You should add the ngDefaultControl attribute to your input like this:
<md-input
[(ngModel)]="recipient"
name="recipient"
placeholder="Name"
class="col-sm-4"
(blur)="addRecipient(recipient)"
ngDefaultControl>
</md-input>
Taken from comments in this post:
angular2 rc.5 custom input, No value accessor for form control with unspecified name
Note: For later versions of @angular/material:
Nowadays you should instead write:
<md-input-container>
<input
mdInput
[(ngModel)]="recipient"
name="recipient"
placeholder="Name"
(blur)="addRecipient(recipient)">
</md-input-container>