Set DoubleAnimation with Binding to an external object - wpf

Question

I have the following Style that contains an animation used to expand a Border:
<Style TargetType="{x:Type Border}" x:Key="BorderAnimations">
<Setter Property="FlowDirection" Value="RightToLeft" />
<Style.Triggers>
<EventTrigger RoutedEvent="MouseEnter">
<BeginStoryboard>
<Storyboard >
<DoubleAnimation
Storyboard.TargetProperty="Width"
BeginTime="0:0:0"
From="" To="420" Duration="0:0:0.2" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
<EventTrigger RoutedEvent="MouseLeave">
<BeginStoryboard>
<Storyboard >
<DoubleAnimation
Storyboard.TargetProperty="Width"
BeginTime="0:0:0"
From="420" To="90" Duration="0:0:0.2" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</Style.Triggers>
</Style>
I want to set the From property to the generics' button Width. Here I have the generic Button style:
<Style TargetType="{x:Type Button}">
<Setter Property="Foreground" Value="White" />
<Setter Property="FontSize" Value="80" />
<Setter Property="HorizontalAlignment" Value="Right"/>
<Setter Property="VerticalAlignment" Value="Center" />
<Setter Property="Background" Value="{DynamicResource MainBlue}" />
<Setter Property="Height" Value="{Binding
ElementName=MainUCPanel, Path=Height,
Converter={StaticResource ArithmeticConverter},
ConverterParameter=Int32.Parse(values[0]) / 6}" />
<Setter Property="Width" Value="{Binding Path=Height, RelativeSource={RelativeSource Self}}" />
<Setter Property="DataContext" Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type view:DesktopUCMain}}, Path=DataContext}" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Border Background="{TemplateBinding Background}" BorderBrush="Transparent" BorderThickness="0" CornerRadius="5" x:Name="bd">
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
Margin="5" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" RecognizesAccessKey="True"/>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Cursor" Value="Hand" />
<Trigger.ExitActions>
<BeginStoryboard>
<Storyboard>
<ColorAnimation Storyboard.TargetProperty="(Button.Background).(SolidColorBrush.Color)" To="#FF1E90FF" Duration="0:0:0.2" />
</Storyboard>
</BeginStoryboard>
</Trigger.ExitActions>
<Trigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<ColorAnimation Storyboard.TargetProperty="(Button.Background).(SolidColorBrush.Color)" To="#27ace3" Duration="0:0:0.2" />
</Storyboard>
</BeginStoryboard>
</Trigger.EnterActions>
</Trigger>
</Style.Triggers>
</Style>
I've tried to set it as:
From="{Binding RelativeSource={RelativeSource AncestorType={x:Type Button}}, Path=ActualWidth}"
But it's not working...
NOTE: these styles are located on a ResourceDictionary.xaml. How can I achieve the animation to get this width?
EDIT: Thrown exception:
Cannot freeze this Storyboard timeline tree for use across threads.