
      rotateing[3]= false;

     rotZ=0;
     
 for(var i=0;i<num;i++){        
         var angle=i*Mathf.PI*2/num;

         var pos=Vector3(Mathf.Round(Mathf.Cos(angle)),Mathf.Round(Mathf.Sin(angle)),0)*radius;
         
         var    obj=Instantiate(thinRingPrefab,pos,Quaternion.Euler(0,0,rotZ));
         rotZ+=90;
         
         arr.push(obj);
     }
 }
 
 function FixedUpdate(){

 rotateTime = 4;
   rotateDegrees=90;
   if(counterTime <4){
      for(var i=0;i<arr.length;i++){
      tprefab=arr[i];
      if(i==3)
      nextPrefab=arr[0];
      else
      nextPrefab=arr[i+1];
     
      RotateAllWalls(i,tprefab.transform,this.gameObject.transform, nextPrefab.transform ,-(Vector3.forward), rotateDegrees, rotateTime);
      }
      }else{
      
      counterTime = 0;
      rotateing[0]=false;
      rotateing[1]=false;
      rotateing[2]=false;
      rotateing[3]= false;
      }

    }

      function RotateAllWalls (temp:int ,thisTransform : Transform, otherTransform : Transform, nextTransform : Transform, rotateAxis : Vector3, degrees : float, totalTime : float) {
     if (rotateing[temp]) return;
     
     rotating = true;
     rotateing[temp]= true;
     
     var startRotation = thisTransform.rotation;
     var startPosition = thisTransform.position;
     
     var endRotation = nextTransform.rotation;
     var endPosition = nextTransform.position;
     
     thisTransform.rotation = startRotation;
     thisTransform.position = startPosition;
    
     var rate = degrees/totalTime;
     
     for (var i = 0.0; i < degrees; i += Time.deltaTime * rate * rotateSpeed) {
                yield;
         thisTransform.RotateAround(otherTransform.position, rotateAxis, Time.deltaTime * rate * rotateSpeed);
     }
  
     thisTransform.rotation = endRotation;
     thisTransform.position = endPosition;

     rotating = false;
     rotateing[temp]= false;
     counterTime++;
 }
 

}