Locking and Limiting a rotation 2d

Hi!

My game makes the player go up in a rotational arc when a button is pressed, and in a much larger arc downwards when not pressed. What I currently need it way to limit how far these arcs go before they are stopped, or changed into a different type of arc.

More specifically, The downward arc needs to stop entirely when it reaches -90 degrees (or straight down). As for the upward arc, it needs to turn on itself permanently from 90 degrees (or straight up) to 270 degrees (AKA -90), where it automatically turns off the constant upward arc.

Here's my script:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour {
 
 
     public float moveSpeed;
     public float rotateSpeed;
     public float negativeRotateSpeed;
 
     private bool didLower = true;
     
 
     private Rigidbody2D myRigidbody;
     // Use this for initialization
     void Start () {
     
         myRigidbody = GetComponent<Rigidbody2D> ();
 
     }
     
     // Used for Graphics and Inputs
     void Update () {
 
         transform.position += transform.right * Time.deltaTime * moveSpeed;
 
 
     
         if (Input.GetKey(KeyCode.Space) || Input.GetMouseButton(0) ) {
             
 
             transform.Rotate(0, 0, Time.deltaTime * rotateSpeed, Space.Self);
 
             didLower = false;
         }
         if (didLower = true) {
 
             transform.Rotate (0, 0, Time.deltaTime * -rotateSpeed/negativeRotateSpeed, Space.Self);
 
         }
 
 
     }
 
     // Used for Physics
     void FixedUpdate () {
 
  
 
 
 
     }
 
 }
 

Thanks in advance!